Study On Damage Of Laminates Due To Impact Bending

Laminates are often subjected to impact loading in working environment.In order to take full advantage of the material properties,it is necessary to gaining the dynamic properties of laminates to design.So it is vitally important to study the dynamic mechanical properties of laminates.In this paper,the damage of carbon / epoxy laminates due to impact bending is studied.Based on the quasi-static bending tests and drop weight impact bending tests,the strength correction coefficient is gained,the bending failure model of laminates is established,and the effect of loading rate on the bending resistance properties of laminates is studied.The reliability of the proposed strength correction coefficient and the rationality of the bending failure model are verified by comparing with the testing results.In addition,the gained strength correction coefficient is further applied to the failure study of multilayer laminates,and the bending properties of laminates are predicted.The specific studies and conclusions are as follows:(1)Quasi-static and drop impact four-points bending trials of unidirectional carbon / epoxy laminates are carried out.And the effects of different loading rates on the damage of unidirectional laminates due to bending are analyzed respectively.Delamination of the interface between fiber and matrix results in laminated buckling of the fiber bundle.The bending capacity in dynamic case is from 13% to 22% higher than that in quasi-static case,which is due to the less interface delamination damage under low speed impact loads according to in the quasi-static case.With the increase of loading rate,the damage mode changes from interface debonding to the matrix cracking near interface.(2)According to the four-points bending trial under different loading rates,a modification factor of dynamic failure strength for composite,which is based on open rate,is introduced.A laminates model with uniform delamination is established,and the dynamic bending failure simulation is carried out.The simulation results are in good agreement with the experimental data,which indicates that the failure analysis model used is reasonable.(3)Based on the open rate,the strength correction coefficient is used to predict the dynamic bending behavior of different laminates in bending failure simulation.The failure mode and the bending resistance of the laminates are predicted,which provides a reference for the study on resistance properties for the normal carbon / epoxy laminates due to impact bending.