ENGINEERING MATERIAL 100

Size: px

Start display at page:

Download "ENGINEERING MATERIAL 100"

Jack Harvey
6 years ago
Views:

Department of Applied Chemistry Division of Science and Engineering SCHOOL OF ENGINEERING ENGINEERING MATERIAL 100 Experiments 4 and 6 Mechanical Testing

1 Department of Applied Chemistry Division of Science and Engineering SCHOOL OF ENGINEERING ENGINEERING MATERIAL 100 Experiments 4 and 6 Mechanical Testing and Applications of Non-Metals Name: Yasmin Ousam Shafei Mahmoud Khalil Student ID: 7E0A7588 / Group: B2 Due Date: May 25, 2010 Lecturer: Dr. Zeya

2 Table of Contents 0.0. Abstract Introduction Experiment 4: Mechanical Testing Aim Introduction Objective Theory Proof stress Stress Strain Young s Modulus of Elasticity Tensile Strength Yield Strength Yield Point % Proof Stress Ductility Elastic Deformation Plastic Deformation Apparatus Procedure Observations and Results Tensile test results Elongation results Fracture Appearance Data from the curve Calculated Values Calculations Young s Modulus Graphs

3 Experiment 6: Applications of Non Metals Aim Introduction Objective Theory Young s Modulus of Elasticity. 11 Tensile Test Apparatus Procedure Observations and Results Tensile Test Results Elongation Results for Nylon Failure Appearance Data from the Curve Calculated Values Calculations Young s modulus Graphs.. 15 Cantilever Bend Test Apparatus Procedure Observations and Results Sample and Measurements Measurements Graphs Discussions Conclusion References Declaration.19 3

4 0.0. Abstract In experiments 4 and 6, we will be testing some mechanical properties, ex: (ductility and tensile strength) of metals and nonmetals. Those properties define how a metal or non-metal can resist and withstand under force or stress when a load or more are added Introduction This lab report is divided into Experiments. In Experiment 4, we will be testing Carbon steel, a metal and observing and noting down its elongation results. While, in Experiment 6, which is divided into: Tensile test and Cantilever beam test, we will be testing Nylon, a non-metal and using an Aluminum bar to observe the effects of increased loads and their deflections. Experiment 4: Mechanical Testing Aim The purpose of this experiment is to investigate the tensile strength parameters and ductility for carbon steel Introduction The mechanical properties of a material, whether it is a metal or a non-metal play an important role in construction of structures especially in material sciences and mechanical engineering. The tensile strength of a material is the maximum amount of tensile stress that can be subjected to before failure. On the other hand, failure can vary from material to material. To sum up, there are 3 definitions for tensile stress: 1- Yield strength: The stress at which material strain changes from elastic deformation to plastic deformation, causing it to deform permanently. 2- Ultimate tensile strength: The maximum stress a material can bear before fracture happens. 3- Breaking strength: The stress beyond the ultimate tensile strength, where fracturing occurs upon reaching this point Objective The main idea of this experiment is to measure the mechanical properties of metal (Carbon Steel) by performing a tensile test and getting to know the elongation and 0.2 % proof load. 4

5 5.0. Theory 5.1. Proof stress is a stress that causes a system to be in a specified small, permanent deformation and may result in the extension of a tensile test piece or material. It can also be defined as the stress used to demonstrate the material s ability to persist service loads. The proof stress will produce 0.2 % extension for steel quoted in N/mm 2. This value is close to the yield stress in materials which don t exhibit a definite yield point Stress is the measure of the average force that acts perpendicularly to the surface of the body per unit area in a body. It has the SI unit of Pascal (symbol Pa or N/m 2 ) Strain is the deformation unit under a load. In other words, it is the measure of the change in length of a body divided by its original length when a there is a force acting on the body which causes the changes. It has no units Young s Modulus of Elasticity is equal to stress ( ) over strain ( ). It is the measure of the stiffness of slope of the graph strain versus stress. Young s Modulus ( ) has the unit of Pascal (symbol Pa or N/m 2 ). A low modulus means that the specimen or structure will be flexible while stiff and inflexible will occurred in a high modulus Tensile Strength is the maximum force of load applied to the specimen before it fractures divided by the original cross sectional area. The ultimate tensile strength of a material represents the maximum stress that a material can withstand before its deformation when a force is applied on it Yield Strength is the stress at the yield point which is defined as the stress required to start a particular amount of plastic deformation when the material is loaded. The material is elastic below the yield strength and is viscous above the yield strength Yield Point is the point indicated when the permanent deformation of a stressed material will occur; it is the end of the elastic region. Yield Point is also known as the elastic limit from the stress-strain curve which can represent the initial progress from linearity of the curve. 5

