Friction, lubrication, wear and corrosion

Question 1

Galvanic corrosion

Answer 1

two dissimilar metals are electrically coupled together.

Question 2

Pitting corrosion

Answer 2

Localized corrosion attack in which small pits or holes form. The pits ordinarily penetrate from the top of a horizontal surface downwards in a near-vertical direction. This is an extremely insidious type of corrosion, often going undetected and with very little material loss until failure occurs.

Question 3

Crevice corrosion

Answer 3

increase in the concentration of chloride ions, low pH, and low oxygen tension furthers the breakdown of the passivation layer by creating the conditions that make the metal oxide film soluble.

Question 4

Fretting corrosion

Answer 4

synergistic combination of wear and crevice corrosion of two materials in contact. It results from micro-motion between the two, which disrupts the protective film of a metal.

Question 5

Stress corrosion

Answer 5

Metals that are repeatedly deformed and stressed in a corrosive environment show accelerated corrosion and fatigue damage

Question 6

Key facts about synovial fluid

Answer 6

Non Newtonian( shear stress is not proportional to shear rate).

Pseudoplastic(undergoesshearthinning).

Thixotropic (undergoes shear thinning with time when sheared at a constant rate).

Question 7

Factors determining lubrication

Answer 7

Magnitude and direction of loading
Geometry of bearing surfaces/ surface roughness
Material properties of the surface
VELOCITY AT WHICH BEARING OPERATES
VISCOSITY OF THE LUBRICANT

Question 8

MECHANISM OF WEAR

Answer 8

Abrasive wear: Two-body abrasive wear and third body abrasive wear

Abrasive wear can be minimized by manufacturing a hard and smooth femoral head and avoiding extraneous material in the interface.

Adhesive wear : occurs when a junction is formed between the two opposing surfaces as they come into contact

Fatigue wear: This is a form of failure that occurs in structures subjected to dynamic and fluctuating stresses