4) Testing Materials

Question 2

Stress.

Answer 2

Units of stress: Nm-2 called “Pascal”

Stress = force/area σ = F/A Several types e.g. Tension (stretching), compression, torsion (twisting) …

Question 3

Strong/Strength.

Answer 3

(Units: Pa) STRONG: A large STRESS is needed to cause failure. STRENGTH: The maximum stress a material can withstand before failure. can be 2 types of failure: yielding and breaking/fracture

Question 4

Weak

Answer 4

Is the opposite of strong

STRONG: A large STRESS is needed to cause failure

therefore WEAK: a small STRESS is needed to cause failure

Question 5

Toughness

Answer 5

The energy required to create new surface area. J/m2

The energy absorbed per unit volume. J/m3 Resists crack propagation (= passing through).

Question 6

Brittle

Answer 6

Opposite of tough. Brittle materials do not undergo much plastic deformation. They break soon after their elastic limit. Cracks pass easily through the material and fracture tends to be sudden and catastrophic. Can be brittle and strong.

Question 7

Hard

Answer 7

Resistive to dents or scratches (Units: Pa)

Question 8

Elastic

Answer 8

Changes shape when a stress is applied but returns to its original shape when stress removed (without loss of energy). elastic deformation = temporary change of shape

Question 9

Plastic

Answer 9

Does not return to its original shape after deformation. Plastic deformation is a permanent change of shape. (think of spring past elastic limit)

Question 10

Ductile

Answer 10

Can easily be drawn into a wire.

Question 11

Malleable

Answer 11

Can easily be hammered or pressed into a shape.

Question 12

Strain

Answer 12

Strain = Extension / Original length

Question 13

Young Modulus

Answer 13

Young Modulus = stress / strain

Question 14

UTS

Answer 14

The maximum stress a material can withstand.Ultimate tensile strength = ability of a material to withstand longitude stress

Question 15

Yield strenth

Answer 15

The stress a material can withstand without permanent deformation.Yield strength = extension / original length

Question 16

Yield

Answer 16

The stress at which an elastic material under increasing stress ceases to behave elastically.

Question 17

Breaking strength

Answer 17

The stress coordinate on the stress-strain curve at the point of rupture.

Question 18

Stiffness

Answer 18

Stiffness is the rigidity of an object — the extent to which it resists deformation in response to an applied force.

Question 19

Resistance (R)

Answer 19

A material’s opposition to the flow of electric current; measured in ohms

Question 20

Conductance (G)

Answer 20

The degree to which an object conducts electricity, calculated as the ratio of the current that flows to the potential difference present. This is the reciprocal of the resistance, and is measured in siemens or mhos

Question 21

Resistivity (ρ)

Answer 21

A measure of the resisting power of a specified material to the flow of an electric current.

ρ = RA/L

Question 22

Conductivity (σ)

Answer 22

A material’s ability to conduct electricity.Electric current can flow easily through a material with high conductivity.

σ = GL/A

Question 23

Give 3 examples of a conductor

Answer 23

CopperSilver Aluminium

Question 24

Give 3 examples of a semiconductor

Answer 24

DiamondCadmium arsenideMercury(II) iodide

Question 25

Give 3 examples of an insulator

Answer 25

GlassFoam Vinyl (sound dampening)

Question 26

strain

Answer 26

stain = extension / original length