Simultaneous shearographic and thermographic NDT of aerospace materials

The paper describes the simultaneous use of digital shearographic and infrared thermographic techniques when testing aerospace structures made of honeycomb and composite materials. Non-destructive testing of the structures was accomplished using a proprietary portable shearographic system, produced at the Mechanical Engineering Department of the University of Cape Town, and a relatively inexpensive newcomer to the infrared thermography field, known as IRISYS Universal Thermal Imager. Simply, both systems were employed to image the component simultaneously and record the effect of it cooling down after being heated with the hot air from a hair drier or a heating lamp. The techniques proved effective in identifying defects such as the crushed honeycomb core in a section of the wing of an unmanned aerial vehicle (UAV) and the delaminations at different depths in the main rotor blade of an Oryx helicopter. The images indicating the defects as produced by the shearographic system are visually more dramatic, particularly when enhanced by phase stepping and colour techniques. On the other hand, the thermographic images, besides indicating the position of the flaw, gave information regarding the temperature of the region of the defect relative to the cooler surrounding material. In addition, there was the indication that during the cooling down, the infrared system continued to indicate the presence of the flaws/defects for a longer period of time than the shearographic system. It is suggested that in similar tests, the temperature data be coupled to the out of plane displacement gradients with a view to providing quantitative thermal stress results.