Shape Memory AlloysSeth R. Hills

ECE5320 Mechatronics Assignment #1

Outline– Reference list– Links for more information– Major applications– Basic working principle illustrated– A typical sample configuration in application– Major specifications– Limitations– Selection Criteria– Cost information– Where to buy

References:

• http://www.cs.ualberta.ca/~database/MEMS/sma_mems/sma.html

• http://smart.tamu.edu/• http://www.abc.net.au/science/news/stories/s832

821.htm• Shape memory alloy micro-actuators for medical

applications; J. Peirs, D. Reynaerts, H. Van Brussel, K.U.Leuven - P.M.A. Celestijnenlaan 300B, 3001 Heverlee

To explore further check out these websites and articles:

• http://www-civ.eng.cam.ac.uk/dsl/sma/smasite.html• http://www.fz-juelich.de/iwv/iwv1/index.php?index=6

5• http://www.nims.go.jp/Smart/eng/papers_e.html• http://www.fzk.de/stellent/groups/public/documents/p

ublished_pages/6__6_3__index_ia3f27b85c-2.php

• Nanomuscles • Surgical instruments

– Tissue Spreader– Stents (angioplasty)– Coronary Probe– Brain Spatula

• Endoscopy: miniature zoom device, bending actuator

• Force sensor• Smart skin (wing

turbulence reduction)

Major applications:

Definition of a Shape Memory Alloy

http://smart.tamu.edu/overview/smaintro/simple/definition.html

Shape Memory Alloys (SMAs) are a class of metal alloys that can recover apparent permanent strains when they are heated above a certain temperature.

Basic working principle

• SMAs have two stable phases - the high-temperature phase, called austenite and the low-temperature phase, called martensite.

• the martensite can be in one of two forms: twinned and detwinned, as shown in Figure 1.

• A phase transformation which occurs between these two phases upon heating/cooling is the basis for the unique properties of the SMAs.

http://smart.tamu.edu/overview/smaintro/simple/definition.html

http://smart.tamu.edu/overview/smaintro/simple/definition.html

The Effects of Cooling in the Absence of an Applied Load

• Upon cooling in the absence of applied load the material transforms from austenite into twinned martensite. (no observable macroscopic shape change occurs)

• Upon heating the material in the martensitic phase, a reverse phase transformation takes place and as a result the material transforms to austenite.

http://smart.tamu.edu/overview/smaintro/simple/definition.html

Thermally-Induced Transformation with Applied

Mechanical Load • If mechanical load is applied to the material in

the state of twinned martensite (at low temperature) it is possible to detwin the martensite.

• Upon releasing of the load, the material remains deformed. A subsequent heating of the material to a temperature above the austenite finish temperature (A0f*) will result in reverse phase transformation (martensite to austenite) and will lead to complete shape recovery.

• This process results in manifestation of the Shape Memory Effect (SME).

http://smart.tamu.edu/overview/smaintro/simple/definition.html

http://smart.tamu.edu/overview/smaintro/simple/definition.html

•It is also possible to induce a martensitic transformation which would lead directly to detwinned martensite. •If load is applied in the austenitic phase and the material is cooled, the phase transformation will result in detwinned martensite. --Very large strains (5-8%) will be observed. --

Shape Recovery

• Reheating the material will result in complete shape recovery.

• The transformation temperatures in this case depend strongly on the magnitude of the applied load.– Higher applied load values will lead to higher

transformation temperatures. – There is usually a linear relationship between

the applied load and the transformation temperatures

Example of Biomedical Application:

The Superelasticity of NiTinol appears to be much more physiologic compared to stainless steel, for example.

(http://www.memory-metalle.de/html/01_start/index_outer_frame.htm)

Sample Application:New metallic muscles that flex with little heat• By evaporation and subsequent condensation in

a thin noble gas atmosphere, pure platinum is converted into particles less than 5 nanometers in size.

• These particles are then compacted into a nanoporous body. The solid which is generated is immersed into a conductive fluid (electrolyte) that fills the cavities. Via this electrolyte, an acid or a base, electric charges can be transported to all the nanoparticles of the solid.

http://www.abc.net.au/science/news/stories/s832821.htm

Sample Configuration:

• Application of an electric voltage causes the electric charge of the electrolyte to change. As a result, electric charges are also induced on the surfaces of the nanoparticles.

• This changed charge makes the atoms change their number of conductionelectrons and, hence, their chemical identity

http://www.fzk.de/stellent/groups/public/documents

Discussion of Application

• An advantage to this new shape memory alloy is its’ efficiency. No other alloy or polymer can compare to its’ strength and efficiency to weight ratio.

• Nanomuscles weigh just one gram but can lift 140 grams, and are preferred to electric motors as they are far cheaper to produce.

Major Specifications

• Pseudoelasticity

• Displacement Range

• Fatigue life

• Electromechanical ratio

Limitations• Heat Dissipation• Range of Motion• Stiffness/Flexibility• Relatively expensive to manufacture and

machine compared to other materials such as steel and aluminum.

• Most SMA's have poor fatigue properties; this means that while under the same loading conditions (i.e. twisting, bending, compressing) a steel component may survive for more than one hundred times more cycles than an SMA element.

Selection Criteria

• Range• Sensitivity• Repeatability• Linearity and Accuracy• Impedance• Nonlinearities• Static and Coulomb Friction• Frequency Response

Cost Information

• Nanomuscles cost 50 cents each compared to US$300 for an equivalent electric motor.

Where to buy:

• http://www.memory-metalle.de/html/01_start/index_outer_frame.htm