Shape Memory Alloy Torsion Tube Experiment

 

 

Part A.

 

Introduction

 

Brief introduction on SMA materials. This information may also be presented on the CRCD website.

 

 

Apparatus

 

The SMA Tube is held in place by a torsion test frame.  The frame is designed to where a specimen is constrained at one end where there is a Transducer Techniques TRT-500 Torque cell. The other end of the specimen is free to rotate. The rotation is measured by a rotational potentiometer near the free end. The specimen is heated by heating elements placed around the tube. Thermocouples are arrayed over the inner and outer surface of the tube in order to measure the temperature at these locations. Temperature, load, and rotation values are collected from the experiment approximately once a second.

 

The computer uses the temperatures to establish a temperature profile throughout the specimen and to help control the heating elements. The temperatures at multiple locations are collected and analyzed to calculate the average temperature at five evenly distributed points along the length of the specimen.

 

The load applied to the tube is measurered through the load cell. The strain of the specimen is measure red using the potentiometer (a variable resistor with a rotating slider). The control program for this experiment then calculates the stress ands strain the tube experiences. These values and the various temperatures are output to the data file torsiondata.txt for later analysis.


 

 

Part B.

 

Initial Calculations

 

 

An SMA tube has been heated from 20 degrees Celsius to 100 degrees Celsius, to where it is in its austenite phase. The tube has an outer radius of 0.437 cm and an inner radius of 0.279 cm. A torque of 0.366 kg*cm has been applied to the right side of the tube while the left side has been fixed. The tube is 5 cm long. Calculate the twist at x = 5 cm. Calculate the shear strain for the SMA tube. Calculate the max shear stress.

 r = avg. radius

J=(p/32)*(Do4- Di4)

 

Twist (Rotation)            ______________

Shear Strain                  ______________

Shear Stress                 ______________

 

 

Now the same tube has been cooled to 20 degrees Celsius where it is in its martensite phase. Calculate the twist at x = 5 cm. Calculate the shear strain for the SMA tube. Calculate the max shear stress.

 

Twist (Rotation)            ______________

Shear Strain                  ______________

Shear Stress                 ______________

 

Sketch Strain vs. Temperature for both the austenite and the martensite phases of the material.

 

Part C.

 

Setup

 

Write the steps necessary for the students to begin the experiment. Have students open computer data file and the computer data acquisition program.

 

Data Acquisition

 

  1. Begin video/program. Note the initial strain and temperature of the torque tube.
  2. At conclusion of experiment print the strain versus temperature graph.

 

 

Part D.

 

Development of SMA Strain Equation

 

 

  1. Based on your initial calculations from Part B label the austenite and martensite phases on the Strain vs. Temperature Graph from the above experiment.

 

  1. Label the four transition temperature points.

 

  1. Simplify this graph by using straight lines to connect the transition temperature points. Sketch the linearized graph. 

 

  1. Determine the equation for the transition region between the austenite and martensite phase for cooling from the linearized graph. Also determine a similar equation for heating.

 

  1. Develop a piecewise linear strain equation as a function of temperature to represent the data from the SMA torque tube experiment for both heating and cooling. (Hint: There are six regions of interest.)

 

 

 

 

 

Part E.

Conclusions

 

  1. Explain the rotation of the shape memory alloy tube throughout this experiment. Why does the tube display this behavior? 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  1. Comparing the equations from Part B with the equations you derived in Part D. What term represents the Shape Memory Effect?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Properties of SMA Tube

 

      

Material Property

Austenite

Martensite

Thermal conductivity coefficient 

 
0.18 W/cm * deg C

 

0.086 W/cm * deg C

Young’s Modulus*

83 GPa

35 GPa

Poisson’s Ratio

0.33

0.33

Coefficient of Thermal Expansion

11.0E-6/deg. C

6.6E-6/deg. C

Density

6.45 g/cu.cm

6.45 g/cu.cm

Shear Modulus

29 GPa

11 GPa

 

* Highly nonlinear with temperature (this will be ignored for this assignment)

Note these properties are for NiTi, I need to find the properties for K-NiTi10Cu