Composite Material Damage Model Including Strain Rate-dependent Nonlinear Shear Stress Strain Relationship

Fiber reinforced composite materials have been extensively applied in civil engineering,mechanical engineering,aerospace and ocean industries due to their superior performance,such as high stiffness-to-weight ratio,high strength-to-weight ratio,good energy absorption capability and fatigue resistance.However,their mechanical behavior and failure modes are rather complex,for example,the pronounced nonlinearity,strain rate dependent-mechanical behavior and material properties degradation due to damage accumulation etc.In order to accurately predict the mechanical response of fiber reinforced composite materials,it is of significance to establish a material constitutive model that considers these factors.In this dissertation,a damage constitutive model of composite materials is established considering their shear nonlinearity,strain rate dependent-behavior and material properties degradation due to damage accumulation.Many fiber reinforced composite materials demonstrate pronounced strain rate-dependent mechanical behavior in shear direction.First,a strain ratedependent nonlinear shear stress strain relationship is developed based on analyzing and curve fitting of reported experimental data of off-axis unidirectional fiber reinforced composite laminates subjected to compressive loadings at various strain rates.Within the framework of continuum damage mechanics,a damage model is developed to simulate damage initiation and evolution.Then,a progressive damage model which takes into account strain rate-dependent nonlinear shear behavior is developed by combining both the strain rate-dependent nonlinear shear stress strain relationship and the damage model.Explicit integration algorithm is derived for the proposed progressive damage model and implemented in finite element procedure Abaqus v6.14 through user-defined material subroutine VUMAT.The development of explicit integration algorithm solves the problems of premature abortions of numerical analyses due to numerical difficulties when strain softening material models are adopted.The proposed progressive damage model is validated by progressive failure analysis of off-axis AS4/3501-6 carbon fiber/epoxy composite laminates under various strain rate loadings.The predicted results demonstrate that strain ratedependent mechanical behavior of composite materials can be well captured by the proposed model.