Cylindrical void growth vs. grain fragmentation in FCC single crystals: CPFEM study for two types of loading conditions

TL;DR

This study uses CPFEM to analyze how cylindrical void growth and grain fragmentation in FCC single crystals depend on loading conditions, initial orientation, and stress or strain biaxiality, revealing scenarios that promote grain refinement.

Contribution

It provides a detailed CPFEM analysis of void evolution and grain fragmentation under different loading conditions and orientations in FCC crystals, highlighting factors influencing grain refinement.

Findings

Void evolution depends on initial lattice orientation and loading mode.

Stress and strain biaxiality significantly affect void size and shape.

Certain conditions lead to enhanced grain fragmentation.

Abstract

The crystal plasticity finite element method (CPFEM) is used to investigate the coupling between the cylindrical void growth or collapse and grain refinement in face-centered cubic (FCC) single crystals. A 2D plane strain model with one void is used. The effect of the initial lattice orientation, similarities, and differences between stress- and strain-driven loading scenarios are explored. To this end, boundary conditions are enforced in two different ways. The first one is based on maintaining constant in-plane stress biaxiality via a dedicated truss element, while the second one is imposing a constant displacement biaxiality factor. Uniaxial and biaxial loading cases are studied. For the uniaxial loading case a special configuration, which enforces an equivalent pattern of plastic deformation in the pristine crystal, is selected in order to investigate the mutual interactions between the evolving void and the developed lattice rotation heterogeneity. Next, biaxial loading cases are considered for three crystal orientations, one of which is not symmetric with respect to loading directions. It is analysed how stress or strain biaxility factors and initial lattice orientation influence the void evolution in terms of its size and shape. Moreover, the consequences of variations in the resulting heterogeneity of lattice rotation are studied in the context of the grain refinement phenomenon accompanying the void evolution. Scenarios that may lead to more advanced grain fragmentation are identified.