Chapter 6 - Mechanical Properties

Question 1

What are the feature of Plastic deformation?

Answer 1

• Stress and strain are not proportional to each other
• The deformation is not reversible
• Deformation occurs by breaking and rearrangement of the atomic bonds

Question 2

How do you calculate the safety factor?

Answer 2

N = yield stress/working stress

Question 3

What is the tensile strength?

Answer 3

this is the maximum stress supported by a material (~100-1000 MPa)
Highest point on a stress strain graph

Question 4

Where is the fracture strength on a stress-strain graph?

Answer 4

Last moment of data

Question 5

If tensile strength is maintained what will happen to the specimen?

Answer 5

It will eventually break

Question 6

What is Ductility?

Answer 6

• the measure of the deformation at fracture.

- defined by either the percentage elongation or the percentage reduction in area

Question 7

What is toughness?

Answer 7

• The ability of a material to absorb energy up to fracture, by elastic and plastic deformation
• The area under the stress-strain graph

Question 8

What is hardness?

Answer 8

A measure of the materials resistance to localized plastic deformation (dent or scratch)

Question 9

What does a large value of hardness mean?

Answer 9

• resistance to plastic deformation or cracking when compressed
• better wear properties

Question 10

Name some hardness tests?

Answer 10

Rockwell, Brinell, Vickers

Question 11

What is the process of hardness testing?

Answer 11

• Usually a small indenter (sphere, cone, or pyramid) is forced into the surface of a material, under a controlled magnitude and weight of loading
• then the depth or size of indentation is measure

Question 12

Why are the Rockwell, Brinell or Vikers tests popular?

Answer 12

Due to its easy and non destructive nature, even though it approximates

Question 13

What are stress & strain?

Answer 13

Size independent measures of load and displacement