Open Access

ARTICLE

Stress Concentrations Caused by Embedded Optical Fiber Sensors in Composite Laminates

by Kunigal Shivakumar¹, Anil Bhargava²

1 Research Professor and Director, Center for Composite Materials Research, Department of Mechanical Engineering, North Carolina A&T State University, Greensboro, NC 27411
2 Graduate Student, Center for Composite Materials Research, North Carolina A&T State University, Greensboro, NC 27411

Computers, Materials & Continua 2004, 1(2), 173-190. https://doi.org/10.3970/cmc.2004.001.173

Abstract

The fiber optic sensor (FOS) embedded perpendicular to reinforcing fibers causes an `Eye' shaped defect. The length is about 16 times fiber optic radius (R_Fos) and height is about 2R_Fos. The eye contains fiber optics in the center surrounded by an elongated resin pocket. Embedding FOS causes geometric distortion of the reinforcing fiber over a height equal to 6 to 8 R_Fos. This defect causes severe stress concentration at the root of the resin pocket, the interface (in the composite) between the optical fiber and the composite, and at 90° to load direction in the composite. The stress concentration was calculated by finite element modeling of a representative micrograph. The FE results agreed reasonably with analytical and experimental data in the literature for a similar problem. The stress concentration in axial direction was about 1.44 and in transverse direction at the interface was -0.165 and at resin pocket was 0.171. Under tensile loading, the initial failure was by transverse matrix cracking (fiber splitting) at the root of the resin pocket, then that lead to final fracture by fiber breakage. Under compression loading, the failure initiation was by interfacial cracking due to large transverse tensile stress and the final fracture was by compression. Fracture stress calculated from the analysis using the maximum stress criteria agreed reasonably with test data.

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