Standard Test Method for Tension Testing of Nickel-Titanium Superelastic Materials
ASTM F2516 covers the tension testing of Nitinol which is a material used to make stents in the biomedical industry. These stents are used to hold open collapsed veins or arteries to allow for normal bloodflow. Nitinol, also known as Nickel-Titanium, is a highly elastic metal that also has shape memory. These unique properties make it very useful in a host of other applications including kidney stone retrieval baskets, eye glass frames, and micro antennas.
This article will provide a brief overview of the test as well as recommend the perfect grip for a successful tensile test. For more information on the particulars of this test procedure, you must refer to the official ASTM records.
Nitinol Testing requires a thin strip of the material to be pulled in tension at a specified rate. The F2516 procedure involves tensioning the sample initially and then bringing it back down. After that initial flexion the specimen is then pulled again until failure. The accompanying video only shows the final portion of the test.
There are several types of grips that may be used to test Nitinol. Mechanical action wedge grips are the most common fixture, however other types of grips may be used as well. In the video we demonstrate a special type of tension fixture that is most commonly used for testing wire. This grip spreads the stress out over a larger area which ensures that the sample will rupture somewhere in the middle, away from the grip face. Depending on the exact mix of Nickel-Titanium, a fixture like this may need to be used.
There are a couple of unique analyses that can be captured using this test. These include the lower plateau strength, upper pleateau strength, and the residual elongation.