Lock-in thermography and fatigue limit of metals

Thermography was performed on stainless steel 316L and aluminium alloy 7010 samples as they were submitted to a sinusoidal mechanical stress (traction/compression). For each stress amplitude value the temperature data were recorded in 5 s. A specific signal demodulation procedure was used to extract the first two Fourier components and the mean temperature rise. From their particular dependence on the stress amplitude, characteristic stress values could be derived. In some instances, these values are very close to the fatigue limit of the considered material.