Stress Intensity Factors for the Mixed Mode in a Three-Dimensional Crack (Determination by the Caustics and Photoelastic Methods)

In fracture problems, stress intensity factors obtained theoretically or by experimental analyses have been effectively applied as a quantity of the magnitude of the stress field occurring in the highly stressed region at the vicinity of the crack tip. In actual construction materials, the combined action of stress intensity factors under complex stress conditions often exists in most cases. In this paper, an experimental technique is presented for determining the mixed-mode stress intensity factors K₁₁ and K₁₁₁ separately for a three-dimensional cracked-body problem. The stress intensity factor K₁₁ is determined by the photoelastic method with an isochromatic fringe loop, and the stress intensity factor K₁₁₁, which is often not easy to evaluate with experimental and calculation method, is determined by using the method of reflected caustics in combination with the stress-freezing method. It was found that by using the present experimental technique, the mixed-mode stress intensity factors K₁₁ and K₁₁₁ and for a three-dimensional crack can be easily separated.