Frequency dependent deformation reversibility during cyclic loading

High-frequency testing (HFT) is useful for accelerated fatigue testing of conventional materials that typically serve under low-frequency loading conditions, as well as for the assessment of the robustness of microelectromechanical systems which typically experience high-frequency service conditions. Using discrete dislocation dynamics, we attempt to elucidate the effect of loading frequency on the reversibility of cyclic deformation. We demonstrate that the HFT induces a higher fraction of reversible cyclic deformation because of a larger portion of elastic/anelastic deformation due to limited dislocation mobility, and a higher degree of reversibility in plastic deformation owing to the less occurrence of cross-slip. <b>IMPACT STATEMENT</b> Dislocation-based frequency effects on high-cycle deformation reversibility in metals are elucidated. Hysteresis energy is shown to dissipate even under ideal, damage-free conditions, contrary to popular assumptions of energy-based fatigue models.

高频测试（High-frequency testing, HFT）可用于对通常在低频载荷工况下服役的常规材料开展加速疲劳试验，同时也可用于评估通常处于高频服役工况的微机电系统（microelectromechanical systems）的鲁棒性。本研究采用离散位错动力学（discrete dislocation dynamics），旨在阐明加载频率对循环变形可逆性的影响。研究结果表明，由于位错迁移受限，弹性/滞弹性（elastic/anelastic）变形占比更高，因此高频测试会诱导出更高比例的可逆循环变形；同时由于交滑移（cross-slip）的发生频次更低，塑性变形的可逆性程度也更高。<b>影响声明（IMPACT STATEMENT）</b> 本研究阐明了基于位错的频率效应对金属高周变形可逆性的影响。研究发现，即便在理想无损伤工况下，滞后能量仍会发生耗散，这与当前基于能量的疲劳模型的主流假设相悖。