Study On Crashworthiness Of Car Bumper System

Safety, environmental protection and energy conservation are the three principal problems of the 21st century. Meanwhile, how to improve the crashworthiness of vehicles has been an assignable issue during the analysis of passive safety of the automotive. In the case of car crash, bumpers have their indispensable roles in car body protection. Bumper crashes are the most common scenes in car crash accidents, and bumper is also the first part of car body involved in the collision. Improving the crashworthiness of bumper effectively will help improve the performance of passive safety of automobile. Thence, researching the crashworthiness of bumper for automobile is particularly important.At the beginning of the dissertation, statistical data of road traffic accidents in our country since 2000 is analyzed, and researching on vehicle frontal impact is particularly important. Secondly, recent developments of crashworthiness optimization and thin-walled components are briefly summarized. Then, the main theoretical backgrounds are introduced. Finally, in order to improve the crashworthiness of bumper, writer studies the crashworthiness structure and crashworthiness mechanism, and optimized structure and innovative mechanism are used in the bumper system.On the researching of crashworthiness structure, base on explicit finite element technique, design of experiment, response surface method, writer establishes a similar relationship between sectional sizes as design variables and structural specific energy-absorption as objective function, and optimizes sectional sizes of cone-shaped thin-walled components with different sections(round, square, and regular hexagon). In addition, according to the evaluation index of crashworthiness structure, cone-shaped thin-walled components with different sections are conducted a comparative analysis, the results show that conical thin-walled component is best. And a new type of energy absorption device with sandwich structure using conical thin-walled component is designed. The simulation results show that the device using conical thin-walled component is better than the device using cylindrical thin-walled component. The device using conical thin-walled component can absorb all the impact energy in the low-speed collision and medium-speed collision, and the device can absorb 30.28% of the total energy. Accordingly, it better enhance the crashworthiness of bumper system. On the researching of crashworthiness mechanism, by researching on the relationship between transmission angle of four-bar linkage and force transfer, a variable stiffness mechanism is proposed combining springs and double-slider mechanism. First of all, writer conducts a theoretical analysis with the mechanism. Afterward, the mechanism is verified by a number of tests. For further researching, a method to establish virtual prototype of the mechanism is proposed, and is verified by comparative analysis of the simulation results with the experimental results. Then, a program design of energy-absorption bumper bracket using the mechanism is proposed, and virtual prototype of energy-absorption bumper bracket is established. Finally, it is compared with the other two programs (bumper bracket using rigid rod and using spring) on rigid-plastic characteristics and crashworthiness. Results show that energy-absorption bumper bracket is the best.