A development of a method for estimation of the endurance limit of the material using infrared thermography data

The experimental study of energy dissipation processes in titanium alloy Ti-6A1-4V under the quasi-static tension was carried out based on infrared thermography technique. The infrared scanning technique initially developed as method of nondestructive testing is based on measuring the intensity of electromagnetic radiation of material in infrared wavelength. Infrared thermography allows one to detect temperature changes on the surface of the sample, to calculate the power dissipation energy of internal sources and to develop a methodology for assessing the critical state transition of the material. In this paper, it has been shown that the deviation from the linear temperature evolution on the applied stress, corresponding to the classical theory of thermoelasticity, can be observed for stress significantly below the yield stress of the material. Based on obtained data the technique of determining the threshold of energy dissipation for quasi-static deformation was proposed and connection between this tension and the fatigue limit of the material was suggested. Fatigue limit calculated according to the infrared thermography for quasi-static loading of the samples was compared with the reference value of the fatigue limit obtained from cyclic tests. It has been shown with sufficient accuracy that the proposed method could be used to estimate the fatigue limit of the material by the temperature field of the sample surface in quasi-static tests. The analysis of the experimental data allows us to conclude that the temperature measurement accuracy achieved at the present time allows one to register the heat dissipation caused by the microplasticity processes and, as a consequence, to develop a new method for forecast the material behaviour under long (cyclic) loading.