Extended thermoelastic stress analysis applied to carbon steel and CFRP

Thermoelastic Stress Analysis (TSA) by means of radiometric full field measurements has been primarily developed over 20 years ago. Although the underlying physics concerning the linear thermal response with respect to the loading as well as dissipative and nonlinear effects have been extensively studied in the past the potential of applications in the field of non destructive testing does not seem to be exhausted, yet. As an extension of the classic thermoelastic analysis the use of second harmonic temperature amplitudes for spatially resolved damage detection due to cyclic plasticity in ferritic low-alloy carbon steel is demonstrated. Temperature variations of several mK are found to be useful as a fatigue damage indicator. Furthermore the application to partially delaminated CFRP coupons under cyclic peeling load reveals that the classic thermoelastic measurement is able to visualise the locally stressed woven fibre ply. In contrast, the evaluation of the spatial temperature response at the double loading frequency clearly allows to detect the delamination front of homogeneous coupons whereas the dominating bending stress distribution is efficiently suppressed.