Shape-Memory Actuator: Hysteresis Loop & Stroke Decay (2D)

A NiTi shape-memory-alloy wire actuator is driven through repeated heat/cool cycles using the Liang–Rogers cosine phase-fraction model, exactly as in the 3D coil simulator — but here the mechanism is shown as two live graphs instead of a physical spring. The top panel is a martensite-fraction-versus-temperature phase diagram: the working point traces a closed hysteresis loop each cycle, and that loop visibly widens and shifts to higher temperature as functional fatigue accumulates. The bottom panel plots the recoverable actuation stroke against cycle count, tracing out the same exponential-saturation decay that governs the loop drift. Sliders for applied load, maximum heating temperature and cycle rate, plus play/pause, reset and a 200-cycle fast-forward, let you explore how stress accelerates the saturation and how a fatigued actuator needs a hotter pulse to fully switch phase.