Mechanical Properties

Question 1

What types of mechanical properties are there?

Answer 1

Strength
Stiffness
Toughness
Hardness
Creep
Fatigue

Question 2

What is Strength?

Answer 2

Material Strength is normally considered as Stress

Question 3

What is Stress?

Answer 3

The measure of what the material feels from externally applaied forces

Question 4

How to measure Stress?

Answer 4

𝜎 = sigma (Yield Stress)
𝜎 = 𝐹/𝐴 (Force (P) / Cross-sectional area the force acts on)

Question 5

What is Stifness (E)?

Answer 5

The extent to which and object resists deformation in response to an externally applied force.

Question 6

How do we measure Stifness?

Answer 6

Elastic Moduli (E) = 𝜎 / stress = (F/A) / (dl/l)

Question 7

How do we measure in tension?

Answer 7

Youngs Modulus = Y = Δ𝜎/ Δ𝜀

Question 8

What is elasticity?

Answer 8

The ability of an object or material to resume its normal shape after being stretched or compressed.

Question 9

What is plasticity?

Answer 9

The quality of being easily shaped or moulded.

Question 10

What is Elastic deformation?

Answer 10

It is state where deformation is recoverable once a load stress has been removed.

On the Stress/ Strain curve this is liner up until the yield point when the material starts to show plastic deformation

Question 11

What is Plastic deformation?

Answer 11

It is when there has been permenant deformation after a load stress has been removed.
0.2% Proof Stress

Question 12

What is a benifit of Ductile materials?

Answer 12

Failure is not sudden or catastrophic, it give warning of impending failure

Question 13

Examples of ductile materials?

Answer 13

Mild Steel
Aluminium
Copper

Question 14

Examples of Brittle Materials

Answer 14

Cast Iron
Concrete
Brickwork
Glass

Question 15

What is Heat realated stress?

Answer 15

Thermal Expansion and Contraction

Question 16

How is the coefficience of thermal expansion measured?

Answer 16

ppm (parts per million) /C

Question 17

What is Toughness?

Answer 17

The ability to absorb energy from an impact.

Question 18

What test do we use for measuring the toughness of a material and what two properties lend themselves to toughness?

Answer 18

Charpy V-notch test
Strength and Ductility

Question 19

What is Hardness? How do we Test for it? What two properties lend themselves to this?

Answer 19

A materials resistance to indentation under load stress
Vickers Hardness test and Brinell Test
Strength and stifness

Question 20

What is Creep? How is it measured? Where is is most common?

Answer 20

Creep is deformation or displacement (strain) over time without increase load. Strain reduces any stress.
It’s mesured as strain/ time
most common in plastics and lead

Question 21

What is material fatigue?

Answer 21

A materials ability to withstand cyclical loading.
Can be measured in UTS ultimate tensile strength
Eg aluminium, if a stress is halved from 300n/mm2 to 150n/mm2 it can go from withstanding 10 cycles to 10,000