Assessment Cover Sheet

Transcription

1 Assessment Cover Sheet Assessment Title: Chassis Assignment 3 (Stress analysis) Programme Title: Bachelor of Engineering Technology Course No.: ENB6913 Course Title: Mechanical Project 4 Student Name: Yahya Isa Saif Student ID: Tutors: Syed Imam Due Date: Date submitted: By submitting this assessment for marking, either electronically or as hard copy, I confirm the following: This assignment is my own work Any information used has been properly referenced. I understand that a copy of my work may be used for moderation. I have kept a copy of this assignment Assessor: Date of Marking: Grade/Mark: / Comments: 1 P a g e

2 Contents Contents... 2 Table of figures:... 4 Table of Tables:... 5 Synopsis:... 6 Introduction:... 7 Analysing situations:... 8 Forces that act on the chassis: Tube properties: Tubes material properties: Failure modes: Static loading: Cyclic loading (fatigue): Ductile and brittle failure: Fracture in ductile and brittle failure: Crack Propagation (ductile material): Fatigue failure (ductile materials): Failure theories: Maximum shear stress: MAXIMUM DISTORTION ENERGY: Maximum normal stress: Modified Mohr: Factor of safety\ displacement: Displacement: Finite Element Analysis: Definition: Chassis (FEA) steps: Chassis Finite Element Analysis: FEA analysis during braking: Strain analysis: Displacement analysis: FOS: P a g e

3 FEA analysis during Acceleration: Displacement analysis: FOS: FEA analysis during Cornering: Displacement analysis: FOS: Methods of joining: Selection of method of joining: Heat treatment: Post weld heat treatment (PWHT) (Stress relieving): Conclusion and future recommendations (optimization): Appendix (A) Appendix (B) Appendix (C) Appendix (D) Reference: P a g e

4 Table of figures: Figure 1, Gravity and longitudinal acceleration (acceleration)... 7 Figure 2, Gravity and longitudinal acceleration (braking)... 7 Figure 3, Gravity and lateral acceleration (cornering)... 7 Figure 4, forces that effect on vehicle during cornering (front view) ( milliken, 2002)... 8 Figure 5, vehicle reaction force. (Nuffield Foundation, 2011)... 9 Figure 6 creep test specimen (Suranaree University of Technology, 2007) Figure 7, stress versus strain (Suranaree University of Technology, 2007) Figure 8, Stress versus rupture time (Suranaree University of Technology, 2007) Figure 9 Strain versus time (Suranaree University of Technology, 2007) Figure 10 creep rate versus strain (Suranaree University of Technology, 2007) Figure 12 creep strength curve (Suranaree University of Technology, 2007) Figure 12 creep data curve (Suranaree University of Technology, 2007) Figure 13, Sinusoidal loading (fatigue test, 2013) Figure 14, Sinusoidal loading (fatigue test, 2013) Figure 15, spectrum loading (fatigue test, 2013) Figure 16, Ferrous and nonferrous S-N curves (S-N curves, 2011) Figure 17, stress versus strain graph (Tensile properties, 2012) Figure 18, ductile and brittle materials Figure 19, ductile and brittle fracture (ductile and brittle fracture, 2008) Figure 20, Neck (Ductile Fracture 2, 2013) Figure 21, Micro voids (Ductile Fracture 2, 2013) Figure 22, Coalesce (Ductile Fracture 2, 2013) Figure 23, Fracture (Ductile Fracture 2, 2013) Figure 24. microvoid and shear slip (Ductile Fracture 2, 2013) Figure 25, Cup and cone fracture. (Duralumin, 2013) Figure 26, fatigue failure Figure 27maximum shear stress (failure theories, 2010) Figure 28 Von Mises stress (Failure Criteria, 2013) Figure 29 Maximum normal stress (Failure Criteria, 2013) Figure 30Mohr's Circle (Failure Criteria, 2013) Figure 32, Meshing system (FEA). (sciepub, n.d.) Figure 33, selecting the material for the chassis Figure 34, converting the chassis to solid Figure 35, putting the fixtures Figure 36, adding the acceleration Figure 37, applying the material for chassis components Figure 38, creating the component contact Figure 39, creating the contact set Figure 40, creating a mesh Figure 41, vehicle components Figure 41, Stresses on the chassis Figure 42, Stresses on side bottom members Figure 43, strain on the whole chassis Figure 44, displacement on the whole chassis Figure 45, FOS during braking Figure 46, Stresses on the chassis during acceleration P a g e

5 Figure 47, Stresses on side bottom members Figure 48, displacement on the whole chassis (during acceleration) Figure 49, FOS during acceleration Figure 50, Stresses on the chassis Figure 51, Stresses on side bottom members Figure 52, displacement on the whole chassis (during acceleration) Figure 53, FOS during cornering Figure 42, welding machine (hotrod, 2010) Figure 43, MIG and TIG welding (mechanical-engineering, 2011) Figure 44, Brazing (Brazing practice, 2013) Figure 45, Gas blow torch (directindustry, 2011) Figure 46, welding structure parts (section view) (BASIC WELDING, n.d.) Figure 47, Residual stress versus soaking time (PWHT Determines the Quality of Weldments, 2012) Figure 60, Residual stress versus reliving temperature Figure 61, typical thermal treatments for weldment. (Khan, 2007) Figure 50, finding the chassis mass in KG through using solid work software Figure 51, creep test device. (CREEP TESTING MACHINE, n.d.) Figure 52, tensile test device. (matcsi, 2010) Figure 65, failure theory (Failure Mechanics, 2013) Figure 66, failure theory (Failure Criteria, 2013) Table of Tables: Table 1, forces on the chassis Table 2, tubes dimensions Table 3, mild steel (AISI 1020) properties (abstained from solid works) Table 3, decision matrix P a g e

6 Synopsis: The main aim of this assignment is to analyse various types of the stresses that are acting on the chassis during cornering, acceleration and braking; this report consists of nine sections. The first section is an introduction; it shows the forces on the chassis (gravitational force and lateral or longitudinal force). The second section is failure mode; it analyses various types of failure modes. The third section is failure theory; it shows some of theories for both ductile and brittle materials. The forth section is failure criteria; it estimates the FOS and the maximum deflection for the design. Finite Element Analysis is the fifth section; it defines the meaning of the concept (FEA), and shows the steps for doing the analysis for the chassis. Chassis Finite Element Analysis is the sixth section; it analyse the stresses, displacement and FOS on the chassis during acceleration, braking and cornering. Method of joining is the seventh section; t shows various type of joining methods, and selects one of them for manufacturing the chassis. Heat treatment is the eighth section; it demonstrates post weld heat treatment process. The last section is conclusion which is summary of the entire report outcome. 6 P a g e

7 Introduction: The main aim of this report is to analyse the stresses that act on a chassis that designed and modified by me in order to estimate whether if the initial design can withstand the forces that are acting on it, if it is suitable for the racing fields or not and if the design requires some modifications (optimisations). To achieve this aim I will use Finite Element Analysis (FEA) feature in solid-works software to analyse the whole structure of the chassis; specifically I will use assembly feature in order to add the components of the car (engine battery, etc.) on the chassis as a loads that are acting on it as shown on the figures below; I will add two force as well which they are the gravitational acceleration that acts downward, also the longitudinal acceleration due to weight transfer during braking or acceleration or lateral acceleration during cornering as shown on the figure below: Figure 1, Gravity and longitudinal acceleration (acceleration) Figure 2, Gravity and longitudinal acceleration (braking) Figure 3, Gravity and lateral acceleration (cornering) 7 P a g e

8 Analysing situations: In this repot I will simulate the chassis design through using FEA in Solid-Works software in three different situations which they are acceleration, braking and cornering. The total stress on the design, the displacement and FOS where the minimum actual FOS is 2 (see FOS section) will be analysed in order to test the design stiffness and durability. To analyse the design I should place the vehicle components (engine, battery, ETC) with their specific weights on the chassis. In addition, I should find the lateral acceleration during cornering and longitudinal acceleration during acceleration and braking: Lateral Acceleration during cornering: Assuming that the cornering is in a steady condition where the driving in a smooth road, the cornering at constant speed and a constant longitudinal acceleration. Z Figure 4, forces that effect on vehicle during cornering (front view) ( milliken, 2002) Where, 1. : Centre of gravity = W = N. 2. : Centre of gravity height m. 3. : The weight of the left hand side of the vehicle. 4. : The weight of the right hand side of the vehicle. 5. : The track width 1.67m. 6. : The lateral acceleration =. During cornering the centripetal force is equal to the frictional force, to find the maximum turning velocity we assumed that the turning in a corner with a radius of 100 m: The friction force = = The centripetal force = 8 P a g e

