Determining the load-time history of fibre composite materials by acoustic emission

Abstract

Acoustic emission was monitored during the axial loading of unidirectional fibre composite tensile specimens. The material consisted of strong, brittle fibres (E glass) embedded in a viscoelastic matrix (epoxy). It was found that when the load was held constant the acoustic emission output continued, but at a decreasing rate with time at load. As the load level was increased, the acoustic emission output at load continued for a longer period. It is suggested that the acoustic emission under constant load is a result of fibre fracture which continues after loading ceases because of the viscoelastic nature of the matrix which allows stress redistribution with time. The experimental results from acoustic emission are compared with computer calculations for fibre fracture based on theoretical considerations. Good agreement is noted between the theoretical and experimental results.