Investigations concerning quantitative determination of local damage in ductile materials

Abstract

Ductile fracture of metallic materials can be described by void nucleation, growth and coalescence. The first coalescence of voids defines crack initiation. A quantitative description of material damage by the means of continuum‐mechanics is a very current theme. Using Gurson's model and the yield equation modified by Needleman and Tvergaard a quantitative description of damage condition is possible by connecting stress triaxiality and void volume fraction. In this paper failure curves, in which the effective plastic strain is plotted as a function of stress triaxiality, will be generated by a new yield equation, which is a further development of the Gurson model. The failure curves will be shown for crack initiation and other damage situations. An advantage of the further developed yield equation, compared with the conventional one, can be seen in the fact that not one constant, which is independent of the material, but several material specific values are used. These values can be determined by density measurements at different void volume fractions. The procedure for determination of failure curves will be shown and subsequently test results will be discussed.