International Baccalaureate: Design & Technology
Topic 3: Materials
This topic aims to ensure understanding of the relationships between materials choice, manufacturing processes and the concepts of designers. Design technology is intimately involved with material properties and the way they interlock with manufacturing processes. The intention of this topic is to gain an overview of this relationship while emphasizing the choices available to designers.
3.1 Introducing and Classifying Materials
3.1.1
State that materials can be classified into groups according to similarities in their microstructures and properties.
3.1.2
Explain that several classifications are recognized but that no single classification is “perfect”. It is convenient to be able to classify materials into categories (albeit rather crude in nature) which have characteristic combinations of properties.
3.1.3
State that, for this course, materials are classified into groups: timber, metals, ceramics, plastics, textile fibres, food and composites and that some of these groups have subdivisions. In each group there can be subdivisions, eg for timber (natural wood or composite), metals (ferrous or nonferrous), ceramics (earthenware, porcelain and stoneware), plastics (thermoplastics or thermosets), textile fibres (natural or synthetic), food (vegetable or animal origin) and
composites (difficult to classify due to variability and the continual development of new ones).
Note: For completeness and because of its importance as a design material, food is included here in the matrix although it is dealt with in detail as an option.
3.2.1
Define the physical properties of density, electrical resistivity, thermal conductivity, thermal expansion and hardness.
3.2.2
Explain a design context where each of the properties in 3.2.1 is an important consideration.
• Density is an important consideration in relation to product weight and size (eg for portability). Pre-packaged food is sold by weight/volume and a particular consistency is required.
• Electrical resistivity is an important consideration in selecting particular materials as conductors or insulators for particular design contexts.
• Thermal conductivity is an important consideration for objects which will be heated, which must conduct heat or which must insulate against heat.
• Thermal expansion (expansivity) is an important consideration where two dissimilar materials are joined, such as glazed metals. These may then experience large temperature changes while staying joined.
• Hardness is an important consideration where resistance to penetration or scratching is required. Ceramic floor tiles are extremely hard and resistant to scratching.
3.2.3
Define the mechanical properties of tensile strength, stiffness, toughness and ductility.
3.2.4
Explain a design context where each of the properties in 3.2.3 is an important consideration. The tensile strength of ropes and cables is an important safety consideration in climbing and in elevators. Stiffness is an important consideration when maintaining shape is crucial to the performance of an object eg aeroplane wing. Toughness is an important consideration where
abrasion and cutting may take place. Ductility is an important consideration when metals are extruded (do not confuse this with malleability—the ability to be shaped plastically).
Aesthetic characteristics
3.2.5
Outline the characteristics of taste, smell, appearance, texture and colour.
3.2.6
Explain a design context where each of the characteristics in 3.2.5 is an important consideration.
3.2.5–3.2.6
Some of the properties are relevant to only one materials group eg food, while others can be applied to more than one. Although these properties activate peoples’ senses, responses to them vary from one individual to another and they are difficult to quantify scientifically, unlike the other properties.
3.3 The IB Properties/Materials Matrix
3.3.1
Explain how all the groups and sub-groups specified in 3.1 can be organized into a properties/materials matrix.
3.3.1–3.3.2
The matrix is designed to give an overview of the relative values of the properties for each material group.
3.3.2
Explain the relative values of the properties in the IB properties/materials matrix.