9 = 29.7 (Harbin, 2013) Lateral acceleration (a) = Longitudinal Acceleration during braking and acceleration: The vehicle mass Kg. The vehicle weight is. The friction coefficient between the tire and the dry road is 0.9. The reaction force is. The friction force = The acceleration or the deceleration can be found through using Newton s Second law which is. Another method, the acceleration is equal to the gravity multiplies by the frictional force: Figure 5, vehicle reaction force. (Nuffield Foundation, 2011) 9 P a g e

10 Forces that act on the chassis: Part Mass in Figure: Chassis without roll cage mass 92Kg(obtained from solid-works) see appendix A Radiator 12Kg Battery 11.8Kg Fuel tank 33Kg Two Passengers 150Kg Engine + transition 200Kg Assembly Table 1, forces on the chassis 10 P a g e

11 Tube properties: Tube size: 25 mm square tube with 2 mall wall thickness 21 mm square tube with 2 mall wall thickness 38 mm diameter round tube with 3 mm wall thickness Location: All of the chassis except the side members and roll cage For side members only. For the roll cage (I did not analyze it due to an error during simulation) Table 2, tubes dimensions Tubes material properties: Material name: AISI 1020 Default failure: Max von Mises Stress Yield strength: (MPa) Tensile strength: (MPa) Elastic modulus: (MPa) Poisson's ratio: 0.29 Mass density: 7900 Shear modulus: N/(MPa) Thermal expansion coefficient: 1.5e-005 /Kelvin Table 3, mild steel (AISI 1020) properties (abstained from solid works) Failure modes: Static loading: Static loading is a stationary force or couple applied to a material, and to be stationary the force or the couple must be constant in the magnitude, in the point or points of application, and in the direction. There are many examples of static loading forces such as, axial tension or compression, a shear load, a bending load, or any combination of these. In addition, the material starts yielding (become permanently distorted) or fail (separated into two pieces or more) if the applied stress (load) exceeds the material s strength (UTS). For instance, during static the chassis is subjected to a bending stress due to the weight of car components (battery, engine, etc.) that are placed on the chassis; where if the chassis not stiff enough it s member (square tubes) will bend during static. In addition, two tests are important for static loading which they are Creep test and rapture test. 11 P a g e

12 Creep test: Creep is a concept used when a material is subjected to a constant load like a tension load; the length of the material will increase through the increasing of the time until the material fail, therefore, it is a time-dependent failure mechanism. (Suranaree University of Technology, 2007) There are two main examples of creep applications: 1. Creep test: The creep test measures the dimensional changes that occur through applying a constant load to a tensile specimen maintained at a constant temperature, (Suranaree University of Technology, 2007) Figure 6 creep test specimen (Suranaree University of Figure 7, stress versus strain (Suranaree University of Technology, 2007) From the figure above the shape of creep curve will slightly change according to the magnitude of the applied stress at a constant temperature where the higher load is the more strain and faster failure 2. Rupture test: The rupture test measures the effect of temperature on the. It is similar to the creep test since the material is subjected to a higher stress level until the material fails and the time at failure is measured. (Suranaree University of Technology, 2007) Figure 8, Stress versus rupture time (Suranaree University of Technology, 2007) As shown on the figure above the rupture strength and the time of failure are plotted in a straight line and the changing of the slope refers to the structural changes in the material. 12 P a g e

13 Creep stages: When applying a constant tensile load on a material, the martial will deforms in three stages: The first stage called primary creep where the creep rate is decreasing and the creep resistance of the material increases to material deformation. The second stage called Secondary creep that shows a nearly constant creep rate, and the average value of the creep rate during this period is called the minimum creep rate. The last stage is tertiary creep; it shows a rapid increase in the creep rate because of the effectively reduced cross-sectional area of the material. (Suranaree University of Technology, 2007) Creep deformation processes: Figure 9 Strain versus time (Suranaree University of In the first stage the deformation occurs by slip systems; more slip systems operate at high temperature and slip bands are coarser and widely spaced. The second stage is Subgrain formation; the Creep deformation produces imhomoginiety especially around grain boundaries, letting dislocations to arrange themselves into a low-angle grain boundary. The last stage is grain boundary sliding; and it produced through the shear process and promoted by decreasing strain rate or increasing temperature. (Suranaree University of Technology, 2007) Figure 10 creep rate versus strain (Suranaree University of Technology, 2007) Two of the most important curves for engineers and designers are creep data curve and creep strength curve: Figure 12 creep strength curve (Suranaree University of Technology, 2007) Figure 12 creep data curve (Suranaree University of Technology, 2007) Creep strength curve: shows a material stress at a given temperature, which produces a steady-state creep rate. (Suranaree University of Technology, 2007) Creep data curve: shows a plot of the material stress and time to produce different amounts of total strain. (Suranaree University of Technology, 2007). 13 P a g e

14 Cyclic loading (fatigue): When an object is made from a specific material is subjected to vibrating or oscillating forces such as, sitting on and standing from a thin chair continuously until it breaks; the failure mechanism of materials under repetitive loads called fatigue failure. Furthermore, fatigue is a concept refers to a material becomes tired and will fail at a stress level below the yield strength of the material. Material fatigue is an important point for engineers to study because statics indicate to fatigue failure is the responsible for 90% of all failures of metallic structures such as bridges and machine components failure. (Failure Mechanics, 2013). The three stages of fatigue: First a microscopic crack will begin to form called the initiation site. Under the cyclic loading the microscopic crack starts to propagate. The material fails when the crack grows large enough. (Failure Mechanics, 2013) Loading types: Fatigue cracks initiate begin to form based different factors such as, the loading pattern must contain minimum and maximum peak values with a large enough of variation between the amplitudes, the reverse loading cycle and the peak stress must be sufficiently high; since if the peak stresses are too low no crack initiation will occur also the material must experience a sufficiently large number of cycles of the applied stress. (fatigue test, 2013) There are two types of loading that could initiate a fatigue crack, which they are sinusoidal loading and spectrum loading: Sinusoidal loading is divided into two types. The first type occurred when the loading is going from a tensile stress to a compressive stress. In this type of loading (stress cycle) the maximum and minimum stresses are equal. Tensile stress is considered as the positive cycles, and compressive stress is the negative cycles as shown on the figure below: Figure 13, Sinusoidal loading (fatigue test, 2013) 14 P a g e

15 The second type of sinusoidal loading that causes also materials fatigue is a loading with the minimum and maximum stresses both in the tensile as shown on the figure below: Figure 14, Sinusoidal loading (fatigue test, 2013) The second type of loading is spectrum loading that the loading has variable-amplitude on the graph; for example, when the chair experiences changing in loading patterns. Furthermore, in variable-amplitude loading, cycles that exceeding some peak threshold will aid to fatigue cracking. The figure below shows spectrum loading graph: (fatigue test, 2013) S-N curve Curves: Figure 15, spectrum loading (fatigue test, 2013) S-N curve curves show the relation between the alternating stress amplitude ( ) versus number of cycles ( ) to failure: There are two distinct types of S-N curves: Figure 16, Ferrous and nonferrous S-N curves (S-N curves, 2011) 15 P a g e

16 The first type of S-N curves occurred in ferrous (iron based) alloys like carbon steel, which the stress amplitude starts decreasing through the increasing number of cycles until the curve becomes horizontal which means through the increasing number of cycles the stress will remain the same, therefore the material will not fail, this called fatigue limit or endurance limit. (the upper curve) (Failure Mechanics, 2013). The second type of S-N curve occurred in Nonferrous alloys like Aluminium that there is no fatigue limit for the material, thus the S-N curve continues downwards and fatigue failure will occur after a certain number of cycles.(the lower curve) (Failure Mechanics, 2013) Tensile test: Tensile test is a mechanical test where any material is subjected to a pulling force from both sides until the material specimen changes its shape or break. From this test, much information about the material can be tested such as, percentage of elongation(less than 5% brittle or more than or equal 5% ductile), yield point, tensile strength, ultimate strength of the material and the material ductility. In addition, this test shows how a material reacts when tension force is applied to it. (Tensile strength, 2013). Furthermore, stress (the forced applied divided by the cross sectional area before the testing) and strain (material elongation divide by the original length of the material) are found in order to draw the Stress versus strain diagram, which represent the relationship between the load applied to the material and the deformation of the material (ductile or brittle), caused by the load. (Tensile properties, 2012)The graph below shows the result of a tensile test for a ductile material: Figure 17, stress versus strain graph (Tensile properties, 2012) From the graph above the stress versus strain graph has three stages. In the first stage the curve starts increasing in a linear curve until it reaches to a point called the yield point, which is a transition point that when the applied force exceeds it the material will deform permanently, and the slope of the linear line (difference in stress divided by difference in strain) represent the young modulus of the material (stiffness), which is the ability of material to undergoes stress, deforms, and then returns to its original shape after the stress is removed. The second stage called uniform plastic deformation; it starts after the Yield point 16 P a g e

