Effects of Out-of-Plane Deformation on Stress Rupture of Unidirectional Polymer Matrix Composites

Abstract

Abstract The use of composite materials instead of conventional engineering materials is more frequently considered, especially for applications with dominant weight constraints. Polymer matrix composites offer advantages such as relative ductility or lower cost of manufacturing compared to other composites. The different cases of loading for these materials need to be explored. Out-of-plane loading is an important case, and the literature is sparse when it comes to large displacements for these materials. Such large displacements can occur for a variety of applications. Some unidirectional fiber reinforced polymer matrix composites are, for example, stocked in rolled tapes. Even at room temperature, this large deflection of the material could result in the degradation of its properties over a long period of storage. In service, the bending load can be combined with thermal or chemical loads. Intuitively, the combination of the mechanical load and elevated temperature could accelerate the degradation process. The practical case that lead to this research was the study of polymer matrix composites for replacement of one layer of the steel armor in flexible pipes used by the oil industry in ocean water. The temperature of the oil circulating inside the pipe creates an elevated temperature. The effects of the combination of the quasi-static bending load intrinsic to the pipe geometry and aggressive environments are unknown and need to be investigated. The present paper relates the recent advances in characterizing stress rupture for unidirectional carbon fiber reinforced polymer matrix composites in end-loaded bending and extends our earlier modeling efforts (Russell et al., 1997, Mahieux et al., 1997). Experimental observations are presented, and three life-prediction models are discussed in the following sections.