A3.1 Material classification and properties

A3.1.1 Materials are classified based on their physical, chemical and mechanical properties.

Guidance: You should be able to explain how and why materials are classified and discuss the advantages of classifying materials in terms of physical, chemical and mechanical properties.

There are several ways that materials can be classified; However, for our purposes in DP Design Technology we will focus on the three most relevant ones listed below 

A3.1.2 Materials are classified according to their source or origin.

Guidance: You should be able to understand that materials are classified into natural and human-made, including for example timbers, polymers, metals, glass, textiles, composites, smart materials and biomaterials.

Natural materials

These are materials that occur in nature and can be used with minimal processing.

• Timbers: Wood from trees, used in construction and furniture making.

• Natural textiles: Cotton from cotton plants or wool from sheep, used in clothing.

• Natural polymers: Cellulose from plants or natural rubber from rubber trees.

• Biomaterials: Any material created by, or derived from, biological organisms, including plants, animals, bacteria and fungi.

Human-made materials

These are materials that are created or significantly modified by human intervention.

• Synthetic polymers: Such as polyethylene, nylon, or PVC, created through chemical processes.

• Metals: While metals occur naturally, they often require significant processing (mining, refining, alloying) for use.

• Glass: Made by melting and cooling silica and other materials.

• Synthetic textiles: Like polyester or nylon, created through chemical processes.

• Composites: Combinations of two or more materials, such as fiberglass (glass fibers in a polymer matrix).

• Smart materials: Engineered to have properties that change in response to external stimuli (e.g., shape memory alloys).

A3.1.3 Identifying the most suitable material for a product is a complex and challenging task, involving the consideration of physical, chemical and mechanical properties and aesthetic characteristics

Guidance: You should be able to evaluate the physical, chemical and mechanical properties to ensure the selection of the most appropriate material for a specific purpose.

Identifying the most suitable material for a product requires careful consideration of multiple factors. Product designers must evaluate a range of physical, chemical, and mechanical properties, as well as aesthetic characteristics, to ensure they select the optimal material for a specific purpose.

Selecting for physical properties

When evaluating physical properties, designers usually consider factors such as density, thermal conductivity, and electrical conductivity. 

For example, when designing a lightweight yet durable bicycle frame, a designer might compare the density-to-strength ratios of materials like aluminum alloys, carbon fiber composites, and titanium, and choose the material that best matches the design context they are designing for.

Selecting for chemical properties

Chemical properties are crucial for determining a material's resistance to corrosion, reactivity with other substances, and environmental stability. 

A designer creating outdoor furniture would need to select materials that can withstand exposure to UV radiation, moisture, and temperature fluctuations. They might consider the chemical resistance of various polymers or the natural weather resistance of certain wood species.

Selecting for mechanical properties

Mechanical properties such as strength, elasticity, and fatigue resistance are essential for ensuring a product can withstand the stresses it will encounter during use. 

For instance, when designing a high-performance sports shoe, a designer would evaluate the tensile strength and elasticity of different synthetic fabrics and foam materials to create a shoe that offers both support, comfort, durability, and flexibility.

Selecting for aesthetic properties

Aesthetic characteristics, while not strictly physical or chemical properties, play a significant role in material selection. Designers must consider factors like color, texture, and finish to ensure the material aligns with the product's visual design and brand identity. 

For a high-end lamp, a designer might choose materials like glass and polished metal for their premium look and feel, while ensuring these materials also meet the necessary durability and functional requirements.

A3.1.4 Physical properties include aspects of a material that can be measured and observed without it changing in any way.

Guidance: You should be able to explain density, thermal expansion, thermal conductivity, melting point, electrical resistivity and electrical conductivity.

A3.1.5 Chemical properties include aspects of a material that lead to it chemically reacting with another.

Guidance: You should be able to explain corrosion resistance, reactivity (food safe), hygroscopy and flammability.

Chemical properties are characteristics that describe how a material interacts with other substances at a molecular level, often resulting in changes to its composition or structure. These properties are crucial in product design, influencing material selection for safety, durability, and functionality

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A3.1.6 Mechanical properties include aspects of a material affected by the application of a force.

