Experimental and numerical investigation on structural effects of laser pulses for modal parameter measurement

In this paper it has been described part of the research devoted to the dev elopment of a complete non-intrusive experimental modal analysis procedure based on laser techniques both for excitation and for measurement. In parti cular, attention has been focused on the thermal effects generated by laser pulses on the excited structure. An analytical model of the energy exchang e between the light pulse and the target surface is proposed together with a finite element model of thermal and mechanical behaviour of the structure under excitation. Both the models (analytical and numerical) have been exp erimentally validated by measuring the thermal and the vibration responses induced by the laser pulses. The experimental part of the study has been pe rformed on a cantilever beam excited with laser pulses from an Nd:YAG sourc e (532 nm, 100 mJ/pulse) using an high-speed infrared camera and a scanning laser Doppler vibrometer. Results from this work can be used to improve un derstanding concerning the features of laser excitation and to establish a mechanical equivalent system of forces and moments, useful in order to incr ease the accuracy in the measurements of modal parameters when laser pulses are used as excitation sources. (C) 2000 Elsevier Science Ltd. All rights reserved.