RJM, 9/16/06All photos and figures - Copyright, Prentice Hall Chapter 5 – The Role of Tribology in...

RJM, 9/16/06 All photos and figures - Copyright, Prentice Hall

Chapter 5 – The Role of Tribology in Engineering Materials

Tribology comprises the science and technology of interacting surfaces in relative motion; that is, friction, lubrication and wear. Tribology is a vast and interdisciplinary subject, ranging from the fundamental physics of surface contact and adhesion to the application of advanced materials and lubricants to solve practical industrial friction and wear problems.


Motivation:

• Most common forms of metal failure:– Corrosion– Fatigue (cyclic loading)– Wear (surface abrasion due to excessive

friction or lack of lubrication) = TRIBOLOGY

– CASE STUDIES (my own)


What is Friction

• Force tangential to the interface of two contacting bodies = Ff.– Dynamic and static– Dynamic produces

heat

NFf

Friction Force

Coefficient of friction s and d

Normal Force

Assumptions: Ff independent of contact area, = constant


More Complicated Models Exist:

• Contact Mechanics

In actuality, as N increases, contact area increases, thereby affecting . is a non-linear function of N. What else might vary with??


More Complicated Models Exist:

F = Fa + Fp + Fs + Fn NFf


What about contact stresses???

Recall: Pitting stress in gear teeth


How to Measure ???

• Do you want s or d???

• For most stress analysis want s – why??


Good for measuring s. You should know how to derive this.

Good for measuring s

and d.


Typical Friction Force Curves

s = Fa/Nd = Fb/N

Stick- Slip – difficult to get a


Figure 3-8: Average n for various materials in reciprocating motion of an annular ring rider (.1 sq in) on a type 316 stainless steel counter face at 20 C 50% relative humidity at various normal forces. The stroke was 50 mm and the frequency was 0.5 Hertz. The friction force was averaged for eight cycles for each test.


CASE Study:

• Compression seal. Coefficient of friction was key for proper design and analysis.


Friction Testing – Slide flat EPDM samples across ABS slab

CASE Study


Coefficient of Friction Results:

•Incumbent Material = 0.15, 0.13•M-858-2(2) = 0.23, 0.17•M-858-2(6) = 0.30, 0.30•M-858-2(7) = 0.24, 0.21•M-858-2(8) = 0.23, 0.22•M-858-2(9) = 0.37, 0.38•M-858-2(10) = 0.31, 0.31•M-858-2(12) = 0.36, 0.33•M-858-2(13) = 0.25, 0.29•M-858-2(14) = 0.29, 0.25•M-858-2(15) = 0.21, 0.24•M-858-2(16) = 0.21, 0.28


4” seal section shownActuator Force/Displacement

Fixed to load frame

ABS

Polycarbonate

Test Set-up for K and Stress Relaxation:

Seal glued with 3M CA40H Adhesive



L/D Curves for All 4" Samples

0

50

100

150

200

250

300

350

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

Deflection (in)

Lo

ad

(lb

)

4" Sample #1

4" Sample#2

4" Sample #3

4" Sample w/ Polycarbonate contact

4" Sample #1 Immersed

4" Sample #2 Immersed

Load Only


L/D Curves - FEA vs. Measured Results

0

50

100

150

200

250

300

350

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

Deflection (in)

Lo

ad (

lb)

Measured - Incumbent Sample #1

Measured - Incumbent Sample#2

Measured - QC-19095 Sample 1"

Measured - QC-19095 Sample 2"

FEA Results - Incumbent Seal

FEA Results - QC-19095

FEA Results - Modif ied QC-19095

Note:1. All results for 4" seal length.2. FEA results - hyper data, 60 duro EPDM, friction = 0.25.

Note, modified seal slightly stiffer at lower deflections and softer at higher deflections!


Stiffness Summary:


WEIGHT USED: SLED + 1LB WEIGHT (704g)



5.4 Definition of Surface Wear

• Wear - Damage to a solid surface involving progressive loss of material due to contact and relative motion with another surface. 13 types of wear!!

• Erosion – Damage to a solid surface involving progressive loss of material due to mechanical interaction between that surface and a fluid, impinging liquid or solid particles. 5 kinds of erosion


Figure 5.14 – Major Categories of wear and specific types of wear in each category.