17 where the curve increasing uniformly until it reaches to the highest point of the curve which represents the ultimate tensile strength (UTS) of the tested material. Furthermore, the maximum stress level reached in this test (UTS) represents the material ability to withstand external forces without breaking. The last stage is non-uniform plastic deformation that the curve starts decreasing until it reaches to the fracture point that the material cut into two pieces. (tensile, 2012). Ductile and brittle failure: Ductile materials are materials deform before fracturing, and the material ductility is measured by finding the percentage of elongation at the fracture point. Materials that have 5% or more percentage of elongation are considered as ductile, while when the material elongation is below than 5% it considered as brittle material. Furthermore, brittle material yields very little before fracturing, the yield strength is approximately equal to the ultimate tension strength. (Static loading theory, 2011). Mild steel grade 1020 is a type of ductile materials. Figure 18, ductile and brittle materials. Fracture in ductile and brittle failure: A B Figure 19, ductile and brittle fracture (ductile and brittle fracture, 2008) The figure above (part A) shows the fracture in ductile material that called cup and cone; since, part B shows the fracture in brittle material where the cut is street and the surface of it is rough. 17 P a g e

18 Crack Propagation (ductile material): The crack continues to grow during this stage as a result of repetitive loadings. In ductile materials the crack propagation occurs in several steps. Initially as a result of the tensile load, the material stretches and experiences plastic deformation. Beyond some point the material will begin to neck: (Ductile Fracture 2, 2013): Neck Figure 20, Neck (Ductile Fracture 2, 2013) With continuing stress the material continues to plastically deform and small openings begin to appear inside the material at the centre of the necked region. These holes are known micro voids (Ductile Fracture 2, 2013): Micro voids Figure 21, Micro voids (Ductile Fracture 2, 2013) The micro voids grow and coalesce from a continuous cavity within the centre of the necked region. Once the cavity in the centre of the specimen reaches a certain size the sample will fail by fast fracture (Ductile Fracture 2, 2013): Coalesce Figure 22, Coalesce (Ductile Fracture 2, 2013) The fast fracture region typically occurs at 45 degree to the plane of the tensile load (the angle at which the shear load is the greatest).this result in a lip around the fracture surface. (Ductile Fracture 2, 2013): Figure 23, Fracture (Ductile Fracture 2, 2013) The flat region which resulted from the initial microvoid coalescence is typically quite rough in appearance while the surface of the shear lip is typically quite smooth. (Ductile Fracture 2, 2013) Figure 24. microvoid and shear slip (Ductile Fracture 2, 2013) 18 P a g e

19 Fracture shape: Figure 25, Cup and cone fracture. (Duralumin, 2013) The left picture represents the cone and it consists of two regions; the first region in the middle is the flat region which resulted from the initial microvoid coalescence. The second region is the surface of the shear lip is typically quite smooth. The right picture is the cup, it consist also with two regions, rough in the middle and smooth in shear slip. Fatigue failure (ductile materials): Figure 26, fatigue failure. The figure above shows failure in a pedal (for ductile material) arm failed because of fatigue failure; it s obvious that the fracture surface consist of two distinct regions; the first one(the bigger and lighter region) is smooth (burnished) produced as a result of the rubbing of the bottom and top of the crack as it is growing. The second is granular, produced as a result of the rapid failure of the material, it contains marks called clamshell marks (beach marks), these marks produced through the crack propagation, and the distance of them depends on the stress magnitude. (fatigue, n.d.). Failure theories: If a material is subjected to increasing loads it eventually fails. Furthermore, it is easy to estimate the point of failure of a material that is subject to a tensile force, since it is more complicated to determine the points of failure when the material is subjected to a number of loads in different directions where some of them are tensile loads, and some of them are shear loads. Scientists developed many theories for calculating the stresses. For instance, there is maximum shear stress theory and maximum distortion energy (von Mises stress for ductile materials) for ductile materials. Since there is Maximum normal stress, and Modified Mohr for brittle materials; there is more theories but I don t have enough time to explain more. 19 P a g e

20 Maximum shear stress: Maximum shear stress occurs in ductile materials, which the plane Stress only. When the maximum shear stress exceeds the material Strength, thus the material yields. Furthermore, for a given plane the maximum in-plane shear Stress is equal to the average of the in-plane principal Stresses:, (failure theories, 2010) The two maximum Out-of-Plane Shear Stresses are: is the Maximum Shear Stress. is the Maximum Principal Stress. is the Minimum Principal Stress. Note that the out-of-plane principal stress ( ) for the strain plane condition is zero. The failure occurs when the maximum of the Three Maximum Shear Stresses reaches the shear yield stress. From the figure above failure occurs if the in-plane principal Stresses lie outside the shaded zone. Figure 27maximum shear stress (failure theories, 2010). Under a Uniaxial load,.thus, the axial yield stress is = =. The Maximum Shear Stress Theory predicts that the Shear Yield Stress is half the Axial Yield Stress. When the In-Plane Principal Stresses are the same sign (1st and 3rd quadrant), the Maximum Shear Stress in the system is Out-of-Plane. When the In-Plane Principal Stresses are opposite sign (2nd and 4th quadrant), the Maximum Shear Stress in the system is In- Plane. (Failure Criteria, 2013) In short, in Max Shear Stress the material fails when: 20 P a g e

21 Factor of Safety: MAXIMUM DISTORTION ENERGY: First, Von Mises Equivalent Stress ( ) defined as the Uniaxial tensile stress that creates the same distortion energy as any actual combination of applied stresses. In addition, ductile materials will fail when the Von Mises Equivalent Stress ( ) exceeds the Axial Yield Stress ( ). The von Mises Equivalent Stress is defined by: (failure theories, 2010) Von Mises equation: Figure 28 Von Mises stress (Failure Criteria, 2013) Total stress ( ) = Factor of Safety: The material fails (yields) when Maximum normal stress: Is a state happens when the maximum normal stress in any direction of a brittle material reaches to the material strength, therefore the material fails. 1. In tension stress failure occurs when: 2. In compression stress failure occurs when: Where, is the stress applied on the material. : is the ultimate strength in Tension : is the ultimate strength in Compression In brittle materials is much greater than. Figure 29 Maximum normal stress (Failure Criteria, 2013) 21 P a g e

22 Modified Mohr: The Mohr Theory of Failure (Coulomb-Mohr criterion or internal-friction theory) is based on the famous Mohr's Circle. Mohr's theory is used in predicting the failure of brittle materials. Mohr's theory suggests that failure occurs when Mohr's Circle at a point in the body exceeds the envelope created by the two Mohr's circles for uniaxial tensile strength and uniaxial compression strength. This envelope is shown in the figure below. (Failure Criteria, 2013) Figure 30Mohr's Circle (Failure Criteria, 2013) The left circle is for uniaxial compression at the limiting compression stress sc of the material. Likewise, the right circle is for uniaxial tension at the limiting tension stress. The middle Mohr's Circle on the figure (dash-dot-dash line) represents the maximum allowable stress for an intermediate stress state. All intermediate stress states fall into one of the four categories in the following table. Each case defines the maximum allowable values for the two principal stresses to avoid failure. (Failure Criteria, 2013) 22 P a g e

23 Factor of safety\ displacement: The factor of safety (FOS) can be estimated through specifying five elements which they are; the properties of the material, the applied stresses, geometry, failure analysis and the desired reliability. Estimating the contribution for the material : The properties of the material (the specific chosen material for the chassis) will be obtained from Solid Works software or from a trusted internet source like (mat-web). Therefore, all of the properties are well known; though we will not do a special test to ensure the properties of the specific chosen material. However, the supplier do not grantee that the tubing sections have a constant thickness where some points of the tubes may be thinker or thinner than the spiced thickness. In addition, the material can expose to some of the environmental conditions such as, corrosion and rust that lead to the material wear. Therefore we will put the safety factor as 1.1 Estimating the contribution for the load stress : In this part the nature of the loads that act on the vehicle during static, acceleration, declaration, cornering and bumping are well known as a separate situation. In combined situations like acceleration and cornering in the same time or bumping and cornering in the same time the loads are not well known. Therefore we will put the safety factor as 1.2. Estimating the contribution for geometry : The students will build the chassis manually by their self and due to the lack of welding experience for the reason that most students did not weld anything before or study a welding course; therefore, there is a big possible that the manufacturing dimensions will be out of tolerances and not closely held. Therefore we will put the geometry safety factor as Estimating the contribution for failure analysis : The failure analysis is not well developed where we did not calculate the failure due to cumulative damage or fatigue stresses. Therefore we will put the failure analysis safety factor as P a g e

