Simulation of IIHS Roof Strength Analysis on Toyota Corolla Chassis ME 65100: ADVANCED FINITE ELEMENTS METHOD MASTER OF SCIENCE (MECHANICAL ENGINEERING) SUBMITTED BY HARSHAL DHAMADE VIGHNESH SHETTY TEJESH DUBE DEPARTMENT OF MECHANICAL ENGINEERING INDIANA UNIVERSITY-PURDUE UNIVERSITY INDIANAPOLIS FALL 2018 ADVANCED FEA FINAL PROJECT REPORT ME 65100 ABSTRACT Amongst the types of crashes encountered, a rollover on the side or turning turtle can have grievous consequences for the occupants. In this project, FMVSS 216 standards were studied in order to carry out a quasi-static load test experimentation on Toyota Corolla BIW. An explicit solver was used in LS Dyna to solve the set up and IIHS rating system was studied by comparing the strength – to – weight ratio (SWR) of vehicle with plate displacement. 2 ADVANCED FEA FINAL PROJECT REPORT TABLE OF CONTENTS 1. Introduction a. Crashworthiness b. Crash rules and regulations in USA c. New Car Assessment Program (NCAP) 2. Types of crash tests a. Front Impact Overview b. Side Impact Overview 3. Roof Crush a. Testing Procedure b. Result Calculation 4. Methodology a. Model Creation b. Finite Element Modeling c. Contact Modeling d. Material Modeling 5. Boundary Conditions a. Constraints b. Loading c. Convergence criterion and Energy Plots 6. LS Dyna Model Simulation Results a. Testing results and SWR Calculation b. Results obtained from the model i. A,B,C pillar stress contours ii. Roof and roof cross member plastic strain iii. Maximum Reaction Force iv. SWR for current model 7. Conclusion 8. Future Scope 3 ME 65100 ADVANCED FEA FINAL PROJECT REPORT ME 65100 1. INTRODUCTION [IRJET] The greatest challenges faced by the automotive industry are been to provide safer vehicles with high fuel efficiency at competitive cost. [1] Automotive design with economy, safety and aesthetics has been a great challenge to design engineers. But along with these advantages of light weight, more fuel efficiency and corrosion resistance, safety is very important criteria for vehicle manufacturers, as vehicle rollover crashes are frequent accidents worldwide. [4] Vehicle rollover crashes are causing many fatalities like severe neck, head and spine injuries around the world. Therefore, passenger safety is an important concern in the automotive industry, and this is gradually growing every year. [3] a) Crashworthiness Automotive Vehicle Safety Standards Earlier, in February 2009, the IIHS (Insurance Institute of Highway Safety) announced a new rating system based around roof crush testing. The rating is must to ensure the safety of the passengers during rollover accident of car. Although their procedure is like that of FMVSS 216 (Federal Motor Vehicle Safety Standards), which is the American safety standards used for roof crushing test.[6] The requirement of this test set up is to earn the highest rating of 4.0 times the vehicle's weight. The rating is 4, specified by both IIHS and FMVSS to increase the safety of the passengers. This paper overview the IIHS test procedure and present data from both the FMVSS 216 and IIHS test protocols. Readers of this paper will gain a much broader understanding of roof crush testing and the impact it will have on future vehicle designs. Fig 1. Testing Procedure 4 ADVANCED FEA FINAL PROJECT REPORT ME 65100 Roof Crush Resistance Test A rectangular block measuring 30 inches wide and 72 inches long is used to apply the load on car roof with 1.5 times the unloaded vehicle weight with different angle inclination to rectangular block as indicated in below figure. And the moving distance of roof structure must be less than 127mm or 5 inches as per FMVSS standards. b) Crash rules and Regulations in USA [BSsimulia] The National Highway Traffic Safety Administration (NHTSA) mandates the use of certain test procedures to determine automobile roof crush resistance. NHTSA roof strength standard, FMVSS 216 seeks to reduce the risk of death and serious injuries in rollover crashes. [1] In the test the force-deflection behavior of the roof structure is measured by quasi-statically pressing a precisely positioned rigid plate against the automobile. In geometrical approach the geometry of roof and its supporting members i.e. A pillar, B pillar etc. must change. [2] [371] As part of the design process, the test is often simulated analytically. There are different standards and testing procedure depending on the vehicle type and governing bodies around the globe, some them are mentioned below. [2] [371] 1. Controlled Rollover Impact System (CRIS) : A fixture holding the vehicle is mounted on a semi-tractor and trailer. The fixture can be adjusted to drop the vehicle a given height giving it a defined vertical velocity. 