Stress-intensity factors in plates with a partially patched central crack

The fatigue and fracture performance of a cracked plate can be substantially improved by providing patches as reinforcements. The effectiveness of patches is related to the reduction they cause in the stress-intensity factor of the crack. Hence, an accurate evaluation of SIF in terms of various parameters is required for reliable patch design.In this paper, the influence of patch parameters on the opening-mode stress-intensity factor for a plate with a central crack is studied by employing transmission photoelasticity. Cracked plates made of photoelastic material are patched on one side as well as both sides by epoxy, phenolic and E glass-epoxy composite materials. The patch is located on the crack in such a way that the crack tip is not covered. Magnified isochromatic fringes are obtained by using a projection microscope of 50 magnification, converted into a polariscope. Irwin's method with extrapolation is employed to compute the stress-intensity factor from photoelastic data. The reduction in the stress-intensity factor is presented in graphic form as a function of pathch parameters, namely stiffness, width and length.