Tribology 101 Webinar-1 Intro and Basics 29-Jan-2013

Tribology 101 Introduction to the Basics of Tribology SJ Shaffer, Ph.D. Bruker-TMT [email protected]

Outline

Origin/Definition of Tribology (Term and Field) Encompassing Fields Fundamentals of Tribology:

Surfaces in Contact Friction Lubrication Wear

Concluding Words Upcoming Topics in Series

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What is Tribology ?

Tribology comes from the Greek word, tribos, meaning rubbing or to rub

And from the suffix, ology means the study of

Therefore, Tribology is the study of rubbing, or the study of things that rub.

This includes the fields of:

Friction, Lubrication, and Wear.

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Tribology is a new word

Coined by Dr. H. Peter Jost in England in 1966 The Jost Report, provided to the British Parliament

Ministry for Education and Science, indicated Potential savings of over 515 million per year ($800 million) for industry by better application of tribological principles and practices.

But Tribology is not a new field!

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The First Recorded Tribologist 2400 B.C.

Transporting the statue of Ti from a tomb at Saqqara, Egypt

Figure taken from History of Tribology, by Duncan Dowson.

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Transporting the statue of Ti from a tomb at Saqqara, Egypt

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The first recorded tribologist pouring lubricant (water?) in front of the sledge in the transport of the statue of Ti.

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A more famous Tribologist 500 years ago

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Leonardo Da Vinci

Ball Bearing

4-Ball Test Geometry Sled Friction Test Geometry


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Leonardo Da Vinci

Ball Bearing


ASTM D5183 - COF ASTM D2266, D2596 EP ASTM D4172, D2783 - Wear

ASTM D1894 Static and Kinetic COFs of Plastic Film & Sheeting


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Leonardo Da Vinci

Ball Bearing


Two Observations: 1. The areas in contact have no effect on

friction. 2. If the load of an object is doubled, its

friction will also be doubled. ASTM D5183 - COF ASTM D2266, D2596 EP ASTM D4172, D2783 - Wear

ASTM D1894 Static and Kinetic COFs of Plastic Film & Sheeting

Tribology 101 - Basics

Applications and Fields which

Encompass Modern Tribology

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Tribology is All Around Us, In Applications from Simple to Complex and Scales from Small to Large

Individual Components

Assemblies or Products

Manufacturing Processes

Construction/Exploration

Natural Phenomena

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Individual Components

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Gears

Bearings Brake & Clutch Pads

Assemblies or Products

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Engines

Curling Stones

Rock Climbing Shoes

Pocket Watch

Manufacturing Processes

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Rolling

Stamping

Turning

Grinding/Polishing

Construction/Exploration

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Mine Slurry Pumps

Excavator

Chunnel Digging Drill

Oil Drilling Rig

Space Shuttle

Natural Phenomena

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Plate Tectonics

Wind Erosion Water Erosion

Wear Friction

On/Off Stiction: Gecko Feet

Super-hydrophobicity:

Lotus Leaf

Tribology 101 - Basics

In Parallel to these different Scales,

There are Many Areas of

Engineering and Industry which

have a Need to Use/Understand Tribology

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Tribology is also in Virtually every Area of Engineering and Industry

Aerospace Agriculture Automotive

Engine: Piston ring/cylinder, Bearings, valve seats, injectors

Brakes/clutch Tooling/Machining/Sheet metal

forming Coatings Providers

Low Friction Wear Resistant

Thin Films or Hardfacings

Cosmetics/Personal Care Dental Implants Energy

Nuclear Wind Fossil Solar

Fabric/Clothing Flooring Food Processing Highway/Transportation

Depts. Lubricant Manufacturers Medical Diagnostics Medical Implants Military Pharmaceutical Shoe Manufacturers Sports Equipment Companies Universities/Educators

Mechanical Engineering Materials Science Engineering Physics Chemistry

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Commonality in Tribology

What do All These Diverse Fields and Applications have in Common? What do we need to think about as engineers and scientists when we design products or friction/wear experiments?

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Commonality

Every Application has:

Surfaces in Contact, and

in Relative Motion

(e.g. sliding, rolling, impacting)

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Tribology Basics - Surfaces in Contact

So lets begin by looking

closely at a surface

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The Surface is not Simple

Bulk Material Properties Handbook

values

Surface Properties Disturbed Material

Oxide

Adsorbed Contaminants

Lubricant

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The Surface is not Simple

Bulk Material Properties Handbook

values


Oxide


Lubricant

mms - cms

nms - ms

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Nor is it Flat!

