OS1804 Effect of Three-dimensional Stress Field on Measurement of Mixed-mode Stress Intensity Factor by Caustic method

Three-dimensional (3-d) stress field exists in the very vicinity of a crack tip within the singular stress field of plane stress. The paper examines the effect of the 3-d field to the measurement of stress intensity factors by the caustic method where the crack is under the mixed mode loading of mode I and II. The experimental studies show that the 3-d field extends as far as half the thickness of plate specimens under the mixed mode loading condition. This result is the same as that of mode I loading. The values of KI in the 3-d field are smaller than the true K_I value, and those of K_ in the 3-d field are larger than the true value of K_.