Analysis Of Microvoid Growth And Cavitation In Visco-elastic-plastic Solids Under Thermal Shock

The study of microvoid growth and cavitation in visco-elastic-plastic materials can provide a basic theoretical analysis for the damage evolution and life assessment of metal materials and structures under high temperature thermal shock,and the nucleation and evolution of microvoid in materials can be analyzed by use of solid mechanics.Therefore,it has important academic research value.The viscous effect of metal materials is more significant under high temperature and thermal shock,and the growth of microvoid needs to consider the time evolution process.In this paper,based on the engineering background of high temperature nickel based alloy and aluminum alloy,the problem of microvoid growth and cavitation in metal materials under thermal shock are systematically studied on the basis of the theory of thermal visco-elastic-plasticity.The main research work is as follows:1.Through the laser thermal shock test of a series of high temperature nickel base alloy targets,and the possibility of microvoid nucleation in high temperature nickel based alloy materials under strong thermal shock was confirmed.It is observed that under the effect of the strong laser thermal shock,the original intact superalloy materials will produce isolated microvoid and dense voids groups in the heat affected zone.It provides an important experimental basis for the following theoretical study of microvoid growth and cavitation.2.By using the Laplace integral transformation and the numerical inversion method,the semi analytical and semi numerical solution of the dynamic growth of micropores in viscoplastic materials is obtained.The effect of the inertia effect and the thermal viscosity effect on the micropore growth is analyzed.3.The initial unyielding deformation stage and the effect of moving interface after yielding are considered.According to the problem of void growth in two kinds of solid materials with elastic-viscoplasticity and visco-elastic plastic,based on the Perzyna visco-elastic-plastic constitutive,the mathematical model is established to solve by dividing time and space,and the direct integral method is adopted to simplify the problem in mathematics as a first order nonlinear ordinary differential equation that is satisfied with the position function of the moving interface.Finally,the semi-analytical and semi-numerical solution of the quasi-static void growth is given,and the effect of the nonlinear effect of the moving interface on the microvoid evolution is revealed.4.The parameters of high temperature nickel based alloy materials are selected in numerical examples.The effects of temperature,heating rate,elastic viscosity,plastic viscosity and yield stress related temperature on the time and spatial distribution of stresses and displacement,the evolution of moving interface and the dynamic growth of the microvoid with time are discussed.The results show that the viscosity will intensify the stress concentration during the initial stage near the hole wall.Under the high temperature and the greater heating rate,the viscous effect on the micrvoid growth will be more obvious,while the hysteresis and damping effect will be played.At the same time,the size of micropore growth is nonlinear dependent on the thermal shock load.5.The problem of thermal cavitation in viscoelastic perfectly plastic material under thermal shock is studied,and the critical temperature of microvoid nucleation is given.Considering the small viscoelastic deformation in the unyielding region of the material,and introducing the logarithmic strain to describe the ideal plastic large deformation in the yield region,the mathematical model with moving interface is established,and the corresponding semi analytic semi numerical solution is given.Last,letting the limit state of the original radius of the microviod to tend to zero,taking aluminum alloy as an example,the critical temperature of cavitation is 93%of the melting point temperature.