24 Estimating the contribution for reliability : Solid works software uses thousands of equations to analyse the stress on each small part of the wishbone (software splits the wishbone into thousands of meshes); therefore, we can rely on sold works simulation; since it s still theoretical calculations Therefore I will put the 1.1 as safety factor for reliability. Therefore, Displacement: The allowable range of displacement for the chassis design should be 1 mm or lower; I selected 1 mm as a maximum displacement for several reasons first is to provide stable driving without any sudden shocks (good for handling), also, to do not effect on the suspension geometry (camber, caster and toe) due to the chassis is connected with suspension system so the large displacement will effect on the suspension geometry which leads to tires wear and the instability of the vehicle as well. Furthermore, I select 1 mm to avoid the design failure. Finite Element Analysis: Definition: Finite Element Analysis (FEA) is computer program uses a finite element technique to study a design with a specific material; it analyses how the applied loads (stresses) will effect on the design through giving specific results (graphs and tables). FEA analysis is done through generating a mesh of points in a shape of the design that has information about the used material properties and the design at each point for the doing the analysis. The benefits of (FEA) are, it can assist in finding the design reactions against the stresses that are acting on the design, it can analyse the effect of heat transfer, fatigue and vibration as well. The main benefit of (FEA) it can help in finding the weakness points in the design before manufacturing it, and determining the design required modifications to meet the design requirements (specifications). (Introduction to Finite Element Analysis, 2008). 24 P a g e

25 FEA types: There are two methods can be used for the analysis, modelling and modelling; the modelling is simple and lets the analysis to be run on normal computers (recommended for building 30 computers), however, it gives less accurate results. Since, the modelling, generates more accurate results (requires fast computers with high specifications such as Ram, processor, etc.). In both modelling methods, the programmers can add numerous functions in order to make the system behave linearly or non-linearly. The linear systems are less complex; typically they do not take into account the plastic deformation. The non-linear systems analyse the plastic deformation, test a material in a specific design in all the way to fracture, etc. (Introduction to Finite Element Analysis, 2008) Meshing system in FEA: In FEA the software (any software applies FEA) uses very complicated system of points called nodes; these nodes create a mesh on the tested design as shown on figure below. The mesh is programmed to have the material and design properties which describe how the structure will react to the stress that the design will expose to. (Introduction to Finite Element Analysis, 2008) Figure 31, Meshing system (FEA). (sciepub, n.d.) The loads that can be applied in FEA: 1. Pressure, thermal, centrifugal static loads and the gravity. 2. Thermal loads that are from solution of heat transfer analysis. 3. Convection and heat flux. 4. Gravity dynamic loads. 5. ETC (based on the used software). (Introduction to Finite Element Analysis, 2008) FEA gives a results for maximization and minimisation of: 1. Displacement, velocity, acceleration and force. 2. Volume, temperature, mass. 3. Stress and strain energy. 4. Synthetic (User defined). (Introduction to Finite Element Analysis, 2008) 25 P a g e

26 Chassis (FEA) steps: In order to analyse the chassis and the stress that are acting on it, we should do some steps in order to get right simulation without any error; the table below shows the steps for doing the FEA in solid-works: 1. Applying the material to the chassis: Figure 32, selecting the material for the chassis. Before doing this step we should go to new study than static. Click on apply material (1) than Choose the required material (2), and finally apply the changes than close the window (3). 2. Converting the chassis members to solid bodies: Figure 33, converting the chassis to solid. Click on parts than chassis file (1) than select all of the chassis members (2), and finally click on treat as a solid (3). The purpose of step is to convert the chassis from beams to a solid to assemble it with remaining members. 26 P a g e

27 Now go to assembly option insert the vehicle components, than choose mate option; finally connect the face of the component with the face of the required chassis member through using coincident option. For the engine part, for the engine part I assembled it directly on the bottom layer members since it is an approximated position; I can put it in a right way but this will creates some errors in my simulations. 3. Adding the fixtures: Figure 34, putting the fixtures. Click on fixture advisor (1) than Choose fixed geometry (2); select the required faces that you should put the fixture on them than apply the changes (3). 4. Adding the acceleration: Figure 35, adding the acceleration. Click on external force (1) than select gravity (2), add the normal gravity (3).Finally add the longitudinal acceleration or lateral acceleration (4), for the acceleration direction see the introduction. 27 P a g e

28 5. Applying the material to vehicle components: Figure 36, applying the material for chassis components. Right click on the component (1) click on apply the material (2). Finally repeat the steps that mentioned in stage one. 6. creating the connection on the assembled design: B Figure 37, creating the component contact. Figure 38, creating the contact set 28 P a g e

29 Click on connection adviser (1) than select component contact (2); check the box exactly as shown on part B in figure 33.click contact set(3), select automatic find contact set(4), select the whole chassis and click find contact set(5), and finally chose bonded than apply the changes (6). The purpose of the two steps (contact set and component contact) is to connect all of the chassis members together, and to connect the chassis with the assembled components in order to mesh the component and getting the simulation without any error. 7. creating a mesh: Figure 39, creating a mesh. Click on create mesh under run option (1) click on curvature based mesh (2). Check draft quality mesh (3). And finally run the design. converting the vehicle components to masses: Figure 40, vehicle components. This is an additional step I did it to convert the vehicle component from solids to mass in order to get the results only for the chassis (for the displacement simulation only). First right click in the component (1), click on treat as remote mass (2). 29 P a g e

30 Chassis Finite Element Analysis: FEA analysis during braking: Stress analysis A1 A2 B C Figure 41, Stresses on the chassis Note: I suppressed all of the vehicle components. As we can see the stress is not distributed uniformly on the chassis members (the stress range is from 0 MPa (minimum) to MPa (maximum)); the highest stress on the chassis members is at point A which is equal to 203.3MPa. The value of this the stress is not very accurate at point A1 because there was an error in trimming the members (A2) where the value of the stress should be between 135.5MPa to 169.4MPa. This point Still exposing to high amount of stress due to at this point the bottom side member is exposing directly to the weight of the passenger. Furthermore, this point is an attachment point where it connects between three members; which this attachment point receive the stress from three members leading to stress concentration. In addition, this point is a heat affected zone, where the heat of cutting the members and welding them stresses the material causing residual stresses. In figure 41, it is obvious that the stress is higher at the rear of the car; this happened because the heaviest components are placed at the rear of the car (engine 200 Kg, each passenger 75 Kg), so the stress at the rear of the chassis members is higher than the front of the chassis members. One 30 P a g e

31 of the biggest stresses on the chassis is at point B (one of the bottom layer members) because it expose to the weight of the engine and the weight of the left passenger. The second highest stress after point A is at point C (end point of bottom side member) where the stress concentrates more because it is an attachment point, this member carries the engine directly; therefore it get high stress from the engine weight. The location of the engine is not right where actually the engine is mounted through using brackets in the bottom layer members, top layer members and the roll cage; so the actual stress is lower at point C. In this analysis I did not include the roll cage where the roll cage is heavy component will increase the stress on the members that will be placed on them, however, adding the roll cage will increase the torsional rigidity of the chassis. I placed the engine on the bottom side members and I removed the roll cage in order to make the analysis easier. The figure below shows the stress on the side bottom members only (for every points): Figure 42, Stresses on side bottom members Figure 42 shows the stresses on the side bottom members in all meshes (all of the points that solid-works calculated the stress on them separately); it is obvious that there is a big amount of variation in the total stress (Von Mises stress) for each mesh as a separate part. Most of the total stresses are equal to approximately 10 MPa to 25 MPa; since the remaining stresses are from 25 MPa to 95 MPa where the stress is higher at these points because either these point are exposing the stresses of the heavy components or if they are attachments point due to stress concentration. 31 P a g e

32 Strain analysis: Figure 43, strain on the whole chassis. As we can see the strain figure is similar to the stress figure, the difference is only that the stress figure is shows stress values and strain figure shows the strain value. To explain this, the strain is directly proportional to the stress that is exposed to. To expand, the stiffness of the material (young modulus) is equal to the stress divided by strain ; since the young modulus is constant for the material; thus when the stress increases the strain increases as well. This makes the two stress and strain figure similar so l don t need to repeat the stress analysis. For the displacement (deflection) part; the displacement is affected by magnitude of the stress that the member will expose to also the length of the member (based on how the member connected and how the force is applied). For example when Appling the member to bending stress from the middle it is the member is similar to simply supported beam, so the highest deflection will be at the middle. The deflection of simply supported beam is, where W is the load in newton L is the length of the beam E is the young modulus and I is second moment of area. Displacement analysis: 32 P a g e

33 E C B Z D A Figure 44, displacement on the whole chassis. As we can see, the displacement range is from approximately 0 mm to mm; this means that the maximum displacement (deflection) on the chassis members is lower than the allowable amount deflection (1 mm). From figure 44, the displacement is not equal; some of the biggest displacements are at point A, B, C, and D; since one of the smallest displacements is at point E. The displacement is high at point A and B because they expose to bending stress due to the weight of the engine. Point C and D expose to higher amount of deflection than point A and B; the deflection occurred due to the longitudinal weight transfer from the rear to the front which causes torsion to the members C and D. The highest bending is at point Z which it exposes to the weight passenger also the torsional force due to longitudinal weight transfer. The deflection at point E is too small because this member does not carry any components (no loads that act on it); expect the small effect of longitudinal weight transfer. 33 P a g e

