Materials Yr 1

What is a ‘composite’?

• mixture of 2 or more materials

• tough matrix

• strong filler

• good strength to weight ratio

Name 3 composites?

• fibreglass reinforced plastics (GRP)

• carbon fibre - epoxy resin

• concrete

What is an ‘electronic material’?

• crystalline structure

• specific electrical characteristics

• semi-conductive

Name 2 electronic materials

• silicon & germanium chips

What are the general characteristics of ‘metals’?

• strong

• ductile

• electrical conductor

• thermal conductor

• non-transparent (opaque)

• shiny

What are the general characteristics of ‘ceramics’?

• strong

• brittle

• electrical insulator

• thermal insulator

• may be transparent

• heat resistant

What are the general characteristics of ‘polymers’?

• weak

• very ductile

• electrical insulator

• thermal insulator

• range of transparency

• low densities

What are the different properties of materials?

• physical

• mechanical

• chemical

• economical

• electrical

• acoustic

What are ‘physical properties’? Give examples

inherent property derived from internal atomic arrangements

e.g

• density

• shape/structure

• size

• porosity

• moisture content

What are ‘mechanical properties’?

reaction of a material to the application of external forces

What are ‘chemical properties’?

interaction of a material with the elements in its working environment

What are ‘economical properties’?

viability of a material to be manufactured into useful products

What happens in ‘elastic deformation’?

1. initial

2. small load - bonds stretch

3. unload - returns to initial

• REVERSIBLE!!

• Linear elastic

• Non-linear elastic

What happens in ‘plastic deformation’?

1. initial

2. small load - bonds stretch & planes shear

3. unload - planes still sheared

• PERMANENT!!

• Linear elastic

• Plastic stress

What are the different ‘types of loading’?

1. Tensile

2. Compressive

3. Shear

4. Torsion

What is ‘stress’?

• the magnitude of the applied force as experienced by the sample

$$\sigma=\frac{F}{A}$$

• $\sigma=$ Stress (Pa or Nm^-2)

• $F=$ Force or load (N)

• $A=$ Cross sectional area (m²)

What are the different ‘types of stress’?

• Engineering: used for engineering applications

$$\sigma_{e}=\frac{F}{A_0}$$

$A_0=$ original cross sectional area

• True

$$\sigma_{t}=\frac{F}{A_{t}}$$

$A_{t}=$ instantaneous cross sectional area

What are the different types of ‘engineering stress’?

• Tensile

$$\sigma=\frac{F_{t}}{A_0}$$

• Shear

$$\tau=\frac{F_{s}}{A_0}$$