Ultrasonic spectroscopic analysis of impact damage in composites by using laser vibrometry

Contemporary composite materials are continuously being modified and improved in accordance with growing quality requirements of aerospace systems. New manufacturing technologies stimulate development of appropriate (novel) nondestructive testing (NDT) methods and respective hardware for detecting and characterizing hidden defects. One of the recent improvements in this area is related to combining acoustic stimulation of test objects and scanning laser vibrometry. This paper describes an ultrasonic spectroscopic approach to laser vibrometry applied to hybrid composite materials subjected to impact damage. The meander-shaped signal for resonance stimulation was applied to enhance the detection of multi-component defects. It has been shown that wide-band frequency stimulation provides some advantages in regard to mono-frequency excitation because it activates more zones of multi-component defects thus allowing more accurate estimation of defect size.