34 FOS: E Z C D B F Figure 45, FOS during braking A Point A B C D E F Z FOS As shown on figure 45, the minimum FOS on the chassis is 1.69 which is located at point Z; we know that the amount of stress is higher than the actual; for all of the reaming parts the FOS is higher than 2 which is the required FOS for the design (see FOS section). This mean all of the chassis design is safe during braking except point Z that exposes to more stress, and due to the displacement is lower than 1 mm; it is recommended to heat treat the chassis especially for the joint like point Z in order, to minimise the stress concentration and stress relief. 34 P a g e

35 FEA analysis during Acceleration: Stress analysis A D B C Figure 46, Stresses on the chassis during acceleration. Note: I suppressed all of the vehicle components. During acceleration the locations of the highest stresses are similar to the braking situation because the main cause of stress concentration is the weight of the components (especially for engine and passenger loads), and the attachment points that they expose to higher stresses. During acceleration the maximum von Mises stress decreased from 203.3MPa (during braking) to MPa. As we can see the stress is not distributed uniformly on the chassis members (the stress range is from 0 MPa (minimum) to MPa (maximum)); the highest stress on the chassis members is at point A which is equal to 101.3MPa. The value of this the stress is not very accurate at point A because there was an error in trimming the members where the value of the stress should be between 91.2 MPa to 169.4MPa. This point Still exposing to high amount of stress due to at this point the bottom side member is exposing directly to the weight of the passenger. Furthermore, this point is an attachment point where it connects between three members; which this attachment point receive the stress from three members leading to stress concentration. In addition, this point is a heat affected zone, where the heat of cutting the members and welding them stresses the material causing residual stresses. In figure 46, it is 35 P a g e

36 obvious that the stress is higher at the rear of the car; this happened because the heaviest components are placed at the rear of the car (engine 200 Kg, each passenger 75 Kg), so the stress at the rear of the chassis members is higher than the front of the chassis members. One of the biggest stresses on the chassis is at point B (one of the bottom layer side member) because it exposes to the weight of the left passenger also; it is an attachment point where it exposes to more stress from the attached members. Furthermore, point D (the side member in the bottom layer of the chassis) exposes to high amount of stress as well due to the load of the passenger that pushes this member (bend it), and the longitudinal weight transfer from front to rear that adds more load on the member (more bending stress). The second highest stress after point A is at point C (end point of bottom side member) where the stress concentrates more because it is an attachment point, this member carries the engine directly; therefore it get high stress from engine mass. The location of the engine is not right where actually the engine is mounted through using brackets in the bottom layer members, top layer members and the roll cage; so the actual stress is lower at point C. In this analysis I did not include the roll cage where the roll cage is heavy component will increase the stress on the members that will be placed on them, however, adding the roll cage will increase the torsional rigidity of the chassis. I placed the engine on the bottom side members and I removed the roll cage in order to make the analysis easier. In addition, the effect of longitudinal weight transfer due to acceleration force is not very clear in stress analysis; in displacement analysis it is clearer. The figure below shows the stress on the side bottom members only (for every points): Figure 47, Stresses on side bottom members Figure 47 shows the stresses on the side bottom members in all meshes (all of the points that solid-works calculated the stress on them separately); it is obvious that there is a big amount of variation in the total stress (Von Mises stress) for each mesh as a separate part. Most of the total stresses are equal to approximately 0 MPa to 20 MPa; since the remaining 36 P a g e

37 stresses are from 25 MPa to 95 MPa where the stress is higher at these points because either these point are exposing the stresses of the heavy components or if they are attachments point due to stress concentration. Displacement analysis: E D B C Z A Figure 48, displacement on the whole chassis (during acceleration) As we can see, the displacement range is from approximately 0 mm to mm; this means that the maximum displacement (deflection) on the chassis members is lower than the allowable amount deflection (1 mm). From figure 48, the displacement is not equal; the light blue arrows shows the effect of the acceleration force where the displacement increased more in these points, this occurred due to the longitudinal weight transfer from front to rear which increases the stresses in these points. Some of the biggest displacements are at point A, B, C, and D; since one of the smallest displacements is at point E. The displacement is high at point A and B because they expose to bending stress due to the weight of the engine. Point C and D expose to higher amount of deflection than point A and B; the deflection occurred due to the longitudinal weight transfer from the front to the rear which causes torsion to the members C and D. The highest bending is at point Z which it exposes to the weight of the passenger at this 37 P a g e

38 point, and point Z expose to more bending force due to longitudinal weight transfer. The deflection at point E is too small because this member does not carry any components (no loads that act on it); expect the small effect of longitudinal weight transfer. FOS: Z C A E D B F Figure 49, FOS during acceleration Point A B C D E F Z FOS As shown on figure 49, the minimum FOS on the chassis is 2.89; it is located at point Z. The minimum FOS is higher than the required FOS (2). As a consequence that the highest displacement is lower than 1 mm, and the actual FOS is high the chassis design is safe during acceleration. For optimising the design it is recommended adding light weight roll cage for decreasing the stress on the chassis members, and taking into account selecting an appropriate member (a member that is not expose to high value of stress) to mount the roll cage. Therefore, the roll cage will assist in increasing the torsional rigidity of the chassis and helps the passenger from roll over and side accidents. 38 P a g e

39 FEA analysis during Cornering: Stress analysis C D A2 B A1 Figure 50, Stresses on the chassis Note: I suppressed all of the vehicle components. As we can see the stress is not distributed uniformly on the chassis members (the stress range is from 0 MPa (minimum) to MPa (maximum)); the highest stress on the chassis members is at point A which is equal to 219.2MPa. The value of this the stress is not very accurate at point A1 because there was an error in trimming the members (A2) where the value of the stress should be between MPa to 164.4MPa (I discovered the new error in the cornering situation). Therefore, for future analysis I need to double check the trims, and try to fix them if possible for getting more accurate results. This point is still exposing to high amount of stress due to at this point the bottom side member is exposing directly to the weight of the engine. Furthermore, this point is an attachment point where it connects between three members; which this attachment point receive the stress from three members leading to stress concentration. In addition, this point is a heat affected zone, where the heat of cutting the members and welding them stresses the material causing residual stresses. In figure 50, it is obvious that the stress is higher at the rear of the car; this happened because the heaviest components are placed at the rear of the car (engine 200 Kg, each passenger 75 Kg), so the stresses at the rear of the chassis members are higher than the stress on the front of the chassis members. 39 P a g e

40 One of the biggest stresses on the chassis is at point B (one of the side members in the bottom layer of the chassis) because it expose to the weight of the engine and the weight of the left passenger. The second highest stress after point A is at point D than C (end points of bottom sides member) where the stress concentrates more because they are attachment points, these members carry the passengers; therefore these members get high stress from the passengers weight. Again, the stress analysis do not describe the effect of cornering force very well, I will describe the effect of lateral weight transfer in displacement section more clear. Figure 51, Stresses on side bottom members Figure 51 shows the stresses on the side bottom members in all meshes (all of the points that solid-works calculated the stress on them separately); it is obvious that there is a big amount of variation in the total stress (Von Mises stress) for each mesh as a separate part. Most of the total stresses are equal to approximately 5 MPa to 25 MPa; since the remaining stresses are from 25 MPa to 115 MPa where the stress is higher at these points because either these point are exposing the stresses of the heavy components or if they are attachments point due to stress concentration. 40 P a g e

41 Displacement analysis: E D Z A C B Figure 52, displacement on the whole chassis (during acceleration) As we can see, the displacement range is from approximately 0 mm to mm; this means that the maximum displacement (deflection) on the chassis members is lower than the allowable amount deflection (1 mm). From figure 48, the displacement is not equal; the light blue arrows shows the effect of the acceleration force where the displacement increased more in these points, this occurred due to the lateral weight transfer from the left of the car to the right of the car (during cornering to the left). To clarify, the light blue arrows show some of the points that got higher displacement (deflection) after cornering to the left. Some of the biggest displacements are at point A, B, C, and D; since one of the smallest displacements is at point E. The displacement is high at point A and B because they expose to bending stress due to the weight of the engine. Point A exposes to higher displacement than B due to the weight transfer from left to right where the member at point A will experiences more load, therefore more stress, and thus more displacement. Point C and D expose to higher amount of deflection than point A and B; the deflection occurred due to the lateral weight transfer from the left of the vehicle to the right of the vehicle. To expand, point D will expose to maximum weight transfer which causes bending. For 41 P a g e

42 point C, it will expose higher bending force due to weight transfer and also, the member in point C will be in torsion as well. The highest stress is at point Z, because the chassis member (for point Z) exposes the maximum weigh transfer which led to bend the member, and the passenger weight, therefore, point Z expose to high amount of deflection (comparing to the reaming chassis members) due to the bending stress. The deflection at point E is too small because this member does not carry any components (no loads that act on it); expect the small effect of lateral weight transfer. FOS: C A E D F Z B Figure 53, FOS during cornering Point A B C D E F Z FOS As shown on figure 53, the minimum FOS on the chassis is 1.6 which is located at point Z; we know that the amount of stress is higher than the actual; for all of the reaming parts the FOS is higher than 2 which is the required FOS for the design (see FOS section). This mean all of the chassis design is safe during cornering except point Z that exposes to more stress, and due to the displacement is lower than 1 mm; it is recommended to heat treat the chassis especially for the joint like point Z in order, to minimise the stress concentration and stress relief. 42 P a g e

