A Photoelastic Investigation into the Effects of Cracks and Boundary Conditions on Stress Intensity Factors in Bonded Specimens

Abstract

An investigation into the influence of cracks in bonded specimens is conducted. Photoelastic specimens containing a bondline are subjected to a constant displacement boundary condition created by bonded end grips. Specimens containing various crack orientations are analyzed to determine stress intensity factors at the induced crack tips. Specimens containing interface and sub-interface cracks were investigated. Two global geometries were used in this investigation, square and rectangular. The constant displacement boundary condition was induced on the specimen through dead weights hung from bonded aluminum end grips. Stress intensity factors were determined using photoelastic techniques. The stress intensity factors were examined to determine trends in the results as a function of changes in geometry. The effects of the induced boundary condition, the specimen geometry, and the bondline were investigated. The results from this investigation were compared to known solutions with a similar specimen geometry. These tests exhibited influences from the bondline, the boundary conditions, and the specimen geometry. The bondline tended to decrease the stress intensity factor for specimens with small crack lengths and tended to increase the stress intensity factor for specimens containing long crack lengths. As the crack length increased so too did the stress intensity factor. A reduction in the bondline to crack distance with sub-interface crack specimens caused a reduction in the stress intensity factor. A reduction in the global height of the specimen caused a reduction in the stress intensity factor also. The results from this investigation will aid in the understanding of the influence of interface and sub-interface cracks in bonded specimens.