In the conventional lock-in infrared thermography for thermoelastic stress measurement, thermoelastic temperature change is correlated with external reference loading signal. The present authors developed a self-reference lock-in thermography which enabled us to conduct thermoelastic temperature measurement without external reference signal. In the self-reference lock-in thermography, reference signal is constructed from a part of the same sequential thermal image data. Temperature change in a region of interest was correlated with that in a remote area for reference signal construction. Proposed self-reference lock-in thermography was applied for crack identification based on the detection of significant thermoelastic temperature change due to the stress singularity in.the vicinity of crack tips. In this study, the feasibility of the proposed technique was demonstrated for the fatigue crack detection and measurement in actual steel bridges.
