Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Engineering Science and Mechanics

First Advisor

Loren W. Zachary


An experimental study was conducted to determine the stress intensity factors at a crack tip resulting from the interaction between two edge cracks. The experimental technique used the caustics reflected from a transparent model. Six pairs of equal length edge cracks in a plate subjected to extension were used. Six ratios of the distance between the two cracks and the crack length were investigated. An interaction between two edge cracks of lengths 0.3[superscript]'' and 0.4[superscript]'' was also studied. The effect of the distance between the cracks upon the determination of the stress intensity factors was investigated;An iterative least square technique was developed to extract mixed mode stress intensity factors together with the exact location of the crack tip from an overdetermined set of data points. The accuracy of the technique was improved by using a digital image analysis system;The method of caustics was extended to the determination of the stress-optical constants by applying the method in the region very close to a circular hole in a thin plate. A new technique was developed to determine the two stress-optical constants associated with the caustics reflected from the rear face and transmitted through an optically isotropic model.



Digital Repository @ Iowa State University,

Copyright Owner

Nashwan Thanoon Younis



Proquest ID


File Format


File Size

133 pages