Incremental closure method to estimate changes in contact stress distributions for partially closed fatigue cracks in mode I loading

Abstract

Crack closure is the phenomenon of fatigue cracks experiencing compressive contact stresses between crack faces, even under no remote load. Applied remote loads alter the distribution of contact stresses and opening displacements along the crack plane. A nondestructive evaluation technique, vibrothermography, motivated calculating these distributions as a function of remote load, to model crack motion during the vibrothermographic process. The proposed incremental closure method estimates such distributions using a two-stage superposition of crack tip solutions. The first, superimposes a continuum of crack tip solutions over a short, explicit peeling increment at the effective crack tip. The second, superimposes these increments over a range of effective crack tip positions. This approach provides a fast, straightforward way to characterize the peeling open of partially closed cracks. This method can be applied inversely to determine the preexisting closure state. Predictions from this method compare well with finite element simulations of the crack peeling process.