Mechanical Response of Materials with Physical Defects. Part 3. A Material Testing Program for Size and Rate Effects.

Abstract : A fundamental problem of structural analysis is the prediction of the final failure made. Traditional approaches to the extreme forms of failure, i.e. plastic collapse and fracture instability, invoke a particular failure criterion to address one assumed failure mode. The appearance of the other mode is precluded by such an approach. A criterion is presented which addresses both macrocrack propagation and local changes in material properties using strain energy density. The damage state of the material at a particular instant of its load history is assumed to be governed by loading versus unloading behavior of the material's constitutive law. Macrocrack instability is assumed to occur when the size of the core region around the crack tip exceeds the predicted growth increment. This core region is defined by the closed contour of constant strain energy density equal to the maximum value addressed by the constitutive law. Crack growth increments occur in the direction of minimum strain energy density. The length of the crack growth increment is governed by the relative toughness of the material in the direction of propagation.