TRIBOLOGY RELIABILITY

\

AGENDA Introduction – 5 minutesWebinar – 45 minutesQ&A – 10 minutes

Who Are We?Ops A La CarteHQ in Santa Clara, CA

Ops A La Carte Founded in 2001 Named top 10 fastest growing, privately-held companies in

the Silicon Valley in 2006 and 2009 by the San Jose Business Journal.

Over 1450 projects completed in 10 years Over 500 Customers in over 30 countries Over 100 different industries, 6 main verticals CleanTech, MedTech, Telecom, Defense, Oil/Gas, Consumer

We run FREE monthly webinars.

• Ops Solutions – Ops provides end-to-end solutions that target the corporate product reliability objectives • Ops Individual “A La Carte” Consulting – Ops identifies and solves the missing key ingredients needed for a fully integrated reliable product• Ops Training – Ops’ highly specialized leaders and experts in the industry train others in both standard and customized training seminars• Ops Testing – Ops’ state-of-the-artprovides comprehensive testing services

Touchscreens – ALT to determine the life of the screen.

Pumps – ALT to determine life of pumps.

Robotics – ALT to determine the repeatability and robustness

Valves – ALT to determine life of valves.

Gaskets – ALT to determine degradation pattern.

Fans/Blowers – ALT to determine life of fan.

Drills – ALT to determine wear pattern of drilling equipment.

Ops Mechanical ReliabilityProjects

Upcoming Events we are atInternational Reliability Innovations Symposium (IRIS)March 16, 2012, San Jose, CA and webinar

Ops A La Carte helped organize the conference and we were on the paper review committee.

SMTA Solar ConferenceMarch 21-23, 2012, Webinar

Ops A La Carte's Mike Silverman will be giving a presentation at this conference on "Reliability Risks in the Solar Industry."

Upcoming Events we are atIPC Conference on Test & InspectionMay 15-17, 2012, Costa Mesa, CA.

Ops A La Carte will be giving a presentation at this conference on "New Techniques for More Effective ESS".

SMTA Conference on Soldering and ReliabilityMay 15-18, 2012, Toronto.

Ops A La Carte's Peter Arrowsmith will be giving a presentation at this conference on "Improving Product Reliability Using Accelerated Stress Testing".

Upcoming Events we are atMD&M East May 22-24, 2012, Philadelphia, PA

Ops A La Carte's Mike Silverman will be giving a 3 hour class on "Medical Reliability Testing - Identifying Testing Requirements Early."

Applied Reliability Symposium June 13-15, 2012, New Orleans, LA

Ops A La Carte's Mike Silverman will be giving a presentation on "Calculating ROI When Implementing a Design for Reliability Program".

Other Reliability Events

Certified Quality Engineer Preparation Class

Date(s): April 17 to May 29, 2012Time: 6pm-10pm one night a week, 7 weeksLocation: San Jose, CA and Webinarhttp://www.opsalacarte.com/Pages/education/edu_10cqe.htm

Annual Reliability SymposiumMay 7-11, 2012 in Santa Clara, California and via webinar

TRACK ONE - DFX TOOLS

• Design for Reliability (DfR): May 7-8

• Design for 6 Sigma (DfSS): May 9

• Design for Mechanical Reliability (DfMR): May 10

• Design for Warranty (DfW): May 11 morning

• Design for Software Reliability (DfS): May 11 afternoon

TRACK TWO - REL TOOLS: ALT/DOE/RCA

• Design of Experiments (DOE): May 7-8

• Best Accelerated Reliability Tests (BART): May 9-10

• Root Cause Analysis (RCA): May 11

Upcoming Reliability Webinars

Design for Robustness

Date: April 4, 2012, 8:30amLocation: Webinar

This is our next webinar in our free webinar series

See link from our website www.opsalacarte.com

Webinar StatsThis is our 20th Webinar (see Ops site

for past webinar topics/content)

We run these webinars once a month

We partner with other companies

We partner with societies (IEEE, ASQ, and others for broader reach)

Webinar StatsSome of the past topics Solar Reliability Medical Reliability Root Cause Analysis Green Reliability Soft Errors Software Reliability Prognostics Best Reliability Testing Lead Free and Reliability Simulation and Reliability Design of Experiments

Webinar StatsFuture Topics FMEA/TS16949 Accelerated Reliability Tests, Different Options for Return on Investment for Design for Reliability Software Reliability

What would you like to see? Let us know at info@opsalacarte.com

Registration DemographicsFor this webinar we have signed up 100 Registrants 10 Countries

Registration Questions1. Do you have portions of your product

that can wear due to mechanical wear?

2. Do you know how to characterize the life of all your wearout mechanisms?

Registration Questions1. Do you have portions of your product that can

wear due to mechanical wear?

