Current Work: Shape Memory Alloys

In order to utilize a shape memory alloy, the properties of the alloy need to be known.  Charlotte Lelieveld from the TU Deflt has done work in creating smart composites materials, i.e. materials that incorporate shape memory alloys and shape memory polymers (1-2).  Pictures of her work is given below:

 

Image

Smart Composite using Shape Memory Polymers and Shape Memory Alloys

Image

Prototype of smart composite when the structure is activated


In order for me to create a similar, I need to know the properties of both the shape memory alloy and shape memory polymer. The properties of relevant importance to me are listed below:

Shape Memory Alloys (3):
1. Density (g/cc): 6.5
2. Electrical Resistivity (micro Ohms/cm): 76 (Martensite)/82 (Austenite)
3. Thermal Conductivity (W/m deg C): 18
4. Elastic Modulus (GPa): 40 (Martensite)/75 (Austenite)
5. Specific Heat Capacity (J/kgK): 322

The power to heat the SMA strips, can be found through estimating the energy by (1):

E = Power*time = mass*Specific Heat Capacity* change in temperature

The power may be calculated from Joule’s law:

P = Voltage^2/Resistance

The resistance in each wire is given by:
R = resistivity * length/cross-sectional area

References:
1. Lelieveld, C. M. J. L. (2013). Smart Materials For The Realization Of An Adaptive Building Component. Ph.D. doctoral Thesis, Delft University of Technology.
2. http://materiability.com/smart-composite-shape-memory-materials/
3. http://memry.com/nitinol-iq/nitinol-fundamentals/physical-properties

Current Work: Shape Memory Polymers and Heating Applications

Currently, I am working on incorporation of heating through electronic sources.  I have made a sample that contains 20 guage nichrome wire from Jacobs.  The data on the wire is given below:

Data for varying guage lengths of Nichrome wire

Data for varying guage lengths of Nichrome wire (1)

From this data, I used Mathematica to curve fit to a second order polynomial.  The equation for the polynomial is given as:  Amps = 7.55359*10^-6*T^2+0.00549092*T+2.47994.  An image of the curve fit data is given below:

Amperes vs. Temperature curve for 20 guage Nichrome wire

Amperes vs. Temperature curve for 20 guage Nichrome wire

For the 20 guage nichrome wire, a temperature of 30 deg C can be obtained with the application of 2.65 Amps.  The sample with the nichrome wire, as well as, a sample that contains carbon black, and a sample that contains embedded shape memory alloy is seen in the picture below:

Top Left:  Shape Memory Polymer with Embedded Nichrome Wire, Top Right:  Shape Memory Polymer with Embedded Carbon Black, Bottom Left:  Shape Memory Polymer with Embedded Shape Memory Alloy

Top Left: Shape Memory Polymer with Embedded Nichrome Wire, Top Right: Shape Memory Polymer with Embedded Carbon Black, Bottom Left: Shape Memory Polymer with Embedded Shape Memory Alloy

Note that the weight percentage of carbon black is too high, and the sample created was a gummy consistency.

References:

1.  http://jacobs-online.biz/nichrome_wire.htm

Auxetic Shape Using Shape Memory Alloys/Polymers

There is a video of an antenna made from shape memory alloy.  The video is given here:  http://shelf3d.com/RGDufoVQ7hg#Chiral%20shape%20memory%20alloy%20antenna.  The antenna is seen below:

Demonstrator deployable antenna with a chiral (auxetic) structure - it expands in all directions when pulled. The antenna is made with shape memory alloy ribbon and it activates with an air dryer.

Demonstrator deployable antenna with a chiral (auxetic) structure – it expands in all directions when pulled. The antenna is made with shape memory alloy ribbon and it activates with an air dryer.

This auxetic shape was achieved using shape memory polymer, as well.  Jonathan Rossiter and collaborators at the University of Bristol, have created the chiral structure.  An image below describes how the auxetic structure works:

Screen Shot 2014-03-14 at 9.24.59 PM

Contraction of chiral structures; (a) expanded and (b) compressed triangular element, (c) a single structural element at maximum extension and (d) at maximum contraction (1)

The structured made from the shape memory polymer is given below:

(a) As-fabricated deployed state of laser cut SMP hexachiral auxetic, (b) compressed storage state, (c) deployed structure after shape recovery

(a) As-fabricated deployed state of laser cut SMP hexachiral auxetic, (b) compressed storage state, (c) deployed structure after shape recovery (1)

Incorporating a structure like this one might be useful for my purposes.

References:

1.  Rossiter, J. et. al., Shape Memory Polymer Hexachiral Structures with Tunable Stiffness.  Smart Materials and Structures. 23 (2014).

Current Work: Shape Memory Polymers with Color Change

I recently tried again to incorporate more Solar Color Dust colors into a shape memory polymer.  I made four samples of the following ratios:  1.57 ml Epon 826/2.43 ml Jeffamine/3.12 ml NGDE.  This ratio corresponds to a glass transition temperature of approximately 40 deg C.  For these samples, the Solar Color Dust was mixed according to the instructions per the website (10 grams of dust to 1 pint of epoxy).  Three of the samples contained just Solar Color Dust and epoxy, while the fourth contained Solar Color Dust, epoxy, and Castin Craft blue dye.  Pictures of the samples are given below for heated and unheated specimens:

Shape Memory Polymers with Embedded Color Powders and Dyes After Curing

Shape Memory Polymers with Embedded Color Powders and Dyes After Curing

Left to Right: Castin Craft Blue Dye and 0.24 g of Rubine Red Solar Color Dust, 0.24 g of Magenta Solar Color Dust, 0.26 g Sky Blue Solar Color Dust, 0.22 g Green Solar Color Dust

