Use of imbedded fiber optic thermal sensors to monitor the health of composite structures

We investigated a thermal nondestructive evaluation (NDE) technique based on thermography that uses optical fiber sensors to detect damage within a laminated graphite epoxy composite specimen. Two sets of composite samples were used for testing, one set had fiber optic sensors imbedded between the layers and the other set did not. Thermocouples were attached to the front and back surfaces of all coupons for comparison. Damage was initiated in the samples at various levels with a simulated impact system and damage was confirmed with X-ray. Results suggest that the thermal approach is more sensitive to damage than the X-ray evaluation used. The test apparatus in addition to the results obtained from both sets of samples are presented.