Int. Journ. of Fracture 20 (1982) 223-239. 00376-9429/82/03/0223-17500.20/0 223 © 1982 Martinus Nijhoff Publishers, The Hague. Printed in The Netherlands An investigation of stress intensity factors for plates with equal and unequal parallel edge cracks D.D. RAFTOPOULOS and B. FARAHMAND The University of Toledo, Department of Mechanical Engineering, Toledo, Ohio 43606, USA (Received September 16, 1980) ABSTRACT A semi-theoretical and experimental method is used to investigate thin plates with parallel edge cracks of equal and unequal length loaded in tension. Plates with equal and unequal periodic parallel edge cracks are treated under two separate cases: a) varying the length of the crack, and b) varying the crack spacing. Experimental observations show that in plates where the width of the specimen is much larger than the length of the cracks the stress intensity factor is in agreement with that Of equal parallel edge cracks of semi-infinite plates. However, when the ratio of the length of the crack to the width of the specimen is no longer small, the stress intensity factor deviates considerably from that of the semi-infinite plates. Furthermore, in the case of unequal periodic parallel edge cracks, the size of the caustic of the shorter crack becomes very small (it cannot be observed and measured) when the difference in the depth of the larger and short crack becomes equal or greater than one half of the crack spacing. Notation a = Crack length. a~ = Shorter crack length in the unequal periodic parallel edge cracks case. a2 = Longer crack length in unequal periodic parallel edge cracks case. b = Crack spacing. Ct,~ = Optical constant for the transmitted (Ct) and reflected (Cr) beam. d = Distance from crack tip to the free edge of the specimen. Dt~.~= Transverse diameter of the caustic for transmitted (D,) and reflected (Dtr) beam respectively. /3,.~ = Transverse diameter of transmitted (/3,) and reflected (/)tr) caustic for parallel edge cracks. fl(D, L, t) = A function that behaves as the stress intensity factor. gl = A function that defines the diameter of the caustic. K = Non-dimensional stress intensity factor. KL = Theoretical stress intensity factor. /(t = Semi-theoretical and experimental stress intensity factor. M = Bending Moment. N = Tensile Load P = Applied stress. q = D,AD, t = Thickness of the specimen. w = Width of the specimen. y~ = A function that defines the variation of the crack length. Zo = Specimen distance to the screen. 3' = A term that appears in Eqn. (1) and is a function of (w, N, t) or (w, M, t) for tension or pure bending respectively.