materials vocab

Question 1

Stress

Answer 1

Measures in Nm^-2 // Pascals Pa
The force applied divided by the cross sectional area it is applied to.
Greek sigma is used for stress.
Stress=F/A

Force per unit area of cross section acting perpendicular to an area .
(types of stress: tension(stretching), compression, torsion (twisting))

Question 2

Elastic deformation

Answer 2

A temporary change of shape that occurs when stress is applied. when stress is removed the object/material returns to original shape. (without loss of energy)

Question 3

Plastic deformation

Answer 3

A permanent change of shape which occurs when stress is applied

Question 4

Strong

Answer 4

a large amount of stress is required to cause failure

Question 5

Strength

Answer 5

The maximum stress a material can withstand before failure.

some materials have two values for strength as there are two types of failure: yielding and breaking/fracture

Question 6

Weak

Answer 6

Opposite of strong, a small amount of stres is required to cause failure.

Question 7

Toughness explanation

Answer 7

(Units usually: J/m^2)
When some materials are stressed past their elastic limit, they do not immediately break but undergo considerable plastic deformation before breaking. In doing so they absorb large amounts of energy before breaking.

Question 8

Toughness strictly speaking

Answer 8

• The energy required to make a new surface area, units in this case are J/m^2
• The energy absorbed per unit volume, in this case units are J/m^3

Must understand that a tough material:

• needs a large amount of energy to break it
• (usually) undergoes a large amount of plastic deformation before breaking
• resists crack propagation (cracks passing through)

Question 9

Brittle

Answer 9

the opposite of tough, hence brittle materials do not undergo much plastic deformation (if any). They break soon after the elastic limit is reached. Cracks pass easily though the material and fracture/failure tends to be sudden and catastrophic.
Brittle materials can still be strong.

Question 10

Hard

Answer 10

resistant to dents of scratches

Question 11

Ductile

Answer 11

Can easily be drawn into a wire. (this is a plastic (permanent) response to a tensile force)
A material which can undergo large amounts of plastic deformation when subjected to tensile stress

Question 12

Malleable

Answer 12

Can easily be hammered or pressed into shape. (plastic /permanent response to compressive forces)
A material which can undergo large amounts of plastic deformation when subjected to compressive force.

Question 13

strain

Answer 13

Change in length per unit length, the relative change in shape or size of an object due to externally applied forces. (no unit/dimensionless)

Question 14

Young modulus (E)

Answer 14

Stress/strain

A measurement of elasticity, ratio between stress and strain. (unit of pressure Pa)

Question 15

elasticity

Answer 15

Ability for a material to regain its shape after being distorted.

Question 16

elastic energy

Answer 16

energy stored in a body whe its shape is changed

Question 17

Plasticity

Answer 17

describes the deformation of a solid undergoing non reversible changes to its shape in response to applied forces.

Question 18

Yield

Answer 18

yield strength or yield point is the material property defined as the stress at which the material starts to deform plastically.

Question 19

Ultimate tensile strength

Answer 19

UTS is measured by the maximum stress that a material can with stand while being stretched or pulled before breaking.

Question 20

Breaking stress

Answer 20

same as UTS.

Maximum stress a material can withstand before breaking

Question 21

stiffness

Answer 21

A measure of the force needed to change the shape of an object. (opposite of flexibility)

Question 22

Resistance

Answer 22

The resistance of a resistor is defined as the potential difference / current. The unit of resistance is ohms, equal to one volt per ampere

By definition is the measure of friction a component presents to the flow of electrons through it,
symbol: R
units : ohms
greater resistance =less conductance

Question 23

Conductance

Answer 23

A measure of a materials ability to allow electric current to pass through in relation to applied voltage (E)
conductance is the reciprocal of resistance, so is measured in smho,

Question 24

Resistivity

Answer 24

A measure of the resisting power of a specified material to the flow of electric current.
S/m

Question 25

Conductivity

Answer 25

Defines the materials ability to conduct electricity, electric current can flow easily through a material with high conductivity.
measured in siemens per meter.