Tribology

Question 1

What are the 2 types of fluids?

Answer 1

Newtonian and Non newtonian

Question 2

What are the characteristics of a newtonian fluid?

Answer 2

Linear shear stress/strain relationship

Question 3

Definition of friction?

Answer 3

Resistance to motion of surfaces gliding over one another

Arises from adherence of one surface to another

Question 4

What is the equation for friction?

Answer 4

F= mu f x w

Question 5

What influence does the apparent contact area have on friction?

Answer 5

NONE

Question 6

Define roughness?

Answer 6

Ra = mean height of the asperities

Question 7

What is viscosity?

Answer 7

Friction between 2 layers within a fluid - resistance to flow

Question 8

What is shear with regards to fluids?

Answer 8

Rate of deformation of a fluid when subjected to shear stress

Question 9

What is the characteristic of non-newtonian fluids ie synovium?

Answer 9

Apparent viscosity changes with shear rate

Question 10

Name the different types of non-newtonian fluids? 5

Answer 10

Pseudo-plastic
Dilatant
Plastic
Thixotropic
Rheopexic

Question 11

What is characteristic of Plastic fluids?

Answer 11

Rigid body at low stress - viscous at high stress (ALL GOLD TOMATO SAUCE)

Question 12

What is characteristic of DILATANT fluids?

Answer 12

They exhibit shear thickening (Water flower mix)

Question 13

What is the characteristic of pseudo-plastic fluids?

Answer 13

Shear thinning (Paint)

Question 14

What are the 2 time dependent non newtonian fluid characteristics?

Answer 14

Thixotropic

Rheopexic

Question 15

What is a Thixotropic fluid?

Answer 15

Pseudoplastic quality over time (Honey)

Question 16

What is characteristic of Rheopexic fluid

Answer 16

Dilatant quality over time - rare (industrial materials)

Question 17

What are the qualities of synovial fluid? 4

Answer 17

1. Non- newtonian
2. Pseudoplastic
3. Thixotropic
4. Viscoelastic

Question 18

What are the 2 broad categories of lubrication

Answer 18

1. Boundary

2. Fluid film

Question 19

How does one distinguish the 2 categories of lubrication?

Answer 19

Lambda ratio

Question 20

What is the lambda ratio

Answer 20

fluid film:roughness

Question 21

From what lambda ratio is lubrication considered boundary?

Answer 21

<1

Question 22

From what lambda ration is lubrication considered as fluid film?

Answer 22

3

Question 23

What is boundary lubrication?

Answer 23

Monolayer of lubricin/phospholipid

Question 24

Name the 3 dynamic fluid film lubrication types?

Answer 24

1. Hyrdodynamic
2. Elastohydrodynamic
3. Micro-elastohydrodynamic

Question 25

Name the 3 static fluid film lubrication types?

Answer 25

1. Squeeze film 2. Weeping 3. Boosted

Question 26

What is MEHD lubrication?

Answer 26

Asperities are 'flattened' out under high loads increasing the lambda ratio

Question 27

Lubrication in metal on poly?

Answer 27

Boundary

Question 28

Proposed lubrication in metal on metal?

Answer 28

Fluid film

Question 29

What factors influence lubrication in prosthetic joints? 5

Answer 29

1. Magnitude and direction of loading 2. Geometry/ roughness 3. Material properties 4. Velocity at which the bearing operates 5. Viscosity of lubricant

Question 30

What is radial clearance?

Answer 30

Radius of cup - radius of head

Question 31

What is the definition of wear?

Answer 31

Unwanted progressive loss of a bearing surface

Question 32

What are the two broad types of wear?

Answer 32

Mechanical and chemical

Question 33

Define wettability?

Answer 33

Affinity of a surface material to a lubricant

Question 34

What is wettability measured with?

Answer 34

Theta contact angle <45 = hydrophilic >90 = hydrophobic

Question 35

Define hardness/notch sensitivity?

Answer 35

Ability of a material to resist scratching

Question 36

How many types of mechanical wear are there?

Answer 36

4 modes | 3 types

Question 37

What are the 3 types of mechanical wear?

Answer 37

1. Adhesion 2. Abrasion 3. Fatigue

Question 38

What are the 4 modes of wear

Answer 38

1. Wear btw 2 articulating surfaces 2. Wear between bearing and non-bearing surfaces (Head with metal cup - poly worn away) 3. 3rd body wear 4. Two non-bearing surfaces

Question 39

What are the 2 quantifications of wear?

Answer 39

Volumetric (related to square radius of the head) | Linear (height)

Question 40

Describe fatigue wear

Answer 40

also called delimitation - failure under ultimate tensile strength due to repeated loading cycles

Question 41

What is the formula governing wear?

Answer 41

``` V = LX/H V - volume L - Load X - Sliding distance H - hardness ```

Question 42

What is chemical wear/corrosion?

Answer 42

Gradual degradation of a metal by electrochemical attach in electrolytic environment in the body

Question 43

What is the main feature leading to corrosive wear?

Answer 43

Disruption of the passivation layer

Question 44

What are the types of local corrosive wear?

Answer 44

1. Crevice | 2. Pitting

Question 45

What are the 5 types of general corrosive wear?

Answer 45

1. Galvanic 2. Fretting 3. Stress (Fatigue) 4. Inter/intragranular 5. Inclusion

Question 46

6 consequences of wear?

Answer 46

1. Synovitis 2. Aseptic Osteolysis and loosening 3. Systemic distribution (Metallosis) 4. Immune reaction (Pseudotumours) 5. Increased joint friction 6. Misalignment and catastrophic failure

Question 47

Name the 4 steps of aseptic loosening?

Answer 47

1. Particulate/debris formation 2. Macrophage activation (TNF a, IL1, IL6) 3. Prosthesis micro motion 4. Debris dissemination (Increased hydrostatic pressure)

Question 48

Metal on poly advantages?

Answer 48

1. Longest track record 2. Low cost 3. Most modularity

Question 49

Metal on poly disadvantages?

Answer 49

1. Smaller head - impingement | 2. Increased wear vs metal on metal

Question 50

Best wear properties but worst mech properties of all bearing surfaces?

Answer 50

ceramic on ceramic | Also lowest coefficient of friction