Shape-Memory Alloys: Transformation as a Function
Explain superelasticity and shape memory through reversible martensitic transformation.
Two related effects
Shape-memory recovery occurs after heating a deformed martensite. Superelasticity occurs when stress induces martensite and unloading reverses it.
Transformation temperatures
Composition and heat treatment set the characteristic transformation temperatures and therefore the operating window.
Functional fatigue
Repeated transformation can shift response, accumulate residual strain or nucleate cracks even when conventional stress is modest.
Design considerations
Constraint, loading path, temperature uniformity, joining and surface quality influence actuator or medical-device performance.
Engineering takeaway
Treat the phase transformation as the working mechanism and qualify stability over the required number of cycles.