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1 Research Paper DESIGN AND ANALYSIS OF AUTOMOTIVE ROOF BY USING MODERN MATERIALS FORMS LIKE PLASTICS AS AN EFFECTIVE ALTERNATIVE 1 Mahesh Suresh Sabale, 2 N.Vivekanandan, 3 Swapnil S. Kulkarni Address for Correspondence 1 ME- Mech/ Design -Pursuing, 2 Asst. Prof. (M.Tech Industrial Safety Engineering, NIT Trichy, Gold Medalist), Department Of Mechanical Engineering, Pimpri-Chinchwad College Of Engineering, Nigdi, Pune-44, 3 Director-Able Technologies India Pvt. Ltd., Pune India ABSTRACT An increasing pressure on vehicle manufacturers internationally and also several countries are mandating to reduce vehicle emissions. Thus light weight strengthening solutions are required to increase roof strengths while minimizing structural mass. This study discusses a design for vehicle roof with plastic form materials and study load carrying capacity with minimum component weight without failure. The objective of this new design is to satisfy the stiffness and strength requirement with new material design. In this study, vehicle rollover was investigated the implementation of adequate material models for accurate treatment. The benefits of this new material include reduced mass and hence more efficiency. The performance of the structures with regard to regulatory standards is compared between the initial and new models. The vehicle roof with new design and new material is able to secure a substantial margin of the survival zone as well as to meet the requirement specified by standard. KEYWORDS: Automotive Roof, Lightweight, Strength requirement, Plastic form material. 1. INTRODUCTION With the growing concerns on energy conservation and vehicle emission it is increasing pressure on vehicle manufacturers internationally to provide lighter weight components for vehicles. In order to minimize energy consumption, lightweight has become a critical issue because, weight is a key factor for the fuel consumption. The lighter the vehicle more will be the fuel efficiency. Generally, the lightweight design can be addressed from three aspects of applications of novel materials, structural optimization and advanced processing technology, of which novel material application is counted as the most effective approach. Plastics and its forms have been increasingly used in automotive industry for their advantages of lightweight, corrosion resistance and easy manufacturing. But along with these advantages of light weight, corrosion resistance and more fuel efficiency, safety is very important criteria for vehicle manufacturers. As vehicle rollover crashes are frequent accidents worldwide. Vehicle rollover crashes are the cause of many fatalities and severe head, neck and spine trauma around the world. Since 2000 in the United States alone, more than 10,000 people every year have been killed in vehicle rollovers [4]. Therefore, passenger safety is an important issue in the automotive industry, and this concern is gradually growing every year. Guaranteeing the physical safety of passengers is not only a marketing consideration, but has also become an obligation stipulated by international standards that are now in place in several countries as well as a requirement by governmental organizations. According to a survey of the literature regarding rollovers accidents, passengers can be ejected, partially ejected, or become the victims of roof intrusion, all of which may be fatal. For this reason, the Federal Motors Vehicle Safety Standards enacted Regulation No. 216 and ECE R66 are the standards for the vehicle strength of superstructure to provide protection to occupants during rollover accidents through the provision of a survival space. Thus, vehicle design must strictly satisfy regulatory standards, while the structural design must carry the required load with the minimum component weight without failure. Therefore, rollovers are simulated using the finite element analysis (FEA) program, and researchers have found good agreement between the tests and the simulation analysis. 2. LITERATURE REVIEW Increasing demands are being placed on vehicle manufacturers to reduce vehicle masses in order to reduce engine emissions, for example the United States Corporate Average Fuel Economy (CAFE) regulations which now mandate improvements in fuel efficiency for passenger vehicles of around 5% every year until 2025 [1]. According to study, Rollover collisions carry a higher risk of death and serious injury than any other type of motor vehicle crash. In 2005, there are approximately 11 million MVCs in the United States. Amongst these, 2.6%of vehicles rolled over. Despite these small numbers, 21% of fatal crashes and 30% of all occupant fatalities involved a rollover event (NHTSA.2005) Also it is observed that there is association between the degree of roof crush and mortality, spine injury, and head injury in rollover crashes [2]. Due to the high frequency of injuries and casualties in rollover accidents, the ECE R66 code ensures bus structures have a minimum resistance to rollovers. In this paper discussed the developed a technique to simulate bus rollovers according to with the requirements of ECE R66. This technique allowed both initial and composite roll bar models to be analyzed. This study demonstrated that inexpensive composite roll bar structures can provide significant improvements in rollover strength compared to initial bus structures of the same weight. The survival space for the composite roll bar bus was significantly increased in the full scale rollover test compared to that for the initial bus. Thus, in combination with reduction in lateral deformation and effective containment design, the roll bar reduces the likelihood of passenger ejection in a rollover accident. The excellent corrosion resistance of composite materials compared to conventional steel is an additional benefit that prevents the degradation of the bus superstructure and extends the operational lifetime of the vehicle [3]. Notwithstanding the limitations of the numerical approach, study has demonstrated the substantial potential for vehicle roof strengthening provided by fiber-epoxy strengthening systems.the bonding of carbon fibers to the vehicle roof structure

