The stress intensity factors for plexiglass plates containing edge cracks and subjected to either pure bending or tension are determined herein. The method of investigation was based on a semi-theoretical and experimental approach, where the stress intensity factors are expressed in terms of the measured diameter of the caustic, the crack length, and the width of the specimen. First, two basic crack arrangements (single and double edge cracks) were studied and then the method was utilized for the investigation of more complicated crack arrangements which are difficult or maybe impossible to be investigated otherwise. In particular, the stress intensity factor for plates having a sharp V-notch of various angles 0, and semi-infinite plates containing equal parallel edge cracks subjected to pure bending and tension respectively, were investigated in order to verify the validity of this method. NOTATION crack length crack spacing optical constant for the transmitted (C,) and reflected (C,) caustic for a single edge crack is given as (w -a) and for a double edge crack as (r -U) diameter of the caustic for transmitted or reflected caustic transverse diameter of the reflected caustic transverse diameter of the transmitted caustic "D,, r the function which behaves as the stress intensity factor and is equal to L (w -a)
for single and a&, , d for double edge cracks respectively @---a) a function that expresses the diameter of the caustic non-dimensional stress intensity factor theoretical mode one stress intensity factor semi-theoretical and experimental stress intensity factor bending moment tensile force applied stress QiD,, radius of the constrained zone for transmitted or reflected caustic thickness of the specimen width of the specimen a function that expresses the length of the crack distance from the specimen to the screen proportionality constant that has the unit of (length)5'2 transmitted and reflected proportionality constant transmitted or reflected constant which involves optical constant of the material (C,,,) thickness of the 1 specimen (t) and distance Z0 and in all cases is equal to __ Z&J angle of apex WI2