Fracture Prediction for an Advanced High-Strength Steel Sheet Using the Fully Coupled Elastoplastic Damage Model with Stress-State Dependence

In this study,the numerical simulations of sheet metal forming processes are performed based on a fully coupled elastoplastic damage model.The effects of stress triaxiality and Lode angle are introduced into the damage evolution law to capture the loading-path-dependent failure.The proposed constitutive model is implemented into the finite element(FE)code ABAQUS/Explicit via the user-defined subroutine(VUMAT).Next,the identification procedure for DP780 based on the hybrid experimental-numerical method is presented in detail.The numerical results of simple tests are compared with the experiments,and obvious improvement is observed for the proposed model under various loading paths.Finally,the model is applied to predict the edge fracture during sheet blanking process.The predicted global load–displacement responses and crack paths have a good agreement with the experimental results,indicating that the model holds great potentials in simulation of metal forming processes.

Edge chipping resistance of ceramics:Problems of test method

An unconventional method for determining the fracture resistance of brittle materials is discussed.This method employs a conical indenter to chip the rectangular edge of the specimen.Particular features of the method are the use of small specimens and the evaluation of the resistance of materials to the nucleation,initiation and propagation of a crack.It is shown that this method is somewhat similar to the Hertzian fracture method and to the way that early man selected stones to make tools and weapons.Measured data of the fracture resistance of ceramics is presented.It is confirmed that if a ceramic material is similar to the model material of linear elastic fracture mechanics(LEFM),then those fracture resistance values are directly proportional to the critical stress intensity factors(baseline).For elastic and inelastic ceramics,R-lines characterizing the fracture resistance to crack growth are plotted.It is shown that proportionality lines(edge chipping resistance versus critical stress intensity factor)may be straight lines for ceramics with similar structure(such as Y-TZP and Mg-PSZ).The effect of rounding of the conical indenter tip(10-800μm)on chip scar shape is indicated.Other aspects in the fracture behavior of ceramics during edge chipping are also analyzed.The advantages and disadvantages of the method are discussed.Further studies in this mechanico-physical research area are suggested.