Bulk Material Properties


Oxide


Lubricant

All engineering surfaces have a roughness, and this roughness plays an important role in tribology.

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Nor is it Flat!

Bulk Material Properties


Oxide


Lubricant

All engineering surfaces have a roughness, and this roughness plays an important role in tribology. Surface Roughness comes from all prior history of the part: Manufacturing, handling and prior use in application.

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We need to think about

Physical - Surface Roughness Dictates Contact Area

Dictates Contact Stresses

Lubricant Paths or Reservoirs

Chemical - Intervening Layers Chemical Compatibility

Shear Strength

Lubricant Properties, e.g. Viscosity

2 Aspects of a Surface:

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Paths or Reservoirs for Lubricants/debris


Shear Strength

Lubricant Properties, e.g. Viscosity


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Ground

Bead Blasted




Lubricant Paths or Reservoirs


Shear Strength

Lubricant Properties, e.g. Viscosity, EP or boundary-forming


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Surface Characterization Variety of Methods available, if needed

Physical Characterization Roughness

Macro Waviness and Form (CMM) Micro Surface Roughness

Stylus Profilometers (contact) Optical Profilometers (non-contact) AFM (sub-micron)

Hardness Indent, Scratch

Chemical Characterization Infrared, XPS, Raman, Auger Lubricant Shear propertiesViscometry

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Tribology 101-Basics Summary of Surfaces in Contact

Tribo-Forces are Dictated by Interaction of Asperities Asperities have Mechanical and Chemical

Properties Methods Exist to Characterize these

Properties

Asperity Geometry and Distribution result from Manufacturing Method, Handling and Prior Rubbing History

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Friction Fundamentals

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Friction Fundamentals Conceptual Definition of Friction

Friction is the resistance to relative motion between two

bodies in contact.

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Where does the resistance come from?

Microscopic forces of molecular Adhesion.

Microscopic forces of

mechanical Abrasion.

When objects touch there are forces between them.

(includes electrostatic, Van der Waals, metallic

bonds)

(includes elastic and plastic deformation)

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Where does friction come from?

Remember, there are also contaminants at the interface

Oxides,

Adsorbed films,

Adsorbed gases,

Foreign or domestic particles

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Friction Fundamentals The COF

The Coefficient of Friction: A simple

constant of proportionality.

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The Coefficient of Friction: A simple

constant of proportionality.

Or is it?

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Friction Fundamentals Measuring Friction:

The Coefficient of Friction

Very Simple Relation:

F=N N

F

= F/N = COF

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Suppose a colleague wants to know:

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What is the

COF of steel?


A: Well, dear colleague, you can use from 0.1 to 0.6. Take your pick.

Is that close enough for your needs?

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What is the

COF of steel?


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Well not really.

?


Then I guess well need a bit more

information.

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Well not really.

?

Friction Fundamentals The COF What we need to know

What steel? Stainless steel: 304, 316 , a 400-series or hardened 17-4PH or the like? Carbon steel: if so is it pearlitic or martensitic? Tool Steel?

Well I need to use it in water, so stainless steel, I guess. What is the function? What is the mechanism? Im designing a gear-driven mechanism, and I need to size the motor, assuming some

frictional loss in the gears, so I need the COF. Gears Then, it needs to be hardened. How about the driven gear, whats its material? The same, I suppose. Im not sure thats a good idea, depending on the contact stress, sliding velocity and

surface finish. Do you know these parameters yet? Not yet, Ill probably use standard values from my gear design handbook. OK, I gather you need low friction, how about lubricant or use of a lubricious coating, are

these permitted in the design? A coating is OK, but I dont think a liquid lubricant is permitted in this application. OK, a coating then. How long will it need to last? For the life of the mechanism. Cant you just tell me the COF? Really, I need more information, because Ill likely need to run a test, depending on how

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All things considered, The COF is Somewhat Complicated

Surface roughness plays a role Lubricant plays a role Surface chemistry plays a role Contact Stress plays a role Contact geometry plays a role Environment plays a role Temperature plays a role Sliding speed plays a role

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All things considered Its not so bad after all

Fortunately, while it appears complicated,

friction is relatively easy to measure,

(Only two things: Normal Load and Friction Force)

But, we have to measure it under the right

conditions.

