Comparison of Self-Heating Behavior Between Continuous and Interrupted Control Modes

In gigacyclic fatigue testing, reaching 10⁹ cycles within a reasonable duration is challenging, leading to the use of ultrasonic fatigue machines operating at 20 kHz (UFT). However, the high testing frequency causes significant temperature rises, potentially enhancing microplasticity and leading to premature failure. This study compares two control modes in gigacyclic fatigue: continuous and interrupted (pulse-pause) during self-heating tests on UFT. Two materials with distinct thermal properties, steel 42CrMo4 and aluminum alloy AA2024-T351, were tested. The temperature evolution was measured using an infrared camera. Then, a local expression of the heat equation is used to estimate the intrinsic dissipation, denoted as $d_1$. Results showed that both modes led to temperature increases with higher displacement, but pulse-pause caused a smaller temperature rise. Reducing the pulse time relative to the pause time decreased temperature variation. For 42CrMo4 steel, self-heating was more pronounced than for AA2024-T351, and the $d_1$ value increased with displacement amplitude.