Chassis and Impact Attenuator Design for Formula Student Racing
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CHASSIS AND IMPACT ATTENUATOR DESIGN FOR FORMULA STUDENT RACE CAR MECH 5825M Professional Project Chassis and Impact Attenuator design for Formula student Race car Ahmed Oshinibosi Project Supervisor: Prof. D.C Barton 30th August 2012 AKNOWLEGDEMENT Firstly, I would like to appreciate the effort of my supervisor, Professor David Barton who is the head of school of mechanical engineering for his invaluable contribution towards the successful completion of this project. Secondly, I am indebted to my employer, Tallent Automotive Limited who did not only provide financial assistance to me in order to pursue this postgraduate Master’s degree, but also gave me the permission to utilise the company’s software packages to carry out this project. I also want to use this opportunity to thank the faculty of engineering for awarding me the International Excellence scholarship which also contributed towards my tuition fees. ABSTRACT Generally, in the automotive industry, weight reduction, cost of engineering design and reduction in vehicle development cycle time are becoming increasingly focused on. In order to tackle this, Computer Aided Engineering (CAE) is popularly being used to lead design process. This is more efficient than just using CAE as a verification tool. In the design of the F15 chassis, suitable Finite Element Analysis (FEA) optimisation techniques have been adopted from the early design stage. The design problem in view of weight reduction and increasing torsional stiffness has been solved by means of topology optimisation and also by applying gauge optimisation at the later stage of the design phase to optimise the size of structural members of the chassis. Initial topology optimisation generated efficient load paths which were translated into two main concepts: Concept I & II - all tube design and Concept III - tube and sheet component design. All these proposals achieved specific torsional stiffness considerably higher than previous F14 chassis giving at least 4kg of mass savings. Similarly, in the development of the impact attenuator, surrogate FE models were built and parametric studies were set up to observe the influence of wall thickness, semi-apical angle, indentations and protrusions on crash performance. Subsequently, optimisations were set up to evaluate optimum values of these parameters. In the end, a conical frustum shell-type impact attenuator which incorporates asymmetric indentations and protrusions was proposed. Specific energy absorption was maximised and impact force minimised for this design. The effectiveness of the impact attenuator was measured by comparing the force transmitted through the chassis “with and without the crash tube" into the cockpit area. The crash tube reduced the amount of force transmitted into the cockpit area of the chassis to an appreciable level. Moreover, the acceleration measured at an area close to driver’s position was also decreased. CONTENTS List of figures ………….…………………………………………….…………………….. i List of Tables ……………………………………………………………………...……... iv List of symbols …………………………………………………………………………… v 1. Introduction …………………………………………………………………………… 1 1.1 Design challenge …………………………..……………………………………… 1 1.1.1 Chassis ……………………………………………………………………... 1 1.1.2 Impact attenuator ………………………………………………………….. 1 1.2 Aim ………………………………………………………………………………….. 2 1.3 Objective …………………………………………………………………………… 2 2. Literature Review …………………………………………………………………….. 3 2.1 Chassis structures ………………………………………………………………… 3 2.1.1 Monocoque chassis ……………………………………………………….. 3 2.1.2 Space frame chassis ……………………………………………………… 3 2.2 Design and performance requirements ………………………………………… 4 2.2.1 Chassis design configuration ……….……………………………………. 4 2.2.2 Torsional stiffness …………………………………………………………. 6 2.2.3 Structural requirements …………………………………………………… 7 2.2.4 Crash worthiness ………………………………………………………….. 8 2.3 Computer Aided Engineering (CAE) design approach ………………..…….. 12 2.3.1 Structural design and optimisation ……………………………………... 13 2.3.2 Design of Experiments ………………………………...………………… 16 3. Chassis development ……………………………………………………………… 20 3.1 Design optimisation ……………………………………………………………… 20 3.1.1 Topology optimisation ………………………………...…………………. 21 3.1.2 Interpretation of topology and further optimisation I ……….…………. 23 3.1.3 Interpretation of topology and further optimisation II …………………. 26 3.1.4 Interpretation of topology and further optimisation III ………………… 27 3.2 Discussion ………………………………………………………………………... 27 4. Impact attenuator development ………………………………………………….. 29 4.1 Finite Element simulation of crash …………………………………………….. 29 4.1.1 Finite Element modelling ………………………………………………... 30 4.1.2 Mesh independency and solution convergence test …………………. 