lab 5 - February 13, 2007 To: Professor Li Mechanics of...

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February 13, 2007 To: Professor Li Mechanics of Material Instructor From: Patrick McAdams (AA) Student Test Engineer Re: Super-Elastic Behavior of Nickel Titanium Alloy Wire Summary: In this laboratory, Nickel-Titanium (NiTi) wire was used in a tension test to observe the shape memory effect demonstrated by this material. From the values measured, a stress vs. strain curve was made. Within this curve, there was an initial linear relationship between stress and strain. This relationship is the elastic modulus which was found to be 21.15 GPa which is a 24.7% error as compared to published values. This error can be attributed to noise in the data. After the initial elastic behavior, there was a stress plateau. The specimen followed a different stress vs. strain curve as it was unloaded. After unloading, the NiTi was the same length as before loading. This is explained through a phase change in the NiTi from austenite to martensite during loading. Introduction: NiTi is a super-elastic or pseudo-elastic alloy. Alloys such as NiTi that exhibit super-elasticity are a part of a group of metals known as shape memory alloys (SMA’s). These metals are unique in that they have the ability to return to the initial shape after deformation. This property is possible to a phase transformation between austenite and martensite. This phase change is explained in more detail in the Discussion section). The reason this unique property is important is because it has many engineering applications. This material is used in actuators to help control vibrations in buildings and other structures, which helps minimize earthquake damage. NiTi is also used in eyeglass frames to minimize deformation.
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This note was uploaded on 04/08/2008 for the course ME 354 taught by Professor Jiangyuli during the Winter '07 term at University of Washington.

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lab 5 - February 13, 2007 To: Professor Li Mechanics of...

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