Microstructural topology effects on the onset of ductile failure in multi-phase materials – A systematic computational approach

Abstract

Multi-phase materials are key for modern engineering applications. They are generally characterized by a high strength and ductility. Many of these materials fail by ductile fracture of the, generally softer, matrix phase. In this work we systematically study the influence of the arrangement of the phases by correlating the microstructure of a two-phase material to the onset of ductile failure. A single topological feature is identified in which critical levels of damage are consistently indicated. It consists of a small region of the matrix phase with particles of the hard phase on both sides in a direction that depends on the applied deformation. Due to this configuration, a large tensile hydrostatic stress and plastic strain is observed inside the matrix, indicating high damage. This topological feature has, to some extent, been recognized before for certain multi-phase materials. This study however provides insight in the mechanics involved, including the influence of the loading conditions and the arrangement of the phases in the material surrounding the feature. Furthermore, a parameter study is performed to explore the influence of volume fraction and hardness of the inclusion phase. For the same macroscopic hardening response, the ductility is predicted to increase if the volume fraction of the hard phase increases while at the same time its hardness decreases.

Topology and Morphology Influences on the Onset of Ductile Failure in a Two-phase Microstructure

“…Farther away, we observe some scatter around Ī D = ϕ hard = 0.25, the ensemble averaged hard phase volume fraction. The observed probability distribution is consistent with that found in [4] using square elements.…”

“…In the numerical results presented here -as well as in [4] -we observe close to the corners of the cell a slightly elevated probability of soft phase (i.e. a lower than average probability of hard phase).…”

“…The purpose of this contribution is to verify some of the assumptions we have made in [4]. In that work, use was made of idealized geometries whereby individual particles were modeled as square elements.…”

How collective asperity detachments nucleate slip at frictional interfaces

“…We currently do not have a theory for the value of exponent θ, but preliminary observations indicate that θ is non-universal. Building a theory to understand θ should explain the following observations (presented in detail in Appendix D): (a) The blocks for which x σ is very small following a macroscopic slip event typically lie in a shallow well followed by another shallow well in the block [56]. (b) As a consequence, when triggered they tend to lead to small slips, and are less likely to trigger slip in other sites.…”

“…We also compute the average yield strains bounding the next and previous local minima in the same block, as well as its left and right neighbours. Following [56], we can compute:…”