Real-World Case Studies: Material Selection and Forces

This lesson examines real-world case studies that demonstrate material selection and the role of forces in product design, as required by AQA GCSE D&T (8552), Sections 3.2.1 and 3.2.2. Studying real products helps you understand how the theoretical concepts of material properties, forces, and selection criteria are applied in practice. These case studies are also excellent examples to reference in exam answers and your NEA.

---

Case Study 1: The Forth Road Bridge / Queensferry Crossing

The Challenge

Crossing the Firth of Forth in Scotland requires a bridge spanning approximately 2.7 km. The bridge must support heavy traffic loads, resist wind forces, and last for decades in a harsh marine environment (saltwater spray, storms, temperature changes).

Forces Acting on the Bridge

Force	Where It Acts	Caused By
Tension	Suspension cables / stay cables	The weight of the deck pulling the cables downward
Compression	Towers / piers	The weight of the deck and traffic pressing down on the supports
Bending	Deck sections	Traffic loads between supports cause the deck to sag
Torsion	Deck and towers	Wind forces acting asymmetrically can twist the structure
Shear	Connections between deck and supports	Vertical loads create shear at support points

Material Choices

Component	Material	Why
Stay cables	High-tensile steel wire	Extremely high tensile strength; can support thousands of tonnes
Towers	Reinforced concrete	Excellent compressive strength; concrete is strong in compression, steel reinforcement handles any tensile stresses
Deck	Steel box girder with concrete surface	Steel provides strength and stiffness; concrete surface provides grip and wear resistance
Protective coating	Specialist marine-grade paint system	Prevents corrosion from saltwater spray; extends service life

Reinforcing and Stiffening

The deck uses a box girder cross-section — this is effectively a hollow rectangular tube. The box shape provides excellent resistance to bending and torsion while being lighter than a solid cross-section. This is an application of the bending stiffening technique studied earlier.

AQA Exam Tip: Bridges are a favourite exam topic because they involve multiple forces acting simultaneously. If a bridge question appears, identify ALL the forces (tension, compression, bending, torsion, shear) and explain where each acts. This demonstrates comprehensive understanding and accesses higher marks.

---

Case Study 2: Corrugated Cardboard Packaging

The Challenge

Packaging must protect products during transport and storage while being lightweight, cost-effective, and environmentally responsible. A typical corrugated cardboard box must support stacking loads (up to 4-5 boxes high in a warehouse), resist impact during handling, and protect the contents from compression.

Material Selection

Corrugated cardboard is made from two or more flat sheets (liners) bonded to a fluted (wavy) inner sheet.

Layer	Material	Function
Outer liner	Kraft paper (from softwood pulp)	Provides a printable, protective outer surface
Fluted medium	Semi-chemical pulp paper	Creates the corrugated wave pattern that provides strength and cushioning
Inner liner	Kraft or test liner paper	Provides a smooth inner surface to protect contents

How Forces and Reinforcement Apply

Principle	Application in Corrugated Cardboard
Webbing	The fluted medium acts as a web between the two liners, similar to the web in an I-beam
Ribbing	The corrugations act as continuous ribs that resist bending and compression
Compression resistance	The arch shape of each flute resists crushing forces from stacking
Cushioning	The air pockets in the flutes absorb impact energy, protecting contents

Environmental Credentials

• Made from renewable raw materials (trees from managed forests).
• Approximately 80% of corrugated cardboard in the UK is recycled.
• Cardboard is biodegradable if it does end up in landfill.
• Lightweight, reducing transport fuel costs and carbon emissions compared to heavier packaging materials.

Real-world fact: Amazon ships approximately 7.7 billion packages per year worldwide. The vast majority use corrugated cardboard, making it arguably the most important packaging material in the world.

---

Case Study 3: IKEA LACK Coffee Table

The Challenge

Design a coffee table that is extremely affordable (retail price under ten pounds), lightweight enough for a single person to carry, flat-pack for efficient shipping, and aesthetically acceptable.

Material Selection and Construction

The LACK table demonstrates exceptionally clever material selection and engineering:

Component	Material	Why
Tabletop and shelf	Honeycomb paper core with fibreboard (HDF) skin	Extremely lightweight yet rigid; honeycomb core provides stiffness through webbing with minimal material
Legs	Hollow particleboard tubes	Lightweight, inexpensive, adequate compressive strength for a coffee table
Surface finish	Melamine foil or paint	Provides an attractive, wipeable finish at minimal cost
Feet	Nylon pads	Protect floors, prevent scratching

How Reinforcement Techniques Apply

The LACK table is a masterclass in lightweight engineering:

• The honeycomb paper core uses the webbing principle — a lightweight lattice structure provides stiffness without solid material filling the entire volume. The tabletop weighs only about 3 kg despite being 78 cm x 78 cm.
• The hollow tube legs use the bending principle — a tube resists compression and bending more efficiently than a solid section of the same weight.
• The fibreboard skins act as the flanges of an I-beam structure, with the honeycomb core acting as the web.

AQA Exam Tip: The IKEA LACK table is an excellent example to use in exam answers about material selection, reinforcement techniques, cost-effective design, or sustainability. It demonstrates how intelligent design can achieve functionality at minimal material cost.

---

Case Study 4: Carbon Fibre Bicycle Frame (Road Racing)

The Challenge

Design a bicycle frame for competitive road racing that is as light as possible, extremely stiff for efficient power transfer, strong enough to withstand the forces of aggressive riding, and aerodynamically optimised.

Forces on a Bicycle Frame

Location	Primary Forces
Down tube	Tension and compression from pedalling forces and rider weight
Top tube	Bending from rider weight and road impacts
Chainstays	Torsion from pedalling forces; bending from wheel loads
Head tube	Compression and bending from steering and braking forces
Seat stays	Tension from rear wheel loads
Bottom bracket	Torsion from pedalling

Material Selection

Material	Weight (frame)	Stiffness	Strength	Cost
CFRP (carbon fibre)	700-900 g	Excellent — tuneable	Excellent	Very high (one thousand to five thousand pounds+)
Aluminium alloy (6061)	1200-1500 g	Good	Good	Moderate (three hundred to one thousand pounds)
Steel (chromoly)	1800-2200 g	Good	Excellent	Low to moderate (two hundred to eight hundred pounds)
Titanium (3Al/2.5V)	1200-1500 g	Good	Excellent	Very high (two thousand to five thousand pounds+)

Why Carbon Fibre Wins for Racing

CFRP is the material of choice for professional racing frames because: