Vibrothermography is a nondestructive evaluation (NDE) technique that has shown great promise in detecting tight cracks that can often be missed using other NDE methods. Vibration applied to a structure containing cracks forces crack faces to rub together and generates frictional heat imaged with an infrared camera. The closure state of a crack controls the locations and magnitude of heat generation in a vibrated crack. Noncontacting regions of cracks and regions under large closure stresses generally do not rub together to generate heat. Heat is generated at contacting regions of crack faces under low closure stresses. Regions along a crack that generate heat can be modulated based on externally applied stresses. The closure state of a crack, the level of applied vibration, and externally applied stresses influence the regions of a crack that will generate heat and those that will not. Due to the nature of the heat generation process, some cracks that are not detectable using other NDE methods are readily detectable using Vibrothermography.
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