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Summary of Friction Fundamentals The equation is simple, but measuring it correctly requires care:

When assessing a systems tribology need, we must consider: Materials, Coating, Lubricant Contact Area, Geometry, Stress Surface Roughnesses Sliding Speed Sliding Mode (unidirectional, reciprocating, multidirectional) Duty Cycle (continuous contact, intermittent contact) Environment Temperature, Humidity,

Atmosphere (air, exhaust gases, vacuum) Friction is NOT a Material Property

Friction is a System Property No such thing as the COF of steel, or the COF of rubber

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Lubrication Fundamentals

Lubrication Fundamentals

The role of a lubricant is to: Reduce Friction

Prevent / Minimize Wear

Transport Debris away from Interface

Provide Cooling

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Lubrication Fundamentals: Lubrication Regimes, with liquid present

* - composite surface roughness = (rq12 + rq22)1/2

In Liquid Lubrication, Regimes can be based on: Fluid Film Thickness

The Lambda Ratio is defined as the ratio of the fluid film thickness to the composite surface roughness*

> 3 full film (thick film) lubrication, hydrodynamics

1.2 > > 3 mixed or thin film lubrication < 1.2 boundary lubrication

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Lubrication Regimes: The Stribeck Curve

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Speed*Viscosity Load

Journal Bearing

Thick Film

Thin Film, Mixed

Bou

ndar

y

Lubrication Regimes: Boundary Lubrication Solid Lubricants

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Solid Lubricants Compounds with Low Shear Stress

MoS2, Graphite, WS2, HBN Behave like a deck of cards

Bonded Films DLC Resin-bonded PTFE Impregnated porous anodizing

Summary of Lubrication Fundamentals:

Key Factors in Lubricant Effectiveness Fluid Shear Properties

Viscosity, Viscosity Index Pressure-Viscosity Index

Chemistry Reactivity with the Surface Boundary Film-Forming Properties Extreme Pressure Constituents Shear strength of solid lubricant or coating

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Wear Fundamentals

Wear Fundamentals Conceptual Definition of Wear

Removal (or displacement) of material from one body when subjected to contact and relative motion with another body.

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Wear Fundamentals - Wear Modes

6 Primary Wear Modes:

1. Abrasive Wear, Scratching

2. Adhesive Wear, Galling, Scuffing

3. Fretting/Fretting Corrosion

4. Erosive Wear, Cavitation, Impact, Electro-arcing

5. Rolling Contact Fatigue, Spalling, Delamination

6. Tribo-Corrosion

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Wear Fundamentals

Abrasive Wear, Scratching

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The harder material scratches the softer material.

Wear Fundamentals

Adhesive Wear, Galling, Scuffing

Galling of Stainless Steel Samples

10 mm

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Begins as local welding Material compatibility is important for adhesive wear.

Stacking fault energy, crystal structure, natural oxide formation all influence adhesive wear.

Wear Fundamentals

Fretting/Fretting Corrosion

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Experiments generally have zones of no-slip, and slip.

Small adhesive pull-outs occur at the boundary.

Often these oxidize, so sometimes called fretting corrosion.

Small amplitude displacement (< 50 m).

Wear Fundamentals

Erosive Wear, Cavitation, Impact, Electro-arcing

Cavitation Damage

1 cm

Steam Control Valve

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Fluting Damage

Dependency on particle size, shape, composition, angle of impingement, as well as ductility of target

Particle Classification

Wear Fundamentals

Rolling Contact Fatigue, Spalling, Delamination

Spalled Bearing Inner Race

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Propagation to surface of sub-surface-initiated cracks

Reversing sub-surface shear each time the roller or ball passes over the surface.

Accumulation of these stresses leads to subsurface crack formation, usually at a microstructural inhomogeneity.

Cracks grow toward surface and particle spalls off.

Debris typically gets rolled over, creating additional damage.

Wear Fundamentals

Tribo-Corrosion

Erosion-Corrosion

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Wear in the presence of corrosion can have synergistic effect.

Can happen with erosion or sliding wear.