2. Jordan Rollover System (JRS) : This test is attained by mounting a vehicle on an axis that permits it to roll and be dropped. Fig. 3 and 4 shows the actual laboratory test and FE test model. As the vehicle is rotated by means of pneumatic system, a roadway segment is run underneath, and the vehicle is dropped so that its roof strikes the road as it would in an actual rollover. 3. Federation of Motor Vehicle Safety Standards No.216 (FMVSS 216) : It specifies a quasi-static test procedure that measures the force required to push a metal plate into the roof at a constant rate. It requires a reaction force equal to 1.5 times the weight of the vehicle be reached within 5 inches or 127mm of plate displacement. This is commonly referred as the Strength to Weight Ratio (SWR). The standard applied to vehicles like vans and light trucks with a GVWR (Gross Vehicle Weight Rating) of 2,722 kilograms (6,000 pounds) or less. The new standard also broadens the scope of covered vehicles to include those up to GVWR of 4,536 kilograms (10,000 pounds). 4. The Insurance Institute of Highway Safety (IIHS) has developed its own rollover crashworthiness rating. The IIHS specified for a GOOD rating in their program will be Strength to Weight Ratio (SWR) of 4.0 in a one-sided platen test condition like the existing FMVSS 216 test procedure. For an ACCEPTABLE rating, the minimum SWR is 3.25 and MARGINAL rating value is 2.5. Anything lower than 5 ADVANCED FEA FINAL PROJECT REPORT ME 65100 that is rated as POOR as shown in fig.8 This rating system is based on the institute research showing that occupants in rollover crashes benefit from stronger roofs. c) New Car Assessment Program (NCAP) [BSsimulia] For roof crush simulation, a force is applied quasi-statically to the side of the forward edge of the vehicle roof structure through a large rigid block. The chassis frame and the car’s sills are constrained to a rigid horizontal surface. The force applied to the block and the displacement of the block are recorded throughout the test to characterize the roof crush resistance. [1] Accurate and efficient finite element modeling of the roof crush resistance test can facilitate the design of safer automobiles as well as reduce development and testing costs. In Explicit the central difference time integration rule is used to advance the solution. The conditional stability of this approach requires the use of small-time increments. It can, therefore, be computationally impractical for the modeling of quasi-static events in their natural time scale. Event acceleration techniques must be employed to obtain an economical solution. [3] [abaqus] As the event is accelerated, however, inertial forces may become dominant. The goal is to model the process in the shortest time period in which inertial forces remain insignificant. Two methods to obtain an economical quasi-static solution with an explicit dynamic procedure are [4] to increase the loading rates and to perform mass scaling. In which the duration of the event is reduced artificially by increasing the rate at which the load is applied. in the second method the material density is increased artificially, which leads to an increase of the stable time increment. Both methods are used at the same time for the present analysis. 6 ADVANCED FEA FINAL PROJECT REPORT ME 65100 2. TYPES OF CRASH TESTS 1) Frontal Impact Overview [crash safety overview] This standard specifies performance requirements for the protection of vehicle occupants in crashes. The purpose of this standard is to reduce the number of deaths of vehicle occupants, and the severity of injuries, by specifying vehicle crashworthiness requirements in terms of forces and accelerations measured on anthropomorphic dummies in test crashes, and by specifying equipment requirements for active and passive restraint systems. Fig 2. Types of Front Impact This standard applies to passenger cars, multipurpose passenger vehicles, trucks, and buses. In addition, Pressure vessels and explosive devices, applies to vessels designed to contain a pressurized fluid or gas, and to explosive devices, for use in the above types of motor vehicles as part of a system designed to provide protection to occupants in the event of a crash. 