Yes 83%

No 17%

Registration Questions2. Do you know how to characterize the life of all

your wearout mechanisms?

Yes 21%

No 79%

Agenda Introduction to Tribology

Stribeck Curve-Rolling element bearing

Hertzian Contact Mechanics

Wear and Wear Mechanisms

Tribology Tribology is the science and engineering of interacting

surfaces in relative motion.

Includes the study and application of the principles of friction, lubrication and wear.

Annual cost of friction and wear-related energy and material losses is over $700 billion -- 5% to 7% of the United States’ $14 trillion gross national product (DOE, 2010)

Every aspect of tribology impacts product reliability

Tribology is a branch of mechanical engineering, but…

Tribology Gets Complicated

Key Aspects of Tribology Friction and Wear, Fluid Film Lubrication,

Elastohydrodynamic Lubrication,

Surface Properties and Characterization, Contact Mechanics, Magnetic Recordings,

Tribological Systems, Seals, Bearing Design and Technology, Gears, Metalworking, MEMs, Lubricants, and Artificial Joints

Friction Regimes Friction regimes for sliding lubricated surfaces have been

broadly categorized based on film thickness (h) versus the average distance between asperity contacts (R) :

Solid/boundary friction – Boundary Lubrication, h=0

Fluid friction – Elastohydrodynamic and Mixed, h~R

Mixed friction – Hydrodynamic Lubrication, h>R

“Stribeck curve”-Basic curve clearly show the minimum value of friction as the demarcation between full fluid-film lubrication and some solid asperity interactions.

Stribeck et al Stribeck and others systematically studied the variation of

friction between two liquid lubricated surfaces (5 Dec 1905)

Journal Bearings used in the research easy to recreate results

Curve is friction against function of a dimensionless lubrication parameter ηN/P, where η is the dynamic viscosity, N the speed (e.g. revolutions per minute of a bearing) and P the load projected on to the geometrical surface. [STLE]

Leads to understanding of wear behavior based on regime

Stribeck Curve

f versus ηN/P, the latter called Sommerfeld no.

Reliability of Surfaces in Contact Reliability of mechanical elements is a tribological

phenomenon based on wear characteristics

Each regime leads to different failure modes and Weibull curve can be used to model elastohydrodynamic and hydrodynamic lubrication

Application to mechanical elements is advanced since industry is established well ahead of electrical and electronic industries – e.g. mechanical roller bearings

Rolling Element Reliability Seemingly identical rolling bearings operated under identical

conditions may not last the same amount of time

Impractical to test a statistically significant number of bearings, so engineers rely on standardized bearing-life calculations to select and size bearings for a particular application.

Calculations continue to evolve and become more accurate over time, reflecting the collective experience of the bearing industry, including recent advances in manufacturing, tribology, materials, end-user condition monitoring, and computation.

Bearing Life Equations RATING LIFE EQUATIONSThe equation from ISO 281,

2007 or the American Bearing Manufacturers Association (ABMA) Standards 9 and 11 figures basic, non adjusted rating life by:

L10 = (C / P)p in millions of revolutionswhere C = basic dynamic load rating, lb;

P = equivalent dynamic bearing load, lb;

p = life-equation exponent ( p = 3 for ball bearings; and p = 10/3 for roller bearings)

Tribology of A Roller Bearing

Bearing Life Definitions Basic life or L10 as defined in ISO and ABMA standards is

the life that 90% of a sufficiently large group of apparently identical bearings can be expected to reach or exceed.

Median or average life, sometimes called Mean Time Between Failure (MTBF), is about five times the calculated basic rating life.

Service life is the life of a bearing under actual operating conditions before it fails or needs to be replaced for whatever reason.

Specification life is generally a requisite L10 basic rating life based on experience in similar applications by manufacturer.

Roller Bearing Example Roller bearing is to be selected to withstand a radial load of

4kN and have an L10 life of 1200h at a speed of 600 rpm. The rated life is 3000 hours and nominal speed of 500 rpm.

CR=F*[(LD/LR)(ND/NR]1/a

where

CR is rated loadLD/LR ratio of actual life to rated life ND/NR ratio of actual speed to rated speed

F is the loada is the bearing exponent (3 ball and 10/3 roller bearings )

Sample Solution CR=F*[(LD/LR)(ND/NR]1/a

CR=4[(1200/3000)(600/500)3/10

CR=3.21kN

Engineer looks through bearing journals with rated load for the roller bearing with the right dimensions for application

In reality, bearing manufacturer’s do all this for you and have complete databases of rated life for applicable loads for bearings specific to the application

Tribology Poll Question 1 Does your company use mechanical or

electromechanical components in their products?

a) all the timeb) some timesc) rarelyd) never

(Hertzian) Contact Mechanics Study of deformation of solids in contact where deformation

can be elastic, viscoelastic and plastic.

