| Micromechanical models have been developed in this study to predict the longitudinal mechanical behavior of unidirectional continuous fiber composite materials under a uniaxial applied effective strain of sufficient magnitude to cause irreversible damage in the form of brittle fiber fracture, interface damage resulting in a compliant interphase region, and matrix plasticity. A single fiber composite (SFC) specimen that consists of a single silicon carbide fiber embedded in an aluminum matrix with a thin interphase layer was used to investigate these effects. The objective of this research was to create a micromechanical model to predict the longitudinal constitutive behavior of the composite as damage occurs and to determine if the interfacial shear stress can be estimated from the fiber fragment length at a given effective strain.; The aluminum matrix was modeled as either linear elastic, elastic-perfectly plastic, linear strain hardening, or power-law strain hardening. Before fiber fracture, the interphase layer forms a perfect bond between the fiber and matrix. During fiber fracture, the interphase is damaged and the interfacial bond becomes imperfect. The imperfect interface may be compliant or compliant and weak, and was modeled as a spring layer with vanishing thickness. The fiber fragments are assumed to be uniformly distributed such that the fragment lengths are equal at each load level. The Weibull distribution was used to relate the fiber fragment length to the tensile strength of the fiber. An increase in the applied effective strain causes successive fiber fractures, in that the fragments become increasingly shorter. The SFCs studied had either no fiber fractures, one fracture, or successive fractures; one of the four matrix material types; and either perfect, compliant, or compliant and weak interfaces.; The finite element method was used to provide numerical solutions for the state of stress and fiber length at a given applied effective strain which were used to construct effective stress-strain plots and effective strain-fiber fragment length plots. Classical elasticity and mechanics of materials modeling techniques were used to derive analytical constitutive relationships. The analytical and finite element derived constitutive relationships were compared as a means of evaluating the quality of the analytical models. |
