15. Detection of Early Stage Material Damage Using Thermophysical Properties

This paper presents a preliminary study on the effects of fatigue induced microstructural damage on the thermophysical properties of carbon fiber polymer composites commonly used for aerospace applications. The goal is to identify thermal properties that may serve as viable indicators of early stage material damage during structural health monitoring (SHM). A series of fatigue tests were conducted on multilayer composite specimens with peak stress σ_max = 0.55σ_u (the static strength) and stress ratio R = 0.1. The cyclic load was paused periodically at predefined cycle intervals starting from 100 cycles through end of test at 150 k cycles. At each pause, the front side of the specimen is instantaneously heated with a high intensity flash followed by temperature measurements by two thermocouples attached at the front and back sides the rectangular specimen. Simultaneously, IR images are recorded using high speed camera. Changes in thermophysical properties including heat transfer rate (Q), thermal conductivity (k), heat capacity (c) were computed as functions of fatigue cycles. Preliminary data shows that the time-temperature (T-t) evolution is correlated to the number of fatigue cycles or consumed fatigue life of the specimens.