A complete Gurson model approach for ductile fracture

Recently, a complete Gurson model has been introduced by the authors. The complete Gurson model is a combination of the modified Gurson model which deals with microvoid nucleation and growth, and a physical microvoid coalescence criterion based on the plastic limit load model by Thomason. By comparing finite element cell modeling analyses, the complete Gurson model is accurate for both non-hardening and hardening materials. One attractive feature of the complete Gurson model is that material ductile failure is exclusively linked to the microvoid nucleation parameter, and the nucleation parameter in many cases can be determined without metallurgical examinations. Furthermore, the so-called critical void volume fraction f(c), has been eliminated from material constants. In this paper, two simple microvoid nucleation models for modeling ductile fracture are discussed, and a method which applies multi-tension specimens including both smooth and notched cylindrical specimens for determining the microvoid nucleation parameter is introduced. Once the microvoid nucleation parameter has been determined from the tension specimens, the characteristic length parameter which describes the stress/strain gradient effect can be fitted from fracture mechanics tests. Material ductile crack resistance behavior is then a function of the microvoid nucleation parameter, the length parameter and the specimen geometry. For modified boundary layer models, it has been found that the crack resistance curves can be normalized by the T stress, and the T stress can be possibly taken as the geometry controlling parameter for ductile crack growth. (C) 2000 Elsevier Science Ltd. All rights reserved.