Effect of variation in applied force on transformation temperature of NiTi shape memory alloy

1. Prepared By:
Shashin Vyas

2.  Abstract
 Introduction
 Experiment Setup
 Results And Discussion
 Conclusion
 References

3.  Phase Transformation Temperature is one of the
most important parameters for the Shape Memory
Alloys (SMAs).
 Because of offering large deformations and forces,
SMAs are promising materials for actuation in
space applications.
 For determining transformation temperatures of
the SMA Nitinol, a novel method is carried out
which uses dead weight.

4.  The wire is heated up to approximately 80 degree
Celsius with direct current. And then the
temperature is decreased to cool down the wire.
 All the temperatures are obtained and recorded
with variation in applied force.

5.  Shape memory alloys are metal alloys that remember
their original shape.
 If deformed, they recover their original shape upon
heating.
 One type of shape memory alloy is Ni-Ti (Nitinol).
 It has two stable phases, the high temperature Austenite
phase and the low temperature martensitic phase.
 It is quite fascinating field of research mainly in
aviation technology and Medial Science.

6.  For Designing and Optimizing The Application of
SMAs it’s required to understand its behavior.
 The Phase Temperature for the Shape Memory Alloys
Such as the Austenite Start (As), Austenite finish (Af),
Martensite start (Ms), Martensite finish (Mf) are the
Basic Temperatures that should be determined before
designing the system.
 In This Experiment a Linear Variable Displacement
Transducer (LVDT) consisting of a stack of masses
actuated vertically by an SMA wire is used.

7.  The Experimental setup contains force sensors
displacement measurement and thermocouple to
determine the phase transformation temperatures.
 The Wire was heated up with the direct current and the
testing was done with different value of dead-weight
load to the wire.

9.  The Nitinol wire of 0.5mm diameter and length
351mm was used for the study.

10.  The Setup used for the experiment are:
DC regulated power supply, a clamping device for
SMA wire, a type J-thermocouple for temperature
measurement, multimeter and linear variable
displacement transducer (LVDT) As Shown in above
figure.
 Through Physical Loading of dead weights from 0.5kg
to 3.15kg In steps, Stress is induced in the SMA wire.
And displacement in initial condition is set to zero.

11. The Experiment is divided into two parts:
1] Heating Cycle:
The wire is heated and as the temperature increases, it
starts to contract. The temperature is increases to the
maximum level of 75 degree centigrade.
2] Cooling Cycle:
The DC Power supply is turned off and the wire is
allowed to cool. The data of change in temperature and
displacement were taken as the wire returns to its
original condition.

12.  In The Fig. 2, The Strain V/S Temperature plot for a
particular load is given.

17.  Here, Austenite Start (As), Austenite finish (Af)
Temperature will be obtained from the heating process
curve while Martensite start (Ms), Martensite finish
(Mf) Temperature from the cooling process curve.

19.  This method is one of the simple methods for
Determining Phase transformation temperatures for the
shape memory alloys.
 It can be observed that For NiTi wire, Austenite start
and finish temperatures are 38.3 and 46.6 degree
Celsius. While martensite start and finish temperatures
are 29.9 and 27.9 degree Celsius respectively.
 The phase transformation temperatures are affected by
the applied force. And it increases with increase in
applied force.

20.  Mohammad H Elahinia and Mehdi Ahmadian,
2005, an enhanced SMA phenomenological
model:II. The experimental study, smart meter.
Struct 14, 1309-1319.
 J. Rena and, K.M. Liewa, “Meshfree modelling and
characterisation of thermomechanical behavior of
NiTi alloys,” Engineering Analysis with Boundary
Elements 29 (2005) 29–40.

21. Any Query ?

22. THANK YOU 