7 ADVANCED FEA FINAL PROJECT REPORT ME 65100 Fig 3. Test Configuration Specified Test Parameters: Work done in the system = (Average force on vehicle impacting the wall) + (Crush + Rebound of Vehicle) Dissipation of Kinetic Energy into the Vehicle structure, by optimized deformation for maximum energy absorption by the structural members and away from the occupant. The Energy Dissipation Rate is directly proportional to the Injury. Deformation by optimizing the deformation mode by refining the parameters that contribute to the axial crushing of the concerned structural members. Maximizing the crush space. Minimizing the intrusions in the members onto the occupant chamber, to avoid occupant injury/fatality. 8 ADVANCED FEA FINAL PROJECT REPORT ME 65100 2) Side Impact Overview This standard specifies performance requirements for protection of occupants in side impacts. The purpose of this standard is to reduce the risk of serious and fatal injury to occupants of passenger cars, multipurpose passenger vehicles, trucks and buses in side impacts by specifying strength requirements for side doors, limiting the forces, deflections and accelerations measured on anthropomorphic dummies in test crashes, and by other means. This standard applies to passenger cars, and to multipurpose passenger vehicles, trucks and buses with a gross vehicle weight rating (GVWR) of 4,536 kilograms (kg) 10,000 pounds (lb) or less, except for walk-in vans, or otherwise specified. Fig 4. Structural criteria for side impact. 9 ADVANCED FEA FINAL PROJECT REPORT ME 65100 3. ROOF CRUSH 1. Actual Testing Procedure [IIHS Protocol] [7] Roof strength evaluations consist of a quasi-static test conducted on a vehicle’s roof in a manner like tests used to judge compliance with Federal Motor Vehicle Safety Standard 216 (Office of the Federal Register, 2009). The main differences between the procedure specified by the Insurance Institute for Highway Safety (IIHS) and that specified by the US federal government are that the IIHS procedure: ● Specifies testing one side of a vehicle’s roof, does not include a headroom criterion, ● Specifies testing to a given displacement instead of a given force level, and ● Specifies setting the vehicle’s pitch angle during testing based on the measured on-road pitch angle. An overall rating is assigned based on the peak strength-to-weight ratio (SWR) measured within 127 mm of plate displacement. TEST VEHICLE SELECTION AND CURB WEIGHT MEASUREMENT Curb weight values used for calculating SWR are based on IIHS measurements of a vehicle, not the manufacturer’s specified curb weight. Test vehicle selection criteria is provided in Appendix B. Vehicle curb weight is measured with full fluid levels using scales manufactured by Longacre Racing Products (Computer scales DX series 72634). Fig 5. Testing Side View TEST VEHICLE PREPARATION With the vehicle on a level surface, the on-road pitch angle at the front door sill is measured on both sides of the vehicle. Unless the vehicle manufacturer requests otherwise, roof racks and other nonstructural items that may be contacted during the 10 ADVANCED FEA FINAL PROJECT REPORT ME 65100 test are left as installed from the factory. Any trim or other components are removed if they interfere with supporting the vehicle along its rocker panels. For vehicles with vertical pinch weld flanges on the bottom of the rocker panels, the vehicle support system consists of one I-beam (HR A-36 W4X13) for each rocker panel. Each I-beam has a clamping system incorporated on the top that is tightened against the pinch weld flange to clamp the system in place. Fig 6. Fixtures for testing. Testing Roof strength evaluations are conducted on a quasi-static test system manufactured by MGA Research Corporation (Figure 3). The system consists of an upright assembly and attached loading head that can be fixed at varying heights from the ground as well as at pitch angles ranging from -5 