Nitinol Wire Testing

Nitinol (or NITI) is a nickel titanium alloy often used in the medical device industry. Nitinol can be produces in sheet, tube, and wire form and is popular due to shape memory and superelasticity properties. These properties make Nitinol ideal for applications including stents, blood filters, orthodontic arches, spinal implants, surgical instruments, dental instruments, shaped helical forms, endoscopic guide tubes, and distal protection devices. Although the properties of Nitinol are very useful they come at a price; it is difficult and expensive to produce Nitinol and it is also difficult to manufacture products out of Nitinol. For this reason, it is critical to test Nitinol to ensure high performance and integrity of Nitinol products. There are a number of ASTM standards that address standards and testing Nitinol. ASTM F2004-05 Standard Test Method for Determination of Transformation Temperature of Nickel-Titanium Shape Memory Alloys by Thermal Analysis ASTM F2005 Standard Terminology for Nickel-Titanium Shape Memory Alloys ASTM F2063 Standard Specification for Wrought Nickel-Titanium Shape Memory Alloys for Medical Devices and Surgical Implants ASTM F 2082 Standard Test Method for Determination of Transformation Temperature of Nickel-Titanium Shape Memory Alloys by Bend and Free Recovery ASTM F2516 Standard Test Method for Tension Testing of Nickel-Titanium Superelastic Materials ASTM F 2516 is pull to failure test that provides information of strength, ductility, and superelasticity of Nitinol wire. This tensile test specifically investigates the upper plateau strength, lower plateau strength, residual elongation, tensile strength, and elongation. There are a number of challenges associated with tension tests of Nitinol wire. One of these is gripping the wire without problems such as slippage, or stress fractures occurring. Horn style pneumatic grips from TestResources are an excellent way to grip wire without causing damage. The load on the wire is distributed around a uniquely shaped horn and then held firmly by a pneumatic grip. Links to these grips can be found below. Nitinol wire is a superelastic material that has an elastic strain up 30 times that of most metals. This can create problems for extensometers during tensile tests. To resolve this problem TestResource advises the use of an Non Contacting Laser Extensometer. More information can be found in the link below. TestResources has all the necessary Nitinol testing equipment for tensile testing according to ASTM 2516. Call or Email our dedicated applications engineers with an questions about tensile testing Nitinol wire. References "Nitinol Specification Guidelines." Nitinol Property Specifications and Guidelines. Web. 05 June 2012. http://jmmedical.com/resources/120/Nitinol-Specification-Guidelines.html. "Nickel Titanium." Wikipedia. Wikimedia Foundation, 06 Jan. 2012. Web. 05 June 2012. http://en.wikipedia.org/wiki/Nickel_titanium. Nitinol Wire. Digital Image. Biomedical Textiles in Implantable Medical Devices. Design News, 8/30/2010. Web. 6/12/2012. http://www.designnews.com/document.asp?doc_id=229324&dfpPParams=ind_183,aid_229324&dfpLayout=article ASTM has many standards related to Nitinol wire because of its many uses in the medical and dental industries. ASTM F2516 is particularly useful for determining mechanical properties of nitinol wire. TestResources universal material testing machines are effectively used for determining the strength of wire. TestResources test machines meet the requirements specified in many standard test procedures for constant-rate-of-extension and constant-rate-of-load machines. This allows the machines to be programmed to perform many unique testing procedures. Load cells are fitted to specific load applications to ensure the highest resolution of tests.

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