C1.

Project title: Pseudoelastic properties and transformation characteristics of NiTi shape memory alloys

NiTi (Nitinol) Shape Memory Alloy (SMA) is now having many medical and engineering applications. Besides the shape memory phenomenon, the excellent pseudoelastic (PE) property of SMA has attracted even more engineers to use SMAs. The transformation properties of SMA are usually characterized by Differential Scanning Calorimetry (DSC) thermal analysis or electrical resistance methods. However, the transformation temperature thus determined usually cannot give accurate prediction of the pseudoelastic properties and actuation behavior. Hence, more mechanical tests (e.g. tensile test and bending test at different temperatures) are required to qualify the alloys for specific applications. The product development cycle becomes lengthy because SMA users need to do many mechanicals tests before they can assure that they are using the SMA wisely and correctly 

DSC and electrical analyses can only determine the thermoelastic properties of SMA because the tests are performed with no imposed stress. In real life application, SMAs are used under stresses; therefore, it is necessary to find a convenient thermal-mechanical analysis to replace the DSC analysis. Dynamic Mechanical Analysis (DMA) was found a good method. Yet, there is sufficient understanding on DMA-SMA analysis. There is also no authentic correlation between the DSC and DMA analyses. The aim of this project is to establish a “user friendly” interpretation of the DMA analysis results, thus making the use of SMA easier.

Supervisor: Dr Jonathan C Y Chung (appchung@cityu.edu.hk)

Suitable for: M.Phil. and Ph.D.