Photoelastic determination of mixed mode stress intensity factors

Abstract

Using an idea proposed by G. R. Irwin, equations were developed for the maximum in-plane local shearing stress τ m and average fringe loop inclination θ m near the crack tip in terms of the Mode 1 and Mode 2 stress intensity factors K 1 and K 2 and polar coordinates r and θ measured from the crack tip. A series of photoelastic experiments was performed on specimens exhibiting various edge crack configurations in finite strips under remote tensile loading. Measurements of τ m and θ m were made for progressively smaller fringes and used in the above mentioned equations to solve for K 1 and K 2 on a digital computer. Plots of apparent K vs. r a were made and extrapolated to the crack tip to yield the true values of K 1 and K 2. Results compared favorably with numerical results of Wilson. New results for ‘angle’ cracks were also obtained.