1
Q
Define the “ tensile stress “
A
- it is one of stress types , occurs when two sets of forces are directed away from each other
2
Q
Define the “ compressive stress “
A
- it is one of stress types , occurs when two sets of forces are directed towards each other
3
Q
Define the “ shear stress “
A
- it is one of stress types , it is the result of two sets of forces being directed towards / opposite each other but not in the same direction .
4
Q
Define the “ complex stress “
A
- it is one of stress types , it is a combination of more than one stress as comprehensive, tensile and shear stress
5
Q
Define the “ elastic “
A
- it is a type of strain that can be recovered by just removing the force
6
Q
Define the “ stress “
A
- it is the internal reaction and it is equal in intensity and opposite in direction
7
Q
Define the “ stress “
A
- it is a deformation / distortion produced as a result of the stress produced within the material .
8
Q
Define the “ plastic “
A
- it is a strain that can not be recovered by removing the force .
9
Q
Define the “ curve of stress and strain “
A
- it is when the stress is directly proportional to the strain , until the stress reach the proportional limit
10
Q
Define the “ proportional limit “
A
- it is the greatest stress that the material can withstand without deviation from the law of proportional between stress and strain
11
Q
Define the “ elastic limit “
A
- It is the greatest stress that the material can withstand without permanent deformation —> this value describe the elastic behavior of the material
12
Q
Define the “ yield strength “
A
- it is the stress at which the material exhibit a specific limited deviation from proportionality of stress and strain
- it is the stress at which the material begins to function in a plastic manner
13
Q
Define the “ ultimate strength “
A
- it is the maximum stress that the material can withstand before fracture
14
Q
Define the “ modulus of elasticity “
A
- it represent the stiffness of the material within the elastic range
- it depends on the interatomic forces of the material
- ⬆️ strength of attraction forces , ⬆️ greater modulus of elasticity
- also it depends on the heat or mechanical treatment but it is quite dependent on the composition of the material .
15
Q
Define the “ malleability and ductility “
A
- They are a properties of metals and alloys and indicated workability
16
Q
Define the “ malleability of the material “
A
- it is the ability of the material to be hammered into thin sheets without fracture .
17
Q
Define the “ ductility of the material “
A
- It is the ability of the material to be drawn into wires
18
Q
Define the “ elongation “
A
- it results from application of tensile force
- also indicates workability
19
Q
Define the “ resilience “
A
- it is the amount of energy needed to deform the material to its proportional limit
- it is an important property of orthodontic wires
20
Q
Define the “ toughness “
A
- it is the energy required to stress the material to the point of fracture
21
Q
Define the “ fracture toughness “
A
- it is the amount of energy required to fracture a sample with crack .
22
Q
List the common hardness tests with its usages
A
- Brinell test —> used for alloys and metals
- knoop test —> used for enamel , dentin , metals and alloys
- vickers test —> used for small areas and very hard materials
- rockwell test —> not suitable for brittle materials , it can be used for materials that exhibit elastic recovery
- shore A test —> used for measuring hardness of rubbers
23
Q
Define the “ wear “
A
- it is the loss of the material ( the material moves from its site ) and this one happens when a mechanical action ( surfaces slides against each other ) occurs .
- for example —> a normal mastication may cause attrition of tooth structure and restorations by time
- for example —> “ Bruxism “ is a pathological form of “ wear “
24
Q
Define the “ creep “
A
- it is a slow causing permanent deformation of materials held for long time at stresses below their conventional yield strength —> common in dental amalgam .
