TIME-TEMPERATURE INDICATOR FOR EVALUATING INCIPIENT THERMAL DAMAGE OF CFRP

摘要

Incipient thermal damage is a significant issue for CFRP composites because it is difficult torndetect by common NDE techniques like ultrasound and it can cause fiber-matrix debonding,rndelamination, and matrix embrittlement which can reduce the mechanical properties of therncomposite. Diffuse reflectance infrared transform spectroscopy (DRIFTS) is capable ofrndetecting incipient damage, but it has a small spot size that is not efficient for inspecting largernareas for thermal damage. In our previous work a thermally activated fluorescent probe wasrnshown to activate when the composite was thermally exposed. This “turn-on” type behaviorrncould show that thermal exposure had occurred, but could not provide more details about thernthermal event. In this study a method for estimating the time and temperature of the thermalrnexposure (a so-called time-temperature indicator or TTI) is presented. The basis for this methodrnis combining two different thermally activated probes with different activation kinetics andrnemission wavelengths. Using ratiometric fluorescence to monitor the changes in the fluorescencernspectra, time-temperature response curves can be generated that can be used for estimating therntime and temperature of the thermal exposure.