How can a material sense its environment and respond to it, and what new design possibilities does that open up?
Modern materials developed through invention or improved processing, and smart materials that change a property in response to an external stimulus, including shape-memory alloys, thermochromic and photochromic materials, piezoelectric materials and electroluminescent wire.
A focused answer to AQA A-Level Design and Technology Product Design 3.1.4, covering modern materials and smart materials that change a property in response to a stimulus, including shape-memory alloys, thermochromics, piezoelectrics and electroluminescent wire.
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What this dot point is asking
AQA wants you to distinguish modern materials (developed through invention or improved processing) from smart materials (which change a property in response to an external stimulus), give examples of each, and explain how their behaviour is exploited in products.
Modern materials
They are valued for property combinations that traditional materials cannot match, such as high strength at low weight. The key point AQA wants is that a modern material is "modern" because of invention or improved processing, not because it senses anything: graphene is a single layer of carbon atoms that is exceptionally strong, light and conductive; titanium offers a very high strength-to-weight ratio and corrosion resistance, which is why it is used in implants and aerospace; metal foams trap gas in a metal matrix to give stiffness at very low weight; and high-density modelling foam machines cleanly to make accurate models. These materials open new design possibilities (lighter, stronger, thinner products) but they behave in a fixed way once made. That is what separates them from smart materials, which actively change in use.
Smart materials
Smart materials let designers replace mechanical sensors and moving parts with the material itself, for example a kettle label that changes colour when hot, or a self-adjusting dental brace using a shape-memory alloy. It is worth knowing each one by its stimulus and response. A shape-memory alloy such as Nitinol responds to heat: deformed when cool, it snaps back to a memorised shape above a transition temperature, used in self-adjusting braces, spectacle frames and actuators. Thermochromic pigments respond to temperature with a colour change, used in safety indicators and novelty packaging. Photochromic materials respond to light, darkening in sunlight as in reactive lenses. Piezoelectric materials respond to stress by generating a voltage, and the effect is two-way, so a voltage makes them move; this is used in lighters and gas igniters, sensors, and the tiny speakers and buzzers in greetings cards. Electroluminescent wire responds to an alternating current by glowing, used in safety clothing and displays. The unifying idea, and the one examiners reward, is that the material itself does a job that would otherwise need a sensor, a mechanism and a controller, which can simplify a product, reduce its part count and make it more reliable.
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20196 marksExplain how a shape-memory alloy and a thermochromic material each work, and discuss how each could be used in a product to improve its function or safety. [6 marks]Show worked answer →
A Paper 1 extended item. Markers reward the mechanism plus an applied use for each. Award marks for the shape-memory alloy: it deforms easily when cool but returns to a memorised shape when heated above a transition temperature, and the change is reversible (example: a self-adjusting dental brace that continues to apply force as it warms to body temperature, or a spectacle frame that springs back after bending). Award marks for the thermochromic material: a pigment that changes colour reversibly above a set temperature (example: a kettle or baby-spoon indicator that changes colour to warn that contents are too hot, improving safety). A top answer states the shared idea that a smart material responds to a stimulus and replaces a separate sensor or mechanism, simplifying the product.
AQA 20214 marksExplain the difference between a modern material and a smart material, giving one example of each. [4 marks]Show worked answer →
A short-answer item testing a distinction students blur. Award marks for: a modern material is a new or improved material made possible by invention or new processing, but it does not respond to a stimulus (example: graphene, very strong and conductive, or titanium); a smart material changes one or more of its properties reversibly in response to an external stimulus such as heat, light, electricity or stress (example: a shape-memory alloy, or a thermochromic pigment). Full marks need the responsive-versus-not-responsive distinction plus a valid example of each. Calling graphene a smart material is the common error, because being new is not the same as being responsive.
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