Isolation of Thermal and Strain Responses in Composites Using Embedded Fiber Bragg Grating Temperature Sensors

Abstract

Abstract : In this research, fiber Bragg grating (FBG) optical temperature sensors are used for structural health monitoring of composite materials. The specific goal is to detect the thermal response of a composite to high energy radiation incident on the surface of a composite structure. FBG sensors also respond to axial strain in the optical fiber, thus any structural strain experienced by the composite is also detected. Consequently, this research has focused both on identifying the unique characteristics of each response and on developing feasible methods to isolate the thermal response from the strain response. Isolation ensures that any response to mechanical strain does not mask the response to a temperature gradient present on the composite surface. The isolation strategy developed in this research is characterized by two design features. First, a three-dimensional array of FBG temperature sensors has been embedded in a carbon/epoxy composite structure, consisting of both in-plane and through-thickness sensor arrays. This architectural design component exploits the spatial differences between the temperature profile and the strain profile in a composite structure. Second, an accompanying data processing scheme has been developed that uses the statistical properties of the collected sensor data to interpret and identify each response. The degree to which the isolation strategy increases the functionality of FBG temperature sensors in mechanically strained composite structures is assessed.