Full-field vibration measurement for vibrothermography

Vibrothermography is a nondestructive technique for finding defects through vibration-induced heating imaged with an infrared camera. To model the crack heating process in Vibrothermography, it is essential first to understand the vibration that causes heat generation. We describe a method for calculating internal motions from surface vibrometry measurements. A reciprocity integral and Gauss's law allow representation of internal motion by a surface integral of boundary motion times the Green's Function. We present experimental results showing internal motions calculated from measured surface motions of a vibrating sample. This will ultimately allow estimation of the detectabitity of a hypothetical crack at an arbitrary location in a specimen.