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ASTM F2516
Nitinol Tension Testing

Standard Test Method for Tension Testing of Nickel-Titanium Superelastic Materials - PDF
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ASTM F2516 is the tension test for superelastic nickel-titanium (Nitinol) wire, tubing and strip used in stents, guidewires, orthodontic archwires and other medical devices. Superelastic Nitinol stretches several percent at a nearly flat stress as it changes from austenite to martensite, then returns as the load is removed. F2516 measures those loading and unloading plateaus with a load–unload–reload cycle, then pulls the specimen to failure.

F2516 Loading Protocol

  • Test at 22 ± 2 °C, so the material is in its superelastic range

  • Load in tension to 6% strain

  • Unload to a stress below 7 MPa

  • Reload and pull to failure

  • Use a slow, controlled strain rate set in the standard, so heat from the phase transformation does not distort the plateau stresses

Confirm the strain rates for each segment against your copy of F2516.

Results Reported

  • Upper plateau strength (UPS): stress at 3% strain during loading

  • Lower plateau strength (LPS): stress at 2.5% strain during unloading

  • Residual elongation (Elr): strain remaining after unloading to below 7 MPa

  • Ultimate tensile strength (UTS) and elongation at failure from the final pull

Worked Example

A 0.50 mm diameter wire has a cross-section of 0.196 mm². Force at 3% strain on loading is 98 N, so UPS = 98 ÷ 0.196 = 500 MPa. Force at 2.5% strain on unloading is 39 N, so LPS = 199 MPa. After unloading, 0.2% strain remains (Elr = 0.2%). The wire then breaks at 270 N, so UTS = 1,378 MPa.

Specimens and Equipment

  • Wire, tube or strip, tested full section; report diameter or wall thickness and the gauge length

  • Universal testing machine with a low-capacity load cell for fine wire and precise control of loading and unloading

  • pneumatic grips or wedge grips with smooth or lightly serrated faces; capstan or wire grips stop fine wire breaking at the jaw

  • Extensometer: strain must be measured on the specimen (clip-on, laser or video), because the plateaus are defined at fixed strains

  • Environmental chamber if testing at body temperature (37 °C) as well

Related Standards

  • ASTM F2063 – wrought nickel-titanium alloys for medical devices

  • ASTM F2004 and F2082 – transformation temperature (DSC and bend free recovery)

  • ASTM E8/E8M – tension testing of metals

  • ISO 25539 – vascular device testing

ASTM F2516 FAQ

What is the upper plateau strength in F2516?

The stress at 3% strain while the Nitinol is being loaded, during the austenite-to-martensite transformation.

What is the lower plateau strength?

The stress at 2.5% strain while the specimen is being unloaded from 6%, as it transforms back to austenite.

What is the F2516 loading cycle?

Load to 6% strain, unload to below 7 MPa, then reload and pull to failure, all at 22 ± 2 °C.

Why does F2516 need an extensometer?

The plateau strengths are read at fixed strains (3% and 2.5%), and crosshead travel includes grip slip and machine compliance, so strain must be measured directly on the specimen.

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