What is superelasticity in a shape memory alloy?

Superelasticity is the ability to bend a long way and spring back fully without being heated. Nitinol spectacle frames can be twisted and still return to shape.

Give three uses of shape memory alloys.

Shape memory alloys are used in orthodontic arch wires, medical stents and flexible spectacle frames. Each use exploits the alloy's shape recovery or superelasticity.

Explain how a shape memory alloy wire acts as an actuator.

An electric current heats the wire, which then contracts to its shorter remembered length. The wire pulls a lever or latch silently without a motor.

CCEA A-Level Technology and Design 8900

Material Selection and Wood

Topic overview Material selection criteria Physical and mechanical properties Hardwoods, softwoods and timber stock sizes Pine, ash, beech, oak and mahogany Manufactured boards Wood finishes, veneers and laminates

Metals

Topic overview Ferrous and non-ferrous metals and alloys Metal stock forms and sizes Aluminium, copper, brass and zinc Carbon steels and stainless steel Finishes for metals

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Design for Manufacture, Quality and Safety

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Electronic Control SystemsOption A

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Microelectronic Control SystemsOption A

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Mechanical and Pneumatic ComponentsOption B

Topic overview Open and closed loop mechanical and pneumatic control Safe working with compressed air and mechanisms Levers, linkages and moments Gear types and gear trains Pulleys, belts, chains and shaft fixings Cams, cranks and converting motion Compressed air supply and pneumatic valves Cylinders, shuttle valves, restrictors and reservoirs Pneumatic circuits for logic, timing and speed control

Mechanical and Pneumatic SystemsOption B

Topic overview Hydraulics, system limitations and plant safety Torque, work, power and air consumption Vacuum handling, proximity sensors and 5/3 valves Sequential and cascade pneumatic circuits Cam profiles and follower displacement diagrams Gear geometry, pulley blocks and ratchets Toggles, treadles, shafts and couplings Friction, brakes and clutches Bearings, lubrication and seals

Designing and Manufacturing ProductsOption C

Topic overview Research, questionnaires and specifications Idea generation, critiques and computer simulation Manufacturing planning and product evaluation CFRP, GRP, Kevlar and tungsten carbide Smart materials, nanotechnology and biophotovoltaics Isometric, perspective and assembly drawing Laminating, steam bending, cutting and printing processes Risk assessment and product safety law Scales of production, JIT and cell production Quality assurance, ISO 9001 and continuous improvement Design influences and intellectual property rights

Product Design in Industry and SocietyOption C

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Product and System Design and Manufacture

Topic overview Clients, end users and design briefs Researching existing solutions and writing a specification Generating and appraising design proposals Developing a concept with numerical analysis, ergonomics and aesthetics Working drawings and planning manufacture Testing and evaluating a prototype

Designing and Manufacturing Products

Smart materials, nanotechnology and biophotovoltaics

3 things to know
AS 1 Paper 2

Overview

Shape memory alloys and superelasticity, piezoelectric materials in lighters and sensors, light-emitting polymers, nanotechnology and self-cleaning glass, and biophotovoltaic devices.

What you need to know

Answer each one before you reveal it.

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Key term

What is a shape memory alloy?

Key term

Explain how the shape memory effect works.

Key term

How is a shape programmed into a shape memory alloy?

Questions from this subtopic

Each one with the model answer underneath.

1
What is a shape memory alloy?
Model answer
A shape memory alloy is a metal that returns to a pre-set shape when heated above its transformation temperature. Nitinol, an alloy of nickel and titanium, is the most common.
2
Explain how the shape memory effect works.
Model answer
Below its transformation temperature the alloy has a soft crystal structure that deforms easily. A rise in temperature restores the original structure, and the alloy recovers its remembered shape.
3
How is a shape programmed into a shape memory alloy?
Model answer
The alloy is clamped in the required shape and heat treated at a high temperature. On cooling, that shape is retained as the remembered form.
4
What is superelasticity in a shape memory alloy?
Model answer
Superelasticity is the ability to bend a long way and spring back fully without being heated. Nitinol spectacle frames can be twisted and still return to shape.
5
Give three uses of shape memory alloys.
Model answer
Shape memory alloys are used in orthodontic arch wires, medical stents and flexible spectacle frames. Each use exploits the alloy's shape recovery or superelasticity.
6
Explain how a shape memory alloy wire acts as an actuator.
Model answer
An electric current heats the wire, which then contracts to its shorter remembered length. The wire pulls a lever or latch silently without a motor.

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