Determining Crack Tip Shielding by Means of Acoustic Transmission and Diffraction Measurements

Asperity contact along the fracture surface of a crack is one of the mechanisms of crack closure. This contact shields the crack tip, in part, from the externally applied driving force on the crack. We have now succeeded in using experimental information, obtained under plane strain conditions from acoustic transmission and diffraction experiments in the closure region [1,2] to determine a stress intensity factor, KI(local), which shields the crack tip below a stress intensity factor KIclosure a t first contact during unloading occurs