Lock-in Infrared Thermography for Fatigue Limit Estimation in Ti-6Al-4V Alloy

Lock-in infrared thermography was used to estimate the fatigue limit for Ti-6Al-4V alloy at room temperature. The method detected infrared emitted from specimen during cyclic loading, i.e., temperature change related to frequency (f) of the loading. The temperature change contained reversible component and irreversible component, which related to thermos-elastic effect and plastic deformation, respectively. The latter component was divided from the former one by lock-in analysis to estimate fatigue limit. Estimated fatigue limits corresponded to those obtained from conventional fatigue tests at several stress ratios. A new assessment line was identified as sigma(a) = sigma(w)(1 - sigma(m)/sigma(B))(1/n), where sigma(a) represents the stress amplitude, sigma(w) signifies the fatigue limit, sigma(m) denotes mean stress, sigma(B) expresses tensile strength, and the n exponent for the alloy is about 2.3. The non-failure region of the new diagram was smaller than that of the modified Goodman diagram because of a reduced fatigue limit at near-zero stress ratios in the titanium alloy.

Automated summary

Lock-in infrared thermography was employed to estimate the fatigue limit of Ti-6Al-4V alloy at room temperature by detecting the infrared emitted during cyclic loading. The method separated reversible and irreversible temperature change components to estimate the fatigue limit, which corresponded to results from conventional fatigue tests. A new assessment line was identified in the study, showing a smaller non-failure region compared to the modified Goodman diagram due to the titanium alloy's reduced fatigue limit at near-zero stress ratios.