Choice materials

• The 2/3 part should be a thermoplastic composite consisting Polyethylene and short carbon fiber.
• The rest of the part should be PE.
• Fiber volume fraction will be 50%. This will push the weight value up even as it raises the strength value.
• These effects will be computed later on using the data below.

Carbon Fiber:

[Data from www.sglgroup.com]

Polyethylene:
Tensile Strength 0.20 - 0.40 N/mm²
Notched Impact Strength no break Kj/m²
Thermal Coefficient of expansion 100 - 220 x 10-6
Max Cont Use Temp 65 oC
Density 0.944 - 0.965 g/cm3
[Data from www.bpf.co.uk]

Ideas about design and process

1. The blade could be made in two seperate part and joined. This will help avoid complicated processing methods.
2. Injection moulding could still be used; the double barrel type.
3. This method is most suitable because of it's ability to easily reproduce the thin size of the blade sections, as well as to maintain some level of speed in the production rate.
3. Two moulds have to be designed.
4. The first, 2/3 of the blade's length for the reinforced plastic; the second, for the plain plastic.
5. ´The materials will be melt processed then joined/sealed while still in the semi-molten state.
 

New Insights

1. Clients wants 2/3 of blade to contain fibre, and the rest will be totally "fibre-free"
2. The reinforced section is the part closer to the stick, starting from the joint between the stick and the blade.
3. The joint itself should be made thinner.
4. The blade's cross-section or thickness could be reduced.
5. The weight of the blade should be less than 50g; initially 80g.
6. The reinforced section could be stiffer while the rest of the part can maintain it's current level of flexibility.
7. New colouring method could be proposed to improve the current colour's appeal and durability; ie more shinning and lasting colours. 

Carbon fiber

Carbon fiber is a possible reinforcement.
It's density?
Can it be melt processed with PE or PP?
Is it compatible with these thermoplastics?
Is the cost worthwhile for this product?
Any similar fibers?

Would a thermosett like Polyester be perfect?

Polyester...
Density?
Tensile strength?
Impact strength?

Why PP?

Why think of PP as possible replacement for PE?
-To reduce weight of blade, the volume has to be reduced.
-Reducing the volume of PE will reduce the weight, but also the strength.
-Enough quantity of PE has to be removed to make room for possible reinforcement
-Reducing too much PE will mean:
1. much reinforcement will be needed to make up for strength... cost
2. less plastic for binding the fiber... brittleness?
3. weight issues if fiber is not light

PP has high strength.
Much quantity can be removed and little fiber added.
Original strength will be achieved
But PP is stiff.
Type of reinforcement chosen needs to take care of this.

PE vs PP

Thinking about plastics that are lighter than Polyethylene or in the same density range, Polypropylene comes to mind.
Trying to think about their similarities and differences; both are inert.
PE...
is more flexible,
accumulates less static charge,
is far less stiff
is costlier

Now some figures:

Property	HDPE	LDPE	PP
Tensile Strength	0.20 - 0.40 N/mm²	0.20 - 0.40 N/mm²	0.95 - 1.30 N/mm²
Notched Impact Strength	no break Kj/m²	no break Kj/m²	3.0 - 30.0 Kj/m²
Thermal Coefficient of expansion	100 - 220 x 10-6	100 - 220 x 10-6	100 - 150 x 10-6
Max Cont Use Temp	65 °C	65 °C	80 °C

PP possess higher tensile strength.
However PP is far less wear and weather resistant.

Polyethylene

Facts about Polyethylene...
1. It has different types (grades), with density ranging from 0.857 g/cm3 to 0.975 g/cm3.
2. There are LLDPE, LDPE, HDPE.
2. The lower the density, the higher the impact strength of the part made from it.
3. The lower the density, the less the weight of part made from it.
4. Low density yields high toughness but low creep resistance.
5. Melt flow index (a function of processibility) is independent of density.