to +5 degrees to accommodate testing on the driver or passenger side. The roll angle is permanently fixed at 25 degrees. Four hydraulic actuators control the movement of the platen along two linear guides. The entire system is mounted on a T-slot bed plate anchored to the floor of the test facility. Once the vehicle is positioned correctly, the rocker panel supports are clamped to the two perpendicular I beams, and the beams are marked to allow confirmation that the vehicle position is maintained during the test. For body-on-frame vehicles, the frame 11 ADVANCED FEA FINAL PROJECT REPORT ME 65100 is supported to prevent the weight of the chassis from stressing the body at the body mounts. The roof is crushed to a minimum displacement of 127 mm at a nominal rate of 5 mm/second. Some tests are conducted to a greater displacement to collect additional strength data for research purposes. Force data are recorded from five load cells (Interface Inc. model 1220) attached to the loading platen. Displacement data are recorded from four linear variable displacement transducers (LVDTs) (MTS Temposonics model GH) integrated into the hydraulic actuators. Figure 4 shows the locations of the load cells and LVDTs on the loading platen. (a) (b) Fig 7. (a) Roof Crush setup (b) Actual testing validation. 12 ADVANCED FEA FINAL PROJECT REPORT ME 65100 4. METHODOLOGY To simulate the roof crush in LS Dyna, the following approach is used from modeling to analysis. Further sections describe the steps taken to model the roof crush along with model details to calculate SWR for the BIW of Toyota Corolla. Fig 8. Flowchart of the model. 13 ADVANCED FEA FINAL PROJECT REPORT ME 65100 1) Model Creation a) Hypermesh[thesis] [8/9] Altair’s HyperMesh is a high-performance finite element pre- and postprocessor that is compatible with most widely used finite element solvers. HyperMesh user-interface is easy to learn and supports many CAD geometry and finite element model files, thus increasing interoperability and efficiency. HyperMesh includes a sophisticated suite of easy-to-use tools to build and edit models. For 2D and 3D model creation, users have access to a variety of mesh generation panels besides HyperMesh powerful auto-meshing module. Automatic mid-surface generation, a comprehensive laminate modeler and morphing (to stretch existing FE meshes to new design geometries), and creating surfaces from the existing mesh offer new levels of model manipulation. The surface auto-meshing module in HyperMesh is a robust tool for mesh generation that provides users the ability to interactively adjust a variety of mesh parameters for each surface or surface edge. b) LS Dyna [website] [10] LS-DYNA is a general-purpose finite element program capable of simulating complex real-world problems. It is used by the automobile, aerospace, construction, military, manufacturing, and bioengineering industries. LS-DYNA is optimized for shared and distributed memory Unix, Linux, and Windows based, platforms, and it is fully QA'd by LSTC. The code's origins lie in highly nonlinear, transient dynamic finite element analysis using explicit time integration. "Nonlinear" means at least one (and sometimes all) of the following complications: Changing boundary conditions (such as contact between parts that changes over time) ● Large deformations (for example the crumpling of sheet metal parts) ● Nonlinear materials that do not exhibit ideally elastic behavior (for example thermoplastic polymers) ● "Transient dynamic" means analyzing high speed, short duration events where inertial forces are important. Typical uses include: ● Automotive crash (deformation of chassis, airbag inflation, seat belt tensioning) 14 ADVANCED FEA FINAL PROJECT REPORT ME 65100 Explosions (underwater Naval mine, shaped charges) ● Manufacturing (sheet metal stamping) As the model is solved using an Explicit solver, LS Dyna creates a perfect environment for that in this project. ● 2) Finite Element Modeling a) Geometry i) BIW The BIW (Body in White) for Toyota Corolla 2012 model was taken from CCAC (Center for Collision Safety and Analysis) FE model database. The model was validated against several full‐scale crash tests. It is expected to support current and future research related to occupant risk and vehicle compatibility, as