• Dr.
Apurba Das
Fundamentals of Tribology
(ME-4122)
C4
Date: 31st July 2025
Dr. Apurba Das
Asst. Prof, Dept of Mechanical Engineering
IIEST, Shibpur. P.O- B.Garden, Howrah-711103
Wear Adverse effect
Wear increases: In Machine
1.Power losses, components wear is
2.Oil consumption not desired
3.Rate of component replacement
Removal of material from operating solid surface by:
⮚ Solid : Load, Velocity, Environment, Materials
⮚Fluid (liquid/gas) : Velocity, pressure, Environment,
Materials
Wear Mechanisms: More than 34 mechanisms
❖ Abrasive Wear : Polishing, scouring, scratching,
grinding, gouging…
❖ Adhesive Wear : galling, scuffing, scoring Wear an be classified based on the ways
❖ Cavitation (interaction with fluid) that the frictional junctions are broken,
❖ Corrosive Wear (Chemical nature) that is, elastic displacement, plastic
❖ Erosive Wear displacement, cutting, destruction of
❖ Fatigue surface films and destruction of bulk
❖ Delamination material.
❖ Fretting Wear
8/6/2025 Wear Mechanism 2
Wear Adverse effect
In present course Cycling loading induces due to blunt asperities. Fatigue
cracks start at the material surface and spread to the
1.Abrasive Wear subsurface regions. The cracks may connect to each
2.Adhesive Wear other resulting in separation delamination of the material
pieces.
3.Corrosive Wear
4.Erosive Wear Fretting wear is caused by cycling sliding of two
5.Fatigue surfaces across each other with a small amplitude
(oscillating). The friction force produces alternating
6.Fretting Wear compression-tension stresses, which result in surface
fatigue.
1. Abrasive Wear
❖ Caused by the passage of relatively hard particles/asperities over a
surface.
❖ Micro-cutting: sharp particle or hard asperity cuts the softer surface.
Cut material is removed as wear debris.
❖ Micro-fracture: abraded material is brittle, e.g. ceramic. Fracture of the
worn surface occurs due to merging of a number of smaller cracks.
❖ Micro fatigue: When a ductile material is abraded by a blunt
particle/asperity then cutting is unlikely and the worn surface is
repeatedly loaded and unloaded.
❖ Removal of material grains: Happens in materials (i.e. ceramics)
having relatively week grain boundaries.
8/6/2025 Wear Mechanism 3
Abrasive wear
Two other mechanisms, very similar to abrasive wear are:
❖Erosive wear: Impact of particles against a solid surface.
❖Cavitation wear: Localized impact of fluid against a surface during the collapse of bubbles.
Two basic modes of abrasive wear are
Two body abrasion
Three body abrasion
Two Body Abrasion
❖ Two interacting asperities in physical contact, and
one of them is harder than other.
❖ Normal load causes penetration of harder asperities
into softer surface thus producing plastic
deformations.
❖ To slide, the material is displaced/removed from the
softer surface by combined action of micro-
ploughing & micro cutting.
8/6/2025 Two Body Abrasion 4
Rabinowicz’s Quantitative Law for 2-B Abrasive Wear
Assume conical asperities indenting soft surface during traverse motion.
Assumptions Assumed that all the material displaced by the cone is lost as wear debris.
Load carried by nth asperity
Volume swept by penetrated asperity
x = depth of penetration, L= distance travelled
8/6/2025 Two Body Abrasion 5
Quantitative Law for 2-B Abrasive Wear
Total wear is the sum of individual wear caused by
asperity
The surface is rough and there are many asperities
present on the surface
Dependence on: Normal Load Hardness Micro-structure
8/6/2025 Two Body Abrasion 6
Three Body Abrasion
❖ Material removal from softer surface by hard loose particles.
❖ Lesser sliding distance (< 20%).
❖ K2B = 5*10-3 to 50*10-3; K3B = 5*10-4 to 50*10-4
❖ Generated locally by oxidation or wear-out.
❖ Iron oxides wear debris produced during adhesive
wear cause further damage by abrasion
❖ Clearance larger than particle size and filtration
reduce chances.
Roundness Factor
Such shape difference may result in differences
in wear rate by factor of ten or more.
8/6/2025 Two Body Abrasion 7
Wear Test Process for Abrasive Wear
Wear Test
Cleaning of blocks with acetone
Drying the blocks with paper
Controlling parameter on block on disc wear test
1. Rotational speed 200 rpm
2. Sliding speed 0.9210 m/s
3. Load 5.0 Kg (without current)
4. Wear measurement = weight of the block before
test - weight of the block after test
8/6/2025 Two Body Abrasion 8
Adhesive Wear
Very common in metals
Second most common form of wear in industry. • Mild-wear and severe wear
Real area of contact, A = W/H. For elastic-plastic deformation A = (W/H)n , 2/3 < n<1
Adhesive wear arises from the shearing of the friction junctions.
Weaker junction: Shearing occurs in the interface itself. Mild wear.
Stronger junction: Shearing will occur a little distance within the softer metal. Severe wear.
8/6/2025 Adhesive Wear 9
Laws of Adhesive Wear
Volume of wear
Typical Graph for Wear rate Vs Load
8/6/2025 Adhesive Wear 10
