AE monitoring of the mechanical behavior of pultruded polymer-matrix composites submitted to bending

In this work, a composite material with glass fibers and vinylester matrix, obtained by pultrusion, is subject to a 3-point bending test, first under quasi-static loading and then to fatigue, at relatively low frequency. The acoustic emission technique is used during the tests in order, to clarify the damage threshold and also to monitor its development, during testing. The results showed that the damage threshold occurs well before the end of proportionality. This result allowed us to clearly specify the interval along which the stress fatigue tests have to be performed on this material, namely between the stress threshold for damage and the end constraint of proportionality. The scenario of damage to the material studied suggests a damage mode at low stress (up to the end of proportionality), governed by various microdamage mechanisms of the matrix (matrix microcracking longitudinally and transversely to fibers). At higher stress, the fibers begin to break, in significant numbers, along with a large diversity of damage mechanisms. This is proven by a very broad distribution of amplitudes of acoustic events. © 2013 Lavoisier.