6 Load or Force - kn By: Yasmin Khalil % Proof Stress is calculated using formula below. It is basically a line that is parallel to another straight line of the graph. It is drawn based on the calculated value until the line cuts the curve. Below is a graph that describes Proof stress in more detail. Number of kn read off here. This gives the total force acting on the CSA Graph of Load against Elongation Line drawn parallel to straight part of curve from 0.2% of original gauge length Elongation (mm) Calculate value 5.9. Ductility is a measure of the degree of plastic deformation that the matter can resist before fracture. A material is to be ductile when it can be permanently stretched without fracture by tensile force. But on the other hand, a material that can only withstand little or zero plastic deformation is said to be brittle. Ductility can also be defined as percent elongation (%Elongation) or percent reduction area (% R of Area) Elastic deformation happens when stress and strain is proportional to each other. It is the change in the dimensions of a specimen under loading. But the effects of deformation fade away during the removal of the stress applied and then the material returns to its original position Plastic deformation occurs during the situation when the Hooke s law is no longer being obeyed when the stress is not proportional to the strain anymore. A material will undergo irreversible deformation during the plastic deformation which means that the material will not recover to its original position upon the removal of the stress applied. 6

6.0. Apparatus Carbon Steel and Caliper Computer Universal Testing Machine 7.0. Procedure 1- Use the Caliper to measure the diameter of carbon steel.

4- Tension the cross arm of the machine and reset the machine settings in a way that it will be equal to zero.

them in a graph paper. 8.0. Observations and Results 8.1.

7 6.0. Apparatus Carbon Steel and Caliper Computer Universal Testing Machine 7.0. Procedure 1- Use the Caliper to measure the diameter of carbon steel. 2- Measure the gauge length. 3- Insert the carbon steel rod in the Universal Testing Machine. 4- Tension the cross arm of the machine and reset the machine settings in a way that it will be equal to zero. 5- Observe and record the elongation data from the graph in the computer screen and take 10 points from elongation data and graph them in a graph paper Observations and Results 8.1. Tensile test results Measurements Sample Carbon Steel Bar Gauge Length Diameter (mm) 12.5 Minimum Diameter, after testing (mm) 0.75 Gauge Length, L o (mm) = 100 Gauge Length, L l (mm) = 137 Table 1: The Tensile test results for Carbon Steel 7

8.2. Elongation Result for Carbon Steel Elongation Load (kn) (mm) 3.3 0.2 4.2 0.5 4.7 0.6 15.4 2.9 24.0 4.4 25.2 5.0 25.0 5.5 24.9 6.3 29.9 11.1 35.0 19.6 37.2 34.9 37.1 37.5 35.8 40.0 30.0 42.

43 0.111 284552.85 0.196 302439.02 0.349 301626.02 0.375 291056.91 0.400 243902.44 0.420 Table 3: Stress and Strain for the Elongation of carbon steel 8.3. Fracture Appearance Sample Picture Sketch Description Carbon Steel Rod The carbon steel rod has a relatively strong resistance to the tensile force applied to it.

8 8.2. Elongation Result for Carbon Steel Elongation Load (kn) (mm) Table 2: Elongation result for carbon steel Stress (MPa) Strain Table 3: Stress and Strain for the Elongation of carbon steel 8.3. Fracture Appearance Sample Picture Sketch Description Carbon Steel Rod The carbon steel rod has a relatively strong resistance to the tensile force applied to it. It broke two parts, where the upper section forms a cup at the breaking region and the bottom section forms a cone. Table 4: Fracture Appearance of carbon steel 8

9 8.4. Data from the curve Yield Point Load (kn) % Proof Load (kn) 25 Maximum Load (kn) 37.2 Table 5: Data of Carbon steel s curve 8.5. Calculated values 0.2% proof stress or Y.P Stress (MPa) 2.02*10 ^14 MPa Tensile Strength (MPa) 3.02*10^14 MPa % elongation % % R of Area 37 % Table 6: Calculated values of Carbon steel 8.6. Calculations Cross Sectional Area (A 0 ) = = (.0125/2) ^2 * Pi = 1.23*10 ^-4 m^2 Final Cross Sectional Area (A f ) = = ((7.5*10^-4)/2)^2 * Pi = 4.42*10^-7 m^2 0.2% Proof Stress or Y.P. Stress (MPa) = = (24.9 *10^3) N/ (1.23*10 ^-4) m^2 = 2.02*10 ^14 MPa Tensile Strength (MPa) = = (37.2 *10^3) N/ (1.23*10 ^-4) m^2 9

