Dynamic Stress Concentrations in Fiber-Reinforced Composites with Interface Layers

Abstract

Interface layers in composite materials exist as a natural consequence of material processing or are intentionally introduced into the composite to improve the chemical and physical properties of the composite. These interface layers surrounding the typically fiber reinforcements of the composite can be small, as in the interface between tungsten wire reinforcement and steel, or quite large, as in vapor deposited boron fibers in epoxy. The fiber size has a direct influence on the macroscopic structural properties of the composite as does the existence of the interface layer surrounding the reinforcement. The static structural properties due to the reinforcements can be characterized through ex perimental testing. This should be adequate for non-primary structural composites but composites are now commonly used as primary structural components in both static and dynamic environments. Static and dynamic properties are therefore essential to the proper design of the composite structure. The pertinent quantity of interest in dynamic analysis is the dynamic stress concentration, a ratio of the dynamical stress on the reinforcement to the stress without the reinforcement. The dynamical stress concentrations are the ap propriate area for studying fiber-reinforced composites and the interfacial layers must be included in order to properly model the dynamical interaction with the substructure of the composite. As an added benefit of the analysis, ultrasonic inspection benchmarks for non destructive testing of the reinforced composites are produced from the dynamical stress concentration analysis.