A numerical study on the correlation between the work of separation and the dissipation rate in ductile fracture

The present study reports on calculations of ductile tearing and failure. C rack growth is simulated by a cohesive zone model which, by adapting it to the mechanical behavior of voided cells, is a phenomenological representati on of the micromechanical process of void growth and coalescence. Crack gro wth resistance is given in the form of the dissipation rate versus crack ex tension. The present simulation shows that by a combination of these two concepts a step further in the understanding of the fundamentals of ductile fracture c an be obtained. The application of the cohesive zone model allows for a spl it of the dissipation rate into its two contributions, plastic dissipation rate and separation energy. It is demonstrated that neither the dissipation rate nor one of its components is a material constant. Instead all two qua ntities are found to depend on specimen geometry and size as well as on the amount of crack extension. Thus, while the use of the dissipation rate avo ids some of the basic problems that arise in the use of the J-integral for the characterization of crack growth resistance, it is confirmed that this quantity does not provide a general and simple solution for the transferabi lity problem of fracture toughness data. Due to the micromechanisms of void growth and coalescence, the cohesive zone parameters for ductile tearing, cohesive strength and energy, are predicted to be generally dependent on th e amount of crack growth, specimen geometry and size. It is shown that in the present case of tearing under fully plastic conditi ons, the separation energy is only between 0.5% and 12% of the total dissip ation rate depending on specimen geometry, size and crack extension. Assumi ng the material parameters of a cohesive zone law as a material constant ma y, from an engineering point of view, provide an admissible approximation, especially in situations of high constraint. (C) 2000 Elsevier Science Ltd. All rights reserved.