On Interphase Modeling for Optical Fiber Sensors Embedded in Unidirectional Composite Systems

This paper investigates the local stress of a polyimide coated optical fiber sensor surrounded by a transversely isotropic AS4-3501 graphite/epoxy host material. Spatially varying and spatially constant interphase composite cylinders models are used to understand the behavior of this system to longitudinal and radial normal, in-plane shear, and uniform thermal loading conditions. Interphase thicknesses used in the modeling effort are inferred from electron backscatter and scanning acoustic techniques. The results show that the gradient interphase models used in this paper are not warranted for this material system, that the thermal residual stresses in the core/cladding region can be significant, and that the optical fiber does not degrade the axial strengths of the composite, but the transverse tensile and compressive strengths are reduced by 15 and 60 percent respectively.