Implicit integration procedure for viscoplastic Gurson materials

Constitutive relations and numerical integration algorithms for elastic–viscoplastic ductile materials are investigated. The Gurson yield function is considered, together with a coalescence criterion from Thomason. The constitutive equations are reformulated using the assumption of constant strain rate within an increment. A consistency condition is incorporated into the traditional viscoplastic rate format, and the tangential material operator expression is derived. The algorithm is used to investigate the influence of triaxiality in the critical coalescence values of porosity.