10 = 3.02*10^14 MPa % Elongation = 100 % = (( )/100) * 100 = 37 % % R of A = 100 % = [(1.23*10 ^-4 m^2) (4.42*10^-7 m^2)/ (1.23*10 ^-4 m^2)]* 100 = % Stress = = 24.9*10^3 / 1.23*10 ^-4 = MPa Strain = = (6.3*10^-3 / 0.1) = Young s Modulus = = MPa/0.063 = GPa 8.7. Young s Modulus Load at Yield Point (kn) 24.9 Extension at Yield Point (mm) 6.3 Stress (MPa) MPa Strain (m/m) Young s Modulus (GPa) GPa Table 7: Carbon Steel s Young s Modulus 9.0. Graphs Please refer to the attached graph papers. [Graphs 1 and 2]. Thank you. 10

11 Experiment 6: Applications of Non Metals Aim The purpose of this report is to demonstrate the mechanical properties of the non-metal (Nylon); and to use the simple cantilever equipment to demonstrate the flexural properties Introduction Non-metals have their own mechanical properties, such as: tensile strength, toughness and hardness. These mechanical properties play an important role in determining the usage of a material for construction purposes. In this lab session, the tensile test is being carried out to get to know the tensile strength and ductility of Nylon. A Cantilever bend test is also performed to develop the relationship between deflection and load Objective The main idea of this experiment is: 1) to measure the mechanical properties of the nonmetal (Nylon) by performing a tensile test and getting to know the elongation, tensile strength, etc. and 2) to observe the effects of increased load on the Aluminum bar using the simple cantilever equipment Theory Young s Modulus of Elasticity is defined as the ratio of stress and strain in the region where the material obeys Hooke s law. Stress is denoted by ( ) and is proportional to strain which is denoted by ( ). E = σ / ε (Pa or Nm -2 ) 11

Tensile Test 14.0. Apparatus 15.0. 16.0. 17.0. 18.0. 19.0. Cantilever and Nylon Computer Screen Universal testing Machine 15.0. Procedure 1- Use the Caliper to measure the length, thickness and width of the Nylon piece.

them in a graph paper. 16.0. Observations and Results 16.1. Tensile Test Results Measurements Sample Nylon Gauge Length (mm) 134.

12 Tensile Test Apparatus Cantilever and Nylon Computer Screen Universal testing Machine Procedure 1- Use the Caliper to measure the length, thickness and width of the Nylon piece. 2- Insert the Nylon piece in the Universal Testing Machine. 4- Tension the cross arm of the machine and reset the machine settings in a way that it will be equal to zero. 5- Observe and record the elongation data from the graph in the computer screen and take 10 points from elongation data and graph them in a graph paper Observations and Results Tensile Test Results Measurements Sample Nylon Gauge Length (mm) Original Length (mm) Final Length (mm) Gauge Thickness (mm) 3.04 Final Thickness (mm) 1.1 Gauge Width (mm) Final Width (mm)

By: Yasmin Khalil Reduction in Width (mm) 11.48 7.4 = 4.08 Reduction in Thickness (mm) 3.04 1.1 = 1.94 Table 8: The Tensile test results for Nylon 16.2.

13 By: Yasmin Khalil Reduction in Width (mm) = 4.08 Reduction in Thickness (mm) = 1.94 Table 8: The Tensile test results for Nylon Elongation Data for Nylon Machine Load (N) Extension (mm) Table 9: Elongation result for Nylon Failure Appearance Sample Picture Sketch Description Nylon The nylon stick broke into two parts in a ductile mode. There is a necking part at the breaking of each part, with curves in upward and downward directions. Table 10: Fracture Appearance of Nylon 13

14 By: Yasmin Khalil Data from Curve Yield Point Load (kn) 838 Tensile strength (MPa) 34.9 Maximum Load (kn) 11.4 Table 11: Data of Carbon steel s curve Calculated Values % elongation % R of Area Table 12: Calculated values of Carbon steel Calculations Tensile Strength = Width x Height = * = 3.45 x 10^-5 m = = 34.9 MPa % Elongation = x 100 % = (( )/ ) x 100 = % % R of A = x 100 % = ((3.04 x 11.48) (1.1 x 7.4)/(3.04 x 11.48)) x 100 = % Stress = = (838/( x ) = MPa 14

15 Strain = = (6.9/179.88) = Young s Modulus = = (21.47 MPa /0.0384) = 0.56 GPa Young s modulus Load at Yield Point (kn) 838 Extension at Yield Point (mm) 6.9 Stress (MPa) Strain (mm/mm) Young s Modulus (GPa) 0.56 Table 13: Carbon Steel s Young s Modulus Graphs Please refer to the graph papers attached. [Graph 3].Thank you. 15

Cantilever Bend Test 18.0. Apparatus Hanger with loads Digital meter Aluminum Bar Loads 19.0. Procedure Cantilever beam test machine 1- Measure the thickness, width and length of the cantilever beam.

deflection readings. 20.0. Observations and Results 20.1.

