Stress intensity factor determination error by the method of caustics

Abstract

The caustics created at a crack tip under biaxial loading are examined using both the closed form and the approximate solution. Particular attention is given to the caustics and their initial curves created by rays reflected from the rear and front surfaces of the specimen in addition to those in the transverse direction of the cracked specimen. These quantities can differ by more than 30% depending on whether the exact or the approximate solution is used for determining the stress intensity factors which can deviate as much as 80%. The crack length also affects the outcome. Larger errors are committed by the approximate solution for caustics that are closer to the crack tip. The advantage of using the normalized distance from the crack tip is discussed in contrast to using the absolute distance. Incorrect experimental measurements are also discussed in relation to the resulting error for evaluating the crack tip stress intensity factor.