← Personal and Public Transport
Engineering materials: How are composite materials used in vehicle bodies and structures to balance strength, mass and energy absorption?
Describe the structure and properties of fibre reinforced polymer composites, identify their use in vehicle bodies and crash structures, and justify the selection of composites over steel or aluminium in specific applications
A focused answer to the HSC Engineering Studies Personal and Public Transport dot point on composites. Carbon and glass fibre reinforced polymer, layup methods, properties versus steel and aluminium, examples from supercars and EVs, and worked HSC-style past exam questions.
Have a quick question? Jump to the Q&A page
What this dot point is asking
NESA wants you to describe fibre reinforced polymer composites, identify where they are used in vehicles (bodies, panels, crash structures, suspension), compare them with conventional metals, and justify the selection decision for a specific application.
The answer
What a composite is
A composite combines a reinforcement (fibres, particles) embedded in a matrix (polymer, metal or ceramic) so that the combined material has properties neither phase has alone. For vehicles, the dominant family is fibre reinforced polymer (FRP):
- Carbon fibre reinforced polymer (CFRP). Carbon fibres (typically 7 micron diameter, 3500 MPa tensile, 230 GPa modulus) in an epoxy resin matrix. Used in supercar monocoques, F1 chassis, structural panels of premium EVs.
- Glass fibre reinforced polymer (GFRP). Glass fibres (1500 MPa tensile, 70 GPa modulus) in polyester or epoxy. Cheaper and tougher than CFRP. Used in body panels, boat hulls and Corvette body shells.
- Aramid fibre (Kevlar) composites. Used in armouring and tyre belts for cut resistance and impact toughness.
Layup and curing
Composite parts are made by laying woven or unidirectional fabric into a mould, wetting with resin, and curing.
- Hand layup. Manual placement, atmospheric cure. Used in low-volume parts.
- Pre-preg autoclave. Fabric pre-impregnated with B-stage resin, vacuum-bagged in a mould, cured in an autoclave at about 120 degrees C and 5 bar. Used for F1 and aerospace parts.
- Resin transfer moulding (RTM). Dry fabric in a closed mould, resin injected under pressure. Used for volume automotive parts (BMW i3 passenger cell, Lamborghini Aventador monocoque).
Properties compared
| Material | Density (kg/m^3) | Tensile strength (MPa) | Modulus (GPa) | Specific strength (MPa per kg/m^3) |
|---|---|---|---|---|
| Grade 350 steel | 7850 | 480 | 200 | 0.061 |
| Aluminium 6061-T6 | 2700 | 310 | 69 | 0.115 |
| GFRP (unidirectional) | 1900 | 1300 | 40 | 0.68 |
| CFRP (unidirectional) | 1600 | 1500 to 3500 | 130 to 230 | 0.94 to 2.2 |
CFRP wins on specific strength by an order of magnitude. The trade-off is cost and manufacturability.
Where composites win in vehicles
- Monocoque chassis. Lamborghini Aventador, McLaren 720S, BMW i3 and i8, Alfa Romeo 4C. CFRP saves 100 kg or more versus steel and increases torsional stiffness.
- Body panels. Bonnet, boot lid and roof in many sports cars (Audi R8 carbon roof, Toyota Supra carbon roof option).
- Crash structures. Front and rear crash boxes designed to crush progressively.
- Wheels. Carbon wheels save 5 to 10 kg per corner, reducing unsprung mass.
- Drive shafts. Lower polar moment of inertia gives faster acceleration response.
Where composites lose
- Cost (A$50/kg raw fabric is 25 times the cost of steel)
- Repair (cannot be welded or hammered straight)
- Recycling (thermoset matrix prevents remelting)
- Damage tolerance under impact (delamination is hard to detect visually)
Holden, Ford and Toyota Australia experimented with GFRP body panels in low-volume models (the Brock VL Group A had CFRP front panels), but mass-market vehicles have stayed with stamped steel and aluminium for cost and reparability.
Past exam questions, worked
Real questions from past NESA papers on this dot point, with our answer explainer.
2020 HSC style5 marksJustify the use of carbon fibre reinforced polymer (CFRP) for the monocoque of a Formula 1 car. In your answer, refer to specific properties of CFRP compared with structural steel and identify one disadvantage of CFRP.Show worked answer →
A Formula 1 monocoque is the central structural tub that carries the engine, suspension and driver. It must combine very high stiffness, low mass and outstanding crash energy absorption. CFRP is the standard material because of three property advantages over steel.
- Specific strength
- CFRP has tensile strength up to 3500 MPa and density around 1600 kg/m^3, giving a specific strength about 5 times that of grade 350 structural steel (520 MPa over 7850 kg/m^3). The monocoque is about 80 kg, where an equivalent steel structure would be over 200 kg. Lower mass means higher acceleration at the same engine output and lower lateral load on the tyres in cornering.
- Stiffness
- CFRP has Young's modulus up to 230 GPa, comparable to steel (200 GPa), but at one-fifth the density. The monocoque chassis is very torsionally stiff, which lets the suspension geometry behave predictably without flex.
- Energy absorption
- CFRP fails by progressive delamination and fibre fracture, dissipating large amounts of energy per unit mass. The nose-cone crash structure is designed to crush axially, absorbing the kinetic energy of a 50 km/h frontal impact while protecting the driver.
- Disadvantage
- CFRP is expensive (about A$50/kg for raw fabric, plus autoclave curing). It is impossible to weld or repair locally; damaged sections must be cut out and replaced with new laminate. Lifecycle disposal is limited because thermoset matrices cannot be remelted, although pyrolysis recycling of carbon fibre is emerging.
Markers reward (1) named property comparisons (specific strength, modulus, energy absorption) with figures, (2) the crash energy management point, and (3) at least one credible disadvantage.
Related dot points
- Apply Newton's laws of motion to road vehicles, calculate accelerating and braking forces, and analyse impulse and momentum in crashes
A focused answer to the HSC Engineering Studies Personal and Public Transport dot point on Newton's laws. Acceleration and braking force on a vehicle, impulse and momentum in collisions, the crumple zone, ANCAP testing, and worked HSC-style past exam questions.
- Describe the structure, properties and manufacturing of carbon fibre reinforced polymer used in modern airframes, identify advantages over aluminium, and apply this knowledge to the Boeing 787 and Qantas operations
A focused answer to the HSC Engineering Studies Aeronautical Engineering dot point on aircraft composites. CFRP construction, autoclave manufacturing, Boeing 787 Dreamliner half-composite airframe, fatigue and corrosion advantages, Qantas Project Sunrise, and worked HSC-style past exam questions.
- Describe the production, heat treatment and key properties of aluminium alloys 2024 and 7075, identify their use in airframe structures, and compare them with structural steel and titanium
A focused answer to the HSC Engineering Studies Aeronautical Engineering dot point on aluminium alloys. Production, precipitation hardening, 2024 and 7075 properties, fuselage skins versus wing spars, Australian aviation history, and worked HSC-style past exam questions.