Mechanical response and damage in woven S2-glass reinforced polyester under compression: Experiments and modeling

Mechanical tests and analyses have been systematically conducted in order to characterize the compressive response, failure modes and damage mechanisms of woven S2-glass reinforced composite. This particular composite system has potential for structural armor applications. It is a thick laminate, consisting of a random mode stacking of biaxial, plain weave S2-glass/S2-glass fiber yarns with polyester resin (CYCOM 4102) as binder material. In the first phase of this investigation, the three dimensional macroscopic response of the material was measured under quasi-static uniaxial compressive loading. An analytical model was then developed to describe the elastic response of the composite system as function of the constituent material's properties and volume fractions. The model is based on a unit cell representation of the textile composite geometry and thus takes into account the fiber undulation as a characteristic of the weave and the associated transverse isotropy of the fiber yarns. Quasi-static (i.e. at low to medium strain rates) experiments were performed using the MTS material test system. The uniformity of the material's response was verified by comparing the responses exhibited by different sized and shaped specimens under quasi-static loading. It was found that the overall response was tetragonal, with two of the three orthotropic principal moduli being equal in magnitude.; In the second phase of this study, the failure modes and dynamic compressive responses of the material were characterized from experimental observations. Compression strength tests were performed, and scanning electron microscopy studies of the fractured specimen surfaces were conducted. The failure modes are complex involving a combination of failure mechanisms. The failure stresses and strains along the ply lay-up direction were higher than those along the plane of the lamina. The material's dynamic response was determined using both the split Hopkinson pressure bar and the direct disk impact techniques. The material was found to be significantly strain rate sensitive.; The damage due to repeated compressive loading of a multi-layered woven composite material was examined in the final phase of this investigation. This damage was assessed via macroscopic stress-strain response, the acoustic emission analysis, and scanning electron microscopy. The latter two techniques were employed to identify the damage mechanisms operative at the micro-scale, which enabled correlation with the observed macroscopic stress-strain behavior. Acoustic emission, a transient elastic stress wave generated by the rapid release of energy from a localized source within a material, is an important tool for characterizing damage initiation and propagation. Based on an extensive set of experimental observations, the damage phenomenon within the material was determined. A dimensionless damage parameter is defined and its evolution is modeled based on the results of these experiments.; Finally, in an attempt to understand the material's response under triaxial compressive stress state, compression tests under various confined pressures were performed in the laboratory. The material can withstand high hydrostatic pressures and has a low compressibility factor. The material's compressive response was appreciably affected under high confining pressures. The compressive strength of the material was significantly higher for increasing confining pressures in the direction perpendicular to the fabric planes; in the other two perpendicular directions, the increase was insignificant.