Types of Wear:

Figure 5:20 – Adhesion wear – localized bonding between contacting surfaces

Figure 5-21: Galling wear – severe adhesion actually leads to material flow up from the surface.

adhesion

adhesion


Figure 5-23: Fretting wear of splined shaft– small oscillatory motion abrades surface – looks like rust – surface looks pitted.

adhesion


F5-24: low stress abrasion wear – bushing sliding on shaft

abrasion


Surface fatigue

F 5-27 – Pitting surface fatigue – large roller thrust bearing race – compressive stress developed between roller bearing and race = pitting. Material actually fatigued and removed from surface!!


Surface fatigue

F5-28: Impact wear


Surface fatigue

F 5-30: Brinelling – brinelling of bearing race due to static overload. Note brinelling more of a static failure (indentation) versus fatigue or wear failure.


F 3-27: Factors that affect wear at various size levels.

Key: Bonds between atoms!

Key: Dislocations

Key: Grain Size

Key: Surface asperities

Key: Surface confromance


Figure 5-15: Types of Erosion – Note all involve fluids or smoke (particulates)


Fig5– 16: solid particle erosion due to fly ash.

Types of Erosion

5-17: Slurry erosion due to pumping slurry mixture of silica and water

erosion

erosion



Case Study – WEAR

Requirement: Coat steel flight bars on conveyor of continuous miner with “soft” material for noise reduction. Must meet life requirement of 500,000 tons of coal (min) without significant wear.


Joy Continuous Mining Machines

14CM series targeted for noise reduction

14CM Series12HM Series12CM Series

2010 SME Annual Meeting & ExhibitPhoenix, Arizona


Commitment to Health & Safety

Industry Leading Dust and Noise Reduction Initiatives

Wethead Cutterhead System Dual Sprocket Conveyor



Ongoing Developments

Coated Dual Sprocket Chain



Figure 7-14 – abrasion wear of various plastics


Taber Test – common test for abrasion resistance of elastomers/polymers


Compound No. Rheometer Data Original Physical Properties After Aging 70 hrs at 70°C Compression Set Taber

Ml Mh ts1 tc90

tan Delta @

MhCure Time

Cure Temper

ature

100% Modulu

sElong ation Tensile

Duro meter

∆ 100% Modulu

s∆ Elong

ation∆

Tensile∆ Duro meter

Cure Time

Cure Temper

ature22 hrs

@ 70 °Cmg loss per rev.

XM-AR (1) 3.28 19.59 114 335.97 0.095m35s 155 496 479 3439 67.6 6.1 -1.5 -2.2 210m35s 155 24.4 0.0892

XM-AR (2) 3.72 26.56 105 319.98 0.095m20s 155 870 290 2504 75.1 2.5 -4.5 -5.5 2.810m20s 155 25.3 0.0305

XM-AR (3) 3.56 19.96 111 311.4 0.095m11s 155 590 451 3405 70.6 2.7 -0.7 -3.7 0.810m11s 155 27.4 0.006

XM-AR (4) 2.41 23.36 121.2 355.65 0.075m55s 155 736 352 2562 72 12.9 5.4 8.8 2.210m55s 155 20.3 0.0187

XM-AR (5) 2.62 20.94 126 321.16 0.075m21s 155 498 423 2981 65.6 7.7 8.7 4.7 2.610m21s 155 19.6 0.0163

XM-AR (6) 3.31 24.85 127.8 359.58 0.076m0s 155 683 393 2856 72 3.5 2.3 0.7 2.211m0s 155 9.4 0.0163

XM-AR (7) 0.49 17.82 150 404.82 0.036m45s 155 780 527 4318 68.5 12.3 -20.3 -14.5 1.811m45 155 45.4 0.0261

XM-AR (8) 0.77 20.58 114 381.98 0.046m22s 155 1306 517 4032 74.2 -0.3 -10.8 0.6 2.611m22s 155 34.2 0.164

XM-AR (9) 0.74 23.83 123.6 434.22 0.047m14s 155 695 524 4577 71.2 23.2 -12.4 -2.6 3.612m14s 155 39.2 0.0239

XM-AR (10) 3.69 26.06 61.2 286.38 0.074m37s 155 912 310 2691 76.2 3.6 -9.4 -5.8 0.49m37s 155 25.7 0.0108

Incumbent Mat'l 0.0154


300,000 tons

Key Property: Abrasion resistance?? Tear Strength?? Coef of Friction??

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RJM, 9/16/06All photos and figures - Copyright, Prentice Hall Chapter 5 – The Role of Tribology in...

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