Tutorial 1

Question 1

A fibre reinforced polymer composite contains a weight fraction wf of fibre which is equivalent to a volume fraction of fibre vf. If the fibre density is double the polymer matrix density which of the following statements is true at all fibre contents?

A. wf is greater than vf
B. wf is double vf
C. wf is not related to vf
D. wf is half vf
E. wf is less than vf

Answer 1

A. wf is greater than vf

wf=vf ρf/ρc.

Since ρm < ρf then ρc < ρf and hence ρf/ρc >1.

wf is only double vf

when vf =0 (not a composite), hence A is correct answer

Question 2

Why are thermoplastic polymers rarely found in composite production using standard Pultrusion and Filament Winding equipment?

Answer 2

For both techniques require low viscosity liquids during the fibre impregnation stage. In pultrusion the dies are designed to heat and form simultaneously whereas thermoplastic would normally require cooling at the forming stage.

Question 3

List five fibre related “properties” which influence fibre reinforced polymer composite mechanical performance?

Answer 3

• Fibre Mechanical Properties
• Fibre Concentration
• Fibre Orientation
• Fibre Diameter
• Fibre Length

Question 4

List the common perceived advantages and issues with the use of thermoplastic polymers as composite matrices?

Answer 4

Thermoplastics Advantages:

• Fast processing
• No chemical reactions
• More ductile
• Ease of recycling

Thermoplastics Issues:

• High melt viscosity for impregnation
• Sometimes high process temperatures required
• Control over morphology in crystallising TP’s
• Lower modulus
• Higher creep

Question 5

List the common perceived advantages and issues with the use of thermoset polymers as composite matrices?

Answer 5

Thermoset Advantages:

• Low viscosity
• Can be cheap
• High stiffness
• Low creep

Thermoset Issues:

• Longer processing times
• Lower strain to failure
• Lower fracture toughness
• Control of chemical reaction during processing
• Difficult to recycle

Question 6

Is matched-die moulding technique appropriate for making aerospace grade composite structures? Give two reasons.

Answer 6

Matched-die is generally used for high rates of production. It involves making two dies for heavy pressing and heating up. So it can be fairly expensive mould.

• Aerospace structures generally do not need such high production rate, which involves investment.
• The quality of composites are the most important parameter in aero-structures whereas matched-die gives poorer performances compared to autoclave curing where the heat and temperature are very well controlled.