Mechanical properties

Question 1

Elastic deformation

Answer 1

Deformation that can be recovered when stress is removed

Question 2

Plastic deformation

Answer 2

Deformation that cannot be recovered when stress is removed

Question 3

Stress

Answer 3

Internal force per unit area equal in magnitude but in opposite directions

Question 4

Types of stress (5)

Answer 4

Tension
Compression
Shear
Torsion
Bending

Question 5

Tension

Answer 5

When two sets of forces directed away from each other but in a straight line

Question 6

Compression

Answer 6

When two sets of forces directed to each other and in a straight line

Question 7

Fracture

Answer 7

Cracks that appear at notch
It propagates and fracture occurs

Question 8

Shear

Answer 8

When two sets of forces directed parallel to each other but not in a straight line

Question 9

Torsion

Answer 9

Twisting of body

Question 10

Bending

Answer 10

An applied bending moment

Question 11

Strain

Answer 11

Change in length per original length when load is applied

Question 12

Importance of strain

Answer 12

Clasps and orthodontic wires
Impression materials (deform elastically)

Question 13

Stress-strain relationship
- Proportional limit

Answer 13

Maximum stress at which stress is proportional to strain

Question 14

Stress-strain relationship
- Elastic limit

Answer 14

Maximum stress a material can withstand before undergoes plastic deformation

Question 15

Stress-strain relationship
- Yield stress

Answer 15

Point beyond strains are not fully recovered, stress when a material starts undergo plastic manner

Question 16

Stress-strain relationship
- Yield strength

Answer 16

Stress required to produce a given amount of plastic strain

Question 17

Stress-strain relationship
- Ultimate tensile strength

Answer 17

Maximum stress that a material can withstand before failure in tension

Question 18

Stress-strain relationship
- Ultimate compressive strength

Answer 18

Maximum stress that a material can withstand in compression

Question 19

Stress-strain relationship
- Breaking/rupture point

Answer 19

Degree of permanent deformation up to the point of fracture

Question 20

Stress-strain relationship
- Ductility

Answer 20

Ability of material to withstand permanent deformation under TENSILE stress without fracturing

Question 21

Stress-strain relationship
- Malleability

Answer 21

Ability of a material to withstand permanent deformation under COMPRESSIVE stress without fracturing

Question 22

Stress-strain relationship
- Resilience

Answer 22

Energy absorbed by a material in undergoing elastic deformation up to ELASTIC LIMIT

Question 23

Stress-strain relationship
- Toughness

Answer 23

Total amount of energy a material can absorbed to the point of FRACTURE

Question 24

Stress-strain relationship
- Fatigue strength

Answer 24

Stress that a material cannot withstand under repeated loading dependant to magnitude of load and number of loading repetition
(Development of micro cracks lead to macroscopic cracks and failure)

Question 25

Hardness

Answer 25

Resistance of material to plastic deformation under an indentation load

Question 26

Value of hardness (2)

Answer 26

Low hardness - soft material High hardness - hard material

Question 27

Hardness evaluation methods (4)

Answer 27

Brinell Vickers Knoop Rockwell - degree of permanent deformation, depth of indentation, small size of indentation=hard material

Question 28

Brinell hardness test

Answer 28

Steel ball indenter pressed into surface (diameter is calculated)

Question 29

Vickers hardness test

Answer 29

Square base shaped diamond indenter

Question 30

Knoop hardness test

Answer 30

Knoop hardness indenter point, one axis of diamond pyramid larger than the other

Question 31

Rockwell hardness test

Answer 31

Steel or diamond conical point (depth is calculated)