Modified GTN Model And Application Of Metal Materials Under Complex Loads

The material constitutive model is very important for the analysis of structural fracture and fatigue in the field of Aeronautics,Astronautics and civil engineering.Some researchers have found that ductile fracture is caused by the initiation,growth and coalescence of micro-voids induced by internal inclusions,inextricably.Based on continuum damage mechanics and meso-damage mechanics,the microdefects are equivalent to spherical voids,and the damage state was represented by the evolution of spherical voids in different stress state.In this paper,the GTN(Gurson-Tvergaard-Needleman Model,GTN)model is modified in three aspects of the tensile state,the shear state and the creep of the material,as followed1.The evolution equation of voids combined with equivalent plastic strain was established by considering the uneven growth equivalent growth process for uniaxial tension,and introduced into the continuum damage model by transforming variable.Thus,the damage model was proposed to analysis the fracture ductility of steel and other metals.2.The growth of void volume fraction is controlled by hydrostatic pressure in the GTN model,but the hydrostatic pressure is zero in the pure shear state.Therefore the simulated results are not enough accurate by GTN model in shear state.In this paper,the shear damage state variable was revealed by the ratio of span and ligament.The modified GTN model was proposed to analyze of shear failure of material.Moreover,a simple finite element model was carried out to verify the feasibility of proposed model.3.To describe the creep deformation of porous materials,the overstress of modified UCP(Unified Creep and Plasticity Model,UCP)was calculated by the plastic potential function of GTN model in this paper.The modified model,contained the shear damage variable,combined GTN model and UCP model was proposed to analyze the creep of porous materials.Finally,through the commercial finite element analysis software ABAQUS,the proposed constitutive models are programmed,and the numerical results are coMPared with the experimental results,which verify the practicability and accuracy of the modified constitutive model proposed in this paper.