| In vehicle crash accidents,the injury and mortality rates caused by frontal crash are very high. Carbon fiber reinforced composites structures have good collision safety performance,and are ideally suited for the vehicle body energy-absorbtion. Reasonable design of composite lay-up structures, can not only improve the automotive crashworthiness and protect the occupants, but also make a great contribution to automotive lightweight.The thesis is based on the study of the response and damage failure mechanisms of composite structures under impact loading. In order to improve the crashworthiness of CFRP tube,a finite element crash model was set up using finite element software LS-DYNA. And the ply orientation angle of the CFRP tube was optimized by genetic algorithm. At the same time,the effect of diameter ratio and the cone angle on t he crashworthiness of CFRP tube was analyzed.First of all,carbon fiber composite specimens for tensile,compression,and three-point bending experiments were made. Then the tensile, compression, and three-point bending tests were carried out according to national standards. The tensile and compression strength of the material,Young's modulus and fracture strain and other parameters were obtained. Finite element models according to these three experiment were established and obtained consistent results compared with the test load-displacement curve. The results showed that: Carbon fiber reinforced composites is similar to brittle materials,mainly elastic deformation with no apparent plastic deformation before failure. The strength,fracture failure strain and Young's modulus of composite materials when compressed are lower than the corresponding values relating to tensile, Wherein the difference in Young's modulus is small. It has better computational efficiency and accuracy for using MAT54 which is based on fully chang-chang failure criterion simulates composite material. The finite element model accurately predicts the failure mechanism of three-point bending experiment is due to the compression failure of the upper surface. However,it was failed to reproduce the delamination phenomenon due to the using of single-shell element modeling.Secondly, finite element model for CFRP tube was established and verified. Parametric analysis of GA control parameters,such as population size,the selection operators,crossover,crossover probability and mutation probability,on the effects of convergence and optimization capability for the ply orientation angle problem of composite tube under axial impact have been executed combined with LS-OPT software and GA. The most suitable control parameters value of selection operator,crossover,population size,mutation probability,crossover probability are tournament,BLX, 20, 0.125, 1.0, respectively. And the optimal ply orientation angle is [0/-45/90/45]S2.Finally,we have analyzed the effect of diameter ratio and the cone angle on the crashworthiness of the CFRP tube under axial impact. Results show that there is a linear relationship between the maximum impact force and the diameter ratio. Energy absorption and diameter ratio curve similar to the “W” shape,energy absorption and maximum impact force can be well-balanced when K=1.6. Cone angle almost no effect on the collision energy absorption,while has a great influence on the maximum impact force. The maximum impact force almost unchanged when the cone angle is greater than 12 o. The optimal diameter ratio and the cone angle is respectively 1.6 and 12 o.Research of this thesis obtained some meaningful conclusions,and have a certain significance for the application of carbon fibre reinforced composite in the frontal longitudinal beam. |
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