2012 03 07 reliability & tribology ops a la carte … a la carte tribology and...tribology...
TRANSCRIPT
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TRIBOLOGY RELIABILITY
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AGENDA Introduction – 5 minutesWebinar – 45 minutesQ&A – 10 minutes
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Who Are We?Ops A La CarteHQ in Santa Clara, CA
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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.
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• 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
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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
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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."
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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".
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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".
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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
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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
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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
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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)
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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
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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 [email protected]
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Registration DemographicsFor this webinar we have signed up 100 Registrants 10 Countries
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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?
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Registration Questions1. Do you have portions of your product that can
wear due to mechanical wear?
Yes 83%
No 17%
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Registration Questions2. Do you know how to characterize the life of all
your wearout mechanisms?
Yes 21%
No 79%
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Agenda Introduction to Tribology
Stribeck Curve-Rolling element bearing
Hertzian Contact Mechanics
Wear and Wear Mechanisms
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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…
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Tribology Gets Complicated
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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
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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.
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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
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Stribeck Curve
f versus ηN/P, the latter called Sommerfeld no.
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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
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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.
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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)
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Tribology of A Roller Bearing
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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.
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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 )
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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
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Tribology Poll Question 1 Does your company use mechanical or
electromechanical components in their products?
a) all the timeb) some timesc) rarelyd) never
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(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
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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
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Real Surfaces In ContactEvery surface is rough at a microscopic level – asperities are visible, sometimes referred to as micro asperities or micro roughness
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Micro Asperities Under Load Asperities deform under load
and behave elastically as defined by material limits
Flattening occurs as shown right
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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
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Wear And Wear MechanismsMost Important Mechanism in Tribology – Least
Understood
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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.
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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
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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
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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
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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
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Fatigue Wear
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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
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Corrosive Wear Theory Actual
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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
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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
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Q&A
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Contact Information
Ops A La Carte, LLC
Mike SilvermanManaging Partner
(408) [email protected]
www.opsalacarte.com
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Special offer for webinar participants:
Free 1 hour Reliability Consultation
Offer expires on 3/31/12
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Our Next FREE Webinar will be on April 4th on
Design for Robustness
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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
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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.
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Contact Information
Ops A La Carte, LLC
Mike SilvermanManaging Partner
(408) [email protected]
www.opsalacarte.com