Blog 5

 In this blog, I will be talking about what we have learned in class during weeks 11 and 12, as well as what I did during Practical 3. The big idea for these 3 lessons is  "Materials, materials, and materials". We learned how to further break down the COWS matrix to deciding different materials to use, as well as choose which material can be used and further improved for different purposes. 

1. Week 11 Topic 5 - Materials for design

We are now at the Prototyping and Product Development stage! In this lesson, we were asked to select different materials to perform a task. Then, we will use the COWS matrix to determine which materials are the most suitable. 

How did we know how to score each material? Well, the material properties are important characteristics of each material that play an important part in the final decision. Material properties like strength, ductility, Young's Modulus, and Density are some characteristics that allow us to determine whether that material will be able to fulfill the device's function and main objective. We also had to investigate the economic properties of each material. 

My team was asked to select suitable materials to make a face shield that is being used to protect individuals from the COVID-19 virus. There are two main components of the face shield: 

1. The forehead support 

2. Transparent screen/sheet

Given the limited time we had in class, we split into two groups to "cover more area". Isabelle and I worked on the materials that can be used for the forehead support, while Hong Yi and Hariz worked on the transparent screen/sheet. 

1.1 Materials Selection for forehead support

To be effective and useful, the foam support for the forehead must be lightweight to reduce pressure on the forehead. The material must also be soft to provide comfort to the user.

The foam should be flexible so that it can be bent to provide a larger surface area of protection and fit the forehead of the user.

The foam should have high water absorption so that it will be able to absorb the sweat from the user’s forehead. This will prevent sweat from entering the user’s eyes and causing discomfort.

The foam should be biodegradable to ensure that it does not take a long time to decompose and does not produce any harmful waste. 

Function	To hold up the face shield and ensure that it does not slip from the forehead
Constraints	Lightweight (low density) Flexible (Low modulus of elasticity)  High water absorption  Biodegradable (does not take a long time to decompose and does not produce any harmful waste)
Objectives	Maximize density and water absorption

Four different types of foam were chosen.

The low density is the most important as the support has to be lightweight due to the user wearing the face shield for a long time. The main purpose of the support is to ensure that the user is comfortable while wearing the face shield. Hence, the support should be lightweight to allow the user to continue wearing it after long periods of time. We decided that it should be given the highest weightage of 40%.

High water absorption is also important as the user will sweat due to the humid weather, and wearing a face mask and the face shield together. To ensure that the user will be comfortable wearing the face shield, the foam should be able to absorb the sweat on the forehead and prevent it from flowing down into the user’s eyes, which will be uncomfortable. It is the second most important criterion, hence we gave it a weightage of 30%. 

Between low modulus of elasticity and high biodegradability, we decided that the foam being flexible is more important as the foam can be reused many times before it is disposed of. As the user will be wearing the face shield frequently, the foam should be able to remain in its bent shape and support the face shield without breaking. Hence, a low modulus of elasticity has a higher weightage of 20% compared to biodegradability (10%)

COWS MATRIX: 

Score of 1 (poorest) - 5 (excellent)

The economic properties we chose were the cost of materials and availability of material

The cost of Material should have a higher weightage (60%) as face shields are used widely across the world. A large number of them need to be mass-produced in order to cater to the large numbers of people. Hence, the cost of the material needs to be cheap and affordable in order to accommodate many people. 

Availability of material is also important as the material cannot be scarce. It has to be abundant as it is needed to manufacture a lot of face shield supports. Hence, we gave it a weightage of 40%.

