Seth R. Hills ECE5320 Mechatronics Assignment #1 Shape Memory Alloys Seth 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/s832821.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=65 http://www.nims.go.jp/Smart/eng/papers_e.html http://www.fzk.de/stellent/groups/public/documents/published_pages/6__6_3__index_ia3f27b85c-2.php

Major applications: Nanomuscles Surgical instruments Tissue Spreader Stents (angioplasty) Coronary Probe Brain Spatula Endoscopy: miniature zoom device, bending actuator Force sensor Smart skin (wing turbulence reduction)

Definition of a Shape Memory Alloy Shape Memory Alloys (SMAs) are a class of metal alloys that can recover apparent permanent strains when they are heated above a certain temperature. http://smart.tamu.edu/overview/smaintro/simple/definition.html

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). *austenite finish temperature (Aof) at which the reverse phase transformation is completed and the material is the austenitic phase. 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. -- http://smart.tamu.edu/overview/smaintro/simple/definition.html

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 conduction electrons and, hence, their chemical identity http://www.fzk.de/stellent/groups/public/documents

Nanomuscles

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