43 Method of joining: Two or more materials can be joined through using various methods based on the required type of joint to be permanent or semi-permanent. In permanent joints; the joint cannot be reserved without damaging the material. Since, in semi-permanent joints are designed to be permanent, but the joints can be disassembled without damaging the materials. (Method Of Joining Materials, 2012) Welding: The main method for joining the metals permanently is by welding. There are several types of welding for instance, MIG welding, TIG welding, electric arc welding, oxyacetylene welding, seam welding, etc. All these types of welding use the heat for joining the metals permanently; leading to the two main pieces of the metal to be molten, and using a joining material for mixing them before solidifying. This generates a strong permanent joint. One advantage of welding that it can be repetitive due to robots can be used in welding especially when mass production is required such as, for car industries. (siliconfareast, 2005) During welding process; the temperature of the welding leads to change the microstructure of the welded areas of the working pieces. These areas are defined as, heat affected zone (HAZ) where the tensile strength and toughness of the metal decreases. A residual stresses which grow as the metal cools down and decrease the strength of the welded joints. Therefore, the welding process must be improved to decrease the microstructural changes, and the residual stresses in the welded area. Post welding treatments are used to relieve the residual stresses, and to make the microstructure of the welds more uniform (see Post welding heat treatment section). (Method Of Joining Materials, 2012) A. MIG Welding: MIG welding is a short for Metal Inert Gas welding; it combines two pieces of metal together with a consumable wire that is connected to an electrode current. The wire passes through the welding gun in the same time of the inert gas. The purpose of the inert gas is protecting the electrode from contaminants. (TIG vs. MIG Welding - What's the Difference?, n.d.) Figure 54, welding machine (hotrod, 2010) 43 P a g e

44 Advantages: The quickness; it is fast in producing the welds. Inexpensive price and the Equipment is more accessible. User friendly; because the welds are easier to make than TIG welding, and the step takes less time and is easy to automate than TIG welding. Disadvantages: Generates big amount of sparks, smoke and fume during the welding process. Reliability; possible irregular wire feedback and burn-back may occur with MIG welding. B. TIG Welding: TIG welding is a short for as Tungsten inert gas welding; it uses non-consumable tungsten, along with an inert gas, in order to weld two pieces of metal together. The purpose of tungsten electrode is providing the electricity for the welding process not for the filler. Advantages: TIG welding produce lower amount of sparks, fumes and smoke than MIG welding. Provides more precise, and higher quality welds than TIG. Autogenous Welds do not need a filler material to where TIG welding creates a weld through melting one part to the other. Furthermore, Autogenous welds are typically used during welding thinner materials. Disadvantages: Not user friendly where TIG welding needs more setup time. More expensive and takes more time thicker metals than MIG welding Specifically during welding TIG welding is complicated and needs more skills than the MIG welding. Figure 55, MIG and TIG welding (mechanical-engineering, 2011) 44 P a g e

45 Brazing The third joining process is brazing where it is used to join two work pieces together through using a filler metal that is sandwiched between them, and the filler metal undergoes melting only which the two work pieces do not face any melting. Thus, the temperature that the brazing process can be done must be high enough to melt the filler material. Furthermore, the materials that are used as fillers for the brazing process are those that melt above. In addition, a flux is used as well during brazing process for eliminating the oxide films from the surfaces of the work pieces and preventing oxidation. This ensures a good metallurgical bond among the work pieces, and the filler until the brazing process is done. There are many advantages for brazing joining method for example; they make the joining zones attractive. In addition, the brazed joint offers strength equal to or higher than the work pieces itself. The brazed joints are ductile, so they can withstand a considerable vibrations and shocks. Also, the brazing is done at low temperatures; this reduces the possibility of warping and overheating or melting the metals that will be joined. However, the brazing method of joining that close fit tolerances are required. (Is Brazing Better?, 2005) Soldering: Figure 56, Brazing (Brazing practice, 2013) The forth method of joining the metals is soldering; during soldering process two work pieces of metal are joined together by a third metal called (solder or filler) at a relatively low temperature that is higher the melting point of the filler. Soldering is classified within two types; the first type is hard soldering where the lowest melting point in hard soldering is, and the second type is soft soldering where the melting point is approximately. The stages in soldering process are: 1. First clean and degrease the materials; and the materials can be kept clean through using a flux. 2. The surfaces of the materials must be filled together without any gap. 3. A heat source like a blow torch should be used to heat the materials between the joint in order to ensure that both pieces are uniformly heated. 4. After completing the joints should be left to cool and harden. 45 P a g e

46 Advantages: Figure 57, Gas blow torch (directindustry, 2011) Requires lower power. Low joining temperature. Dissimilar materials can be joined together. There are no residual stresses in the joint parts. User friendly; easily automated joining process. Microstructure is not affected by heat of soldering. Disadvantages: Requires careful removal of the flux residuals to prevent corrosion. Cannot be used for joining large sections. Cannot be used for joining in high temperature applications. (tech, n.d.) Selection of method of joining: All of the previous mentioned methods are about permanent joining methods, however, there is many other Simi-permanent method of joining such as using nuts and bolts for joining; since the permanent joining method is stronger and we do not need to disassemble the chassis. Therefore, I will choose a type of permanent joining method. The available permanent joining method at building 30 is welding (MIG welding and TIG welding); thus I will make the comparison between the two types only Decision matrix (for choosing the type of welding that is available at building 30): Factor Cost Safety User friendly Mark: Mark: 7 Mark: 7 Mark: 10 Total Requirements Less in cost Safe welding method Easy to use MIG welding 7*7 4*7 9* TIG welding 5*7 6*7 6* Table 4, decision matrix Due to, the MIG welding is faster, easier where it do not requires skilled hand for doing it, also, it is cheaper than TIG welding and the equipment is more accessible I will choose MIG welding for welding the members of the chassis. 46 P a g e

47 Heat treatment: As mentioned previously; the stress concentrates more on the attachment points; these attachments points are located at the heat affected zones where the welding stresses the material (residual stress). The figure below categories the parts of weldment structure where it consist of fusion zone (weld metal), fusion boundary, Heat affected zone and the unaffected base metal. (BASIC WELDING, n.d.). Basically, the heat affected zone is a portion of the base metal that has not reached to the melting point, however the material mechanical properties or the microstructure (crystalline structure) have been altered from the heat of welding and cutting. Thus the material in the heat affected zone is stressed, and the material hardness increases (becomes brittle)). (PWHT Determines the Quality of Weldments, 2012). Furthermore, the stress concentration occurs due to a crack on the welding area generated due to a defect during welding which lead to the stress concentration on the welding points. Figure 58, welding structure parts (section view) (BASIC WELDING, n.d.) Post weld heat treatment (PWHT) (Stress relieving): Typically stress relieving is applied for carbon and low alloy steels where the metal temperature is raised to be just below than the transformation temperature, and held for a prescribed time and allowed to cool at a controlled rate. It is a process of uniform heating of a structure to a suitable temperature, holding at this temperature for predetermined period of time, followed by a uniform cooling where an even cooling may causes an extra stresses. The aim of this process is to eliminate the residual stress in metals, reduce the hardness of the weld and adjacent the heat affected zone after welding to recover the acceptable limits; therefore, reducing the possibility of cracking. Thus the benefits of stress relieving are: (Khan, 2007) Relieve the welding residual stresses (the main purpose). Decrease the hardness of the heat-affected zone. Improve ductility and notch toughness. Release the diffusible hydrogen. On the other hand, the extended heating could reduce the tensile strength and notch toughness of the welds. (PWHT Determines the Quality of Weldments, 2012) 47 P a g e

48 The percentage of relief of internal stress is based on the steel type (the material yield strength), the heating rate, soaking temperature and period, the cooling rate, and the temperature difference in the weldment during the heating and cooling cycle. The most important factors for stress relieving rate and the quality of the weld are soaking temperature and time. The more heat is the more stress relieve, and the more time is the more stress relive as shown on the figure below (an example of 2.25Cr-lMo steel welds); this rule is not applied to the curve A because the material was exposed to a high amount of heat for long time which led to increase the stress again. In addition, to ensure a uniform temperature distribution and to minimize the thermal stress; the maximum heating and cooling rates and the maximum temperature difference are to be determined before starting the process. (Funderburk, 1998) A Figure 59, Residual stress versus soaking time (PWHT Determines the Quality of Weldments, 2012) Figure 60, Residual stress versus reliving temperature The figure above shows the average stress remaining (residual stress) versus reliving temperature for three different materials with different yield strength psi (482MPa), 48 P a g e

