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ENGINEERING, AE 2018 HSC 17 MC

Aircraft skins can be constructed using either fibre metal laminate (FML) or sheet aircraft-grade aluminium alloy.

FML is preferred in this application because it has

  1. higher density and lower Young's modulus.
  2. higher density and improved fatigue resistance.
  3. higher strength-to-weight ratio and lower Young's modulus.
  4. higher strength-to-weight ratio and improved fatigue resistance.
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`D`

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  • Higher density and lower Young’s modulus are both negative material properties for aircraft skins, as these skins should be light (lower density) and rigid (higher stiffness/Young’s modulus).
  • Additionally, fatigue resistance is important as aircraft skins are exposed to varying air pressures.

`=>D`

ENGINEERING, PPT 2018 HSC 26d

The components of the bearing assembly used in the fidget spinner are shown.
 

The retainer can be made from either glass fibre-reinforced nylon or stainless steel.

Compare the in-service properties of these materials for use in the retainer.   (4 marks)

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ENGINEERING, AE 2017 HSC 26c

In modern aircraft, the external skin is riveted to the frame using solution treated and quenched aluminium 4% copper alloy rivets. These rivets are used immediately to attach the external skin of the aircraft to the frame.

Describe the changes that occur to the structure and properties of these rivets after installation.   (3 marks)

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Changes to structure and properties of the rivet

  • The microstructure of the rivet, after quenching, is a solid unstable solution of copper dissolved in aluminium.
  • On reaching room temperature, the heat energy created initiates the copper’s precipitation out of solid solution as finely distributed precipitates \(\ce{(CuAl2)} \), which strengthens the alloy considerably.
  • Work hardening is produced by cold working the metal when the rivet head is formed.
  • The rivet is significantly strengthened due to the installation, and its hardness will increase until precipitation hardening is finalised.
  • Corresponding decreases in the ductility of the metal will also be evident. 
Show Worked Solution

Changes to structure and properties of the rivet

  • The microstructure of the rivet, after quenching, is a solid unstable solution of copper dissolved in aluminium.
  • On reaching room temperature, the heat energy created initiates the copper’s precipitation out of solid solution as finely distributed precipitates \(\ce{(CuAl2)} \), which strengthens the alloy considerably.
  • Work hardening is produced by cold working the metal when the rivet head is formed.
  • The rivet is significantly strengthened due to the installation, and its hardness will increase until precipitation hardening is finalised.
  • Corresponding decreases in the ductility of the metal will also be evident. 

♦♦ Mean mark 27%.

ENGINEERING, PPT 2017 HSC 22a

Carbon fibre was originally developed to produce aircraft bodies and high performance vehicles. Carbon fibre is now used in a wide range of applications, including the manufacture of the type of bicycle frame shown.
 

Outline the advantages of carbon fibre bicycle frames over steel bicycle frames.   (3 marks)

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Advantages of carbon fibre bicycle frames

  • Excellent strength to weight ratio, which is a preferred feature and is superior to that of steel.
  • More intricate shapes can be moulded with carbon fibre than steel.
  • Rigid and resistant to corrosion.
  • Wide colour selection available.
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Advantages of carbon fibre bicycle frames

  • Excellent strength to weight ratio, which is a preferred feature and is superior to that of steel.
  • More intricate shapes can be moulded with carbon fibre than steel.
  • Rigid and resistant to corrosion.
  • Wide colour selection available.

ENGINEERING, AE 2019 HSC 25b

Some materials have properties that allow them to be used in the manufacture of both modern racing yachts and aircraft. These materials include Kevlar® aramid fibre, carbon fibre epoxy composites and aluminium alloys.

Complete the table by providing a property which makes each of these materials suitable for the manufacture of both yachts and aircraft.   (3 marks)
 

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Include one of the properties in the second column:

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Include one of the properties in the second column:

ENGINEERING, AE 2019 HSC 24a

An image of an aeroplane is shown with the position of the wing support beam indicated.
 

Assume the engines are supported by the single beam. The beam runs through the plane, wing tip to wing tip.

Compare the use of composite materials with the use of metals for the manufacture of the beam.   (3 marks)

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Answers could include 3 of the following comparisons:

Composite materials vs Metals 

  • Composite materials are lighter than metals.
  • Manufacture: Carbon fibre epoxy composite beams requires specialised equipment whereas metal based inputs can be manufactured using readily accessible tools such as welders, gas torches and plasma cutters.
  • Composite materials are easier to lift due to lighter weight. This allows workers to position them more easily during the construction process.
  • Equipment used for making carbon fibre epoxy moulds likely to be more accurate than in metal fabrication. However, it is possible to achieve similar accuracy in machining metals compared to that of composite materials.
  • Due to the nature of the wing support beam and the stresses placed on it, a metal beam is subject to stress weaknesses (such as scratches and corners of drilled holes) and flaws in welds that create fatigue. Carbon fibre not affected by fatigue cracking.
Show Worked Solution

Answers could include 3 of the following comparisons:

Composite materials vs Metals 

  • Composite materials are lighter than metals.
  • Manufacture: Carbon fibre epoxy composite beams requires specialised equipment whereas metal based inputs can be manufactured using readily accessible tools such as welders, gas torches and plasma cutters.
  • Composite materials are easier to lift due to lighter weight. This allows workers to position them more easily during the construction process.
  • Equipment used for making carbon fibre epoxy moulds likely to be more accurate than in metal fabrication. However, it is possible to achieve similar accuracy in machining metals compared to that of composite materials.
  • Due to the nature of the wing support beam and the stresses placed on it, a metal beam is subject to stress weaknesses (such as scratches and corners of drilled holes) and flaws in welds that create fatigue. Carbon fibre not affected by fatigue cracking.

ENGINEERING, AE 2019 HSC 15 MC

Titanium is used to manufacture aircraft undercarriages that support landing wheels.

Why is titanium used in preference to alloy steel for this purpose?

  1. It has lower density and lower strength.
  2. It has lower density and higher strength.
  3. It has higher density and lower strength.
  4. It has higher density and higher strength.
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`B`

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  • Lower density and higher strength, means the material has a very high strength to weight ratio, or specific strength.
  • This is one of the most beneficial characteristics associated with titanium alloys.

`=>B`