Fatigue tests were carried out on samples of titanium VT1−0 and zirconium alloy Zr−1 wt % Nb in the ultrafine-grained, fine-grained and coarse-grained states in a gigacycle fatigue regime. It was found that the formation of an ultrafine-grained structure led to an increase in the fatigue limit in the gigacyclic region (10 9 cycles) by 1.3 times for titanium and 1.7 times for zirconium alloy when compared to the fine-grained and coarse-grained states. An evolution of the temperature field for titanium and zirconium alloy samples in various structural states in the process of cyclic loading was studied by the method of infrared thermography. It was shown that the process of cyclic deformation in all types of structural states was accompanied by an initiation and expansion of a heat source in a local volume of samples which has a significant impact on the fatigue strength. The increment of the maximum temperature on the surface of ultrafine-grained samples of titanium VT1−0 and zirconium alloy Zr−1 wt % Nb is significantly lower than that for the fine-grained and coarse-grained states. This fact indicates a qualitative change in the mechanism of energy dissipation which is associated with characteristic features of the ultrafine-grained state. When comparing the dynamics of thermal fields for the titanium and zirconium alloy samples in coarse-grained, fine-grained and ultrafine-grained states, it was found that the energy dissipation zone covered a considerable volume of the sample in the process of fatigue tests in case of ultrafine-grained state, whereas in case of coarse-grained and fine-grained states the growth of thermal energy was localized in the gauge area of the sample.
This work is devoted to the comparative analysis of three techniques for measurement of energy dissipation in metals under fatigue crack propagation: use of original contact heat flux sensor, post-processing of infrared thermography data and lock-in thermography. Contact heat flux sensors allow real-time recording of heat source values. Non-contact temperature measurements by infrared thermography techniques make it possible to calculate the heat source field on the specimen surface by solving a heat conductivity equation. Lock-in thermography is a well-established technique for measuring energy dissipation under cyclic loading conditions based on the analysis of the second harmonic amplitude of the thermal signal. This paper describes the results of the experiments with V-notched flat specimens made of stainless steel AISI 304 which were subjected to cyclic loading. It was shown that the values of energy dissipation estimated by different techniques are in good qualitative agreement. Contact and noncontact measurements can be used for investigation of energy dissipation either separately or in combination. Based on the measurements, the power dependence of fatigue crack growth rate on dissipated heat near the crack tip can be obtained.
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