E3 AEROSPACE ENGINEERING RESEARCH

1

• E3 AEROSPACE ENGINEERING RESEARCH
• SHAPE MEMORY ALLOYS (SMAS)
• E3 Teacher Summer Research ProgramAerospace
  Engineering Texas A M UniversityBy Moses
  Z. Horton Ali A. Jafry

2
Introduction to Shape Memory Alloys.

• Shape Memory Alloys (SMAs) are a unique class of
  metal alloys that can recover apparent permanent
  strains when they are heated above a certain
  temperature.
• The SMAs have two stable phases - the
  high-temperature phase, called austenite and the
  low-temperature phase, called martensite. In
  addition, the martensite can be in one of two
  forms twinned and detwinned, as shown in
  Figure . A phase transformation which occurs
  between these two phases upon heating/cooling is
  the basis for the unique properties of the SMAs.
  The key effects of SMAs associated with the phase
  transformation are pseudoelasticity and shape
  memory effect.

3
Schematic of a stress-strain-temperature curve
showing the shape memory effect.
4

Temperature-induced phase transformation of an
SMA without mechanical loading.
5
Thermally-Induced Transformation with Applied
Mechanical Load
6
Temperature-induced phase transformation with
applied load.
7
SMA Stress Strain Temperature Phase Diagram.
8
Pseudoelasticity

• The pseudo elastic behavior of SMAs is associated
  with recovery of the transformation strain upon
  unloading. The super elastic behavior is observed
  during loading and unloading above A0S and is
  associated with stress-induced martensite and
  reversal to austenite upon unloading.

9
Pseudo elastic stress-strain diagram.
10
Schematic of a thermo mechanical loading path
demonstrating pseudo elastic behavior of SMAs.
11
(No Transcript)