On a general constitutive description for the inelastic and failure behavior of fibrous laminates––Part II: Laminate theory and applications

Abstract

These two parts of papers report systematically a constitutive description for the inelastic and strength behavior of laminated composites reinforced with various fiber preforms. The constitutive relationship is established micromechanically, through layer-by-layer analysis. Namely, only the properties of the constituent fiber and matrix materials of the composites are required as input data. In the previous part (Comput. Struct. (submitted)), the lamina theory was presented. Three fundamental quantities of the laminae, i.e. the internal stresses generated in the constituent fiber and matrix materials and the instantaneous compliance matrix, with different fiber preform (including woven, braided, and knitted fabric) reinforcements were explicitly obtained by virtue of the bridging micromechanics model. In the present paper, the laminate stress analysis is shown. The purpose of this analysis is to determine the load shared by each lamina in the laminate, so that the lamina theory can be applied. Incorporation of the constitutive equations into an FEM software package is illustrated. A number of application examples are given in the paper to demonstrate the efficiency of the constitutive theory established. The predictions thus made include: failure envelopes of multidirectional laminates subjected to biaxial in-plane loads, thermo-mechanical cycling stress–strain curves of a titanium metal matrix composite laminate, S–N curves of multilayer knitted fabric reinforced laminates under tensile fatigue, and bending load–deflection plots and ultimate bending strengths of laminated braided fabric reinforced beams subjected to lateral loads. All these predictions are based on the constituent properties which were measured or available independently, and are compared with experimental results. Reasonably good correlations have been found in all the cases. It is expected that the present constitutive relationship can benefit the critical design and strength analysis of a primarily loaded structure made of composite materials.