16 Cantilever Bend Test Apparatus Hanger with loads Digital meter Aluminum Bar Loads Procedure Cantilever beam test machine 1- Measure the thickness, width and length of the cantilever beam. 2- Apply a 10g load to the free end of the cantilever beam. 3- Measure the bending/deflection by the digital meter. 4- Add 10g loads until you have noted down 15 loads vs. deflection readings Observations and Results Sample and Measurements Sample and Measurements Load (g) Deflection (mm) Load (g) Deflection (mm) Load (g) Deflection (mm) Table 14: Cantilever beam load vs. Deflection points 16

17 20.2. Measurements (m) Measurement (m) Thickness of Specimen Width of Specimen Effective Length of specimen Table 15: Cantilever beam specification The formula below is used to find the young s modulus of a material. M Here d E 4Mgt dwt 3 4gt wt M d is the inverse of the deflection versus load graph Slope = ( )/ (100 70) = (.56/30) =.0187 M d = 1/.0187 = E = [(4 x 9.81 x.006^3)/ (0.019 x.0600^3)] x = GPa Graphs Please refer to the attached graph papers. [ GRAPH 4 ]. Thank you. 17

18 22.0. Discussions 1. Why does carbon steel has formed cup and cone shape after fracture? I have observed that the carbon steel has formed a cup and a cone shape after fracture. Which is due to the time when the carbon steel rod started to neck, small cavities formed in the middle of the cross section. And then those cavities grew in a direction perpendicular to the applied load as the deformation continued. Fracture was caused by the rapid creation of a crack around the outer perimeter of the neck, at an angle of around 45 o. Therefore, the two broken pieces formed were in a shape of a cup and a cone. 2. Explain why carbon steel has broken after Ultimate tensile strength. After ultimate tensile strength, carbon steel broke as a result of the external force applied on it. Carbon steel has exceeded its ability to withstand force and its maximum resistance to fracture. 3. Why does 0.2% proof stress is important for your material selection? The metal will deform as soon as forces are applied on it. This deformation is known as elastic deformation when it is up until the 0.2% proof stress. 0.2% proof stress determines the point of permanent damage. When the forces are applied on the material is more than the 0.2% proof stress, it will be permanently deformed and practically unusable. Therefore, 0.2% proof stress is important for material selection in order to know how much force a material can withstand. 4. Compare the stress and strain graphs for non metal (Acetal, Nylon, polycarbonate) In general, fibers have the highest tensile moduli, and elastomers have the lowest, and plastics have tensile moduli somewhere in between fibers and elastomers. Acetal has an UTS of 60, Elongation of 45% and Tensile modulus of 2.7, while Nylon has an UTS of 60, Elongation of 90% and Tensile modulus of 1.8 and PVC has an UTS of 70, Elongation of 100% and Tensile modulus of

19 23.0. Conclusion Finally, I conclude that the tensile test provides information on: proof stress, yield point, tensile strength parameter, elongation and reduction of area. Other than that, the graphs obtained can be used to identify the elastic properties, plastic deformation, fracture points, and deflection of the materials with reference to the applied load. Even if there were some errors done during the experiment; the experimental value of young s modulus proved that the aluminum bar is tough and strong. Aluminum s withstand to a high deflection at the end of the beam proves that it is strong. And according to the graph and young s modulus value of carbon steel, I can wrap up by saying that it has a higher young s modulus than aluminum and can able to withstand a large amount of forces before fracture, as shown in the graph. In addition, the curve of graph sketched is large which symbolizes the strength of a material References Callister, W.D Mechanical Properties. In Materials Science and Engineering: An Introduction, 7 th Edition, John Wiley & Sons,Inc., NY Declaration I, Yasmin Khalil hereby declare that this report is the result of my own efforts and that all the photos were taken by me on Tuesday (May 18 10). The calculations and graphs are based on the results and data gathered by group B2. 19

CITY AND GUILDS 9210 Unit 130 MECHANICS OF MACHINES AND STRENGTH OF MATERIALS OUTCOME 1 TUTORIAL 1 - BASIC STRESS AND STRAIN

CITY AND GUILDS 9210 Unit 130 MECHANICS OF MACHINES AND STRENGTH OF MATERIALS OUTCOME 1 TUTORIAL 1 - BASIC STRESS AND STRAIN CITY AND GUILDS 910 Unit 130 MECHANICS O MACHINES AND STRENGTH O MATERIALS OUTCOME 1 TUTORIAL 1 - BASIC STRESS AND STRAIN Outcome 1 Explain static equilibrium, Newton's laws, and calculation of reaction