The influence of porosity on the deformation and fracture of alloys

Abstract The influence of porosity on the deformation and fracture behavior of two alloys, powder-fabricated Ti and Ti-6Al-4V, with differing levels of matrix strain hardening has been examined both experimentally and analytically. A large strain elastoplastic finite element model based on a regular array of equal-sized spherical voids is used to predict bulk porosity effects; the analysis is in good agreement with the experimentally observed rates of void growth but underestimates the degradation of strength with increasing porosity. The effects of porosity on a local scale, especially as regards fracture, are examined by a model of a porous continuum which contains imperfections whose magnitude depends upon the maximum porosity path within the continuum. At critical values of strain these imperfections cause localization of plastic flow. The predicted values for the strains at localization are in good agreement with measured fracture strains. The analysis thus explicitly recognizes that a primary effect of pores on fracture is to localize deformation into narrow regions of high porosity (“imperfections”) which are present even in random distributions of pre-existing pores and which are the sites of macrofracture initiation.

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