Determination of the fatigue limit in composite materials using IR lock-in thermography

This paper presents a methodology to determine the fatigue limit in composite materials by means of infrared lock-in thermography. IR thermography as a non-destructive, real-time and non-contact technique, allows the detection of heat waves which are generated by the thermo-mechanical coupling and the intrinsic energy dissipated during mechanical cyclic loading of the sample. Cross-ply SiC/BMAS composite dog-bone specimens were subjected to fatigue loading in various stress levels and were concurrently monitored by an infrared camera. The determination of fatigue limit by the traditional method with Wöhler curve has some limitations such as the requirement for a large number of tested specimens and extended experimental time, while using the method proposed in this study these limitations are surpassed. The results obtained by the lock-in infrared thermography technique were found to be in agreement with measurements obtained by the conventional S-N curve method.