49 50000 psi (345MPa) and psi (207 MPa). It s obvious that the average stress remaining is higher in the material with higher yield stress. The figure below shows the soaking temperature for different materials (for carbon steel is from ): Figure 61, typical thermal treatments for weldment. (Khan, 2007) 49 P a g e

50 Conclusion and future recommendations (optimization): To conclude, the design of the chassis was successfully simulated and analysed through using Finite element analysis feature in solid-works software. The minimum actual FOS during braking is 1.89 (lower than the required which is 2), and the maximum amount of deflection is 0.643mm (lower than the maximum allowable deflection which is 1 mm), and the maximum von Mises stress is 203.3MPa. The minimum actual FOS during acceleration is 2.89 (higher than the required which is 2), and the maximum amount of deflection is 0.612mm (lower than the maximum allowable deflection which is 1 mm), and the maximum von Mises stress is 121.6MPa. The minimum actual FOS during cornering is 1.6 (lower than the required which is 2), and the maximum amount of deflection is 0.682mm (lower than the maximum allowable deflection which is 1 mm), and the maximum von Mises stress is 219.2MPa. The difference between the values of FOS, stress and displacement happened as a result of weight transfer which is longitudinal weight transfer during accelerating and braking, and lateral weight transfer during cornering where the weight transfer adds more stresses on different members based on the situation. For both acceleration and cornering situations the FOS is higher than 2 expect some points (the FOS is lower than 2); this happened due to stress concentration in the attachment points where they expose to higher stress from the attached members, and they are heat effected zones where the heat of welding and cutting the material stresses the material and causes residual stress. For optimising the design it is recommended to heat treat the chassis In order to minimise the stress concentration and the residual stress through using post weld heat treatment method. It is recommended also adding light weight roll cage for decreasing the stress on the chassis members, and taking into account selecting an appropriate member (a member that is not expose to high value of stress) to mount the roll cage. Therefore, the roll cage will assist in increasing the torsional rigidity of the chassis and helps the passenger from roll over and side accidents. 50 P a g e

51 Appendix (A) Figure 62, finding the chassis mass in KG through using solid work software. 51 P a g e

52 Appendix (B) Figure 63, creep test device. (CREEP TESTING MACHINE, n.d.) Figure 64, tensile test device. (matcsi, 2010) 52 P a g e

53 Appendix (C) Figure 65, failure theory (Failure Mechanics, 2013) Figure 66, failure theory (Failure Criteria, 2013) 53 P a g e

54 Appendix (D) (Solid-Works study) Model Information Document Name and Reference Structural Member2[38] Treated As Model name: Assem4 Current Configuration: Default Solid Bodies Volumetric Properties Mass: kg Volume: e-005 m^3 Weight: N Document Path/Date Modified 54 P a g e

55 Trim/Extend27[1] Structural Member2[54] Mass: kg Volume: m^3 Weight: N Mass: kg Volume: e-005 m^3 Weight: N Trim/Extend26[1] Structural Member2[6] Mass: kg Volume: e-005 m^3 Weight: N Mass: kg Volume: m^3 Weight: N Structural Member2[55] Mass: kg Volume: e-005 m^3 Weight: N Structural Member2[48] Mass: kg Volume: e-005 m^3 Weight: N Trim/Extend69 Mass: kg Volume: e-005 m^3 Weight: N 55 P a g e

56 Trim/Extend73 Structural Member2[43] Mass: kg Volume: e-005 m^3 Weight: N Mass: kg Volume: e-005 m^3 Weight: N Trim/Extend66 Structural Member2[50] Mass: kg Volume: e-005 m^3 Weight: N Mass: kg Volume: e-005 m^3 Weight: N Structural Member2[24] Mass: kg Volume: m^3 Weight: N Structural Member2[11] Mass: kg Volume: m^3 Weight: N Structural Member2[20] Mass: kg Volume: m^3 Weight: N 56 P a g e

57 Structural Member2[71] Mass: kg Volume: e-005 m^3 Weight: N Structural Member2[66] Mass: kg Volume: e-005 m^3 Weight: N Trim/Extend83 Mass: kg Volume: m^3 Weight: N Trim/Extend64 Mass: kg Volume: e-005 m^3 Weight: N Structural Member2[42] Mass: kg Volume: e-005 m^3 Weight: N Trim/Extend98 Mass: kg Volume: e-005 m^3 Weight: N Trim/Extend109 Mass: kg Volume: e-005 m^3 Weight: N Trim/Extend80 Mass: kg Volume: m^3 Weight: N 57 P a g e

58 Trim/Extend23[1] Structural Member2[16] Mass: kg Volume: m^3 Weight: N Mass: kg Volume: m^3 Weight: N Structural Member2[7] Mass: kg Volume: m^3 Weight: N Trim/Extend10[6] Structural Member2[36] Mass: kg Volume: e-005 m^3 Weight: N Mass: kg Volume: e-005 m^3 Weight: N Structural Member2[26] Mass: kg Volume: m^3 Weight: N Structural Member2[33] Mass: kg Volume: m^3 Weight: N 58 P a g e

59 Structural Member2[67] Mass: kg Volume: e-005 m^3 Weight: N Structural Member2[72] Mass: kg Volume: e-005 m^3 Weight: N Structural Member2[32] Mass: kg Volume: m^3 Weight: N Trim/Extend110 Mass: kg Volume: e-005 m^3 Weight: N Trim/Extend86 Mass: kg Volume: m^3 Weight: N Trim/Extend10[8] Mass: kg Volume: e-005 m^3 Weight: N Trim/Extend27[2] Mass: kg Volume: m^3 Weight: N Trim/Extend85 Mass: kg Volume: m^3 Weight: N 59 P a g e

60 Structural Member2[25] Mass: kg Volume: m^3 Weight: N Trim/Extend88 Mass: kg Volume: m^3 Weight: N Trim/Extend10[1] Mass: kg Volume: e-005 m^3 Weight: N Trim/Extend67 Mass: kg Volume: e-005 m^3 Weight: N Structural Member2[12] Mass: kg Volume: m^3 Weight: N Structural Member2[9] Mass: kg Volume: m^3 Weight: N Structural Member2[46] Mass: kg Volume: e-005 m^3 Weight: N 60 P a g e

61 Structural Member2[28] Mass: kg Volume: m^3 Weight: N Structural Member2[1] Mass: kg Volume: m^3 Weight: N Structural Member2[68] Mass: kg Volume: e-005 m^3 Weight: N Trim/Extend89 Mass: kg Volume: e-005 m^3 Weight: N Structural Member2[17] Mass: kg Volume: m^3 Weight: N Trim/Extend82 Mass: kg Volume: m^3 Weight: N Trim/Extend97 Mass: kg Volume: e-005 m^3 Weight: N 61 P a g e

62 Structural Member2[37] Mass: kg Volume: e-005 m^3 Weight: N Structural Member2[47] Mass: kg Volume: e-005 m^3 Weight: N Trim/Extend10[3] Mass: kg Volume: e-005 m^3 Weight: N Structural Member2[45] Mass: kg Volume: e-005 m^3 Weight: N Trim/Extend10[10] Mass: kg Volume: e-005 m^3 Weight: N Trim/Extend26[2] Mass: kg Volume: e-005 m^3 Weight: N Trim/Extend65 Mass: kg Volume: e-005 m^3 Weight: N Trim/Extend76 Mass: kg Volume: e-005 m^3 Weight: N 62 P a g e

63 Trim/Extend72 Mass: kg Volume: e-005 m^3 Weight: N Structural Member2[2] Mass: kg Volume: m^3 Weight: N Trim/Extend21[2] Mass: kg Volume: m^3 Weight: N Trim/Extend10[5] Mass: kg Volume: e-005 m^3 Weight: N Structural Member2[5] Mass: kg Volume: m^3 Weight: N Structural Member2[69] Mass: kg Volume: e-005 m^3 Weight: N Structural Member2[41] Mass: kg Volume: e-005 m^3 Weight: N 63 P a g e

64 Trim/Extend24[4] Mass: kg Volume: m^3 Weight: N Structural Member2[3] Mass: kg Volume: m^3 Weight: N Structural Member2[15] Mass: kg Volume: m^3 Weight: N Structural Member2[13] Mass: kg Volume: m^3 Weight: N Structural Member2[18] Mass: kg Volume: m^3 Weight: N Trim/Extend25[2] Mass: kg Volume: m^3 Weight: N Trim/Extend90 Mass: kg Volume: e-005 m^3 Weight: N 64 P a g e

65 Structural Member2[27] Mass: kg Volume: m^3 Weight: N Trim/Extend21[3] Mass: kg Volume: m^3 Weight: N Trim/Extend87 Mass: kg Volume: m^3 Weight: N Structural Member2[4] Mass: kg Volume: m^3 Weight: N Structural Member2[10] Mass: kg Volume: m^3 Weight: N Trim/Extend79 Mass: kg Volume: m^3 Weight: N Trim/Extend84 Mass: kg Volume: m^3 Weight: N 65 P a g e

