Superelasticity

Stress-induced martensitic transformation — recoverable strains up to 8%

σ: 0 MPa | ε: 0.000 | ΔK: 0 | Phase: Austenite | Energy: 0 J/m³

σ_s (fwd plateau, MPa) 400

Hysteresis Width (MPa) 100

Recovery Strain ε_r 0.060

E_aus (GPa) 60

Superelasticity occurs when an SMA is loaded above Af at constant temperature. Stress-induced martensite (SIM) forms on the upper plateau and reverts on unloading (lower plateau). The hysteresis loop area = energy dissipated per cycle (good for vibration damping). Compared to conventional elasticity: superelastic strains are 10–50× larger. Superelastic NiTi is used in stents, eyeglass frames, orthodontic wires, and robotic actuators.