Tribology

Question 1

what is the structure of metal?

Answer 1

• metal ions form crystal lattices
• crystals are grouped together into Grains
• grains are separated by dislocations that allow sliding of grains

Question 2

how are metals manufactured?

Answer 2

• casting - Liquid Metal put in a cast
• wrought - takes cast metal and modifies it by stretching or rolling in machines
• work hardening - changes the mechanical properties - cold hardening, annealing and hot hardening
• Shaping
• Alloying
• Quenching
• passivation

Question 3

what is the composition of stainless steel?

Answer 3

316L

• 3% molybdenum
• 16% nickel
• low carbon 0.03%
• 60% iron
• 20% chromium

Question 4

what are the advantages of stainless steel?

Answer 4

• Tough
• stiff - high Young’s modulus
• ductile
• fatigue resistance
• cheap

Question 5

what are the disadvantages of stainless steel?

Answer 5

• stress shielding - makes it bad for I’m nails
• susceptible to corrosion - stress and crevice

Question 6

what implants is stainless steel good for?

Answer 6

Frature fixation plates:
- stiff
- tough
- good fatigue resistance

Question 7

what is the composition of titanium?

Answer 7

Ti64V
- 6% aluminium
- 4 % vanadium
- 90% titanium

Question 8

what are the properties of titanium?

Answer 8

• strong passivation layer - corrosion resistant
• Biphasic - atoms arranged in 2 different phases making it fatigue resistant
• less modulus mismatch
• less stress shielding
• less anterior thigh pain for nails
• biocompatible - inert metal

Question 9

what are the disadvantages of titanium?

Answer 9

• poor wear properties - so can’t be used as a bearing surface
• poor notch sensitivity
• vanadium ions released are cytotoxic
• expensive

Question 10

what is titanium used for?

Answer 10

IM nails
femoral stems
recon plates

Question 11

what are the components of cobalt chrome?

Answer 11

60% cobalt
25% chrome
5% molybdenum

Question 12

what are the properties of cobalt chrome?

Answer 12

• good fatigue and corrosion resistant
• excellent wear
• tough

Question 13

what are the disadvantages of cobalt chrome?

Answer 13

• stress shielding
• expensive

Question 14

what is cobalt chrome used for?

Answer 14

excellent bearing surface
- resistant to scratch

Question 15

what is the relationship between stress and strain in a ductile material

Question 16

what is the composition of ceramics?

Question 17

why is ceramic a good bearing property?

Question 18

what is the difference between the scratch profile of metal and ceramic?

Question 19

what is;
* stress
* strain
* elastic zone
* plastic zone
* ultimate tensile strength
* yield point
* toughness
* hardness
* youngs modulus

Answer 19

• stress - force applied to an area
• strain - change in length over original length
• elastic zone - reversible deformation
• plastic zone - permanent deformation
• ultimate tensile strength - load to failure
• yield point - transition between elastic and plastic zones
• toughness - amount of energy a material can absorb before failure - area under curve
• hardness - surface property - resistance to scratching
• youngs modulus - ability of a material to resist deformation

Question 20

What are isotrophy and anisotrophy?