Search Results

This paper presents an application of shearography, an optical method for full-field strain measurement, for evaluating residual stresses in plastic/composite components. The approach is based on measuring the change in slope of the component surface, which is caused by the release of residual stresses, in the vicinity of a small, shallow blind-hole or of a small indentation made on the underside of the component during testing. The severity of slope-change, and hence the fringe density, gives a measure of the residual stresses in the component. This method does not require laborious mounting of strain gages or transducers whose stiffness could affect the accuracy of measurements, and is therefore practical for use in both production and field environment.

To reduce costs and facilitate automation of joining processes, adhesive bonding has gained popularity as a replacement for conventional mechanical fastener, especially for bonding parts made of plastics and polymer composites. However, the adhesive bonding process is more susceptible to quality variations during manufacturing than traditional joining and fastening methods. Shearography, an optical technique that measures full-field surface deformation, has been extended to inspecting debonds. It detects a debond by measuring the debond's response to applied stresses. This paper describes a technique of shearography using multiple frequency vibration excitation as a means of stressing for detecting debonds with closed boundaries as well as open boundaries. The technique can also be used to detect loosened mechanical fasteners. This process can be fully automated for rapid inspection on factory floors.