J-R Curve Prediction Using Cohesive Model and Its Sensitivity to a Material Curve
V. A. Kozak, I. Dlouhý · NCSU Libraries Repository (North Carolina State University Libraries) · 2007
Cohesive crack models are nowadays widely used to analyze cracking processes in the materials.The importance of the cohesive zone approach is emphasized to analyze the localization and failure in engineering materials.The micromechanical modeling encounters a new problem that is different from assumption of continuum mechanics.The material is not uniform on the microscale but a material element has its own complex microstructure.The concept of a representative volume element (RVE) has been introduced a few years ago.The material separation and damage of the structure is described by the interface element.Using this technique the behavior of the material is split into two parts: the damage of the free continuum with arbitrary material law and the cohesive interface between the continuum elements.The general advantage, compared to classical fracture mechanics, is that, in principle, the parameters of the respective models depend only on the material and not on the geometry.These concepts guarantee transferability from specimen to components over a wide range of sizes and geometries.The paper is focused on prediction of J-R curve by 3D FEM cohesive elements.The corresponding true stress -true strain curve (material curve) appear to be a key problem of this approach application.For forged 42CrMo4 steel the ductile fracture was predicted.J-R curve is calculated by cohesive elements using Warp3D and Abaqus codes.Crack propagation is based on the cohesive element extinction algorithm.The ductile tearing process consisting of initiation, growth and coalescence of voids has been represented by a traction separation law.Interface elements (cohesive elements) representing the damage are implemented between the classical continuum elements representing elastic-plastic properties of the material.