well as barrier crash evaluation, research, and development efforts. Actual Vehicle to Model Mass, Inertia, and CG Comparisons based upon Data from Testing at SEAS, Inc Fig 9. Actual vs FEA Model from CCAC. 15 ADVANCED FEA ii) FINAL PROJECT REPORT ME 65100 Crush Plate Based on IIHS roof strength testing, the crush plate is designed with 762 x 1829 mm dimensions. (a) (b) Fig 10. Crusher Plate (a) Geometry (b) FE model b) Meshing Computational vehicle models need to capture the deformation and interaction of vehicle parts and subsystems occurring during impact. The accuracy with which the crash behavior of a vehicle is simulated depends on the quality of the computer aided design (CAD) data and its meshing. The BIW and Plate assembly was meshed using HyperMesh by Altair. Holes with a radius of more than 5 mm were meshed by surrounding it with minimum six elements. Very small parts, like nut-bolts, also were removed from the geometry, and then spot-welds were created in their places to represent bolts, rivets, and welds. 16 ADVANCED FEA FINAL PROJECT REPORT ME 65100 Fig 11. Meshed BIW c) Mesh Quality Criteria Some default quality criteria are available in HyperMesh, including the following: Min Side Length: Length of the smallest side of an element. Max Side Length: Length of the largest side of an element. Aspect Ratio: Ratio of longest side to the shortest side of an element. Warpage: Deviation of an element or element face from being planar. Min/Max Quad Internal Angle: The minimum/maximum angle of a quad element. Min/Max Tria Internal Angle: The minimum/maximum angle of a triangle element. Percent of Triangular Elements: Ratio of the number of triangular elements to the total number of elements. 17 ADVANCED FEA FINAL PROJECT REPORT ME 65100 For quality criterion was prepared as listed in the table and it is maintained throughout the meshing process. While meshing it was made sure that minimum element size should not be less than 5 mm in order to maintain the minimum time step of one micro second without using mass scaling. Table 1. Mesh quality criteria values No. Quality Parameter Allowable min/max 1 Minimum Side Length 5 mm 2 Maximum Side Length 20 mm 3 Maximum Aspect Ratio 5 4 Maximum Warpage Angle 20º 5 Minimum Quad Internal Angle 45º 6 Maximum Quad Internal Angle 135º 7 Minimum Tria Internal Angle 20º 8 Maximum Tria Internal Angle 120º 9 Percent of Triangular Elements 4.8% d) Model Summary The BIW and Plate were meshed using the mesh quality criteria as given in the previous section in HyperMesh. The element and node information are given in the table below and the element types used in the next section. Table 2. Mesh attributes Part No. of Elements Nodes. Of Nodes BIW 960116 981187 Plate 21755 22080 Fig 12. Model overview 18 ADVANCED FEA FINAL PROJECT REPORT ME 65100 e) Element Description All shell elements include membrane, bending and shear deformation. The default Belytschko-Tsay formulation is the most economical and is used in this problem. For eg. Belytschko-Tsay membrane: (and fully integrated membrane): appropriate for fabrics etc. where bending stiffness is negligible. Huges-Liu Belytschko-Tsay C0 Triangular Shell Belytschko-Tsay membrane Fully Integrated Shell Table 3. Element types and properties Type of Element Rigid Elements Mass Elements Bar Elements (1 D) Weld Elements (1D) Trias Elements (2D) Quad Elements (2 D) Property Welds Welds Spot Welds Welds Surface Surface 19 Number 107 30 5384 915 46641 928794 ADVANCED FEA FINAL PROJECT REPORT ME 65100 3) Contact Modeling In crash analysis, the deformations can be very large and predetermination of where and how contact will take place may be difficult or impossible. For this reason, the automatic contact options are recommended as these contacts are nonoriented, meaning they can detect penetration coming from either side of a shell element. a) Types of Contacts i) ii) Surface to Surface This type of contact is defined between the plate and BIW at the B pillar. In crash analysis, the contact type *CONTACT_AUTOMATIC_SURFACE_TO_SURFACE is a recommended contact type since, in crash simulations, the orientation of parts relative to each other cannot always be anticipated as the model undergoes large deformations. For this model, the plate is defined as the MSID (Master) and