Criteria	Weightage (%)	Polyurethane Foam	Polyethylene (PE) Foam	Low density Plastazote foam
Cost of Material	60	W1000m x L2000m x 40mm $147 Area: 80, 000, 000 For 1mm^2 -> $0.00000184 Score: 5	W1000m x L20000mm x 50mm $145 Area: 100, 000, 000 For 1mm^2 -> $0.00000145 Score: 5	1.6mm x 150mm x 910mm $22.90 Area: 218, 400  For 1mm^2 -> $0.00010485 Score: 3
Availability of Material	40	There was a decrease in the polyurethane foam supply chain in 2021, but there has been an increased demand for the material in 2022. Score: 2	Polyethylene foam can be easily obtained as it can be manufactured in Singapore.  There are many manufacturers available in Singapore Score: 5	There is a decent supply as it is commonly used in packaging products. However, there are limited industries in Singapore that sell this foam.  Score: 3
Total score	100	380	500	300

Score: 1 (lowest) - 5 (highest) 

Based on the above COWS matrix, Polyethylene Foam is the most suitable material to be used as the forehead support.

1.2 Materials selection for transparent screen/sheet

To be effective and useful, the sheet must be transparent to allow the user to see the surroundings while wearing it.

The sheet must be lightweight so that it will not be uncomfortable for the user to wear for a long period of time.

The sheet should be flexible so that it can be bent to provide a larger surface area of protection and be aesthetically pleasing

The sheet should be UV resistant so that it will not degrade under prolonged use under the sun.

Function: To provide the user a layer of protection against viral particles while allowing the user to see

Constraints:

1. Lightweight (Low Density)

2. Transparent (High Light Transmittance value)

3. Flexible ( Low modulus of Elasticity)

4. UV resistant

Objectives: Maximize the UV resistance and Transparency

Based on the description above, polymers have been shortlisted as the possible materials.

Four possible polymers out of all the polymers have been selected as candidates.

Criteria	Weightage (%)	Reason
Light Weight (Low Density)	15	Lightweight is as equally important as flexibility in order to provide comfort and aesthetic value for the user.
UV resistant	30	It has the second-highest weightage as the sheet must be UV resistant so that it will not degrade when the user is using it when under the sun for a long period of time.
Flexible (Low Young’s Modulus)	15	Flexibility is as equally important as light weight in order to provide comfort and aesthetic value for the user.
Optical Transparency (High Light Transmittance Value)	40	It has the highest weightage as the sheet must be transparent so that it can effectively carry out its function without causing inconvenience for the user. The sheet must not block the vision of the user.

COWS MATRIX:

The economic properties we chose were machinability rating and cost of material

Machinability rating	40	The machinability has a lower weightage because the plastics in general may be easier to fabricate and the cost will be the factor that may affect the overall decision of which plastic to choose.
Cost of material	60	The cost has a higher weightage than the ease of fabrication/ manufacturing as the sheet must be cheap so that it is affordable for the user.

Criteria	Weightage (%)	Polyethylene Terephthalate Glycol (PETG)	Polyvinyl Chloride (PVC)
Machinability rating	40	8 Score: 4 4 x 40%=160% https://www.truventor.ai/blogs/types-of-plastics-machining-selection/	8  Score: 4 4 x 40%=160%
Cost of material (Eur/kg)	60	0.43 Score: 5 5x60%=300% https://plasticker.de/preise/pms_en.php?show=ok&make=ok&aog=A&kat=Mahlgut	0.65 Score:4 4x60%=240% https://plasticker.de/preise/pms_en.php?show=ok&make=ok&aog=A&kat=Mahlgut
Total	100	460	400

Score: 1 (lowest) - 5 (highest) 

Based on the above COWS matrix, Polyethylene Terephthalate Glycol (PETG) is the most suitable material to be used for the transparent sheet.

From this lesson, I learned how to further explain why I chose certain criteria for the materials. The criteria chosen have to be explained in detail as to why it is important for the working purpose of the device. Dr Noel told us that some of us did not include these explanations in our CA1 report, hence this lesson was a good exercise for us to really crack our brains and think of ideas💪.

2. Week 12 Topic 6 - Design for materials

This week, we looked into how devices were modified over time and what materials were added/removed to enhance the existing product. For example, a hair dryer that has been modified for over a hundred years. Initially, it was a big and bulky machine that looked like a "torture machine". Now, it is a small handy device that all households have. We also had to research another material to replace the existing material in the product.  

