Shape Memory Alloy Wire Bender (2D)

Temperature

Wire temperature 22 °C

Deform The Wire

Cold — martensite phase. Drag the wire or press Bend.

Live Readout

Phase

Martensite

Shape recovery

Heating range As–Af

45–65 °C

Cooling range Ms–Mf

35–20 °C

How it works

Nitinol (NiTi) has two crystal-lattice phases. Below its martensite-finish temperature (Mf) the lattice is a low-symmetry, "twinned" structure that slides easily under stress — the wire feels soft and holds whatever shape you bend it into. Heating past the austenite-start temperature (As) triggers a diffusionless lattice rearrangement into a rigid, high-symmetry cubic structure; by the austenite-finish temperature (Af) every atom has snapped into the trained lattice, and the wire has fully sprung back to its original "memorized" shape.

The heating and cooling curves don't retrace each other — this is thermal hysteresis. Cooling back down doesn't undo the transformation until temperature drops well below Af, and full martensite only returns once the wire cools under Mf. That gap between the heating branch (As–Af) and the cooling branch (Mf–Ms) is the hysteresis loop plotted below, and it's the same effect that makes shape-memory stents, eyeglass frames and actuators hold a stable state at body or room temperature without drifting back.

Drag any point on the wire while it's below Ms (35 °C) to bend it — deforming only works in the soft martensite phase.
Raise the temperature slider to drive the martensite→austenite transformation and watch the wire recover.
Cool back down and the austenite→martensite branch traces a different path on the graph — the hysteresis loop.

Drag the wire to bend it (cold only) · slide temperature to heat/cool

Austenite fraction vs. temperature — hysteresis loop