Micropolar in-Plane Shear and Rotation Moduli of Unidirectional Fiber Composites with Fiber–Matrix Interfacial Debonding

The mechanical properties of fiber-reinforced composites are significantly affected by the bond between the fiber and the matrix. The objective of this research is to determine the micropolar in-plane shear and rotation moduli of unidirectional brittle matrix composites with fiber–matrix interfacial debonding. Traction and displacement continuity conditions are imposed along the boundary of adjacent representative elements. In addition to a shear test (i.e., symmetric shear loading) for classical in-plane shear modulus, a center rotation test of a nine-cell model is proposed to introduce the asymmetric shear loading and numerically determine the micropolar in-plane shear and rotation moduli by means of finite element analysis. A doubly symmetric fiber–matrix interfacial debonding is utilized in this study. For the shear test, the composites are modeled using a quarter cell whereas for the rotation test, a nine-cell model is proposed to simulate the nonsymmetric nature of micropolar theory. The cell boundaries, in general, do not remain straight for the composites under loading. Parametric studies assessing the effects of debonding angle and the fiber volume fraction on the micropolar in-plane shear and rotation moduli of unidirectional composites are presented, and some basic characteristics of the moduli with interfacial debonding are discussed. Due to matrix domination in determining the shear properties of composites, the effects of an increase in interfacial debonding and fiber volume fraction are notably identified by the reduction of properties under both symmetric and asymmetric shear loading.