CHARACTERIZATION OF PIEZO-FILM SENSORS FOR DIRECT VIBRATION AND IMPACT MEASUREMENTS

Piezo-film sensors were employed in determining the dynamic response of [(0 deg/90 deg)(4)](s) s-glass/epoxy laminates and 2024 aluminum specimens. Simple beam- and plate-type sensor equations were derived based on classical plate theory incorporating the linear piezoelastic constitutive relationship, A series of vibration and impact tests were conducted for the determination of structural dynamic response. Piezo-film sensors, with a thickness and area of 110 mu m and 1 x 1 cm(2), respectively, were connected directly to a voltage measurement device in these tests. The first three bending frequencies of the glass-fiber-reinforced plastic (GFRP) cantilever specimen were examined. Experimental results and those simulated by the MARC finite-element code were found to be in good agreement, with the difference between the two being less than five percent. At frequencies above 3 kHz, piezo-film transducers are capable of closely detecting structural dynamic response in the absence of charge amplification. At frequencies lower than approximately 3 kHz, however, the voltage measured directly from a piezo-fiIm sensor underestimates structural response. A modified piezo-film sensor equation is thus proposed for lower frequency measurements. Effect of frequency and piezo-film's size on tower frequency attenuation is explicitly formulated based on a simple RC circuit analogy. Drop tests were also performed on damped [(0 deg/90 deg)(4)](s) GFRP laminates and aluminum targets, with nine piezo-film sensors being glued to the specimen's distal surface in order to determine the low-speed impact response. Specimen transient central deflection subjected to impact loading was identified based on test findings and the plate-type piezo-film sensor equation. The results were found to be in good agreement with the numerical solution obtained from the MARC finite-element code.