2 components of passenger vehicles can increase the roof strength, and correspondingly the vehicles' roof strength to weight ratio, by nearly two times. Fiberepoxy strengthening therefore has the potential to contribute to greater roof strengths in future vehicle fleets, to maintain compliance with international roof strength regulations mandating increased roof strength requirements. The potential of fiber-epoxy strengthening systems for vehicle light- weighting has also been highlighted in the present study, where as 37 68%mass saving resulted with using fiber composite in place of added steel for equivalent roof strengthening [4]. The finite element analysis is further carried out to quantify the crashworthiness performance of the body structure made of plastic forms materials. The simulation is performed according to the standards.the standards relates the strength of the roof structure to occupant protection in real world rollover crashes, requiring the maximum moving distance of the roof structure to be less than 127 mm (5 in.) when the induced load is 1.5 times of the vehicle weight. [5] 3. PROBLEM DEFINITION To suggest alternative material (e.g. Plastic forms ) to the conventional sheet metal (CRCA rolled sheets) by utilizing CAD/CAM/CAE practices for addressing the Design and analysis phase, and considering the need of Vehicle Manufacturers to provide effective solution by offering a competitive advantages while complying with the relevant standards in Automotive Engineering. 3.1 Aims and Objectives Identifying alternative material (e.g.- Plastic) to the traditional sheet metal (CRCA rolled sheets) to reduce weight. Suggest alternatives over Material and/or Process for mass manufacturing Utilizing CAD/CAM/CAE practices for addressing the Design and Analysis phase The roof to be compliant with the relevant standards in Automotive Engineering To measure strain and deformation at critical locations in the vehicle roof support structure and provide strengthening solution in critical areas. 4. METHODOLOGY The Sheet metal roof for the passenger car is being sought to be replaced by an alternative material. This is being done to establish the feasibility of working with materials for ease of processing or reducing the secondary operations typically required by the conventional sheet metal body. Initially literature review is carried out at by collecting literature from various published resources related to this work. This involves current industrial trend in automotive sector, requirement of OEM s, legal requirements, material properties comparative study experimental testing methods. The principles and concepts behind four wheeler structural (roof) design, material and strength requirements. The potential candidate for required properties material is being explored by the sponsoring company with material supplier. The material properties explored by considering the need of work, to use the same for FEA analysis.cad/cae practices are utilized for addressing design and analysis phase. Different geometries of roofs structures are analyzed and compared the same with conventional sheet metal structure on the parameters used in industry like FMVSS and IIHS. For authentication of inputs received from supplier which are used for FEA, a three point bending testing of standard specimen is done which is generally done in industry to study material behavior in bending. 5. DESIGN AND ANALYSIS 5.1 Automotive vehicle roof Safety point of view vehicle roof plays very crucial role specially roll over kind of accidents, in which vehicle tips over onto its side of roof. And vehicle rollover crashes are the causes of many fatalities and several head, neck and spine trauma around the world. Therefore passenger safety is also very important parameter in front of OEM s. It is not only a marketing strategy but also it is a obligation stipulated by international standards that are now place in several countries, as well as a governmental requirement. For this reason strength is very important criteria for designing vehicle roof. 5.2 Standard experimentation setup The strength of the roof structure to occupant protection in real world rollover crashes, requiring the maximum moving distance of the roof structure should be less than 127 mm (5 in.) when the induced load is 1.5 times of the vehicle weight. For the test the passenger car shall be rigidly placed or positioned on a horizontal surface with the doors locked and the window closed. Furthermore, a flat, rigid block with lower surface a rectangle measuring 30 inches wide by 72 inches long (762mm X 1829mm) shall not move more than 5 inches(127mm),measured as the distance between the original location of the lower surface of the test device and its location as the specified force level is reached, when it is used to apply a force of 1.5 times the unloaded vehicle weight(uvw) or 5000 lbs(22224n),whichever is less,to either side or forward edge of the vehicle. This test can be conducted on either side of the roof structure, the front left or the front right side but not on both sides in one single test and still meet the requirements of the test. The rigid plate shall not move faster than 0.5 inches/second and the force applied on the plate shall not exceed the lesser of 1.5 times the unloaded vehicle weight (UVW) expressed in kilograms multiplied by 9.8 or 5000lbs (22240N).Also the direction of the force shall be downward and perpendicular to the lower surface of the rigid plate and such that it moves in a straight line without rotation. Duration of the test shall not exceed 120 seconds [5]. The orientation of the test device is as described below: The longitudinal axis of the plate is pitched forward at a 5 º angle as viewed from the side of the passenger car. The lateral axis or the roll of the plate is such that it forms a 25 º outboard angle with a horizontal surface as viewed from front of the passenger car. The lower surface of the plate shall always maintain a tangential contact with the surface of the roof.

