Shape Memory Alloy Thermomechanical Testing ME356 Spring April 2016

Objective

Test setup 1.When you arrive at the Instron room (MEB 127), the Instron should be set up with the proper grips and heating and cooling elements set up. Otherwise wait for the TA to set it up for you. Before starting make sure the cooling air valve is closed. Have the TA turn on compressed air. Environmental chamber (cooling system) Cooling line Insulating housing Instron Variac Temp controller Insulating chamber Air supply line Valve Regulator (behind here) Cooling line

2.Expose the grips by sliding the chamber towards the back of the Instron. Jog the grips so that the center-to-center distance of the screws is 100mm. This is your gauge length of the SMA specimen. 3.Secure the SMA wire in the grips by screwing them in place (don’t lose the screws please!!). Make sure the wire is held taut so there is no slack. 4.Jog the grips down a bit so there is slack in the wire (it will contract during heating). 5.Reposition and close the chamber. Make sure nothing is touching the grips, this could snag and affect your load data!

Test procedure Once the TA approves the setup, you can start testing. 1.Turn on temperature controller and heater (variac). Set the controller to 140 °C. Increase the heater voltage to ~50V to begin heating. (Never exceed 55V!) 2.While the chamber is heating, change the load profile in the Instron software (Bluehill 3) to 50 MPa. The TA can help you do this. 3.Once the temperature reaches 140 °C, balance the load cell. Then remove the slack from the wire until the load is ~1N. Reset extension. Variac (heater control) Temperature controller

4.Start the program. This will ramp up the load until 50 MPa is reached, then hold it there until the program is terminated by the user. 5.We will now record extension vs. temperature data as the specimen cools. Turn off the heater, and record the temperature and extension data (by hand!). You should record data every 2 degrees or so, but more often as the extension is changing rapidly! It may help to have more than one person recording data. In general, the slower the temperature change, the better the data will be. 6.As the temperature approaches room temperature, the cooling rate will slow down. Turn on the cooling air slowly to avoid an abrupt change. Modulate the airflow to maintain a constant rate. Continue cooling and recording data until -10 °C. 7.When the temperature reaches -10 °C, begin increasing the temperature by closing the cooling valve. As the temperature rise increases, you may turn on and slowly ramp up the heater voltage, until you return to 140 °C. At this point, the test is done. You should have ~ data points. 8.Terminate the Instron program. Remove the specimen and repeat for 100 and 150 MPa.

Post-test Turn off the heater, temperature controller, and air pressure. Remove wire from grips and generally clean up. Before you leave (!) plot your data, and determine the transition temperatures. Do this before you leave, because if you don’t realize your data is bad, you may be out of luck 