30 4.1.3 Load and boundary conditions …………………………………………. 32 4.1.4 Analysis of initial design concepts ………………...…………………… 32 4.2 Optimisation of conical frustum impact attenuator ………...………………… 36 4.2.1 Parametric study I (based on thickness and semi-apical angle) ….… 37 4.2.2 Parametric study II (based on geometry of protrusions/indentations) 46 4.3 Discussion …………………………………………………….………………….. 53 5. Crashworthiness of chassis and impact attenuator ………….…..………….. 54 5.1 Finite Element modelling ………………………………………….…..………... 54 5.1.1 Loads and boundary conditions ………………….……….….………… 54 5.1.2 Crash analysis …………………………….……………….….…………. 55 5.1.3 Results I (Comparison with Surrogate model) ……………...………… 55 5.1.4 Results II (Effectiveness of impact attenuator) ……………………….. 56 5.2 Discussion ……………………….……………………………………………….. 58 6. Conclusion ……………………………...…………………………………………… 59 7. Future recommendations …………………………………………………………. 61 8. References …………………………………………………………………………… 63 9. Appendices ………………………………………………..………...………………. 67 LIST OF FIGURES Fig. 1. Monocoque chassis structure for Race car [13] ……...………………..…….…3 Fig. 2. Example of Space-frame chassis structure for Race car [2] ………….……… 4 Fig. 3. 95th percentile male with helmet [1] ………………………………….…………. 5 Fig. 4. 95th Requirements for minimum helmet clearance [1] ………….......………... 5 Fig. 5. 95th Side impact zone [1] ………...……………...…………………….………… 6 Fig. 6. Frame Finite Element Model Loading Case [2] ……………..…………………. 7 Fig. 7. Chassis under consideration for structural requirements [1] ………………… 7 Fig. 8. Finite element model of a race car structure with Impact attenuator [18] …. 10 Fig. 9. The racing car of Polytechnic of Turin for season 2008 and FE model of the produced crash absorber [41] ……………………………………………………...…… 11 Fig. 10. Finite element mesh of the Caterham 7 vehicle model [46] ………….……. 11 Fig. 11. Actual and predicted shell model of Caterham 7 impact attenuator [46] .... 12 Fig. 12. The Design approach using ThyssenKrupp eDICT Process [14] …...……. 13 Fig. 13. Optimisation of R56 cross beam [7] ……..…………………………………… 13 Fig. 14. Topology optimisation of a spider vehicle chassis [3] ……………………… 14 Fig. 15. Topometry optimization results [5] ……………...……………………………. 15 Fig. 16. Shape optimisation (Original model on left, new model on right) [11] ……. 15 Fig. 17. General overview of how Hyperstudy works [19] ………......………………. 16 Fig. 18. F14 Chassis (29.7kg) …………………………...……………………………... 20 Fig. 19. Designable and Non-designable regions ……………………………………. 21 Fig. 20. Torsional stiffness load case ………………………………………………….. 22 Fig. 21. Topology results for chassis ………………………...………...……………… 23 Fig. 22. 1D Beam representation of Topology result ………………………………… 24 Fig. 23. Tube cross-section geometry …………………………………………………. 24 Fig. 24. Results after further optimisation I “displayed in 3D”……………………….. 25 Fig. 25. Representation of Topology result using tubes and sheet component “visualized in 3D”…………………………………………………………………………. 27 Fig. 26. General geometry of proposed crash tubes based on FSAE rules ………. 29 i Fig. 27. Convergence of initial peak force vs. Mesh size for conical frustum tube .. 31 Fig. 28. Finite element model of the different crash tubes to be analysed ………… 31 Fig. 29. Description of Load and boundary conditions for crash scenario ………… 32 Fig. 30. Energy absorbed vs. Time for the four design concepts ……...…………… 33 Fig. 31. Section force vs. displacement for the four design concepts ……………… 34 Fig. 32. Deformation patterns of cylindrical tube ……………………………….…….. 34 Fig. 33. Deformation patterns of conical frustum tube ………………………………. 35 Fig. 34. Deformation patterns of square tube …………………………………………. 35 Fig. 35. Deformation patterns of square frustum ……………………………….…….. 35 Fig. 36a. Schematic of the conical frustum …………………………….………………37 Fig. 36b. Schematic of the conical frustum showing how d is varied ……………… 38 Fig. 37. Screen shot showing how Hypermorph was used to modify semi-apical angle ……………………………………….……………………………………………… 38 Fig. 38. Response surface relating Kinetic energy to shape and wall thickness …. 39 Fig. 39. Response surface relating Energy absorbed to shape and wall thickness 40 Fig. 40. Response surface relating maximum section force to shape and wall thickness ………………………………………………………………………………….. 40 Fig. 41. Response surface relating estimated mass to shape and wall thickness .. 41 Fig. 42. Response surface relating specific energy absorbed to shape and wall thickness ………………………………………………………………………………….. 41 Fig. 43. Hyperstudy optimisation history plot of OBJECTIVE (Specific energy absorbed) – 1a …………….……………..………………………………………………. 43 Fig. 44. Hyperstudy optimisation history plot of OBJECTIVE (Specific energy absorbed) – 1b ……………………………………………………………….…………... 44 Fig. 45. Comparison between section-forces of the baseline and optimised conical frustum tube ……………………………………………………………………….….….. 45 Fig. 46.