# Photoelasticity

Photoelasticity is an experimental method to determine the stress distribution in a material. The method is mostly used in cases where mathematical methods become quite cumbersome.  It gives stress bands of principle stresses for amorphous polymer materials.

Here is a video that describes how photo elasticity can be done with a camera and computer screen and a polarizing filter or polarizing sunglasses.

# Shape Memory Polymers: 2D to 3D Shape Geometry Project

I am working on a project with Dr. Ergun Akleman to create 3D structures from 2D structures.  I have managed to create a structure that can fold from a 2D shape to a tetrahedron.  A video of the structure unfolding is given here:  https://www.youtube.com/watch?v=evGOyAA_JfA&feature=youtu.be.  Some pictures of the structure are given below:

Shape Memory Polymer in 2D shape permanent shape that folds into the pyramid configuration.

Shape memory polymer in 3D deformed pyramid shape

# Shape Memory Polymers: Blooming Flower Project

The current project is looking at creating a shape memory polymer that mimic the behavior of blooming flower tea.  A video that describes how blooming flower tea is made is given here:  http://www.youtube.com/watch?v=TLCnHcmhezw.  This is a type of tea called “art” tea and consists of tea leaves in a compact structure that folds over a flower and opens up when exposed to hot water.  A picture of the blooming flower tea is given here:

Blooming Flower Tea: The green compressed balls are what it looks like before it is exposed to hot water.

Some inspiration for this project also comes from origami robots.  MIT and Harvard have created an origami robot that can assemble itself and move from a 1-Dimensional structure.  A video of the robot is given here:  http://www.tested.com/tech/robots/463382-brief-mit-origami-robot-walks-away-laser-cutter/.

In order to work on this project, I have tried some flower baking molds at various degrees of temperatures.  However, there is some difficulty in obtaining the proper folding technique for the opening of the flower. The picture below depicts a flower from the baking mold. I have made one with a glass transition at 70 C and one with a glass transition at 30 C. Since the flower from the baking mold is very flat on the back, the structure does not yield to folding in very well.

Next I tried laser-cutting a flat 2D shape of a flower and folding it in. Pictures of the flat 2D shape are given below.

I have uploaded a video of the shape memory polymer flower blooming here: https://www.youtube.com/watch?v=y7iQLhYO4_U&feature=youtu.be

# Current Work: Laser-Cutting Shape Memory Polymers

I have currently made some hexagonal chiral structures that incorporate color change. Below are pictures of two of these structures that incorporate different color changes.

This chiral shape contains rubine red powder and blue castin craft dye. The change from purple to blue is depicted here.

This chiral contains blue powder and yellow castin craft dye. The change from blue to yellow is depicted here.

I have also been experimenting with using fabric with the colored polymer. Below are pictures of fabric incorporated into the polymer.

This chiral contains rubine red powder with blue dye and blue fabric has been super glued to the back of it.

This chiral has blue powder with yellow dye and yellow fabric super glued on the polymer.

# Current Work: Laser-Cutting Shape Memory Polymers

I recently used a laser-cutter to create a spiral and auxetic shape in the shape memory polymer. After cutting, I placed the material in a hot water bath whose temperature was above 70 deg C. Then applied pressure with my hands and cooled under cold water from the faucet. The results of the spiral and the auextic shapes are given below.

Spiral cut of shape memory polymer using a laser-cutter

Heat induced shape change in laser-cut smp.

Extreme heat induced shape change in laser-cut spiral smp.

Auxetic laser-cut of smp

Curling heat induced shape change of a 2-coil smp

Curling heat-induced shape change of a 3-coil smp

Here is a video of the uncurling of the auxetic amp using a hair dryer: https://www.youtube.com/watch?v=nZGNkn1s4F0&feature=youtu.be

The laser-cutter leaves some burnt edges of shape memory polymer. Also, the integral line segments in the auxetic shape were quite small so did break off when trying to pull them out. For future work, some sanding along the edges could be done to decrease the edge effects from the laser cutter. However, the shape change produced is the desired effect.

# 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:

Smart Composite using Shape Memory Polymers and Shape Memory Alloys

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 (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

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

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

References: