The development of continuum damage mechanics-based theories for predicting forming limit diagrams for hot stamping applications

Abstract

This paper presents a novel plane-stress continuum damage mechanics (CDM) model for the prediction of the different shapes of forming limit diagrams (FLCs) for aluminium alloys under hot stamping conditions. Firstly, a set of uniaxial viscoplastic damage constitutive equations is determined from tensile experimental data of AA5754 at a temperature range of 350-550 C and strain rates of 0.1, 1.0 and 10 s À1 . The tests were carried out on Gleeble materials simulator (3800). Based on the analysis of features of FLCs for different materials forming at different temperatures, a plane-stress damage equation is proposed to take account the failure of materials at different stress-state sheet metal forming conditions. In this way, a set of multiaxial viscoplastic damage constitutive equations is formulated. The model is calibrated from the FLC data at temperature of 350 C and strain rate of 1.0 s À1 for AA5754. A good agreement has been achieved between the experimental and numerical data. The effect of the maximum principal stress, effective stress and hydrostatic stress on the materials failure features and on the shape of FLCs is studied individually and in combination. Using the newly developed plane-stress unified viscoplastic damage constitutive equations, the FLC of materials can be predicted at different temperatures and strain rate forming conditions.

An investigation of a new 2D CDM model in predicting failure in HFQing of an automotive panel

“…The model was calibrated from tensile experimental data of AA6082 at a temperature range of 450 • C-525 • C and strain rates of 0.1 s −1 , 1.0 s −1 and 10 s −1 (Lin et al 2014). A set of multi-axial viscoplastic constitutive equations, incorporating multiaxial damage evolution, is formulated as: …”

An analytical investigation on the wrinkling of aluminium alloys during stamping using macro-scale structural tooling surfaces

“…In this paper, a physical-based, dislocation-driven material model is applied [21]. The list of equations is given below from Eqs.…”

Application of a continuum damage mechanics (CDM)-based model for predicting formability of warm formed aluminium alloy

“…It is well known that the formability of a metal sheet is a function of strain rate and temperature, thus current FLCs, which are based on fixed values of strain rate cannot be used directly to predict the forming limit of sheet metal in warm forming [17,19]. …”

“…The symbol  represents a parameter, which controls the effect of multi-axial stress values and their combination on damage evolution, thus determining formability. Symbol  is for a correction factor to unify for the different strain values measured by uniaxial tensile tests and formability tests [17,19].…”

“…Therefore, the conventional FLD is not an accurate method to predict the formability of the sheet metal forming at elevated temperature. Lin et al [16,17] developed s set of plane-stress continuum damage mechanics (CDM)-based viscoplastic constitutive equations to predict the shapes of FLCs for AA5754 at a temperature range of 350-550 ˚C; however, the determination of the parameters and application in that model were not presented. In this paper the CDM-based constitutive model is introduced, based on fixed forming temperatures and forming rates.…”