3 The initial point contact is 10 inches (254 mm) from the leading edge of the plate and in line with the longitudinal axis on the lower side of the plate. Fig.5. Sedan Vehicle considered for analysis. Fig.1. Test Device Orientation Fig.2. Test Device Location and load application to the roof. For the purpose of this dissertation work, the Test Report shared by the Sponsoring Company or any other third party Test Lab would be compared with the results of Analytical method (CAE Analysis). If needed, a test specimen of the Material (i.e. flat sheet strip. Size 100mmX 50mm) could be tested for ascertaining the mechanical properties Fig.6. Sheet metal roof Car segment : Passenger segment Unloaded vehicle weight : 1634kgs Wheel base : 2760 mm Overall length : 5020mm Overall width : 1850mm 5.5 Metal roof material properties Density : 7890 kg/m 3 Young's modulus : Mpa Poisson's ration : 0.3 Yield stress : 210 Mpa Metal Roof Mass : 11.2kgs Thickness : 0.8mm Joining process : Metal roof with spotweld connections 5.5 Metal Material Curve used for analysis From benchmarking and previous experience below material properties for metal are used for FEA. Fig.3. Images for different vehicles testing. 5.3 Regulatory requirements Strength to Weight Ratio (SWR)=Peak crush force (kn) (UVW(kg) 9.81) FMVSS requirement: SWR 3 *FMVSS: Federal Motors Vehicle safety Standards. IIHS requirement: SWR 4 *IIHS: Insurance Institute for Highway Safety. Fig.4 Roof Strength to Weight ratio 5.4 Vehicle Specification with metal roof Selected an existing general design of 4 wheeler sheet metal roof structure for study is having following specifications. Fig.7. Stress Vs Strain graph for metal MATERIAL SELECTION In the engineering materials, steel is the best material for building structures as it offers greater strength. The main problems with the steel are the corrosion and weight per volume. Composite materials become newest trends in the field of engineering materials. Two or more materials are combined together with the help of engineering techniques to obtained the combined properties of its constituents are called as composite materials. Now days composites finds their usages mostly in aerospace and marine applications as they offered light weight, mechanical strength, corrosion resistivity, ease of maintenance.

