Inspection of thick composite structures, such as Reinforced Thermosetting Resin (RTR) pipes used in the petroleum
industry, using infrared thermography is difficult. This paper investigates the use of step heating thermography to
increase the maximum detectable defect depth and describes techniques to quantitatively characterize defect depth and
severity in thick composites. A procedure to simultaneously determine defect depth and thermal resistance from the early
time surface temperature is described. The procedure is based on fitting the early time surface temperature profile over a
defect to a one-dimensional three-layer analytical model. Experimental testing demonstrates the accuracy of the
A laboratory testing and engineering modeling study was completed to determine the influence of fiber optic coating damage caused by microbend contact on the performance of microbend sensors developed based on relatively low cost single-sided microbending technique using a multimode optical fiber. A testing method was designed, developed and implemented to determine the loads that caused optical fiber glass-coating debonding and coating fracture. Finite Element models of the fiber-deformer system were developed to study the failure modes and predict the stresses that caused this failure. Loads and displacements predicted by Finite Element models were found to be in good agreement with load and displacement values observed during the experimental analyses. It was found that optical fiber coating fracture changes the transmissivity output response but does not affect the recovery of the light transmissivity properties of the optical fiber. Viscoelastic effects were found to influence the behavior of the fiber-deformer system. It was also found that glass-coating debonding and coating fracture during a load-unload cycle are major causes of variability and error during microbend sensor calibration.