Characterization of residual strength in transversely loaded glass-polyester composites by acoustic emission and sentry function

This paper addresses damage evolution in composite materials by using acoustic emission (AE) as a non-destructive testing method to evaluate residual strength of specimens. Two composite samples at different lay-ups (Unidirectional and Cross-ply) were used in this investigation. The three-point bending test was applied on composite samples transversely while damage progression was monitored by means of acoustic emission technique. The test was stopped at three different damage levels, one (Low) corresponding to the load value of 10% before maximum load, the second (Medium) corresponding to the first load drop in the load-displacement curve and the third (High) to the complete failure of the specimen. Depend on loading level, the damage value was variant as it caused different residual strength that was related to acoustic emission signals activities. To find this relationship, firstly, the tensile test was carried out on damaged samples to evaluate the residual strength of them. Secondly, a method based on a special purpose function, called Sentry function, which is defined as the logarithm of the ratio between mechanical energy and acoustic energy, was applied to find out the relationship between the tensile residual strength and acoustic emission activates. Results show that the measurement of the strain energy in specimens and of the acoustic emission energy released by fracture events made it possible to estimate the amount of induced damage and can be effective in residual strength estimation and damage evolution. (c) 2017 Elsevier Ltd. All rights reserved.