Investigation On Dynamic Compressive And Soft Impact Properties Of Twill Weave Laminate

Fiber reinforced composites have been widely applied in the fields of aviation and aerospace,due to the light weight,high strength and other advantages of the material.While impact loads are rather common under the working circumstances of composites,and it is necessary to investigate the mechanical behavior of composites under dynamic impact loads.Within the researches about the impact damage of composites,the studies on the soft impact behavior of composites are still insufficient.This paper focused on the soft impact behavior of twill weave laminate composite,and conducted a series of investigations through experimental and numerical methods.The main work is as follows:Firstly,this paper investigated the in-plane dynamic compressive properties of the twill weave laminate.The stress equilibrium within the specimen was verified to ensure the effectiveness of the experimental results.The upper limit of constant strain rate was obtained both theoretically and experimentally,which reasonably determined the constant strain rate range.On this basis,the stress-strain curves under high strain rates were obtained,the deformation and damage characteristics of the specimens were analyzed.Together with the quasi-static compressive strength,the strain rate effect of compressive strength was analyzed and characterized.Secondly,this paper investigated the high velocity soft impact response of the twill weave laminate.Under different impact velocities,the deformation and failure process of the specimens was observed and analyzed.The deformation patterns of the specimens were obtained,and the failure mechanisms were analyzed.The post-impact residual flexural properties of the specimens were obtained by three-point flexure tests,and the influence of soft impact load on the residual flexural properties was analyzed.Then,this paper established the multi-scale damage model of the twill weave laminate.With the application of multiphase finite element method,the unit cell model of fiber tow was established on microscopic scale.Together with the progressive damage model and periodic boundary condition,the equivalent property parameters of the fiber tow were obtained.On this basis,the geometric model of the twill weave structure was established using multiphase finite element method and absorbed matrix model.The quasi-static compression of the laminate was simulated and analyzed on mesoscopic scale,and the macroscopic material parameters were predicted using the meso-scale model.Finally,an original method was proposed to quantitatively characterize the soft impact property of the twill weave laminate.According to the results of the previous sections,the soft impact finite element model of twill weave laminate was established on macroscopic scale.The strain rate effect of the material properties was take into consideration within the finite element model.The damage,deformation and failure behavior of the material under soft impact was analyzed based on the macro-scale model.The variation of maximum deflection with respect to impact velocity was determined,and the soft impact property was characterized by the impact velocity and failure morphology.Moreover,the impact momentum flexibility(IMF)was proposed according to the relationship between maximum deflection and impact momentum,to quantitatively characterize the soft impact property of the material.The influence of specimen dimensions on the IMF was explored.