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.

https://www.youtube.com/watch?v=8rtts66THp0

images

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:

IMG_0292

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

Shape Memory Polymer Folded Into a Pyramid Shape

Shape memory polymer in 3D deformed pyramid shape

Pyramid_2 IMG_0289

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 Tea

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.

Shape Memory Polymer From Baking Flower Mold

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.

Shape Memory Polymer Flower Folded

Shape Memory Polymer Flower Folded

Shape Memory Polymer Flower Unfolded

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

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).

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/