Longitudinal shear transfer in fiber optic sensors

A coated optical fiber embedded in a host composite matrix is analysed to study the strain transfer to, and the stress and strain concentrations caused by, the optical fiber. The optical fiber and its coating are modeled as concentric, circular inclusions embedded in an isotropic homogeneous matrix. A case of a far-field longitudinal shear stress parallel to both the optical fiber and the structural fibers is considered. The effects of the modulus of the coating as well as its thickness is studied for the strain transfer and the stress and strain concentrations. It is shown that when the coating is softer than the matrix, a thinner coating will induce more shear transfer; when the coating is stiffer than the matrix, a thicker coating will induce more shear transfer. It is also shown that the maximum shear strain is induced in the optical fiber when the shear modulus of the coating is the geometric mean of the shear moduli of the fiber and the matrix.