Guidance: You should be able to explain tensile and compressive strength, stiffness, toughness, hardness, malleability, elasticity, plasticity and ductility.

Mechanical properties are characteristics that describe how materials behave when subjected to various forces or loads. These properties are crucial in product design as they determine the performance, durability, and safety of materials in different applications. 

A3.1.7 Composites consist of two or more materials combined to enhance their properties.

Guidance: You should be able to explain why combining materials can create composite materials more suitable for a specific purpose or context using an example.

Composite materials are engineered materials made from two or more materials with significantly different physical or chemical properties. When combined, they create a new material with characteristics different from the individual components, often superior to either component alone. 

A3.1.8 Smart materials are materials that have one or more properties that can be significantly changed in response to changes in their environment.

Guidance: You should be able to explain how materials can be selected to react to external stimuli, including piezoelectricity, shape memory, photochromicity, magneto-rheostatic, electro-rheostatic and thermoelectricity.

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A3.1.9 Biodegradable materials break down in the environment after disposal or at the end of their useful life.

Guidance: You should be able to explain how biomaterials are a key part of a circular economy and can be used by designers to design out waste.

Biomaterials and the Circular Economy

Biomaterials play a crucial role in the circular economy by offering sustainable alternatives to traditional materials. The circular economy is a model of production and consumption where resources are kept in use for as long as possible, and waste is minimized. Biomaterials align with this model in several ways:

• Biodegradability: Biomaterials are designed to break down naturally in the environment, reducing the need for landfills and minimizing waste. This helps to close the loop in material usage, as the materials can return to the natural cycle and be reused by organisms.

• Renewable resource: Many biomaterials are derived from renewable sources, such as plants, algae, or bacteria. This reduces reliance on finite resources and helps to conserve natural ecosystems.

• Compostability: Some biomaterials, such as plant-based plastics or biodegradable packaging materials, are compostable. This means they can be broken down into nutrient-rich compost that can be used to fertilize soil. This helps to reduce waste and create valuable byproducts.

• Recycling: Even if biomaterials are not fully biodegradable, they can still be recycled or reused in other applications. For example, waste paper can be recycled into new paper products, and used textiles can be transformed into new materials.

• Reduced environmental impact: By using biomaterials, manufacturers can reduce their environmental footprint by minimizing the use of harmful chemicals and reducing waste. This can help to protect ecosystems and promote sustainable development.

• Why is a good understanding of material properties important when designing structural systems? (A3.2)

• When do the physical properties of materials restrict the ability to use certain prototyping techniques? (A2.2)

• How do the properties of a material influence the choice of manufacturing techniques for a product? (A4.1)

• How can the characteristics of a material limit the effectiveness of modelling and prototyping as designs are developed? (B2.2)

• How important is an understanding of the mechanical properties of a material when considering structural and mechanical systems, and their applications? (A3.2, A3.3, B3.2, B3.3)

• Which classifications of properties are important when developing electronic systems and their applications? (A3.4, B3.4)

• How could the continued development of biodegradable materials influence designers’ ability to address aspects of design for sustainability and design for a circular economy? (C2.1, C2.2)

• Why is a thorough understanding of materials key for effective product analysis and evaluation of products? (C3.1)

• How do design decisions related to the properties of materials and components impact a product’s life-cycle analysis? (C3.2)

Linking questions are questions that help you connect different parts of your design technology studies. They can show how ideas and skills are related to each other.

Why are linking questions important?

Linking questions can help you:

• Understand the big picture: See how different parts of design technology fit together.

• Learn more: Connect new information to what you already know.

• Show your knowledge: Demonstrate your understanding of design technology in a deeper way.

How can you use linking questions?

• Connect subtopics: Find relationships between different parts of the course

• Use your skills: Show how you can apply design technology skills in different areas.

• Think about the nature of design technology: Consider the big ideas and principles that guide design technology.

• Apply to the real world: See how design technology can be used in real-life situations.