Abstract
Relations between fracture toughness and microstructural details have been calculated for ductile materials based on a dilatational plasticity constitutive model that has recently been proposed. The model generalizes the Gurson model to account for both void growth and coalescence with explicit dependence on void shape and distribution effects. Based on a small scale yielding formulation of crack growth, toughness trends are determined as a function of yield stress, strain-hardening, initial porosity, void shape and spacing as well as void spacing anisotropy. Distinctions are drawn between the engineering fracture toughness, which is typically associated with 0.2 mm of crack growth, and the theoretical toughness based on coalescence of the crack tip with the first void ahead of it. Comparison with one set of experimental data for a steel is made for which a fairly complete characterization of the microstructure is available.
Highlights
In the context of material science, the fracture toughness, at cracking initiation is usually taken as the relevant parameter for indexing the cracking resistance of materials
Ț Finite element calculations are performed with the voids explicitly modeled by a refined FE mesh [2,3,4,5,6,7,8,9]. These analyses accurately model the growth and coalescence process while properly accounting for the length scale introduced by the void spacing
The distinction between the two criteria highlights the arbitrariness of the concept of initiation toughness and importance of the R-curve, especially for very tough materials with high tearing resistance combined with small void spacings
Summary
In the context of material science, the fracture toughness, at cracking initiation is usually taken as the relevant parameter for indexing the cracking resistance of materials. These analyses accurately model the growth and coalescence process while properly accounting for the length scale introduced by the void spacing This approach still requires a criterion for the final failure of the intervoid ligament in order to simulate crack propagation (e.g. by modeling shear localization within the ligament due to a second population of smaller voids). Three dimensional (3D) aspects of crack initiation and growth have been simulated [18,21,25] The success of this approach is underpinned by the requirement that the microstructural parameters (the void volume fraction, void spacing, etc.) must be set such that the model reproduces experimental crack data for specific specimens.
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