In Mechanical—— Pipe Coupling




The SMA coupling has an internal diameter smaller than the pipe’s outer diameter Cool the coupling using liquid nitrogen so it transforms to martensite phase When in the martensitic phase the coupling can be stretched to a larger ID than the pipe and easily fitted over the pipe. The join can then be heated to return to its original shape and thus exert a large pressure on the pipe.
Shape Memory Alloy
(SMA)
Wu Huixing 2013.4.28
Outline
• • • • Introduction Mechanism Applications Problems
1.Introduction
shape memory effect（SME）
Unbelievable！
In everday life——Thermostatic mixing valve
High temperature: SMA spring (A) is harder than bias spring
Low temperature: SMA spring (M) is softer than bias spring
Transformation without stress
Transformation with stress
load
unload heated
•Applying load detwin the martensite •releasing of the load the material remains deformed •Temperature above A0f reverse phase transformation
Good SME and formability, biocompatible, etc. Expensive?
(Cu-Zn-Al, Cu-Al-Ni)
Cheaper, etc. bad formability and mechanical properties?
(Fe-Mn-Si)
Good mechanical properties, formability etc. Corrosion?
Shape memory ceramics
Shape memory polymers
2.Mechanism——Martensitic transformation
Solid States
① Austenite



T>Tt (High T) Hard, rigid Inelastic Simple FCC structure
1951, SME was found in Au-Cd alloy 1963, SME was found in Ti-Ni alloy Active research
Ti-Ni based alloys
Cu-based alloys
Fe-based alloys
(based on TiNi alloy)
SME —— After plastic deformation, when heated to a certain T , the material may return to original shape SMA —— An alloy having a shape memory effect
Development
shape recovery
3.Applications
In Aerospace——Aerial
“That’s one small step for (a) man, one giant leap for mankind”
——Neil Armstrong
Aircraft Wings
• Normally aircraft use large hydraulic systems which are expensive and need a lot of maintenance.
• Fatigue life
TiNi ——105 ~ 107 CuZnAl ——102 ~ 103
• Self-cost
Relatively expensive to manufacture compared to other metals such as steel and aluminium
SMA Wings
• Aircraft with SMA wings would be much more compact and efficient • SMA wires are placed through the wing which contract when heated and expand when cooled • heated by an electrical current, when it is switched off ,they are cooled by the surrounding air
normal （ budding flower ）
Heated （in bloom）
cooled
reheated
SME&SMA
elastic region load load
Stress(σ )
permanent deformation
unload heat
unload
Strain( ε )
Normal Shape memory alloy
Memory glasses frame
In medical - Teeth
4.Problems
• Sensitive critical transformation temperature:
Ti-50at.%Ni——Ms： 60 ℃ Ti-51at.%Ni——Ms：-30 ℃ As：78 ℃ As：-12℃
Austenite
② Martensite


T<Tt (Low T) Soft, flexible Elastic Complex structure
Martensite
Twinned Martensite
Detwinned Martensite
M0s——martensitic start temperature M0f——martensitic finish temperature A0s—— austenite start temperature A0f—— austenite finish temperature