DT- Unit 4

Define Physical properties

These properties can usually be identified using tests that are NON- destructive However, testing for hardness does cause a little change in shape, which is why hardness is often grouped as a mechanical property.

Mass

Mass is the amount of matter in a material.

It’s often confused with weight because both use kilograms.
But mass stays the same, while weight can change depending on location.

Weight

Weight depends on mass and gravity.
It’s measured as a force—in Newtons.

Volume

Volume is the amount of 3D space something takes up, like a solid, liquid, or gas.

Density

Density is the mass per unit of volume.
It matters for how heavy or bulky a product is.

Design examples: food packaging, instant noodles, foam boxes.

Electrical resistivity

Electrical resistivity measures how well a material resists electric flow.

Low resistivity = good conductor.

It’s key for choosing conductors or insulators.

Thermal conductivity

Thermal conductivity is how quickly heat moves through a material.
It matters for things that need to conduct or block heat.

Thermal expansion (expansivity)

Thermal expansion measures how much a material grows when heated.
It can increase in length, area, or volume per degree (Kelvin).

Important when different materials are joined and face temperature changes.

Hardness

material’s resistance to scratching or penetration.

It’s important for surfaces that need to stay smooth or undamaged (Eg, ceramics

Mechanical Properties

Tensile strength

Compressive strength

Stiffness

Toughness

Ductility

Tensile strength

The ability of a material to withstand pulling forces.

Tensile strength is important in selecting materials for ropes and cables, for example, for an elevator.

Compressive strength

Compressive strength is the capacity of a material or structure to withstand loads tending to reduce size,

Stiffness

The resistance of an elastic body to deflection by an applied force.

Stiffness is important when maintaining shape is crucial to performance, for example, an aircraft wing.

Toughness

The ability of a material to resist the propagation of cracks. Good with resisting high impact of other objects- e.g. hammer

Ductility

The ability of a material to be drawn or extruded into a wire or other extended shape. Ductility is important when metals are extruded (not to be confused with malleability, the ability to be shaped plastically).

What is Young’s modulus, stress and strain

Young’s Modulus (or elastic modulus) measures how stiff a material is.
It’s the ratio of stress (force per area) to strain (stretch compared to original length).
Used to describe how much a material resists bending or stretching.

Aesthetic characteristics

Aesthetic characteristics make products look or feel appealing—or not.

They depend on personal taste, which is influenced by mood, culture, senses, and experience.

Some apply only to food (like taste or smell), while others apply to many materials.
They’re hard to measure because everyone reacts differently.

Smart Materials

have one or more properties that can be dramatically altered, for example, viscosity, volume, conductivity. The property that can be altered influences the application of the smart material.

Types of smart materials

Piezoelectricity

Shape memory alloy (SMA's)

Thermoelectricity

Piezoelectricity

The pressure acting upon the material it gives off a small electrical discharge.

Piezoelectric materials create a small electric charge when squeezed.

Shape memory alloy (SMA's)

metals that return to their original shape after being stretched.
They show pseudo-elasticity—they bounce back without needing heat or electricity.

This happens because their molecules rearrange under load and return when the load is removed.

Thermoelectricity

electricity produced directly from heat.

It involves the joining of two dissimilar conductors that, when heated, produce a direct current.

Hard wood

Beach, Oak, and ash

Softwood

Pine, Spruce, Cedar

Seasoned wood

When living trees are cut down the timber cant be used, because of its moisture, the moisture needs to be removed—> seasoning

Natural timber

Timber saw from the tree

Hardwood and softwood tree

Characteristics of natural timber

Tensile strength

Resistance to damp environments

Longevity

Aesthetic properties

Man- made timber

Plywood- layers of veneer, thin sliced wood glue together

Particle board (chip board)- from different sized chip woods joined with glue and pressed.

MDF (medium desnity fibre wood)- strands of fibre ruled together and pressed into sheets.

Charactersitics of man made timber

• Tensile strength:

  - plywood - high tensile strength all directions

  -particle board and mdf- low

• Resistant in damp environment

  -Exterior plywood - v good

  -interior ply wood- not good

• Longetivity

  -Plywood- high

  -particle board and mdf is low to medium

Treatment of woods

Reduce attack from bugs- by making it poisionus

Protect from weather

Explain    why    timber    as    a    building    material    is    influenced    by    its    physical    properties,    aesthetic properties and environmental impact. (9 marks)​

Physical properties:

Thermal expansion

Timber doesn’t expand

Keeping the structure in the diff climate

Thermal conductivity/ resistance

Doesnt transfer heat quickly

Helps to cool down building

Mass/weight

timbers change depending on density

some buildings need lightweight feature/ high density for the stability

Timbers vary in their hardness, consideration need to given to the selection of timber to reduce wear, and stop scratches

Aesthetic:

Texture

Natural color

Glass