Ductile Damage Analysis Under Cyclic Loading Based On GTN Model

Gurson took the initial void into constitutive relations of material, that made a great progress in Microscopic Damage Mechanics. This model now is used widely and it has been modified by many scholars, one of the most important contributions is GTN model.Furthermore, the GTN model is improved by introducing the back-stress into it, then we also call it modified GTN model. The modified GTN model can be used to describe mechanical response of materials under cyclic loads instead of unidirectional loading. It is found that the stress state has great effect on the evolution of void. In the present thesis, the stress triaxiality can be controlled by imposing different loads on a cell model that contains a void. The higher the stress triaxiality, the faster the voids will grow. According to the calculation of cell model, the parameters of the modified GTN model are fitted. The results demonstrated that the parameter q2has great effect on voids evolution, and the parameter q, has a linear correlation with the growth rate of initial void. Furthermore, the ratcheting behavior under tension-tension cyclic loading can be successfully simulated by the modified GTN model.When applying a tension-compression cyclic loading on the cell model, different results will be obtained. Under this condition the void fraction will increase under tension and decrease under compression. Comparing the result of cell model with modified GTN model by applying different loading, we can get a series of parameters with different values from the ones obtained under tension-tension loading. The applicability discussion for these parameters of modified GTN model implies that the modified GTN model has limitations for multiaxial cyclic loading. There are obvious difference between the results of modified GTN model and that of the cell model under different loading situations with the parameters determined by given stationary loading situation.