Numerical Study On CFRP Tube Under Axial Compression

Carbon fiber reinforced plastic(CFRP)with low density,high specific strength,high modulus and other excellent material properties,is good as lightweight materials.CFRP has been widely used in the areas of aerospace and military,and automotive field pays more and more attention to the application of CFRP.CFRP is not only light in quality,but also has good energy absorption characteristics.It is suitable for energy absorption components in auto-body.CFRP consists of reinforcement and matrix.And the energy absorbing mechanism is complex under axial compression,such as fiber fracture,matrix cracking and splitting delamination.In this paper,the energy absorption characteristics of the composite structure under the axial compression were investigated in the LS-DYNA.Firstly,in this paper,the size of the tube specimen and the test system were determined,and the axial compression test of the CFRP circular tube was carried out.Due to the significant influence of the single-layer composite structure on the energy absorbing characteristics of the composite structure,the tubes made of unidirectional tape layers and braided layers were selected for testing.The failure process and displacement-load curve were obtained.Comparing the results of tests,it was determined that the tube of unidirectional tape layers had better energy absorption characteristics under the same geometrical dimensions,and it would be used as the evaluation criterion for numerical simulation research.LS-DYNA finite element code was used in this numerical simulation,and the material model MAT54 was utilized to define CFRP.The model of single-layer shell element tube was established,which was same as the experimental research.By comparing the numerical simulation results with the experimental results,the validity and accuracy of the numerical simulation method were determined.The axial crushing model of single-layer shell element can effectively obtain the displacement-load curve results of the tube,but it cannot show the splitting delamination macroscopically.The model of multi-layer shell element tube was established,and the influence of element size and the number of element layers on the simulation results was explored.The results showed that the axial crushing model of single-layer shell element could observe the failure process visually,and the displacement-load curve was also consistent with the experimental results.The failure triggering mechanism is an important factor in the energy absorption characteristics of the composite structures,which initiates stable progressive failure.In this paper,the influence of failure triggering mechanism with notch on the energy absorption characteristics was investigated.The shapes of the notch as rectangular,semicircular and trapezoidal were designed,and it was shown that the shapes had little influence on the energy absorption characteristics.In the case of the rectangular notch shape,the dimensions of the notch section were assumed to be 0.3,0.4,0.5,0.6 and 0.7 times of the cross-section size of the round tube,respectively.It was shown that the tube components had the best energy absorption characteristics with the notch whose dimension is 0.6 times of the cross-section size of the round tube.