Hardening Behavior And Fracture Mechanism Of Al2024 Under Variable Path Loading

It's common to find parts be scraped due to ductile fracture in the process of industry production.So it's of great significance to forecast the position and time of crack and crack propagation by using numerical simulation.The accuracy of numerical simulation depends on the flow stress model and damage model selected.Summarizing the existing literature,The material hardening model mainly includes three categories of isotropic hardening,kinematic hardening and combined hardening;The ductile fracture criteria can be roughly divided into two major categories of the coupling and uncoupling fracture criteria.The fracture form and mechanism of the material are closely related to the stress state.In the process of industrial production and parts service,the material is often under complex path loading.However,most of the current studies on fracture models are focused on proportional loading with the simple isotropic constitutive model.Therefore,application of ductile fracture model and the hardening behavior of the material under variable path loading conditions need further study.The stress-strain hysteresis curve was acquired by implementing the test of uniaxial tension-compression cyclic with equal strain control.Combining the result of the standard uniaxial tension test with a smooth round bar,the values of Chaboche combined hardening parameters were obtained.Besides,Al2024 isotropic hardening model was established based on the finite element iteration method and the further extrapolation with Voce++.Based on the isotropic hardening and mixed hardening model,the simulation models of a set of variable path loading tests were established with ABAQUS/Explicit,and the L-H fracture criterion is coupled into the user subroutine VUSDFLD to complete the corresponding parallel simulation.By comparing the simulation and experimental load stroke path,the effect of hardening model on the applicability of L-H criterion under variable path loading was evaluated.The results show that the prediction accuracy of L-H criterion decreases with the pre-loading enhancement.L-H fracture criterion with constant parameters does not give a high accurate prediction of the material fracture under variable path loading.Compared with the isotropic hardening model,the combined hardening model can describe the hardening behavior of the material under complex path loading more accurately.Through the observation of the macro and micro morphologies of fracture surfaces,the corresponding ductile fracture mechanism was studied.The ductile fracture mechanism of tension-torsion tests is tensile-shear hybrid fracture.With the increasing of pre-torsion,the dominated fracture mechanism was converting from tension fracture to shear fracture.In the compression-torsion tests,the main fracture mechanism was shear fracture caused by cyclic shear stress.