4 The configurations of composites are so flexible that it can accommodate any material which is suitable for engineering applications.hence it may categories like plastic composites, plastic metal hybrid composites, ceramic composites, fiber composites etc. In case of reduction in weight, plastics and plastic composites or polymer composites are preferred. The use of plastic for manufacturing components in the automotive industry has been increasing over the last decades. Material selection criteria for vehicle roof Vehicle roof is subjected to the rollover accidents which are most dangerous among all kinds of accidents since it is directly attack occupant s head and neck hence risk to life is more. Vehicle roof is subjected to the rollover accidents which are most dangerous among all kinds of accidents since it is directly attack occupant s head and neck.steel has very less shock absorption capacity and it may transmit shock to the occupant during collision of roof with the ground. Here plastic with the best supporting material can become the solution as plastic were famous for shock absorption capacity. Different plastics like acrylonitrile butadiene styrene (ABS), Polybutylene Terephthalate (PBT) and plastic composites like Glass Fiber Reinforced plastics (GFRP), Carbon Fiber Reinforced Plastic (CFRP) are the suitable for roof application. Mechanical strength, low weight, shock/energy absorption capability, cost and ease of manufacturing are the important parameters for material selection for roof. By studying different-different material properties it is observed that steel having maximum modulus of elasticity among above stated materials. Composite materials like CFRP-Epoxy, aramid Kevlar 49 and Boron fiber having tensile strength more than steel and aluminum and had best flexural properties. Where, in plastic composites SMC is having fair tensile properties but showed better results in flexural cases [13, 14].Plastic composites are having less weight as compared to steel as its density is less. Fig.8. (a) Load vs. disp. Curve of folding metallic structure. (b) Load vs. disp. Curve of glass/polyester composites. From fig.8 (a) and (b), it is observed that Composite materials which consist of two or more materials e.g. glass polyester composites. Glass contributes the strength and polyester became a matrix which is a softer material that absorbs shock. Hence it acts like an ideal energy absorber, compared to the metallic structure, as the load level and energy absorption capacity is more stable. GFRP and Kevlar are the best energy absorbers than boron fiber and CFRP. In plastic composites SMC absorbs maximum energy than BMC and FRP [13, 14].The cost is an important parameter in selection of alternative material from composites. Composite materials are very emerging field so far and day by day new inventions and techniques arrived for their mass production that minimizes the production cost per unit. GFRP, CFRP, Kevlar, boron fiber are costlier than Steel and SMC.And steel is less costly as compared to SMC [15]. As designing any part the main consideration is always the strength of material before its cost. Cost can be minimized by the optimization techniques or cost reduction techniques but compromise in strength is not affordable at all since it directly affects the human health. Excess strength can be a best part in any design but it has no use if it couldn t affordable to customer. For roof application plastic composite has enough strength to pass strength criteria and weight reduction. SMC and BMC had cost advantage as well as good specific strength as compared with steel and aluminum. Basically SMC, BMC and FRP are pretty much similar in configuration, properties but differ in manufacturing techniques and characteristics. SMC and FRP have a wide range of configuration with glass filled content and it has live examples for automotive body too. Hence alternative material with above stated requirements in roof design, plastic composites stands better than in all respect. 5.6 Finite Element Analysis: Finite Element Analysis (FEA) offers a detailed visualization of where such structures bend or twist, indicating the distribution of stress. This allows designs to be created, optimized and finalized in 3D before the design is manufactured. FEA has become a very useful tool, with its ability to allow insight into real world outcomes prior to destructive testing of actual prototypes. The resulting stress and deformation can be measured for simulated rollover loads from nearly any axis, and therefore each component and structure can be re-designed or modified accordingly, until an effective computer model meets the load levels the Company might deem acceptable. Crashworthiness simulation is less expensive and can yield more information than experimental technique.using FEM software for crash simulation is a usual practice today and become an integral part of design and development Process. Crash and occupant safety analysis software must be able to handle large deformations, sophisticated material models (for steel and aluminum, rubbers, structural foams, plastics and most impotently composite material materials), complex contact conditions among multiple components, and short duration impact dynamics.ls-dyna is a state of the art simulation tool that addresses all these complex requirements. And its predictions have been validated by test results in many applications. 5.7 Finite Element Analysis Description The vehicle FE model used is subdivided into different parts; parts are used with shell elements to

