Plastics and Next Gen Materials

Question 1

How are plastics used in aerospace?

Answer 1

Plastics are used in fasteners, joints, seals and textile fibres

Question 2

Why are phenolics used in aircraft interiors?

Answer 2

They do not produce smoke when they burn, so there is still high visibility if there is a fire on the plane

Question 3

Describe the extrusion process for thermoplastics

Answer 3

• Thermoplastic chips are placed into the hopper
• The chips are melted in a heated barrel and pushed into the die by a screw
• Produces a continuous cross-section
• Multiple polymers can be extruded simultaneously for a layered cross-section
• Films and sheets are also produced this way

Question 4

Describe the injection moulding process for thermoplastics

Answer 4

• Thermoplastic chips are placed into the hopper
• The chips are melted in a heated barrel and pushed into the mould by a screw
• Plastic solidifies and is ejected from mould

Question 5

What are the advantages of injection moulding thermoplastics?

Answer 5

Can produce small parts very quickly, flow of the polymer aligns chains which gives good mechanical properties

Question 6

What are orientation effects in thermoplastics?

Answer 6

• Caused by extrusion or polymer flow
• Can lead to dimensional instability especially when subjected to heat
• Short fibres at the edge of the part align which resists shear stress on the part

Question 7

Describe the stentering process of thermoplastics

Answer 7

• Film is extruded
• Film is then stretched in both directions before being rolled onto the spool
• This reduces orientation effects
• Film is often coated in metal to improve barrier properties

Question 8

Describe the thermoforming process of thermoplastics

Answer 8

• Sheet of thermoplastics is heated until leathery
• Placed into mould and pressed/vacuumed in
• Particularly useful to produce aircraft canopies from acrylic with this method as it give good surface clarity

Question 9

Describe how faults in composite structures could be detected

Answer 9

NDT techniques like X-Ray or sensors detecting vibration and acoustic emission in the structure which are a result of fibres breaking

Question 10

Give examples of self-repair systems in composite airframes

Answer 10

• Microcapsule (liquid resin capsules in structure)
• Vascular (tubes of liquid resin in structure)
• Intrinsic (resin automatically reforms in the solid state)