An Analysis on Multiaxial Loading Fatigue through Constitutive Equation Derived in Terms of Dislocation Dynamics

点击翻译按钮获取中文摘要

Multiaial stress is induced around stress-concentrated location such as notch root and crack tip. In the present study, the cyclic strain, crack opening displacement and cyclic stress-strain response were calculated in the vicinity of crack tip by means of elastic-plastic finite element method in annealed copper, where the constitutive equation derived from using the concept of dislocation dynamics was employed. Furthermore, strain was measured by the grid method : the displacement of the grid was measured through the laser microscope observation around the crack tip.Firstly, the analysis was made for the cyclic deformation around the crack tip in the through-thickness center-cracked specimen subjected to the model loading.Secondly, the similar calculation was achieved for the pre-cracked compact tension/shear specimen under the mode II loading.Main results obtained are summarized as follows.(1)Load-displacement response calculated for the through-thickness center-cracked specimen under the mode I loading expressed well the cyclic hardening behavior in the early cyclic deformation process, being in good agreement with the experimental data.(2)The measured crack opening displacement tends to reach the stabe state through it's early increasing stage under the load-controlled condition, which is well expressed by the calculation.(3)The variation range of the cyclic strain during one load cycle and the amount of strain concentration tend to decrease with increasing number of cyclic loading around the crack tip. The Calculation describes quite well such cyclic strain behaviors.(4)The strain calculated around the crack tip in the compact tension/shear specimen subjected to the mode II loading developes in the diredction of θ=0゜just ahead of the crack tip and in the direction of θ= -30゜ in the region distant from the crack tip.