the BIW is defined as SSID (Slave) for the surface to surface contact. The values for friction are given as below: Table 4. Friction values Type of Friction Value Static Coefficient of Friction 0.2 Dynamic Coefficient of Friction 0.2 Viscous Damping Coefficient 20% Edge to Surface In tied contact types, the slave nodes are constrained to move with the master surface. At the beginning of the simulation, the nearest master segment for each slave node is located based on an orthogonal projection of the slave node to the master segment. If the slave node is deemed close to the master segment based on established criteria, the slave node is moved to the master surface. In this way, the initial geometry may be slightly altered without invoking any stresses. *CONTACT_TIED_SHELL_EDGE_TO_SURFACE_CONSTRAINED_OFFS ET contact is given to all the spot welds in this model. For this type of 2 ADVANCED FEA FINAL PROJECT REPORT ME 65100 contact, Spot weld beam elements (PBEAM) are taken as slave (SSID) and corresponding surfaces. The contact thickness for slave and master is given 0.9. iii) Single Surface These contact types are the most widely used contact options in LSDYNA, especially for crashworthiness applications. With these types, the slave surface is typically defined as a list of part ID’s. No master surface is defined. Contact is considered between all the parts in the slave list, including self-contact of each part. If the model is accurately defined, these contact types are very reliable and accurate. However, if there is a lot of interpenetrations in the initial configuration, energy balances may show either a growth or decay of energy as the calculation proceeds. For crash analysis, the contact type *CONTACT_AUTOMATIC_SINGLE_SURFACE are used for contacts between vehicle component on BIW. All components and BIW are considered as Slave. Table 5. Friction values Type of Friction Value Static Coefficient of Friction 0.3 Dynamic Coefficient of Friction 0.3 Viscous Damping Coefficient 20% b) Spot Welds Rigid massless beam (spotweld) : Used for transmission of moments, shear and normal forces. Fig 13. Spot weld reduced models Brittle failure of the spotweld occur when 3 ADVANCED FEA FINAL PROJECT REPORT ME 65100 Spotweld failure due to plastic straining occurs when the effective nodal plastic strain exceeds the input value. This option can model the tearing out of a spotweld from the sheet metal due to plasticity in the material surrounding the spotweld. Contact type 8: nodes spotwelded to surface : Slave nodes are tied to the masters until a failure criterion is reached. Thereafter they can slide on or separate from the masters as in a type 5 contact surface. This type of surface can be used to represent spot-welded or bolted connections. Failure criterion: Table 6. Element Information Type of elements Number of Elements Rigid Weld 107 1D Welds 5384 PBeam 915 4 ADVANCED FEA FINAL PROJECT REPORT ME 65100 4) Material Modeling The types of Materials used for this model and their properties are defined in this section. i) MAT_9 (Null Material) : For solid elements equations of state can be called through this model to avoid deviatoric stress calculations. A pressure cutoff may be specified to set a lower bound on the pressure. This material model has been very useful when combined with the reactive high explosive model where material strength is often neglected. The null material should not be used to delete solid elements. An optional viscous stress of the form is computed for nonzero . ii) MAT_20 (Rigid Material): The rigid material type 20 provides a convenient way of turning one or more parts comprised of beams, shells, or solid elements into a rigid body. Approximating a deformable body as rigid is a preferred modeling technique in many real-world applications. For this model the plate is given MAT_20 material. Two unique rigid part IDs may not share common nodes unless they are merged together using the rigid body merge option. A rigid body may be made up of disjoint finite element meshes, however. LS-DYNA assumes this is the case since this is a common practice in setting up tooling meshes in forming problems. iii) MAT_24 (Piecewise Linear Isotropic Plasticity) : The plasticity treatment in this model is quite it includes strain rate effects and does not use an equation of state. Deviatoric stresses are determined that satisfy the yield function For complete generality a table defining the yield stress versus plastic strain may be defined for various levels of effective strain rate. All the structural components of the chassis are given this material model. 