Shape-Memory Actuator: Cyclic Fatigue & Stroke Degradation

A NiTi shape-memory-alloy wire, coiled into a compact actuator spring, lifts a weight every time it is resistively heated through its austenite transformation and lowers it again as it cools back into martensite — the same working principle behind commercial "muscle wire" actuators, SMA valves and robotic grippers. This simulator drives that coil through real heat/cool cycles using the Liang–Rogers cosine phase-fraction model, then layers on a physically grounded functional-fatigue model: every cycle leaves behind a sliver of irrecoverable strain and a small upward shift in the transformation temperatures, both of which saturate exponentially with cycle count and accelerate under higher applied stress. Watch the coil's stroke visibly shrink and its color swing (blue martensite / orange austenite) become sluggish as the actuator "ages," with live readouts for cycle count, recoverable stroke and transformation-temperature drift, and a fast-forward control to see hundreds of cycles of degradation at once.