2.1 Choosing a material

We were able to use the online library resources to research the different materials available. Some of the criteria we focused on were whether the material is biodegradable and renewable, and its variation across different industries. The material we chose was Paperfoam, which is widely used for packaging. Its lightweight characteristic helps to reduce the energy needed for transportation costs. 

Using the worksheet provided to us, these are some of the ideas we have: 

From this lesson, I learned about the versatility of materials. I did not know that we could use a completely different material to be applied to a device to enhance its function. This also allowed me to put my creative thinking skills to the test as my team and I had to think of different ways that the material can be applied. 

 3. Practical 3

Following the topic of "Materials", in this practical, we focused on investigating different material properties. There are 4 main material properties we examined this week, and they are: 

1. Thermal conductivity 

2. Surface Tension

3. Young's modulus 

4. Viscosity of liquid. 

My group was assigned to investigate the thermal conductivity of a material. The tested material was placed on the test bed with a block of ice on top of it. Steam will be introduced by a steam generator that will heat up the test bed, and the time taken for the ice to completely melt will be recorded. The time taken for the ice to melt is dependent on the thermal conductivity of the material. The longer the ice takes to melt, the poorer the thermal conductivity of the material is. This is because heat from the test bed to the ice is transferred at a slower rate. 

The thermal conductivity can be calculated using Fourier's Law, 

                                                                           Q = −kA (ΔT / Δx)

Read on to find out how we managed to find the thermal conductivity of the material! 😊

3.1 Theory and Calculation

Assuming the rate of heat transfer of the material is equal to the rate of heat transfer of the ice, we were able to use 2 different equations to find the unknown thermal conductivity, k. 

Equations: 

Rate of heat transfer of ice, Qice=mlf+mCpΔT

Rate of heat transfer of material   Q = −kA (ΔT / Δx)

(The latent heat of fusion of ice is added as the ice is changing phase from a solid to a liquid state.)

ΔT would be the temperature difference between the ice and the surface of the test bed. We did not use the temperature of the steam as we would have to assume that the test bed was thin enough such that the heat from the steam would be able to be conducted through easily.

The thickness ( Δx )of the material was given, and we calculated the surface area of the material using the diameter given to us.

Q can be found by using the equation for the rate of heat transfer of ice as the mass, specific heat capacity, and latent heat of fusion of the ice are given.

These are our results from the experiment:

Mass of ice(kg)	0.02006
Diameter of test specimen(mm)	34.5
Surface area of specimen(m)	0.0009348
Thickness of test specimen(mm)	2.2
Latent heat of fusion of ice(KJ/Kg)	333.5
Time taken to melt the ice completely(s)	30min

Calculations:

3.2 Reflection

Our initial calculations were wrong as we only needed to calculate the latent heat of fusion of ice. This caused our initial thermal conductivity to be very large😖 It was wrong as the material was similar to PET, which has a thermal conductivity of 0.3W/m.K. Hence, the thermal conductivity of the material should be close to the value, which we got!😝

Additionally, I also learned that we had to take into account the type of plastic used to hold the ice and the thickness of the metal between the steam and the test material. Our calculations may not be accurate as we just assumed the temperature of the ice to be 0°C, when we should have measured it with an infra-red thermometer to be sure. 

The heat supplied from the steam to the test bed may also not be constant as we opened the steam generator regularly to check the water level in the generator. Some heat may be lost from the steam to the surroundings when we opened it. 

The surface temperature of the test bed isn't entirely constant as we only measured one part of the test bed to be 70°C. That was the part where we would be placing the test material and the ice. The surface temperature also kept changing and we only placed the test material on the test bed when it reached 70°C. By the time we started the timer, the temperature may have changed a little. This may lead to some discrepancies in the calculation as well. 

The main takeaway for me was definitely how to perform calculations to determine k. I did not realize we could make use of the latent heat of fusion of ice and equate it to the rate of heat transfer of the material. This allowed me to appreciate the knowledge that I have gained from my previous module, Heat Transfer and Equipment. I am glad that I was able to put it to use in a different context, and not just in my examinations! 😂