Size-estimates for distributions of microscopic damage from fracture tests on fiber-reinforced polymer-matrix composites: Insight from acoustic emission monitoring

Abstract

Damage development in fiber-reinforced polymer-matrix (FRP) composites under service loads is complex. The main reason for this is the micro- and meso-scale morphology interacting with the different microscopic damage mechanisms. Experimental approaches for investigation of microscopic damage mechanisms in FRP are, e.g., X-ray micro-computed tomography and acoustic emission monitoring. While X-ray micro-computed tomography achieves high local spatial resolution (down to sub-micrometer range), essential for identifying the different mechanisms, time-resolution and material volume that can be investigated are limited. Acoustic emission, on the other hand, is applicable to larger specimens and yields high time resolution (below microseconds) but limited spatial resolution only (a few millimeters at best). This contribution discusses which statistical information on microscopic damage in FRP is provided by acoustic emission based on quasi-static fracture mechanics test standards. Pattern recognition applied to acoustic emission signals allows distinguishing different damage mechanisms, e.g., for understanding delamination processes and correlating these with observed fracture surface features. For micromechanical modelling, acoustic emission will answer questions such as, e.g., “What are average microscopic damage sizes during delamination propagation and how much do they vary?” or “Do these damage sizes depend on fracture toughness, specimen load rates, or resulting delamination speed?” This information is relevant for selecting proper spatial and time resolutions for micro-mechanical modelling of damage accumulation in FRP composites.