(a) Unloading part of thirteen load-depth (-) plots at different loading rates at an ultralow peak load of 1 N, (b) exploded view of Figure 3(a) showing the presence of multiple micro-pop-in and micro-pop-out events at typical 4 selected unloading rates (10−3, 10−2, 10−1, 100 N·s−1), (c) exploded view of Figure 3(b) showing the variation of serrations with the unloading rates, and (d) exploded view of Figure 3(c) showing clearly the occurrences of more number of serrations at lower unloading rates and lesser number of serrations at higher unloading rates.
