0LAUK0 PRE2018 3 Group 13 Material Study

Materials

For the materials regarding the display of the article, we’ve done some research as to which materials would be usable. Since the exact requirements of the materials are not yet calculated, the requirements will mostly based on estimates. The requirements of the materials are that they are sufficiently elastic, easily deformable, durable and have a low friction coefficient. We distinguish between the following material types: Metals, Polymers, ceramics and textiles [1]. For each of these material types we’ll discuss what they include exactly and if applicable which materials could be usable. Since both deformability, durability and friction coefficient are not easily specified, we’ll focus on the elasticity.

Metals

Metals refers to a group of materials that that consists of elements that readily forms positive ions and has metallic bonds. In general, metals conduct electricity and heat relatively well and are overall a popular material type to use. Depending on the type of metal, they could be easily deformable and in our situation durable. The main problem with metals regarding our robot is that in general their elasticity is low. This means that if the material is deformed too much, it will not revert back to its original form. We assume our design would need a decently high elasticity and for these reasons we’ll look into the metals with the highest elasticity. We found the following metals:

Chromoly steel with Cr <= 9%

Chromoly steel is an alloy including both chromium and molybdenum[15]. Chromoly is often used when the strength of mild carbon steel is not enough. You often see this material used in things such as bicycle tubes, molds, pins and chain links. Cost: $0.06 – 0.15 / kg Elasticity: 29.7* 10^6- 30.9 * 10^6 psi [2]

Carbon steel

Carbon steels refers to a steel which contains carbon elements up to 2.1% of its weight. Carbon steel has many different uses based on the percentage of carbon. The higher the percentage of carbon, the stronger the material is[14]. Because of this carbon steels has a range of uses from constructing small things such as fences to construction of buildings and bridges. Cost: $0.86 – 1.03 / kg [3] Elasticity: 29.3* 10^6- 29.5 * 10^6 psi [2]

Polymers

A polymer refers to a type of material in which the material is made from long chains of molecules which may have cross linking bonds affecting flexibility and stiffness. Polymers can be categorized in three different categories. The first category is thermoplastics. Thermoplastics refers to a polymer which can only be flexible or moldable above certain temperature. The thermoplastic with the lowest moldable temperature is 60 °C[4]. Since the temperature is too high for long term exposure to the skin, we can conclude that there are no thermoplastics which can be used for our robot. The second category is thermosetting polymers. Thermosetting polymers refers to polymer which is irreversibly hardened[12,13]. Once hardened the thermosetting polymers cannot be changed in form. For this reason thermosetting polymers are not usable for our robot. The third is elastomer. Elastomer refers to polymers that are capable of recovering their original shape after being stretched or deformed to great extents. This polymer type can be used in our design because of its high elasticity. A good choice for the material for our design would be a certain type or rubber. Rubber is an easily obtainable material and because of its general high elasticity, it could be used in our robot[10,11]. The main problem with using rubber is that rubber generally has a high friction. When the user would use our robot to read over the letters, the high friction will most likely cause a bad experience for the user. This could be solved by applying a low friction rubber coating to the robot to reduce the friction coefficient. Cost: $ 3.46 / kg

Ceramics

Ceramics are solid materials which are composed of inorganic compounds of metal, non-metal and covalent bonds. Ceramics are hard materials which are known to have an even lower elasticity at room temperature than most metals[7,8,9]. Because of this, we will assume for now all ceramics will be unusable for our robot.

Textiles

Textiles are any material, which can be used to create fabrics, cloth or the resulting material[6]. An example of textiles are cotton or wool. There exists multiple kinds of textiles in which each of them has his own characteristics. Depending on how the materials are created, textiles could be elastic and thus be used in our robot. A good candidate for our robot is the textile wool. Wool is a fiber formed of sheep fur which is both elastic and durable[5]. Since wool made up of multiple threads, there could be some hindrance when reading the braille points. This is because threads will have to be spun and thus will not be a perfectly flat layer. This will have to be tested with the users in order to verify the viability of this material.

References

1. https://www.the-warren.org/ALevelRevision/engineering/Materialclasses.html
2. https://www.engineeringtoolbox.com/young-modulus-d_773.html
3. https://agmetalminer.com/metal-prices/carbon-steel/
4. https://www.orfit.com/faq/what-are-low-temperature-thermoplastic-materials-lttps/
5. http://www.campaignforwool.org/about-wool/
6. http://bieap.gov.in/Pdf/CGTPaperII.pdf
7. https://global.kyocera.com/fcworld/charact/strong/rigidity.html
8. https://www.engineeringtoolbox.com/ceramics-properties-d_1227.html
9. http://www.dynacer.com/properties/
10. http://www.newworldencyclopedia.org/entry/Elastomer
11. https://www.britannica.com/science/elastomer
12. https://en.wikipedia.org/wiki/Thermosetting_polymer
13. https://en.wikipedia.org/wiki/Thermoplastic
14. https://www.onealsteel.com/carbon-and-alloy-steel.html
15. https://www.metalsupermarkets.com/what-is-chromoly/
16. https://www.economicshelp.org/blog/301/concepts/understanding-elasticity/