5 ADVANCED FEA iv) FINAL PROJECT REPORT ME 65100 MAT_100 (Spot Weld) : This material model applies to beam element type 9 for spot welds. These beam elements may be placed between any two deformable shell surfaces and tied with type 7 constraint contact which eliminates the need to have adjacent nodes at spot weld locations. For our model, All the Spotwelds are given MAT_100. Fig 14. Spot welds Beam spot welds may be placed between rigid bodies and rigid/deformable bodies by making the node on one end of the spot weld a rigid body node which can be an extra node for the rigid body. In the same way, rigid bodies may also be tied together with this spot weld option. v) MAT_123 : An elasto-plastic material with an arbitrary stress versus strain curve and arbitrary strain rate dependency can be defined with this model. Another model, MAT_PIECEWISE_LINEAR_PLASTICITY, is similar but lacks the enhanced failure criteria. Failure is based on effective plastic strain, plastic thinning, the major principal in plane strain component, or a minimum time step size. Sub-assembly Material configurations : For the model, there are certain subassemblies which are defined with some of the material models explained above. The assembly and their material properties are : Roof and Side Panel Assembly - The material cards given to the BIW components under roof assembly i.e. the A,B,C pillars and the roof are MAT_24 – Steel. 6 ADVANCED FEA FINAL PROJECT REPORT ME 65100 Table 7. Material properties for MAT_24 Property Range Density 7.85 – 7.89 x10-9 tonnes/mm3 Youngs Modulus 210 GPA Poisson’s Ratio 0.3 Yield Strength 180 – 450 MPA Tangent Modulus 5x103 Element Formulation (Belytschko Tsay) 2 Element surface thickness 0.52 – 2.21 mm 7 ADVANCED FEA FINAL PROJECT REPORT ME 65100 5. BOUNDARY CONDITIONS The boundary conditions i.e. constraints, velocities and convergence criterion defined for this model are specified below: 1) Constraints (SPCs) : The single point constraints are basically fixing DOF’s on the nodes of the model. For this model, all 6 DOFs are fixed along the selected nodes as shown in the figure. Fig 15. SPCs along the bottom of the BIW. Along the bottom part of the chassis, the nodes are fixed according to the IIHS testing station mounts. 8 ADVANCED FEA FINAL PROJECT REPORT ME 65100 2) Loading : For loading the plate in downward direction, a local coordinate system was set up for the plate and along negative Z direction of the plate a boundary prescribed motion is given. A load curve is defined for the motion as shown in the figure. Fig 16. Load curve for Boundary prescribed motion Fig 17. Plate initial loading. 3) Convergence Criteria and Energy Plots : The explicit solver for LS Dyna was used to converge the solution. The test runs for around 100 ms till 127 mm deformation of the body by the plate. The maximum velocity was given as 1270 mm/s as per the load curve. To help converge the solution, the following convergence criteria were given, 9 ADVANCED FEA FINAL PROJECT REPORT Time Step End Time Mass Scaling ME 65100 Table 8. Convergence criteria 4.42x10-7 100 ms ~ 5% With the given parameters, a full model for BIW without any structural components takes around 15 – 17 hours on a supercomputer. For quick simulations, further the model was stripped down one containing only side panel roof assembly along with the wind shield and other discarding the front end of the chassis. (a) (b) Fig 18. (a) Energy Plot (b) Crusher plate displacement plot 6. RESULTS 10 ADVANCED FEA FINAL PROJECT REPORT ME 65100 1) Testing results and SWR Calculation : According to the IIHS testing criteria, the main results to be calculated after the testing is done are the Fmax which is maximum resultant force on the body at the point of contact and based on the ratio of Fmax to the kerb weight of the vehicle SWR (Strength to Weight ratio) is calculated. Fig 19. IIHS SWR calculation Fig 20. SWR vs Plate displacement 11 ADVANCED FEA FINAL PROJECT REPORT ME 65100 