Bio-tribo-corrosion is major area

Down-hole drilling environment is another

ASTM Method G119 Standard Guide for Determining Synergism between Wear and Corrosion

Wear Assessment

The Wear Coefficient, k

k volume of material removed per unit load and sliding distance

Units of k are: mm3/Nm Please do NOT reduce the units of k to mm2/N or 1/kPa This has no physical meaning

k can be used to predict component lifetimes, providing the tribosystem does not change wear modes

Duty cycle and directionality can influence wear

Start-stop can be much more damaging than continuous motion

Unidirectional sliding is very different from reciprocating sliding

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Summary of Wear Fundamentals

Like Friction, Wear is a System Property, NOT a Materials Property

There are several distinct wear regimes, though some can operate simultaneously, or sequentially

Observed abrasive wear can results from initial adhesive wear

If you properly simulated the system and wear mode, the wear coefficient, k, can be used to predict lifetimes

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Some Final Words for

Todays Webinar

Tribology Fundamentals Key Concepts

1.COF is not a material property, it is a system property.

2.Wear Rate or wear resistance depends on the wear mode, which is a function of the Tribosystem.

3.If we properly characterize and understand the Tribosytem, the odds are better that we will succeed, because we can make the right choice for materials, contact geometry and chemistry, and make the appropriate measurements to give us the answer we seek for our design. 1/29/2013 65

Means to Assess Tribo-systems

Tribology & Mechanical Testing (TMT)

Universal platform for Tribology studies: Wear, Friction,.. when 2 surfaces meet.

Large load range Wide variety of environments (corrosion, HT, liquid) Wide variety of configurations (rotating & translating motions)

Many different Tribology tests

Linear Stage Block-on-Ring Drive

Reciprocating Drive Rotary Drive

Indentation & Scratch Testing

Indentation & Scratch Tester

Large load range: nano & micro Wide variety of imaging options

(AFM, profiler, optical)

Scratch test example

Indentation example

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Tribology 101 Introduction to the Basics of TribologyOutlineWhat is Tribology ?Tribology is a new wordThe First Recorded Tribologist 2400 B.C.The First Recorded Tribologist 2400 B.C.The First Recorded Tribologist 2400 B.C.A more famous Tribologist 500 years agoA more famous Tribologist 500 years agoA more famous Tribologist 500 years agoTribology 101 - BasicsTribology is All Around Us,In Applications from Simple to Complexand Scales from Small to LargeIndividual ComponentsAssemblies or ProductsManufacturing ProcessesConstruction/ExplorationNatural PhenomenaTribology 101 - BasicsTribology is also in Virtually every Area of Engineering and IndustryCommonality in TribologyCommonalityTribology Basics - Surfaces in ContactThe Surface is not SimpleThe Surface is not SimpleNor is it Flat!Nor is it Flat!Slide Number 27Slide Number 28Slide Number 29Surface CharacterizationVariety of Methods available, if neededTribology 101-BasicsSummary of Surfaces in ContactSlide Number 32Friction Fundamentals Conceptual Definition of FrictionWhere does the resistance come from?Where does friction come from?Friction Fundamentals The COFFriction Fundamentals The COFFriction Fundamentals Measuring Friction:The Coefficient of FrictionFriction Fundamentals The COFFriction Fundamentals The COFFriction Fundamentals The COFFriction Fundamentals The COFFriction Fundamentals The COFWhat we need to knowAll things considered,The COF is Somewhat ComplicatedAll things consideredIts not so bad after allSlide Number 46Slide Number 47Lubrication FundamentalsLubrication Fundamentals:Lubrication Regimes, with liquid presentLubrication Regimes:The Stribeck CurveLubrication Regimes:Boundary Lubrication Solid LubricantsSummary of Lubrication Fundamentals:Slide Number 53Wear FundamentalsConceptual Definition of WearWear Fundamentals - Wear Modes6 Primary Wear Modes:Wear FundamentalsWear FundamentalsWear FundamentalsWear FundamentalsWear FundamentalsWear FundamentalsWear AssessmentSummary of Wear FundamentalsSlide Number 64Tribology FundamentalsKey ConceptsSlide Number 66Tribology & Mechanical Testing (TMT)Many different Tribology testsIndentation & Scratch TestingSlide Number 70

Documents

Tribology 101 Webinar-1 Intro and Basics 29-Jan-2013