Chapter 4:
Materials for Design
Greetings brothers and sisters. It is nice to know that you guys are following up on our content and we hope to provide the best of experience as you read our weekly blogs. Also, wishing you a SELAMAT HARI RAYA especially to all Muslims! I hope you guys were able to enjoy your celebration despite the current pandemic :'). Anyways let's move on to the blog.
Week 4's lesson was asynchronous. We were given the task to recap on our Year One module which was Materials for Design (MFD) where we had to classify the materials, determine their properties through various testing as well as perform material selection based on our needs.
Classification of materials
Materials can be generally classified into 5 categories:
- Natural materials
- Metals & Alloys
- Ceramics
- Polymers
- Composites
Properties of materials
Different materials have different properties Some materials may be prone to breakage, while others may be hard to break. Here we are comparing their tensile strengths where the former has a lower tensile strength while the latter has a higher tensile strength. These properties can be determined by performing tests on the material. This is only one of many examples.
Material selection
Ideally when choosing our materials, we would rely on the COWS matrix to help us decide on the material best suited for our product.
The COWS matrix can be described as:
- Criteria; the properties of materials
- Options; appropriate materials to compare
- Weightage; which property of material is most important
- Scale; rate each option on a ratio scale by assigning it a score or rating against each criterion. The score is calculated as Ratings x Weight
The scores are then evaluated, and solutions with the highest scores are the ones that best meet the criteria.
COWS Matrix Table
Our group was also tasked to complete an assignment which was to select a suitable material for reusable face-masks for medical workers to protect them against the COVID-19 virus
Face guard
Function | The face guard is used to prevent droplets contact with the user or the user's droplets contacting others. |
Constraints | Visibility of the shield when scratched (hardness) Resistant from breath droplets (corrosion resistant) Does not react with the breath droplets when contacted (not reactive) Lightweight (density) Cooling to wear (Thermal conductivity) Hard to be deformed, to be carried around with user (young’s modulus) |
Objectives | Comfortable and safe to the user |
Criteria | Polyvinyl Chloride | Polyethylene terephthalate glycol Plastic | Polycarbonate | Polypropylene |
Corrosion resistance (salt water, water, soap) | Good, Good, Excellent
(PVC Chemical Resistance Chart, n.d.) | Good, Good, Excellent
(Petg Chemical Resistance Data Sheet, n.d.) | Excellent, Excellent, Excellent
(Polycarbonate Chemical Compatibility Chart, n.d.) | Excellent, Excellent, Excellent
(Chemical Compatibility Database from Cole-Parmer, 2021)
|
Hardness | 115
(Vycom VINTEC I® PVC Polyvinyl Chloride (PVC), 2021) | 115
(Matweb, n.d.) | 115
(Matweb, n.d.) | 90
(bpf.co.uk, n.d.) |
Reactiveness (salt water, water, soap) | Good, Good, Excellent (Chemical Compatibility Database from Cole-Parmer, 2021) | Excellent,Excellent, Excellent (Solutions In Plastics, n.d.) | Excellent, Excellent, Excellent (Chemical Compatibility Database from Cole-Parmer, 2021) | Excellent, Excellent, Excellent (Chemical Compatibility Database from Cole-Parmer, 2021) |
Density (g/cm3) | 1.42 (Vycom VINTEC I® PVC Polyvinyl Chloride (PVC), 2021) | 1.26-1.28
(DielectricCFMG, n.d.) | 1.22
(OmnexusSpecialChem, n.d.)
| 0.92
(plastics europe, n.d.) |
Thermal conductivity (W/m-k) | 0.19 (Plastics - Thermal Conductivity Coefficients, n.d.) | 0.162-0.225
(Matweb, n.d.) | 0.19-0.22
(professional plastics, n.d). | 0.1-0.22
(good fellow, n.d.) |
Young’s Modulus (GPa) | 3.32
(Vycom VINTEC I® PVC Polyvinyl Chloride (PVC), 2021) | 1.38
(RTP Company PermaStat® 1100A Polyethylene Terephthalate Glycol Modified (PETG) Anti-Static, 2021) | 0.228-7.9
(Overview of materials for Polycarbonate, Unreinforced, Flame Retardant, 2021) | 0.026-10
(Overview of materials for Polypropylene, Molded, 2021) |
Criteria | Weightage | Polyvinyl Chloride | Polyethylene terephthalate glycol PETG Plastic | Polycarbonate | Polypropylene |
Corrosion resistance (salt water, water, soap) | 30% | 2 | 2 | 3 | 3 |
Hardness | 10% | 3 | 3 | 3 | 2 |
Reactiveness (salt water, water, soap) | 20% | 2 | 3 | 3 | 3 |
Density (g/cm3) | 20% | 2 | 2 | 2 | 3 |
Thermal conductivity (W/m-k) | 10% | 3 | 3 | 3 | 3 |
Young’s Modulus (GPa) | 10% | 3 | 3 | 3 | 2 |
Total | 100% | 230 | 250 | 280 | 280 |
Face guard support
Function | The face guard support is used to cushion the face guard to the forehead of the user |
Constraints | Elasticity (Fit for all ages) Hypoallergenic Lightweight (low density) Cost (To be cheap for the public) Durability Keep the user cool and comfortable (Heat conductivity) |
Objectives | To make the faceguard support that can comfortably be worn around the user's head of all ages, lightweight, durable, affordable and to protect themselves from diseases. |
Values | Wool | Sponge | Cotton | Silk |
Durability usage (year) | 18-54
(cloudfront, 2021) | 2-6 (Daewon Kim, 2016) | 3-8 (cloudfront, 2021) | 2-5.5 (cloudfront, 2021) |
Modulus of Elasticity (GPA) | 61.4
(Liu et al., 2020) | 0.03334
(degryuter, 2014) | 3.7
(Kharkova, 2011) | 23 (Katsuhiko, Takashi and Hikaru, 1989) |
Density (lb/in3) | 0.0009
(Laimutis Steponaitis and Sigitas Vėjelis, 2010) | 0.00231481
(thesleepjudge, 2019) | 0.0549
(cotton, 2021) | 0.0484
(sciencedirect, 2012) |
Costs (USD/lb) | 1.47
(Brester, 2018) | 12.79
(COINCOST, 2021) | 0.64
(ACPS, 2020)
| 0.86
(Sara, Kathleen and Sarah, 2017) |
Heat Conductivity (W/m-K) | 0.04
(Wool Cloth Fiber, 2021) | 0.0695
( j-flex.co.uk) | 0.04
(Thermal Conductivity of some selected Materials and Gases, n.d.) | 0.000397–0.000663
(Ye, Samuel and Xiao, 2019) |
Criteria | Weightage | Wool | Sponge | Cotton | Silk |
Durability (year) | 10% | 3 | 2 | 2 | 2 |
Modulus of Elasticity (GPA) | 20% | 3 | 1 | 2 | 3 |
Density (lb/in3) | 25% | 3 | 3 | 3 | 3 |
Costs (USD/lb) | 25% | 2 | 1 | 3 | 3 |
Heat Conductivity (W/m-K) | 20% | 3 | 3 | 3 | 3 |
Total | 100% | 275 | 200 | 270 | 290 |
We have decided as a group that we will be using polypropylene/polycarbonate for the face shield and silk as our material for the face shield support.
This concludes the end of my blog entry of week 4's asynchronous lesson and I hope to see you readers next week! Once again Selamat Hari Raya to all my muslim friends and family. Wishing you all the best of health during these tough times. Peace.
About author: Amal is one of the founding members of Group 2 of CP5065: Introduction to Chemical Design
Click here to view Amal's page:
Comments
Post a Comment