QUANTITATIVE)LIFE)TESTING,)THE) … Straka Quantitative... · QUANTITATIVE)LIFE)TESTING,)THE)...
Transcript of QUANTITATIVE)LIFE)TESTING,)THE) … Straka Quantitative... · QUANTITATIVE)LIFE)TESTING,)THE)...
QUANTITATIVE LIFE TESTING, THE CHALLENGES BEYOND
ACCELERATION FACTORS Frank Straka
Reliability Manager -‐ CommScope
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INTRODUCTION • Although accelerated life models are base on Physic of Failure
Approach, there are sQll qualitaQve aspects to consider: – The same product has different operaQonal profile depending on the user. – The same product operates in different environments – Product variability in weakness will impact Qme to failure – under the same
accelerated stress different samples of the same DUT will fail at different Qmes.
– The baseline stress one uses will influence the predicQon. • Other qualitaQve aspects include
– The objecQve of the predicQon such as warranty, worse case, or safety – Risks that one is willing to take
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OVERVIEW Discuss influences of baseline model on accelerated life test predicQons. • How these impact acceleraQon models • Explore baseline variaQons • Explore methods of handling variaQons • Use case example
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COMMENTS ON ACCELERATION MODELS • Different type of accelerated tests generally address different failure
mechanisms – this allows tests to be done on different or the same samples.
• To obtain the overall Reliability of various tests, the – % reliability performance can be mulQplied together to achieve an overall
reliability esQmate. – AcceleraQon factors from different tests should not be mulQplied together
unless there is interacQon. • Compliance or standard tests are not necessarily reliability tests. • The more complex the product being tested, the more difficult it is to
conduct accelerated tests. Typically done on components or system elements.
• Basis for Model -‐ IEC 62506 ED. 1.0: (CDV) Methods for Product Accelerated TesQng.
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AcceleraQon Models • the following acceleraQon models will be discussed to illustrate
how baseline can influence the acceleraQon model. – VibraQon – FaQgue TesQng – Thermal Cycle – Time Compression
• The basic informaQon can be extrapolated to other acceleraQon models.
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THERMAL CYCLE • The purpose of this test is to accelerate the stresses caused by repeated
heaQng and cooling of the product. • Variability
– For product with long operaQonal Qmes, the actual temperature above ambient will be used. However, different components inside may operate at different temperatures.
– For product with short operaQonal Qmes where the ulQmate temperatures are not reached, one needs to determine the operaQonal Qme to determine temperatures.
– Number of cycles per day. • Typically the transiQon Qme also needs to be measured, but has small
variability. • Some failures may interact with vibraQon. • Not influenced by ambient.
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THERMAL CYCLE
• Nuse Number of life cycles required • NTest Number of accelerated test cycles required • ΔTUse Temperature change in use • ΔTTest Temperature change of test • m1 exponent for DUT for temperature rate of change • m2 exponent for DUT for difference ΔT • 𝜹↓𝑻𝒆𝒔𝒕 ramp rate of transition in use • 𝜹↓𝑼𝒔𝒆 ramp rate of test (use max of 30°C/min)
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𝐴𝐹= 𝑁↓𝑈𝑠𝑒 /𝑁↓𝑇𝑒𝑠𝑡 = (∆𝑇↓𝑇𝑒𝑠𝑡 /∆𝑇↓𝑈𝑠𝑒 )↑𝑚2 × (𝛿↓𝑇𝑒𝑠𝑡 /𝛿↓𝑈𝑠𝑒 )↑𝑚1
VIBRATION • VibraQon baseline profile varies by use
– Frequency – Severity Level
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VIBRATION 𝐴𝐹= {𝑉↓𝑇𝑒𝑠𝑡 /𝑉↓𝐴𝑐𝑡𝑢𝑎𝑙 }↑𝑚 • m=exponent that ranges between 2 to 7;when unknown, typically 4
is used • Vactual (Grms)= vibraQon profile in use or base line test • Vtest (Grms) = replicaQon of actual use profile at higher G forces
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FATIGUE • Stress that is considerably higher than normal use is conducted on mulQple samples and mulQple stress levels.
• The Qme to failure at a specific reliability objecQve such as L1 (1 % failure) is determined at each stress level through Weibull analysis.
• These L1 informaQon is ploied on an SN curve and this data is extrapolated to the stress level in normal use and the Qme to failure is determined.
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TIME COMPRESSION • Low annual usage products can be evaluated by reducing the
“off” duraQon to accumulate equivalent years of test Qme. • Consumer products such as lawnmowers, exercise equipment,
popcorn maker, etc. fall into this category. – For example a product that has operates for 1 hour 75 Qmes a year, can easily be tested by conducQng tests that total 75 hours.
– Switches are another example, where on-‐off cycles may be only a few Qmes a day whereas many of these cycles can be accomplished in a day.
• The variability in this test is the operaQonal profile environment. • Environmental consideraQons of the off duraQon may impact the
product reliability.
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REALITY • Each test shares the same dilemma to varying degree – what is the actual baseline that should be use.
• Each product operates in a different environment and operaQonal characterisQcs and are not necessarily constant between each product.
Therefore, a product could be very reliability in one environment and unreliability in another.
