Digital Repository, Giornata IGF Forni di Sopra (UD) 2011

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The plastic ‘inclusion’ as a bridge between local crack plasticity and the global elastic field
M. N. James, C. J. Christopher, Yanwei Lu, E. A. Patterson

Last modified: 2011-02-25


This paper presents a novel ‘plastic inclusion’ concept for dealing with the local plasticity which
occurs at the tip of a growing fatigue crack. Such localised plasticity essentially blunts the crack and induces
stresses which act on the applied elastic stress field at the boundary of the elastic-plastic enclave surrounding the
crack. The paper outlines a model of crack tip stresses that explicitly incorporates these stresses and also those
that might arise from crack wake contact. This offers a way of reconciling local crack tip plasticity-induced
stress field perturbations with the driving force of the overall elastic stress field. The outcome is the
identification of a modified crack tip stress intensity factor which should be able to explicitly predict the
magnitude of plasticity-induced crack tip shielding and resolve the many controversies associated with plasticityinduced
shielding. A full-field approach is developed for stress using photoelasticity and also for displacement
using digital image correlation.

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