| Popis: |
Upper-bound methods are used to obtain close approximations to the constraint factor in a three-dimensional model of the intervoid matrix at incipient plastic limit-load failure. This is the condition where homogeneous deformation can no longer continue throughout a ductile porous solid and all subsequent plastic deformation becomes concentrated in the intervoid matrix over a single sheet of microvoids; thus producing a ductile-fracture surface. The results are obtained for square-prismatic unit cells, which can be assembled to give a continuous intervoid matrix and a simple empirical expression is fitted to the results to give a closed-form expression for the constraint factor, for use in subsequent work on the mechanics of ductile fracture. The upper-bound results for the plastic limit-loads are used to illustrate, on a quantitative basis, the truncation of the Berg-Gurson dilational-plastic yield locus, which was illustrated in previous work only on a qualitative basis. |
