Non-Destructive Evaluation in Mechanical Systems using Passive Thermal Methods
Passive non-destructive evaluation (NDE) techniques that utilize temperature measurements can be widely applied due to the many processes that either directly involve heat transfer or output heat as a by-product. Two different passive NDE methods utilizing temperature measurements were developed for particular applications in this work. A technique for identifying flaws in fiber-reinforced polymer (FRP) composite materials during the curing (manufacturing) process is developed. In order to enable this flaw detection method, a technique for estimating the internal temperature of a curing FRP composite in real time using infrared thermography and Kalman filter-based state estimation is also developed. This technique is shown to produce accurate estimates of internal temperature at real-time computational speeds and is validated using experimental data collected during the curing process of a composite wind turbine blade section. The flaw detection method utilized the cumulative values of the Kalman filter corrections during state estimation. The technique is evaluated using numerical experiments and was found to perform well for detecting resin-rich regions but was less effective for detecting resin-deficient regions in a curing composite. A technique for monitoring the flow-accelerated corrosion (FAC)-induced wall-thinning in nuclear power plant pipe elbows was also explored. The change in measured steady-state temperature from the non-corroded initial state to the current state was used as the damage-sensitive metric and estimate the thickness reduction in the pipe wall using a (Gaussian-process) surrogate model of the governing physics. The accuracy demonstrated by the method underlined the potential for utilizing the method as a uniquely cost-effective, easy-to-use, and passive early detection monitor for FAC-induced wall thinning.