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. Geometry: Nitinol Testing requires a thin strip of the material to be pulled in tension at a specified rate. The F procedure involves tensioning the sample initially and then bringing it back down.
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Although nitinol is used in industries ranging from robotics to clothing, it is in the medical field where the material really shines. Medical applications of nitinol include: vascular stents, eyeglasses, orthodontics, prosthetics, surgical applications, and much more. ASTM F is a testing standard designed to measure the plateau strength, residual elongation, elongation and tensile strength of nickel-titanium super elastic metals.
This post is intended to help you understand the basic test procedure and equipment needed to test your nitinol products with certainty. When you are ready to test your product or material to this standard, please refer to and follow the steps in the official ASTM specification. Procedure: Before moving forward with the test, please read and setup your testing setup in accordance with ASTM E8 standard tension testing of metallic materials.
Make sure you are testing in the temperature range indicated in the specification about room temperature. Secure the specimen in fixtures, making sure there is no pre applied load.
ASTM E8 recommends wedge grips like the ones pictured below for testing thin wire a common form of nitinol in medical applications. If you are using an extensometer, be careful not to bend the sample. Depending on the diameter of your specimen, begin moving the crosshead at the specified rate. Continue pulling the specimen until you reach the specified strain percentage. Reverse the direction of the crosshead until the load reaches below the limit indicated in the specification.
Pull the specimen again, this time until break. Residual elongation: difference between strain at a specified load during loading and unloading. Elongation: displacement right before sample break.
Simulated MTESTQuattro graph output Equipment Recommended: A tensile testing system capable of moving the crosshead at the specified rates and apply enough load to bring the specimen to failure. The testing machine should have enough stroke to satisfy the high elongation properties of nitinol. A pair of grips to securely hold your sample. ASTM E8 recommends wedge grips for thin metallic wire sample.
We offer a full line of grips and will custom design grips to hold any type of material. If needed, ADMET offers a full line of long travel and clip on extensometers to help you more accurately measure elongation.
ASTM F2516 Tension Testing of Nitinol How to Guide