Role of plasticity-induced crack closure in fatigue crack growth

Jesús Toribio, Viktor Kharin


The premature contact of crack surfaces attributable to the near-tip plastic deformations under
cyclic loading, which is commonly referred to as plasticity induced crack closure (PICC), has long been focused
as supposedly controlling factor of fatigue crack growth (FCG). Nevertheless, when the plane-strain near-tip
constraint is approached, PICC lacks of straightforward evidence, so that its significance in FCG, and even the
very existence, remain debatable. To add insights into this matter, large-deformation elastoplastic simulations of
plane-strain crack under constant amplitude load cycling at different load ranges and ratios, as well as with an
overload, have been performed. Modeling visualizes the Laird-Smith conceptual mechanism of FCG by plastic
blunting and re-sharpening. Simulation reproduces the experimental trends of FCG concerning the roles of
stress intensity factor range and overload, but PICC has never been detected. Near-tip deformation patterns
discard the filling-in a crack with material stretched out of the crack plane in the wake behind the tip as
supposed PICC origin. Despite the absence of closure, load-deformation curves appear bent, which raises
doubts about the trustworthiness of closure assessment from the compliance variation. This demonstrates
ambiguities of PICC as a supposedly intrinsic factor of FCG and, by implication, favors the stresses and strains
in front of the crack tip as genuine fatigue drivers.

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