PHOTOELASTIC DETERMINATION OF OPENING MODE STRESS INTENSITY FACTORS FROM ISOCHROMATIC FRINGE PATTERNS

Abstract

Methods for determining stress intensity factor, K from isochromatic fringe loops obtained from photoelastic models with sharp cracks were briefly reviewed. A new three parameters approach was introduced following introduction of third parameter in Westergaard's stress function by Etheridge. In this three-parameter method, three different terms in an analytical solution were adjusted to obtain a suitable match between the theoritical and experimental isochromatic loops. A relationship is derived for the maximum shear stress, rr,,, describing shape of isochromatic loops in terms of three fitting parameters ? , k and fi, where is the normalized fitting parameter of K. A computer program 'PROJECT' was developed to generate the analytical fringes for different values of fitting parameters. Another computer program'GEOM' was used to find the six characteristic dimensions describing the size and shape of analytically generated fringe loops. Third computer program'COMPARE' was developed to search the best fitted analytically generated loop with the single experimental isochromatic loop on the basis of six characteristic dimensions by employing a comparison function and also to determine stress intensity factor using fitting parameters corresponding to best fitted analytical loop. This single loop three parameter method was applied to determine stress intensity factors for two types of plate specimens having through crack and surface flaw subjected to biaxial loading conditions. The calculated stress intensity factor values were found to be in good agreement