66 Structural Member2[14] Mass: kg Volume: m^3 Weight: N Structural Member2[19] Mass: kg Volume: m^3 Weight: N Structural Member2[49] Mass: kg Volume: e-005 m^3 Weight: N Structural Member2[8] Mass: kg Volume: m^3 Weight: N Trim/Extend81 Structural Member2[65] Mass: kg Volume: m^3 Weight: N Mass: kg Volume: e-005 m^3 Weight: N Structural Member2[70] Mass: kg Volume: e-005 m^3 Weight: N 66 P a g e

67 Study name Analysis type Mesh type Thermal Effect: Study Properties Acceleration Static Solid Mesh On Thermal option Zero strain temperature Include fluid pressure effects from SolidWorks Flow Simulation Solver type Inplane Effect: Soft Spring: Inertial Relief: Incompatible bonding options Large displacement Compute free body forces Friction Use Adaptive Method: Result folder Include temperature loads 298 Kelvin Off Direct sparse solver Off Off Off Automatic Off On Off Off SolidWorks document (is final\chassisn today\21-5\chassis analysis) Unit system: Length/Displacement Temperature Angular velocity Pressure/Stress Units SI (MKS) mm Kelvin Rad/sec N/mm^2 (MPa) 67 P a g e

68 Material Properties Model Reference Properties Components Name: 1350 Alloy Model type: Linear Elastic Isotropic Default failure criterion: Max von Mises Stress Yield strength: N/mm^2 Tensile strength: N/mm^2 Elastic modulus: N/mm^2 Poisson's ratio: 0.33 Mass density: 2700 g/cm^3 Shear modulus: N/mm^2 Thermal expansion 2.4e-005 /Kelvin coefficient: 1(Boss- Extrude1)(Battery-2), 1(Structural Member2[38])(Chassis template-1), 2(Trim/Extend27[1])(Cha ssis template-1), 3(Structural Member2[54])(Chassis template-1), 4(Trim/Extend26[1])(Cha ssis template-1), 5(Structural Member2[6])(Chassis template-1), 6(Structural Member2[55])(Chassis template-1), 7(Structural Member2[48])(Chassis template-1), 8(Trim/Extend69)(Chassi s template- 1), 9(Trim/Extend73)(Chassi s template- 1), 10(Structural Member2[43])(Chassis template-1), 11(Trim/Extend66)(Chass is template- 1), 12(Structural Member2[50])(Chassis template-1), 13(Structural Member2[24])(Chassis template-1), 14(Structural 68 P a g e

69 Member2[11])(Chassis template-1), 15(Structural Member2[20])(Chassis template-1), 16(Structural Member2[71])(Chassis template-1), 17(Structural Member2[66])(Chassis template-1), 18(Trim/Extend83)(Chass is template- 1), 19(Trim/Extend64)(Chass is template- 1), 20(Structural Member2[42])(Chassis template-1), 21(Trim/Extend98)(Chass is template- 1), 22(Trim/Extend109)(Cha ssis template-1), 23(Trim/Extend80)(Chass is template- 1), 24(Trim/Extend23[1])(Ch assis template-1), 25(Structural Member2[16])(Chassis template-1), 26(Structural Member2[7])(Chassis template-1), 27(Trim/Extend10[6])(Ch assis template-1), 28(Structural Member2[36])(Chassis template-1), 29(Structural 69 P a g e

70 Member2[26])(Chassis template-1), 30(Structural Member2[33])(Chassis template-1), 31(Structural Member2[67])(Chassis template-1), 32(Structural Member2[72])(Chassis template-1), 33(Structural Member2[32])(Chassis template-1), 34(Trim/Extend110)(Cha ssis template-1), 35(Trim/Extend86)(Chass is template- 1), 36(Trim/Extend10[8])(Ch assis template-1), 37(Trim/Extend27[2])(Ch assis template-1), 38(Trim/Extend85)(Chass is template- 1), 39(Structural Member2[25])(Chassis template-1), 40(Trim/Extend88)(Chass is template- 1), 41(Trim/Extend10[1])(Ch assis template-1), 42(Trim/Extend67)(Chass is template- 1), 43(Structural Member2[12])(Chassis template-1), 70 P a g e

71 44(Structural Member2[9])(Chassis template-1), 45(Structural Member2[46])(Chassis template-1), 46(Structural Member2[28])(Chassis template-1), 47(Structural Member2[1])(Chassis template-1), 48(Structural Member2[68])(Chassis template-1), 49(Trim/Extend89)(Chass is template- 1), 50(Structural Member2[17])(Chassis template-1), 51(Trim/Extend82)(Chass is template- 1), 52(Trim/Extend97)(Chass is template- 1), 53(Structural Member2[37])(Chassis template-1), 54(Structural Member2[47])(Chassis template-1), 55(Trim/Extend10[3])(Ch assis template-1), 56(Structural Member2[45])(Chassis template-1), 57(Trim/Extend10[10])(C hassis template-1), 58(Trim/Extend26[2])(Ch assis template-1), 71 P a g e

72 59(Trim/Extend65)(Chass is template- 1), 60(Trim/Extend76)(Chass is template- 1), 61(Trim/Extend72)(Chass is template- 1), 62(Structural Member2[2])(Chassis template-1), 63(Trim/Extend21[2])(Ch assis template-1), 64(Trim/Extend10[5])(Ch assis template-1), 65(Structural Member2[5])(Chassis template-1), 66(Structural Member2[69])(Chassis template-1), 67(Structural Member2[41])(Chassis template-1), 68(Trim/Extend24[4])(Ch assis template-1), 69(Structural Member2[3])(Chassis template-1), 70(Structural Member2[15])(Chassis template-1), 71(Structural Member2[13])(Chassis template-1), 72(Structural Member2[18])(Chassis template-1), 73(Trim/Extend25[2])(Ch assis template-1), 72 P a g e

73 74(Trim/Extend90)(Chass is template- 1), 75(Structural Member2[27])(Chassis template-1), 76(Trim/Extend21[3])(Ch assis template-1), 77(Trim/Extend87)(Chass is template- 1), 78(Structural Member2[4])(Chassis template-1), 79(Structural Member2[10])(Chassis template-1), 80(Trim/Extend79)(Chass is template- 1), 81(Trim/Extend84)(Chass is template- 1), 82(Structural Member2[14])(Chassis template-1), 83(Structural Member2[19])(Chassis template-1), 84(Structural Member2[49])(Chassis template-1), 85(Structural Member2[8])(Chassis template-1), 86(Trim/Extend81)(Chass is template- 1), 87(Structural Member2[65])(Chassis template-1), 88(Structural Member2[70])(Chassis template-1), 1(Boss- Extrude1)(Driver-1), 73 P a g e

74 1(Boss- Extrude1)(Driver-2), 1(Boss- Extrude1)(Engine-2), 1(Boss- Extrude1)(Fuel Tant-5), 1(Boss- Extrude1)(Radiator-1), 1(Boss- 1(Boss- 1(Boss- Tant-5, 1(Boss- 1(Boss- 1(Boss- Curve Data:N/A 74 P a g e

75 Loads and Fixtures Fixture name Fixture Image Fixture Details Entities: Type: 8 face(s) Fixed Geometry Fixed-1 Resultant Forces Components X Y Z Resultant Reaction force(n) Reaction Moment(N m) Load name Load Image Load Details Gravity-1 Reference: Top Plane Values: Units: SI 1(Boss- Extrude1)@Bat tery-2 Name: Boss-Extrude1 Remote Mass: 4.32 kg Moment of Inertia: , , , e-018, e- 020, e-019 kg m^2 1(Boss- Extrude1)@Dri ver-1 Name: Boss-Extrude1 Remote Mass: kg Moment of Inertia: , , , e-016, e- 016, e-016 kg m^2 75 P a g e

76 1(Boss- l Tant-5 Name: Boss-Extrude1 Remote Mass: kg Moment of Inertia: , , ,1.4747e-017, e- 019, e-017 kg m^2 1(Boss- ver-2 Name: Boss-Extrude1 Remote Mass: kg Moment of Inertia: , , , e-018, e- 016, e-016 kg m^2 1(Boss- ine-2 Name: Boss-Extrude1 Remote Mass: kg Moment of Inertia: , , , e-016, e- 018, e-016 kg m^2 1(Boss- diator-1 Name: Boss-Extrude1 Remote Mass: kg Moment of Inertia: , , , e-017, e- 017,-2.208e-011 kg m^2 Connector Definitions No Data 76 P a g e

77 Contact Information Contact Contact Image Contact Properties Type: No Penetration contact pair Entites: 2 face(s) Advanced: Surface to Contact Set-3 surface Global Contact Type: Components: Options: Bonded 1 component(s) Incompatible mesh 77 P a g e