Left to Right: Castin Craft Blue Dye and 0.24 g of Rubine Red Solar Color Dust, 0.24 g of Magenta Solar Color Dust, 0.26 g Sky Blue Solar Color Dust, 0.22 g Green Solar Color Dust

I took each of the samples and added some heat with my hand.  The result is given below:

Castin Craft Blue Dye with Rubine Red Solar Color Dust with Applied Heat from My Hand

Castin Craft Blue Dye with Rubine Red Solar Color Dust with Applied Heat from My Hand

Magenta Solar Color Dust with Applied Heat from Hand

Magenta Solar Color Dust with Applied Heat from Hand

Sky Blue Solar Color Dust with Applied Heat from Hand

Sky Blue Solar Color Dust with Applied Heat from Hand

Green Solar Color Dust with Applied Heat from Hand

Green Solar Color Dust with Applied Heat from Hand

From this experimentation, Rubine Red seems to give the most significant color change out of all the powders an hand.  Also, from the first picture, you can see that there is some clumping inside the epoxy.  This clumping is due to the fact that the powder is not well dispersed within the epoxy.  Therefore, may next time sonication might be used to disperse the particles.  Since, I had some extra material left over, I mixed the Magenta, Sky Blue, and Green epoxy mixtures together and obtained the following result:

Mixture of Green, Sky Blue, and Magenta Solar Color Dust with Epoxy

      Mixture of Green, Sky Blue, and Magenta Solar Color Dust with Epoxy

 

Mixture of Green, Sky Blue, and Magenta Solar Color Dust with Epoxy and Heated with Hand

Mixture of Green, Sky Blue, and Magenta Solar Color Dust with Epoxy and Heated with Hand

Note when all three of these colors are mixed together and not dispersed, the coloring is very beautiful and unique.  However, due to lack of the dispersion, when heat is applied with the hand, not as visible of change is seen in the sample.

Shape Memory Polymers with Polymer Bi-Layers

Xie et. al. has created a shape memory material that contains multiple “temporary shape” through creating a layered polymer material.  This material was created by layering two polymers with different glass transition temperatures.  The first layer was made from a mole ratio of 1.6 mole Epon 826/0.4 mole NGDE/1 mole Jeffamine.  It was placed in the mold and cured at 100 deg C for 40 minutes.  The second layer was made from a mole ratio of 0.8 mole Epon 826/1.2 mole NGDE/1 mole Jeffamine.  This mixture was poured on top of the first layer and cured for an additional 40 minutes at 100 deg C.  Then the mold was post-cured at 130 deg C for 1 hour.  The first layer had a Tg of approximately 48 deg C and the second layer had a Tg of approximately 75 deg C.  The figure below shows the shape setting and recovery process.

In step 1, the molded shape was heated to 90 deg C.  Then a deformation stress was applied.  The sample was then cooled under stress to 56 deg C.  The stress was release to create temporary shape B.  Shape B was then further deformed under larger stress and cooled to below 20 deg C.  The stress was released to create temporary shape C.

(1)  The molded shape was heated to 90 deg C. Then a deformation stress was applied. The sample was then cooled under stress to 56 deg C. The stress was release to create temporary shape B. (2)  Shape B was then further deformed under larger stress and cooled to below 20 deg C. The stress was released to create temporary shape C.  (3)  The polymer was heated to 56 deg C and shape B was recovered.  (4)  The polymer was heated to 90 deg C and shape A was recovered.

References:

1.  http://onlinelibrary.wiley.com/doi/10.1002/marc.200900409/full

Shape Memory Polymers with Embedded Nichrome Wire

Scott Rauscher M.S. from the University of Pittsburgh is entitled Testing and Analysis of Shape-Memory Polymers for Morphing Aircraft Skin Application.  His thesis focuses on the development of aircraft wings that can change geometry to create optimal behavior during all flight times.  He approach is to create a structurally reinforced shape memory polymer material with the reinforcement containing an embedded heating element.  For the heating element, he incorporates Nickel-chrominum wire.  There are two tables from his thesis below that give the properties of Nichrome wire:

Current required for nickel-chrominum wire for 135 C

Current required for nickel-chrominum wire for 135 C

Properties of Nichrome Wire

Properties of Nichrome Wire

His resulting embedded Nichrome sample is given below:

Shape Memory Polymer with Embedded Nichrome Wire

Shape Memory Polymer with Embedded Nichrome Wire

Shape Memory Polymer Mold with Nichrome Wire using Loom Weaving

Shape Memory Polymer Mold with Nichrome Wire using Loom Weaving

References:

1.  http://d-scholarship.pitt.edu/7197/1/Rauscher,Scott,June,2008.pdf

Shape Memory Polymer: Surface Test

This artist is using shape memory polymers with laser cut patterns.  This research is called active patterns which looks into using shape  memory polymers as active facade materials.  The temperature at which the material moved is determined by altering the ratio of its chemical makeup. The overall “behavior” is thus programmed through the geometry of the pattern cut/scored into the polymer.  These polymers are made as a part of project BlackBox Smart Geometry (1).

Laser Cut Shape Memory Polymer

Laser Cut Shape Memory Polymer

Surface Test 1 of Shape Memory Polymer:  http://vimeo.com/27825310

Surface Test 2 of Shape Memory Polymer:  http://vimeo.com/27921902

References:

1.  http://altnresearch.com/category/blackbox/