Hertz formulated the concept of local elastic deformation of two bodies in contact such as a sphere on a plain (1886)

Adhesion at the contact first considered by JKR theory (Johnson, Kendall, Roberts 1970) –more than elastic forces

Bradley provided the model for Van der Waals forces between two spherical bodies in contact

A more involved theory (the DMT theory) also considers Van der Waals interactions outside the elastic contact regime

Hertzian ContactsAll contacts assume elastic deformation based on the geometry and configuration of the contact.

Contact areas define the surface and subsurface stress state:

1. Point Contact – Cone on plane 2. Circular Contact - sphere on a

plane, sphere on sphere3. Line Contact – cylinder on a

plane4. Elliptical Contact – sphere on

a cylinder, cylinder on cylinder

Real Surfaces In ContactEvery surface is rough at a microscopic level – asperities are visible, sometimes referred to as micro asperities or micro roughness

Micro Asperities Under Load Asperities deform under load

and behave elastically as defined by material limits

Flattening occurs as shown right

Tribology Poll Question 2 Does your company experience unanticipated

wear failures of mechanical or electro-mechanical components?

a) all the timeb) some timesc) rarelyd) never

Wear And Wear MechanismsMost Important Mechanism in Tribology – Least

Understood

Wear - General Classification Wear is classified by mechanism: adhesive (mild and severe),

abrasive, fatigue, corrosive and delamination wear

Major problem with wear is that the mechanism of wear alters as the process goes on – transition presents difficulties

Clear picture of wear, but the theory for the particular types is lacking-theory is wear and application specific

Main weapon against wear is to design using hard materials, choosing suitable lubricants, and having a perfect and maintainable filtration system.

Adhesive Wear Most prominent type of wear occurs when asperities touch

and weld together resulting in subsurface tearing

Most common with inadequate lubricating film (h<R); metal oxide film on the surface is worn away allowing micro weld

Adhesion of junction is stronger than cohesion of base metal

Relatively harder material “cuts” into a softer counter surface

“Micro-cutting” can be a useful tool in industrial processes such as grinding, diamond or carborrundum powder polishing, and as most households know, sanding

Abrasive Wear

When there is cyclic surface contact, opposing asperities elastically deform and recover, but ultimately fatigue off

In fatigue wear, the harder the material, the greater its resistance to asperity failure – higher modulus effective

Micro “cracking”

Surface phenomenon Normal stress, E

Subsurface phenomenon Shear stress, G

Fatigue Wear

Fatigue WearIllustration of the facets of

fatigue, including crack propagation, spheric particles and larger fatigue spall particles.

SEM Photograph showing asperity wear including spheric and larger fatigue spall particles

Fatigue Wear

Oxygen, moisture or other active chemicals in the lubricating film form a layer which prevents surfaces adhering together

This formative layer is rubbed off during the contact and has to be reformed before the next contact comes round i.e. this amount of material is worn away

The art of choosing the right additive is to find one just active enough to replace the worn layer e.g. e.p. additives

Extreme pressure (e.p.) additives protect by creating a surface boundary layer increase load carrying capability

Corrosive Wear

Corrosive Wear Theory Actual

Most common in rolling element bearings where stresses are cyclical resulting in larger metallic flakes – delamination

Originally proposed that dislocations pile up at or near the surface due to stress cycles and Hertzian stresses

Postulated that the thickness of the flakes was related to the depth below the surface of Hertzian shear stresses

Delamination Wear

Tribology Poll Question 3

What follow-up Tribology topics do you have interest in?a. Wear and Wear Mechanism Modelingb. Elastohydrodynamic Lubricationc. Wear and Reliability Modeling d. Wear and Accelerated Life Testing e. Otherf. None

Q&A

Contact Information

Ops A La Carte, LLC

Mike SilvermanManaging Partner

(408) 472-3889mikes@opsalacarte.com

www.opsalacarte.com

Special offer for webinar participants:

Free 1 hour Reliability Consultation

Offer expires on 3/31/12

Our Next FREE Webinar will be on April 4th on

Design for Robustness

POLLING QUESTION 4Are there any aspects of Design for Robustness you are most interested in ?a. How Design for Robustness relates to

Design for Reliabilityb. Unique differences between Design for

Robustness and Design for Reliabilityc. Bothd. Othere. I’m not interested in Design for

Robustness and probably will not attend

After signing off the webinar, you will be asked to take a

quick 3 minute survey

If you fill out survey, you will receive a link to the slides and

to the broadcast.

Contact Information

Ops A La Carte, LLC

Mike SilvermanManaging Partner

(408) 472-3889mikes@opsalacarte.com

www.opsalacarte.com