Fiber-reinforced polymer composites test specimen design for selected damage mechanisms

Abstract

Fiber-reinforced polymer composites yield a range of microscopic damage mechanisms even under apparently “simple” load cases, e.g. quasi-static uniaxial tensile tests to failure. Even reducing the fiber-reinforced polymer composite to a single fiber embedded in a matrix will produce several different damage types under quasi-static tensile loading. These are fiber breaks and simultaneous fiber–matrix debonding as well as friction between fiber and debonded matrix, and sometimes, additional matrix cracks. Acoustic emission monitoring of mechanical load tests on material specimens or components is often used to identify the occurrence of damage and attempts at locating the source and identifying the damage mechanism or type in a wide range of materials. The complex damage behavior of fiber-reinforced polymer composites poses a challenge in that respect. Therefore, various approaches (e.g. pattern recognition or neural networks) have been developed to identify the different microscopic damage mechanisms from acoustic emission signals obtained from various load tests. For improved understanding of the damage mechanisms in fiber-reinforced polymer composites as well as for validating the procedures for identifying the types of mechanisms, fiber-reinforced polymer specimens showing a “single dominant damage mechanism”, i.e. occurring in significantly larger number than all others, at least in certain stages of damage accumulation or in localized volume elements, can be designed. The contribution discusses and classifies selected examples of single dominant damage mechanism for fiber-reinforced polymer composites and their application.