Effect of Microstructure Evolution on the Overall Response of Porous-Plastic Solids

Stefano Mariani

doi:10.3390/ma3021031

Abstract

Ductile fracture is the macroscopic result of a micromechanical process consisting in void nucleation and growth to coalescence. While growing in size, voids also evolve in shape because of the non-uniform deformation field in the surrounding material; this shape evolution is either disregarded or approximately accounted for by constitutive laws for porous-plastic solids. To assess the effect of void distortion on the overall properties of a porous-plastic material prior to any coalescence-dominated event, we here present a micromechanical study in which the void-containing material is treated as a two-phase (matrix and inclusion) composite. A cylindrical representative volume element (RVE), featuring elliptic cross-section and containing a coaxial and confocal elliptic cylindrical cavity, is considered. In case of a matrix obeying flow theory of plasticity, the overall yield domain and the evolution laws for the volume fraction and aspect ratio of the void are obtained. Under assigned strain histories, these theoretical findings are then compared to finite element unit-cell simulations, in order to assess the capability of the proposed results to track microstructure evolution. The improvements with respect to the customarily adopted Gurson’s model are also discussed.

Highlights

Ductile tearing in metals is the macroscopic result of a micromechanical process consisting of void nucleation, and growth to coalescence [1,2]
This latter stage becomes dominant at values of the void volume fraction f, which is defined as the ratio between the volume of nucleated voids within a representative volume element (RVE) of the material and the volume of the RVE
In this paper we have proposed a micromechanical analysis of a two-phase composite, constituted by a ductile matrix surrounding a void

Summary

Introduction

Ductile tearing in metals is the macroscopic result of a micromechanical process consisting of void nucleation, and growth to coalescence [1,2]. Void nucleation may be caused either by inclusion cracking or debonding of the inclusion from the surrounding metal, and is strongly sensitive to micro-defects; void coalescence instead represents the final stage of the growth process, and consists in the break-down of microligaments between neighboring voids. This latter stage becomes dominant at values of the void volume fraction f , which is defined as the ratio between the volume of nucleated voids within a RVE of the material and the volume of the RVE itself [2,6], exceeding a critical threshold usually recognized to amount to f ≈ 0.2. The void-containing solid is (virtually) treated as a two-phase composite medium: the matrix material is represented by the fully-dense metal, whereas the inclusions are the voids featuring null elastic and strength properties

Objectives

Findings

Conclusion