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ENVIROMENTAL VARIABILITY EXAMPLES • Switches
– Generally does not control at maximum raQng – Number of on-‐off cycles per day, – Environmental impact of off cycle
• Television sets – Hours of use per day – Indoor use, but not always in a climate controlled room – On-‐off cycles
• Automobiles – City, country, off road and expressway – Speed – Hours of use and/or miles driver – Wide range of operaQonal environments – Mechanical, hardware, sonware
• Treadmills – User weights vary – OperaQonal speed is different – Usage per year varies – Indoor use, but not always in a climate controlled room
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METHOD OF HANDLING • ObjecQves
– Reliability level desired – May be mulQple objecQves
• Test severity Baseline Decisions – Use 85% profile – If operaQonal usage profile is known, the acceleraQon tests can be divided into percentages.
– What is failure • Defining the failure mode and how will it be detected. • SomeQmes Judgement was used when data was not available
or incomplete. • InteracQons with other stress factors are not always be known.
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INFLUENCES • Risks to achieve objecQves.
– ConservaQve vs opQmisQc esQmate – Failure severity – StaQsQcal Confidence – Test severity baseline – May have mulQple objecQves depending on risk
• StaQsQcal Confidence – High degree of confidence may not always be possible – ExtrapolaQng data based on confidence limits may not be accurate – Resources may limit what can be achieved
• Time, Cost, People
• User interface issues were handled by field tests
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Treadmill Case Example
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ApplicaQon • Commercial • Consumer fitness clubs
OperaQonal CharacterisQcs • User weight: 80 to 350 lbs • Speed: 1 to 15 MPH • Temperature: 15 to 35°C • RelaQve Humidity: up to 90% • Hours per year usage: 2200 hours • Warranty: 2 year parts and 1 year labor
Comments • It is not anQcipated that a 350 lb user will run at 15 MPH • Average speed is 5.5 MPH & 85% profile 75%. • Hours per usage range between 500 hours and 3600.
Typically around 2200 hours
ESTABLISHING BASELINE SEVERITY • Base line severity
– 85% users weight: 230 lbs – 85% work out Qme: 45 minutes – 85% speed: 7.5 miles per hour – Hours of use per year: 2200
• Period of interest: – 2 year warranty – Product life Qme 10 years
• Product requirements – Maintenance, C70R95 at 2 years – Non repairable failure, C70R99 at 5 years; C90 if possible
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THERMAL CYCLE ACCELERATION • For electronic components
– Measured temperature at 45 minute duraQon to determined baseline delta – resulted in 40°C rise
– USED maximum measured temperature of components. – Used 6 cycles per day
• We explored and determined what high and low temperature we could stress product without failure – able to use -‐40 / 80°C or 120 change test condiQon.
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VIBRATION WITH TIME ACCELERATION • Electronic board applicaQons
– Established 85% profile by having 230 lb user run at 7.5 MPH and measured vibraQon profile.
– Broke vibraQon profile into x, y, and z parameters and placed profile into field data replicaQon sonware.
– Use Qme truncaQon to eliminate dead spots.
• We then adjusted vibraQon stress to 4 Qmes the levels.
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FaQgue TesQng • Frame tesQng – welds
– Again with 230 lb user running at 7.5MPH, we evaluated the stresses that were occurring in the frame.
– Determined the maximum force with the frequency of occurrence. Established this as the baseline along.
• Test acceleraQon factors – MulQple loads from 450 to 700 lbs. – Frequency of applied load 10 Qmes per second
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FATIGUE TEST • Tape belt life is based on operaQon miles or distance traveled. • Baseline was 230 lb user at 7.5 MPH • Goal was to obtain 12,000 miles unQl replacement or 1 year to
get through warranty • For acceleraQon, we established a simulated user loading at 500
lb and belt speed to 10MPH. – 10 MPH allowed us to achieve miles quicker – Weight accelerated belt wear – Conducted at 400 lbs to be able to extrapolate to 230 lbs and 7.5MPH
• IniQal failure point was mechanical failure of belt – actually it turnout to be wear which increase fricQon and caused slowdown of the speed.
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SUMMARY Establish Framework for baseline
– Handle on Risks – Understand operaQonal environment product – Know where accelerated life tests may not be appropriate – Agreed upon objecQves – Breakdown into simplest elements to test – May need to research operaQonal characterisQcs to establish baseline condiQons
– Similarity to exisQng products may reduce aspects of this
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BIOGRAPHICAL INFORMATION • Frank Straka has been involved in the Quality & Reliability of products for over 25 years. This experience
covers the tesQng and analysis of electronic hardware, sonware, and mechanical products to evaluate their performance and reliability. He has worked in RF design, RF filters, consumer electronics, and the telecommunicaQons industries.
• Mr. Straka’s responsibiliQes have included: – Reliability program management. – Accelerated test methods for electronics, mechanical, and sonware systems. – Reliability Growth – Root cause analysis and correcQve acQon – DFMEA and PFMEA – Reliability predicQons – Environmental tesQng. – StaQsQcal methods
• Mr Straka also represents Andrew CorporaQon as Deputy technical advisor to US Technical Advisory Group for Dependability (IEC TC 56) and member of US Technical Advisory Group on Quality (ISO TC 176). He holds professional memberships in IEEE, IEST, and ASQ
• Mr. Straka has a Bachelor of Science degree in Electrical Engineering from the University of Illinois and a Master of Business AdministraQon from Northwestern University.
• Mr. Straka is ASQ cerQfied as a Reliability Engineer, Quality Engineer, and Quality Auditor. He is cerQfied as a six sigma black belt and is a registered professional engineer.
• Mr. Straka is currently employed as Reliability Manager for CommScope – A manufacture of telecommunicaQon components for the mobile market.
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