Failure diagnosis & reliability assessment of NiTi shape memory alloy spring for micro - Actuators

Shape memory effect reveals the recovery of original shape from deformed shape with residual strain through thermal cycling. This type of super-elastic behavior found in shape memory alloys are generally used as actuators in robotics, control and embedded systems. In the present study, first an experimental setup was developed to perform life tests of Nickel-Titanium Shape Memory Alloy (NiTi-SMA) springs. Laser displacement sensor and J-type thermocouple was used to measure the displacement and temperature respectively. Data was collected through the Data Acquisition (DAQ) device. Acquired data is then used for failure diagnosis and reliability assessment of NiTi-SMA springs. Accelerated life testing models are developed to estimate the parameters of the life distributions. It was observed that with the subsequent cycles, SMA spring starts losing its inherent property of being an elastic object, and thus a decrease in displacement of it was observed with each cycle. Gradual loss of actuation property of the material under accelerated conditions was investigated in detail using Scanning Electron Microscopy (SEM) and Thermo Gravimetric Analysis (TGA).