This thesis presents a photoelastic method to determine stress intensy factors, KI and KII, base don the Newton-Raphson and least square techniques, where the term teta 0x refers to the far field stress distribution is substituted by a complete polynomial in x and y for the better adjustment of the nonsingular stress field. Analyses are made of the number and location of points used to obtain the experimental data with the purpose of estudying their influence on the values of KI an KII determined by the proposed method. The experimentally determined isochromatic fringe patterns are compared with computer plotted fringe patterns generated with the aid of the determined values of KI and KII. Finally, the proposed method is employed for the determination of stress intensity factors in problems simulating cracks near joints of welded plates subjected to tension and beding.