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Basic Orthopaedic Sciences > Tribology > Flashcards

Tribology Flashcards

1
Q

What are the 2 types of fluids?

A

Newtonian and Non newtonian

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2
Q

What are the characteristics of a newtonian fluid?

A

Linear shear stress/strain relationship

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3
Q

Definition of friction?

A

Resistance to motion of surfaces gliding over one another

Arises from adherence of one surface to another

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4
Q

What is the equation for friction?

A

F= mu f x w

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5
Q

What influence does the apparent contact area have on friction?

A

NONE

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6
Q

Define roughness?

A

Ra = mean height of the asperities

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7
Q

What is viscosity?

A

Friction between 2 layers within a fluid - resistance to flow

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8
Q

What is shear with regards to fluids?

A

Rate of deformation of a fluid when subjected to shear stress

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9
Q

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

A

Apparent viscosity changes with shear rate

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10
Q

Name the different types of non-newtonian fluids? 5

A 
Pseudo-plastic
Dilatant
Plastic
Thixotropic
Rheopexic
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11
Q

What is characteristic of Plastic fluids?

A

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

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12
Q

What is characteristic of DILATANT fluids?

A

They exhibit shear thickening (Water flower mix)

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13
Q

What is the characteristic of pseudo-plastic fluids?

A

Shear thinning (Paint)

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14
Q

What are the 2 time dependent non newtonian fluid characteristics?

A

Thixotropic

Rheopexic

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15
Q

What is a Thixotropic fluid?

A

Pseudoplastic quality over time (Honey)

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16
Q

What is characteristic of Rheopexic fluid

A

Dilatant quality over time - rare (industrial materials)

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17
Q

What are the qualities of synovial fluid? 4

A
  1. Non- newtonian
  2. Pseudoplastic
  3. Thixotropic
  4. Viscoelastic
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18
Q

What are the 2 broad categories of lubrication

A
  1. Boundary

2. Fluid film

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19
Q

How does one distinguish the 2 categories of lubrication?

A

Lambda ratio

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20
Q

What is the lambda ratio

A

fluid film:roughness

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21
Q

From what lambda ratio is lubrication considered boundary?

A

<1

22
Q

From what lambda ration is lubrication considered as fluid film?

A

3

23
Q

What is boundary lubrication?

A

Monolayer of lubricin/phospholipid

24
Q

Name the 3 dynamic fluid film lubrication types?

A
  1. Hyrdodynamic
  2. Elastohydrodynamic
  3. Micro-elastohydrodynamic
25
Q

Name the 3 static fluid film lubrication types?

A
  1. Squeeze film
  2. Weeping
  3. Boosted
26
Q

What is MEHD lubrication?

A

Asperities are ‘flattened’ out under high loads increasing the lambda ratio

27
Q

Lubrication in metal on poly?

A

Boundary

28
Q

Proposed lubrication in metal on metal?

A

Fluid film

29
Q

What factors influence lubrication in prosthetic joints? 5

A
  1. Magnitude and direction of loading
  2. Geometry/ roughness
  3. Material properties
  4. Velocity at which the bearing operates
  5. Viscosity of lubricant
30
Q

What is radial clearance?

A

Radius of cup - radius of head

31
Q

What is the definition of wear?

A

Unwanted progressive loss of a bearing surface

32
Q

What are the two broad types of wear?

A

Mechanical and chemical

33
Q

Define wettability?

A

Affinity of a surface material to a lubricant

34
Q

What is wettability measured with?

A

Theta contact angle
<45 = hydrophilic
>90 = hydrophobic

35
Q

Define hardness/notch sensitivity?

A

Ability of a material to resist scratching

36
Q

How many types of mechanical wear are there?

A

4 modes

3 types

37
Q

What are the 3 types of mechanical wear?

A
  1. Adhesion
  2. Abrasion
  3. Fatigue
38
Q

What are the 4 modes of wear

A
  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
39
Q

What are the 2 quantifications of wear?

A

Volumetric (related to square radius of the head)

Linear (height)

40
Q

Describe fatigue wear

A

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

41
Q

What is the formula governing wear?

A 
V = LX/H
V - volume
L - Load
X - Sliding distance
H - hardness
42
Q

What is chemical wear/corrosion?

A

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

43
Q

What is the main feature leading to corrosive wear?

A

Disruption of the passivation layer

44
Q

What are the types of local corrosive wear?

A
  1. Crevice

2. Pitting

45
Q

What are the 5 types of general corrosive wear?

A
  1. Galvanic
  2. Fretting
  3. Stress (Fatigue)
  4. Inter/intragranular
  5. Inclusion
46
Q

6 consequences of wear?

A
  1. Synovitis
  2. Aseptic Osteolysis and loosening
  3. Systemic distribution (Metallosis)
  4. Immune reaction (Pseudotumours)
  5. Increased joint friction
  6. Misalignment and catastrophic failure
47
Q

Name the 4 steps of aseptic loosening?

A
  1. Particulate/debris formation
  2. Macrophage activation (TNF a, IL1, IL6)
  3. Prosthesis micro motion
  4. Debris dissemination (Increased hydrostatic pressure)
48
Q

Metal on poly advantages?

A
  1. Longest track record
  2. Low cost
  3. Most modularity
49
Q

Metal on poly disadvantages?

A
  1. Smaller head - impingement

2. Increased wear vs metal on metal

50
Q

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

A

ceramic on ceramic

Also lowest coefficient of friction

Basic Orthopaedic Sciences (25 decks)

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