Load biaxiality and fracture: A two-sided history of complementing errors

Abstract It is the view of many engineers associated with fracture mechanics, materials science and mechanical design that for bodies containing plane cracks, loads that are applied in a direction that is parallel to the plane of the crack, in addition to the tensile load acting in the direction perpendicular to it, can have no influence upon the fracture behavior of the body. This point of view has persisted for the past sixty years or so, and still continues to persist, despite the paucity of experimental evidence in support of it. This paper traces the two-sided historical genesis of this notion. It shows how a series of oversights or errors, both in the calculation of the elastic strain energy appearing in Griffith's global crack instability hypothesis and in the evolution of Irwin's local theory of the crack-tip elastic stress intensity, have, by coincidence, had the particular effect of nullifying the presence of the loads that are applied parallel to the crack. The mishaps associated with one theory are, in a sense, complimentary to the entirely different set of errors that cause this same null effect to appear in the other theory, in that they give the appearance of consistency between the two theories in this regard. In a subsequent paper, which will serve to synthesize the results of our research work in this area, considerable experimental data will be included that lends support to our contention that loads that are applied parallel to the plane of the crack have a decided influence upon the fracture behavior of the body.

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