Properties of materials With a basic understanding of the origins of properties, materials can be selected or designed for an enormous variety of applications, ranging from structural steels to computer microchips.
Physical properties The IB considers the physical properties of a material to be: - Density, electrical resistivity, thermal conductivity, thermal expansion and hardness.
Physical properties The IB considers the physical properties of a material to be: - Density, electrical resistivity, thermal conductivity, thermal expansion and hardness.
Density
This is the mass per unit volume, of a material. Clearly the density of a material is important to a designer wherever the weight of a product is a major consideration e.g. anything which is portable, packaging, aircraft racing cars etc. Density is important in relation to product weight and size. Electrical resistivity This is a measure of a material s ability to conduct electricity. A material with a low resistivity will conduct electricity well. Thermal conductivity A measure of how fast heat is conducted through a slab of material with a given temperature difference across the slab. Thermal expansion This is a measure of the degree of increase in dimensions when an object is heated. This can be measured by an increase in length, or area or volume. The expansivity can be measured as the fractional increase in dimension per Kelvin increase in temperature. Hardness The resistance a material offers to penetration or scratching. Mechanical properties – those properties which indicate how a material behaves under various loads. Tensile strength: The ability of a material to withstand pulling forces. Compressive strength: The ability of a material to withstand ‘squashing’ forces. Stiffness: The ability of a material to resist deflection or bending. Toughness: The ability of a material to resist the propagation of cracks. Ductility: The ability of a material to be drawn or extruded into a wire or other extended shape. Elasticity: the ability of an object or material to resume its normal shape after being stretched or compressed; stretchiness. Plasticity: When a material is deformed under an external force and remains in the new shape once that external force is removed. Malleability: The ability of a material to be cold worked (i.e. hammered, pressed, folded etc.) the ability to be shaped plastically. Young modulus: Young’s Modulus is known as the measure of stiffness of a given material, usually given as a ratio of stress to strain |
|
|
|
Aesthetic characteristics: Aesthetics - concerned with beauty or the appreciation of beauty.
Taste, smell, appearance, texture, feel and colour, are some of the Hedonic properties humans use to decide if a product, object or place are pleasing to use.
Some of these properties are only relevant to food, while others can be applied to more than one material group. Although these properties activate people’s senses, responses to them vary from one individual to another, and they are difficult to quantify scientifically, unlike the other properties.
Hedonic Properties
Hedonism is the belief that pleasure is the highest goo
Senses
Senses are the means by which many-celled animals tell what is happening in their environment.
Many people think that human beings have only five senses:
Hearing, Sight, Smell, Taste, Touch.
However, there are other kinds of senses that give information about the position and movement of the body and about body needs. These senses include:
Balance, Hunger, Pain, Thirst.
Taste, smell, appearance, texture, feel and colour, are some of the Hedonic properties humans use to decide if a product, object or place are pleasing to use.
Some of these properties are only relevant to food, while others can be applied to more than one material group. Although these properties activate people’s senses, responses to them vary from one individual to another, and they are difficult to quantify scientifically, unlike the other properties.
Hedonic Properties
Hedonism is the belief that pleasure is the highest goo
Senses
Senses are the means by which many-celled animals tell what is happening in their environment.
Many people think that human beings have only five senses:
Hearing, Sight, Smell, Taste, Touch.
However, there are other kinds of senses that give information about the position and movement of the body and about body needs. These senses include:
Balance, Hunger, Pain, Thirst.
Smart Materials |
Smart materials are designed materials that have one or more properties that can be significantly changed in a controlled fashion by external stimuli, such as stress, temperature, moisture, pH, electric or magnetic fields
|
The word piezoelectricity means electricity resulting from pressure.
Shape memory alloys (SMAs) are metals that "remember" their original shapes. SMAs are useful for such things as actuators which are materials that "change shape, stiffness, position, natural frequency, and other mechanical characteristics in response to temperature or electromagnetic fields"
Photochromicity
Photochromicity refers to a material that can described as having a reversible change of colour when exposed to light. One of the most popular applications is for colour-changing sunglass lenses, which can darken as the sun brightens. A chemical either on the surface of the lens or embedded within the glass reacts to ultraviolet light, which causes it to change form and therefore its light absorption spectra. |
|
|
Magneto-rheostatic & Electro-rheostatic: materials are fluids that can undergo dramatic changes in their viscosity. They can change from a thick fluid to a solid in a fraction of a second when exposed to a magnetic (for MR materials) or electric (for ER materials) field, and the effect is reversed when the field is removed. MR fluids are being developed for use in car shock absorbers, damping washing machine vibration, prosthetic limbs, exercise equipment and surface polishing of machine parts. ER fluids have mainly been developed for use in clutches and valves, as well as engine mounts designed to reduce noise and vibration in vehicles
|
|
|
|
The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa. A thermoelectric device creates voltage when there is a different temperature on each side. Conversely, when a voltage is applied to it, it creates a temperature difference.
|