5 model the sheet metal components along with connections between them. The two types of shell elements used are quadrilateral and triangular.the material model assigned to these shell element is a general isotropic elastic plastic material (material type 24 in LS-Dyna).The stress strain relations for the isotropic elastic plastic material is defined with different stress Vs strain points. Table 1 Finite Element Model summary of Vehicle model Plastic Roof with lateral and longitudinal cross section: The lateral and longitudinal construction is strong as well as it avoids sagging of roof. The Construction is as shown in fig Finite Element Analysis Description of Load Plate FMVSS No.216 specified the requirement for rigid unyielding steel plate that is used for application of quasi-static load. The dimensions of the plate are specified as discussed in previous section. Normally about 1 inch (25.4mm) thick plate is used. Generally the load plate is made of ASTM-836 steel. The FE model consist of total 100 solid elements.as the test plate is unyielding in test condition s, rigid material model (type 20 in LS dyna0) is used. Table.2 Finite Element Model summary of load plate A: 25mm B: 70mm C: 30mm Fig.10. Plastic Roof with lateral and longitudinal section The test setup is shown in the below Fig.11 and the plastic strain after loading is shown in fig.12 with new plastic composite material. Plastic strain more than 10 % is shown in red color. 5.9 Finite Element Analysis Description of the Test Setup It is difficult to give displacement to the load plate in that configuration as it required a complex vector to be defined. Since in static test, weight of the load plate is not involved, perpendicular orientation to a global axis is maintained and in its stead the car is oriented with respect to the global axes effectively confirming to the orientation requirements of the quasi static test (FMVSS No.216).Displacement is given to load plate. According to the test requirements, it is necessary to have a fixed contact between the base plate and the car chassis. In conformance to the above requirement, the chassis of the car is fixed in that position by constraining the translation and rotation of the chassis nodes in global co-ordinate system. Also only half side of the vehicle is considered for analysis as to reduce the analysis time. I) Boundary Conditions As per standard test conditions vehicle is clamped at chassis hence for FEA analysis fixed constraints are given at platform (Fig.8). Also only half vehicle is considered for analysis to reduce simulation time. Hence at other half side of the vehicle is given with fixed constraint. (Fig.9) Fig.11. Vehicle with Plastic Roof along with test platen. Fig.12. Plastic strains on roof 5.11 Plastic Material Properties used for Analysis Material properties used for FEA analysis with plastic composites are as given below. And material behavior graph is shown in fig.13. Density : 1200 kg/m 3 Young's modulus : 2556Mpa Poisson's ratio : 0.32 Yield stress : 45 Mpa Adhesive material properties: Material : Epoxy adhesive Density : 1280 kg/m 3 Young's modulus : 120Mpa Poisson's ratio : 0.4 (a) (b) Fig.9 (a) Boundary condition: Fixed at Chassis (b).boundary condition: Fixed at other side 5.10 Roof structure proposal with plastic form material Fig.13.Stress (MPa) Vs Strain for plastic material used for analysis

6 6. ANALYSIS RESULT Force vs. displacement graph gives the maximum or peak force at which material fails and from the SWR formula we get the SWR ratio for, material Fig.14. Force Vs Displacement for Metal roof with new proposal A global Energy plot (Fig.15) shows that kinematic energy is very less as this process are quasi static. Fig.16 (b).three point bending specimen testing 8. RESULT DISCUSSION 1) Material Behavior: By observing material behavior graph used for FEA and graph get from material specimen testing by using three points bending method stress Vs strain behavior is similar.so we can say that material properties used for finite element analysis for FMVSS 216 test procedure are authentic.(fig.17) Fig.15.Global Energy plot Weight of unleaded :1634kgs. vehicle (UVW) Peak Forces : 59739N SWR : STANDARD THREE POINT BENDING TEST PROCEDURE The three points bending flexural test provides values for the flexural stress, flexural strain and the flexural stress-strain response of the material. The main advantage of a three point flexural test is the ease of the specimen preparation and testing. However, this method has also some disadvantages: the results of the testing method are sensitive to specimen and loading geometry and strain rate. Fig.16(a) Three point bending test setup Fig.17. Stress Vs Strain comparison between FEM and testing 2) Strength to weight ratio We can observe from SWR value for a plastic composite material proposal is 3.72 which fulfilling FMVSS requirement to have SWR value of 3. 3) Weight Comparison Comparison between Plastic composite material roofs with steel roof is shown in below table Table.3. Weight reduction About 40 to 50 % weight reduction is possible with new plastic composite form material as compared to steel roof. 9. CONCLUSION From Force-displacement curve and strength to weight ratios, it is concluded that traditional metal roof can be replaced by new tested material along with fulfilling the safety requirements, with significant weight reduction. As there is percentage error between properties used for FEA and properties got from three points bending testing of material is 6%. However design optimization is to be done as Plastic roof needs additional reinforcement for improving strength to weight ratio and also need to explore more to develop manufacturing processes for mass production. REFERENCE 1. Qiang Liu, Yongzhou Lin, Zhijian Zong,Guangyong Sun, Qing Li,. Lightweight design of carbon twill weave fabric composite body structure for electric vehicle. Journal of Composite Structures 97 (2013) 2. Samuel P. Mandell, Robert Kaufmana, Christopher D. Mack, Eileen M. Bulger, Mortality and injury patterns

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