2) Results obtained from the model : After the solution was converged, the following results were calculated from the stripped-down model. a) A,B,C pillar stress contours : Along the roof and side panel assembly, the part which undergoes maximum deformation are A, B and C pillars. The stress contours around that region is shown in the figures. Fig 21. Equivalent Stresses Fig 22. Equivalent Stresses on the Pillars 12 ADVANCED FEA FINAL PROJECT REPORT Fig 23. Maximum stresses along the roof and side panels Fig 24. Equivalent Stresses on the Pillars 13 ME 65100 ADVANCED FEA a) FINAL PROJECT REPORT ME 65100 Roof and roof cross member plastic strain : The equivalent plastic strains are calculated along the roof cross members as the intrusions occur in that region. (a) (b) Fig 25. (a) Effective plastic strain along roof cross member (b) Zoomed in image 14 ADVANCED FEA FINAL PROJECT REPORT 15 ME 65100 ADVANCED FEA b) FINAL PROJECT REPORT ME 65100 Maximum Reaction Force : The maximum reaction force is used to calculate the SWR rating for the given model. Fig 26. Maximum reaction force in N (newton) c) SWR for current model : For current model the SWR rating is calculated using the relationship: SWR = 1.5 * Fmax/m*g SWR = 54997 *1.5/543.7*9.81 SWR = 6.87 Since the weight of reduced chassis is used the SWR is quite high than usual. If we calculate it based on the above reaction forces and original BIW weight it comes around 1.97 – 2 which is acceptable. 16 ADVANCED FEA FINAL PROJECT REPORT ME 65100 2. CONCLUSION The various statistical analyses in this project support the hypothesis that passenger vehicles with a higher SWR in the roof crush test are likely to experience less vertical roof intrusion in rollover crashes than vehicles with a lower SWR. This finding in combination with IIHS’s previous research demonstrating a relationship between roof intrusion and head, neck, or face injuries confirms a relationship between greater roof strength and fewer injuries. This finding also supports the validity of SWR as a measure of roof strength because it was found to be a statistically significant predictor of vertical roof intrusion in real-world rollovers. 3. FUTURE SCOPE The results of the analysis can be improved further by considering additional contact interactions in the vehicle structure. The detailed model uses more complete contact definitions with contact defined for the entire model rather than for the most critical regions. The model under consideration is based on a public domain FEA model and does not represent an actual production vehicle. No information was available to verify the material properties, shell thicknesses, spot weld spacing, and other details that must be specified. These properties have a significant influence on the model behavior. 17 ADVANCED FEA FINAL PROJECT REPORT ME 65100 4. REFERENCES 1) Roof Crush Analysis for Improving Occupant Safety, Sainath Arjun Waghmare, Prashant D. Deshmukh, Swapnil S. Kulkarni, International Journal of Advanced Engineering Research and Studies, Oct-Dec 2013, ISSN2249–8974. 2) Crash Safety Overview, NCAP. 3) Rollover and Roof Crush Analysis of Low-Floor Mass Transit Bus, Pankaj S. Deshmukh, Thesis submitted to Dr Babasaheb Ambedkar Marathwada University, 2002. 4) Automobile Roof Crush Analysis with Abaqus, Abaqus Technology Brief, April 2007, Simulia. 5) Roof Strength Testing and Real-World Roof Intrusion in Rollovers, Traffic Safety Facts Research Note, National Highway Traffic Safety Administration, Aug 2010, DOT HS 811 365. 6) Crashworthiness Evaluation Roof Strength Test Protocol (Version III), Insurance Institute for Highway Safety, Jul 2016. 7) Electronic Code of Federation, FMVSS 208 Ocupant Crash Frontal Impact Protection, 2018, link: www.ecfr.gov/cgi-bin/text-idx?node=se49.6.571_1208 8) Electronic Code of Federation, FMVSS 214 Side Impact Protection, 2018, link: www.ecfr.gov/cgi-bin/textidx?SID=d4f7934ae1a2a7a6b5db134cd041add8&mc=true&node=se49.6.571_12 14&rgn=div8 9) Quasi-static Simulations using Implicit LS-Dyna, Satish Pathy, Thomas Borvall, 14th International LS-Dyna User’s Conference, June 2016. 10) Vehicle Roof Crush Modelling and Validation, Mingzhi Mao, E.C. Chirwa, T. Chen, 5th European LS-Dyna User’s Conference. 11) LS-Dyna Keyword Manual. 12) LS-Dyna Theory Manual. 18