Interaction of cavitating grain boundary facets in creeping polycrystals

Abstract

Interaction of cavitating grain boundary facets in creeping polycrystalsGiessen, E. van der; Tvergaard, V. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. A plane strain unit cell model containing a periodic array of hexagonal grains is used to analyse creep fracture in polycrystalline metals at elevated temperatures, taking into account the effect of sliding at all grain boundaries. The grains deform elastically and by power law creep, and the possibility of cavity nucleation and growth at the grain boundaries is incorporated. For a single cavitating grain boundary facet, or a single facet microcrack, the effect of microcrack density or spacings is studied by varying the number of grains in the unit cell or the aspect ratio of the unit cell. In cases where creep constrained cavitation develops, and for open microcracks, a significant effect of crack density and cell aspect ratio is found. The multi-grain unit cells are also used to study the influence of nonuniform distributions of cavitating facets such as facet clustering, where strong interaction between neighbouring cavitating facets tends to develop.

Delaunay-Network Modelling of Creep Failure in Regular Polycrystalline Aggregates by Grain Boundary Cavitation

“…Compared to the much more detailed analyses carried out very recently by Van der Giessen and Tvergaard (1994aTvergaard ( , 1994b Rice, 1981). Based on this observation, we take for the geometrical factor g* in (15) a value g* = 1/1.5, so that the macroscopic creep strain-rate is in accordance with Equation (3).…”

“…The distribution depends on the material, on the stress level and on temperature. Ductile creep fracture typically accompanies a nonuniform distribution of cavities, while a more homogeneous distribution tends to cause brittle fracture (see, e.g., Van der Giessen and Tvergaard, 1991Tvergaard, , 1994a. As mentioned before, we focus here on brittle fracture at elevated temperatures; accordingly, cavities are assumed to be distributed uniformly over grain boundaries.…”

“…The most recent advance in such a direction is work done by Van der Giessen and Tvergaard (1994aTvergaard ( , 1994b, employing a multi-grain cell model analysis of a planar polycrystal model. In particular, they investigated the influence of the interaction between cavitating grain boundaries and the final linking up of micro- Tvergaard (1994a, 1994b We consider a two-dimensional polycrystal model which is built up of regular hexagonal grains, similar to the model used by Tvergaard (1994a, 1994b).…”

“…However Figure 6) is uniaxial and immediately determined from the generalized stress in the element. So, with reference to Figure 7, the grain stress Q in the grain associated with element k is taken to be given by Tvergaard (1994aTvergaard ( , 1994b Tvergaard (1984) and to the grain boundary cavity growth relations by Van der Giessen and Tvergaard (1991 As mentioned before, grain boundary facets that are perpendicular to the macroscopic principal tensile stress are the most prone to cavitation. Therefore, microcracks will develop most rapidly on such transverse facets.…”

Micromechanical Studies of Cyclic Creep Fracture Under Stress-Controlled Loading

“…3). The results in this section are for (a/L)1 = 0.025, which corresponds to conditions were cavity growth under creep conditions tends to be creep constrained (see [3,7,41). Figure 4 shows the damage evolution, in terms of alb, along the central facet under the same balanced cyclic loading conditions as considered in Fig.…”