Abstract

Laser Opto-Acoustic Method for Nondestructive Porosity Evaluation of Graphite-Epoxy Composites

N.B.Podymova, M.A.Belov, I.M.Pelivanov (Faculty of Physics, Moscow State University, Moscow, Russia); A.A.Karabutov (International Laser Center, Moscow State University, Moscow, Russia)

e-mail: natasha@sasha.phys.msu.su

A laser opto-acoustic method [Gusev V.E., Karabutov A.A. Laser Optoacoustics. AIP, N.-Y., 1993] is developed for nondestructive evaluation of volume fraction of pores (porosity) in graphite-epoxy composites. This problem is of great practical importance since structural defects like pores can substantially reduce the material strength. Laser excitation and piezoelectric detection of ultrasonic pulses took place in investigated composite samples with specially designed "reflection mode" opto-acoustic transducer [Karabutov A.A., Murashov V.V., Podymova N.B. // Mechanics of Composite Materials, 1999, vol.35, N1, p.89-94]. This transducer allows one to obtain the temporal shape and spectrum of backscattered ultrasonic signals in composites by one-sided access to the sample or product. The noise part of these signals - so called "structural noise power" - was found to increase with increasing of porosity of composite. The empirical dependence of porosity vs. structural noise power was obtained for graphite-epoxy composite samples with porosity up to 0,16 and with volume fraction of epoxy matrix 0,31; 0,36 and 0,42. These results confirm the advantages of the laser opto-acoustic method for nondestructive porosity evaluation of composite materials and products during manufacturing and operation.

Section : 9