Week 4

 This week, our lesson has been scheduled to be asynchronous, which mean that it will be done on our own, at our own time. This is probably because this is a revision of what we have learnt previously in Year 1 when we took the module "Materials for Design". One crucial aspect to selecting an appropriate material for a specific function or a single component for an entire product is the COWS Decision Matrix🐄🐮.

COWS simply stands for:

C ⮚ Criteria - Criteria are the set of properties we determine that a material should have in order to be an appropriate material

O ⮚ Options - Options refer to the materials we deem somewhat viable because they belong in a material class that greatly suites the criteria set for the material we will use for the specific function.

W ⮚ Weightage - Not all criteria are equally as important. Therefore, we provide a weightage for each criteria, depending on its significance to the design of the product. This way, we can truly determine which materials have properties that can greatly contribute to the functionality of the product. The sum of the weightages of all criteria should be 100%

S ⮚ Score - We give scores - on a scale of one to three/five - to materials for specific criterion depending on how well it fulfills the criterion, which we then multiply by the criterion's weightage in order to determine the true score of the material with regards to the single criterion. The total score of a material is the sum of the scores determined by all criteria. The highest total score among all options will be crowned as the reigning Miss Universe👑 I mean, we will deem as the most appropriate material for the specific function. The best score attainable by any material will depend on the highest score on the number scale. In this case, either three or five.

In our opinion, we think this method of selection is an excellent, logical way to determine the best option among several options. We mean, it could be used to make logical decisions, even if it isn't about selecting the most appropriate material. It is a viable method for determining the best decision anyone can make when there are multiple variables that can affect the outcome of the decision. However, this cannot be used when we needed to make quick decisions because tbf (to be fair), it can take some time to decide on something when this method is used.

Assignment

Thankfully, we have had some practice on this technique when we were tasked to select a material for a disposable water bottle that does minimal environmental harm.

First, we have to identify the function, constraints and objectives of the bottle.

Function	To contain liquids, such as water, sweetened drinks and carbonated drinks.
Constraints	Corrosion resistant to mild acid and mild alkalis Light weight (low density) Non-reactive to food ingredients (reactivity) Cheap Decomposable
Objectives	Minimise environmental harm

Now that we have this table, we translated this information into a set of criteria which will be the deciding factors of what makes the perfect material for the bottle.

Criteria

1. Corrosion-resistant
2. Density
3. Cost
4. Biodegradability

We then shortlisted the type of materials that would be appropriate for the purpose of a DISPOSABLE BOTTLE.

Materials suitable:

Mainly would be plastic, due to the disposability and low cost.

Eliminate: Metals and Glass.

Since we already have a type of material, we then had to search for plastics or polymers that best fit the design brief. We have decided to evaluate 3 materials - polycaprolactone, polyhydroxybutyrate and compostable PLA blend - using the COWS Decision Matrix.

COWS Decision Matrix:

Viable Materials: Polycaprolactone, Polyhydroxybutyrate, Compostable PLA Blend

Material Chosen:

		Options
Criteria	Weightage	Polycaprolactone (PCL)	Polyhydroxybutyrate (PHB)	Compostable PLA Blend
Biodegradability	40%	Excellent Score: 5 5 x 40% = 200%	Excellent Score: 5 5 x 40% = 200%	Good Score: 4 4 x 40% = 160%
Non-reactive	30%	Excellent Score: 5 5 x 30% = 150%	Poor Score: 1  x 30% = 30%	Excellent Score: 5 5 x 30% = 150%
Corrosion resistant	10%	Excellent Score: 5 5 x 10% = 50%	Excellent Score: 5 5 x 10% = 50%	Excellent Score: 5 5 x 10% = 50%
Low density, r (light weight)	10%	r =1.145  g/cm3 Score: 4 5x 10% = 40%	r = 1.25 g/cm3 Score: 4 4 x 10% = 40%	r = 0.8 g/cm3 Score: 5 5 x 10% = 50%
Cost	10%	Cheap Score: 4 4 x 10% = 40%	Not cheap Score: 2 2 x 10% = 20%	Expensive Score: 1 1 x 10% = 10%
Total	100%	480%	340%	420%

Material Chosen:

Polycaprolactone

Since this assignment required us to do research, the references have been included in our submitted assignment.

And that was how to use the COWS Decision Matrix.