ON THE COMPRESSIVE FAILURE OF FIBER-REINFORCED COMPOSITES

In this paper a combination of experimentation and analysis is used to identify and study the mechanisms that govern the failure of unidirec tional fiber composites under compression. The experimental part inclu des experiments in which the compressive strength and the prevalent fa ilure mechanisms of AS4/PEEK composite are established, tests for esta blishing the constitutive properties of the composite and its constitu ents, and an evaluation of the extent of misalignment of fibers in man ufactured composites. The failure load of the composite was confirmed to be affected by geometric imperfections in the form of fiber wavines s, and failure was found to lead to kink bands with distinct orientati ons and widths. Motivated by the experimental findings, the composite was idealized as a two-dimensional solid with alternating fiber and ma trix layers, each having the measured properties of the two constituen ts. The compressive responses of microsections of finite width with im perfections of various spatial distributions were established numerica lly. The calculated responses are characterized by an initially stiff, stable regime terminated by a limit load instability which is associa ted with the strength of the composite. Following the limit load, the deformation localized into inclined bands with distinct widths. It has been verified that, as the localization process progresses, the fiber bending stresses at the ends of these bands grow to values comparable to those of the fiber strength. The sensitivity of the calculated res ponse to the geometric characteristics of the imperfections was studie d parametrically.