Research On Nonlocal Progressive Failure And Residual Strength Of Laminates With Low-velocity Impact Damage

Carbon fiber reinforced epoxy resin matrix composite has the advantage of low density,high strength and high designability,which leads to the appreciation by people from all works of life.In recent years,the progressive failure analysis based on continuum has been widely used in aerospace composite structure.However,the progressive failure and continuous stiffness degradation of laminates always perform highly non-linearity.It is very important to understand the mechanism of damage evolution after energy dissipation.In fact,progressive failure of composites will encounter strain localization problem.Local severe damage and energy dissipation can lead to the illusion of ellipticity in the quasi-static problem.The most direct manifestation is the dependence of the grid.The failure mechanism of composite laminates under low-velocity impact is very complex and is usually accompanied by the generation of strain localization.The purpose of this paper is to solve the localization problem of composite materials by introducing the nonlocal integral theory developed by Ba?ant et al.into progressive failure model.The results show that the nonlocal progressive failure model can simulate the failure evolution and dynamic response of the composite specimen under different load conditions,at the same time,which can avoid the grid sensitivity effectively.In order to verify the effectiveness of model,the article focuses on the study of aircraft composite structure’s residual compression/shear strength.Specific contents are summarized as follows:Firstly,nonlocal simulation of impact damage and response of T700 / QY8911 and T700 / 3234 composite laminates were conducted with VUMAT subroutine.The accuracy of the nonlocal algorithm in solving the problem of impact model is verified.Secondly,the impact damage is introduced to intact structure through restart analysis to complete the whole process of low-speed impact-compression / shear simulation.The results are in good agreement with the experiment.Finally,the damage characteristics of impacted beam web under shear loads are obtained.The results show that the composite structure destroyed in the direction of 45°under the collective effect of buckling and fiber failure.Based on the nonlocal progressive failure simulation,the damage tolerance assessment of the composite structure was initially completed.