4.1: Properties of Materials

IBDP Design Tech, Unit 4.1

Properties of Materials

Materials are selected for manufacturing products based primarily on their properties

Nature of Design

New materials have given scope for “smart” new products or enhanced classic designs. Choosing the right material is a complex and difficult task with physical, aesthetic, mechanical and appropriate properties to consider. Environmental, moral and ethical issues surrounding choice of materials for use in any product, service or system also need to be considered

Aims of Design

The development of new materials allows designers to create new products, which solve old problems in new ways.

Mass

The amount of matter contained in a space. Mass is constant and is measured in kg.

The mass of an object is constant, regardless of where it is measured.

Weight

Weight is technically a force and is measured in Newtons (N). Weight will change depending on the gravity.

Volume

Volume is the amount of 3-dimensional space a solid, gas, or liquid occupies

Density

Density is the relationship between mass and unit of volume. It is measured in mass/volume such as 40kg/m2

Electrical Resistivity

Electrical resistivity is a materials ability to conduct or resist electricity

Thermal Conductivity

Thermal conductivity measures how fast heat moves through a material.

For objects that are to be heated, or used around heat, thermal conductivity is important for designers to consider.

Thermal Expansion

The degree to which a material increases its dimensions when heated. Different materials may expand at different rates. For designers, thermal expansion is important to consider when joining two different metals together such as when designing cooking ware or any items that receive heat or flame.

Hardness

Hardness is the resistance of a material to scratching or penetration.

Tensile Strength

The ability of a material to resist pulling forces

Compressive strength

The ability of a material to resist pushing forces

Stiffness

The ability to resist deflection (bending) by a force. the object can maintain its shape when a force is applied to it.

Toughness

The ability to deform (change shape) but resist cracking and not fracture under impact. If a material breaks into numerous small pieces when impacted, it has a low degree of toughness.

Ductility

The ability to be drawn or extruded into a wire-like form.

Elasticity

The ability to a material to bend and then return to its original shape

Plasticity

The ability of a material to be formed into a new shape. When the material is bent or deformed beyond its yield it does not return to its original shape.

Young’s Modulus

Young's Modulus will indicate when a material will bend, then break.

Young's Modulus is a measure of the stiffness of an elastic material. It is the ratio of stress to strain of a material as force is applied along its length. Each material has its own unique modulus.

Stress and Strain are usually plotted on a graph, as below, and show the relationship between the amount of force applied (Stress) to how much the materials changes in length.

Form and Shape

The shape and form of the material can influence how users interact and engage with it. We have different reactions to organic and geometric shapes.

Texture

How something feels or looks.

Appearance

This refers to the colour or pattern of the material.

There is much research about the psychological and cultural meanings of different colours. Designers should consider how their target users will interpret these meanings.

Sound

The sound a material makes when it is touched or manipulated can also be part of the user experience. The noisy sound of a bag of chips opening is part of the eating experience -- it heightens expectations

Smell

Smell has very powerful connections with memory. The smell of a material is largely a concern for food, however product designers should consider it.

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Smart Materials

Smart materials are *reactive materials.* They change their properties when exposed to stimuli such as electrical charges, moisture, or temperature.

Piezoelectricity

The ability to release an electric charge when deformed. When an electric current is passed through a piezoelectric material its volume will increase or it will vibrate.

Shape Memory

Shape memory alloys (SMAs)have a pseudo-elastic property that allows them body to return to its original shape after deforming. Their shape changing property can be stimulated by either a change in temperature or the application of an electrical current. When the load is released, the body returns to its original shape.

Photocromacity

The ability to change color when exposed to light.

Magneto-rheostatic

Fluids that undergo a change in their viscosity (thickness) when a magnetic force is applied. The change can change from a thick fluid to a solid almost almost instantaneously.

Electro-rheostatic

Fluids that undergo a change in their viscosity when an electrical force is applied. The change can be almost instantaneous. The change can change from a thick fluid to a solid almost almost instantaneously.

Thermoelectricity

Two different conductors, that when joined together generate electricity when heat is applied. The materials of the conductors determine the amount of electricity generated. The most common material is Bismuth telluride (Bi2Te3)