Research On The Structural Design Method Of Micro-car's Frontal Rail For Crashworthiness Under Frontal Impact

In recent years, the domestic sales of micro-cars increase sharply with the rapid development of automobile industry. Compared with ordinary passenger vechile, the frontal part of micro-car is relatively short, which makes the structural design of vehicle body for safety under frontal impact more difficult. Frontal rail absorbs considerable proportion of kinetic energy by plastic deformation, and the energy absorption efficiency largely depends on the structural design of the frontal rail, which directly affects the crashworthiness and safety performance of micro-car under frontal impact. Though plenty of researchs on the structural design of frontal rail have been carried out, thorough investigations on the structural failure mechanisms in the crushing process of frontal rail are rare, not to mention researchs by combining structural design of front rail and safety optimization. Based on existing researchs, this article will carry out in-depth studies on crushing deformation and failure mechanism of frontal rail, and pose corresponding structural design methods, with which structural optimization will be applied to the frontal rail of the target vehicle, improving the crashworthiness and safety of micro-car under frontal impact.Taking vehicle safety under frontal impact as the theme, this article carries out researchs as follows:(1) Analysis of the influence of frontal rail structure on frontal crash safety with vehicle body acceleration as basisEquivalent and simplify vehicle body acceleration curves under frontal impact to two-step curves following the energy conservation law, and input the curves before and after simplified into vehicle-occupant system dynamics model to obtain occupant injury and validate the rationality of this simplifying method. Then comparative analysises are carried out to study the influence of structural strength of front vehicle body on occupant safety with total deformation and second-order acceleration kept respectively. Finally, on the structural characteristics of micro-car body, analysises are proposed to study the influence of frontal rail structure on occupant safety and then the research objects of frontal rail structure are set.(2) Study the influence of structrural parameters on crushing characteristic of weldedsuper-folding element by numerical methodThe welded super-folding element(WSFE) is proposed in this article for the first time, on the basis of traditional super-folding element(SFE), to characterize the spot-welded sections and distinct the structural differences between spot-welded and traditional closed sections. Numerical analysises are employed to study the influences of structural parameters of WSFE on its crushing characteristics, the results show that the angles at the edge of the thin-walled parts account for large influences on crushing characteristics of WSFE, and a wider flange can prevent deformation failure in the crushing process, more researchs on WSFE with different thickness combinations are also carried out. The deformation mode of WSFE is found to be different from that of the traditional SFE in analysis, and samples are selected to be comparatively analyzed, validating the hypothesis proposed in the content. Revice is tried to be applied on the theoretical formula for inspecting the causes of the differences.(3) Research and validation of strucrual design method of front railAnalyze the crushing characteristics of traditional top-hat and double-hat sections by dynamic axial impact test. Inspect the deformation mechanism and causes of structural failure, and then summarize a series of structural design methods for preventing structural failure and improving energy absorption efficency. Design methods are proposed for preventing structural failures, such as spot-weld tearing, irregular deformation of flange and local bending, and then tests are launched to validate the structural feasibility. The arrangement of triggers has been researched to analyzing its influence on the deformation mode and energy absorption efficiency, and the crushing characterisics of thin-walled columns are found to be improved by a more reasonable trigger arrangement. Stiffers are studied in this article to figure out its influence on improving energy absorption efficiency of frontal rail, and more super-finite elements on section and more narrow side of super-finite element can improve significantly the energy absorption efficiency as well as structural crushing stability.(4) Structural design and optimization of target-vehicle's front rail for crashworthinessReform the structure of target-vehicle's front rail using the strucrual design method of front rail as the basis, and then optimize the structure of front rail after reformation combined with optimal latin hypercube method, least square support vector regression method, space shrinking regression method and NSGA-II muti-objective optimization, improving the crashworthiness of target-vehicle under frontal impact and lightweighting the frontal rail structure. The full-vehicle model under frontal impact is simplified as a sled model, which has been validatied, for reducing the calculating consumption. The structural design method and optimization method have been validated as reasonable by comparing the vehicle body curves and occupant injuries before and after optimization.