Detection of crack closure in time-resolved acoustic microscopy

Acoustic microscopy with time-of-flight measurements of short pulses has been used to detect the closure of short cracks. Operating the microscope in the pulse mode, the reflections from inclined cracks have been measured and a diffraction model for calculating the amplitude of these reflections as a function of the lens position was developed. The detected signal amplitudes depend on the size of the crack and on the contact between the crack faces