New Concepts on Caustics and Applications

A new formula of experimental evaluation of the stress intensity factor was proposed depending on the area of the caustic. From series of experiments, which were performed in single edge-cracked specimens made of Lexan (PCBA), it was found that the values of the stress intensity factor KI,, which were based on the diameters of the caustics, were varied with the load, the crack length and the caustic shape because the caustic become oval in higher loads or higher crack lengths. This means that the stress intensity values which are evaluated by the two diameters of the caustics (Dt , Dl), are significantly differed. The accurate stress intensity factor KI can be experimentally evaluated by the area of the formed caustic. According to the new formula of the stress intensity factor of the stress optical constants were evaluated. The present work illuminates the complicated problem of the stress intensity factors evaluation by the caustic diameters and establishes the new accurate of the caustic area approach for the evaluation of the stress intensity factors at crack tip and the stress optical constants of the transparent materials.