Russel Smith and Daniel Carpenter: Managing Fatigue Failures of Longwall Hydraulic Equipment
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Transcript of Russel Smith and Daniel Carpenter: Managing Fatigue Failures of Longwall Hydraulic Equipment
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Managing Fatigue Failures of Longwall Hydraulic Equipment
26th Mechanical Engineering Safety Seminar 4th August 2016
Russell Smith Daniel Carpenter
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Your Machinery has been performing flawlessly for years
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Your Job is to keep the machinery running
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Suddenly, your key machine starts failing, and no one
seems to know why
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You find the failures are due to fatigue, and design effective
remedial strategies.
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Learn about fatigue and how to manage it
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Familiarise yourself with the causes and characteristics of fatigue failure.
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Overload failures require just a single load application.
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Overload failure occurs at less than the theoretical bond
strength.
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Dislocations can move at very low stresses, and pile-up at stress concentrations and form cracks.
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Overload failures often display bend-before-break
characteristics
Necking Elongation
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Fatigue failures often display ratchet marks, beach marks, and striations.
Ratchet Marks Beach Marks
Striations (microscopic)
Final Fracture
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80 - 90% of component fractures are due to fatigue.
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Normal Distribution
Mean = 3
-1 0 1 2 3
Standard deviation = 1
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Fatigue failures follow a lognormal distribution. Median
Median = 2
Geometric SD = 2
1 2 4 8 16
Mean
Number of Cycle
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Fatigue lives for identical components can vary by a factor of 10.
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Understand the key inputs needed for reliable fatigue
design.
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Cycle counts are required for all repetitive events.
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Dynamic responses add to the planned behaviour.
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Fatigue damage from cycles of different magnitudes is not
a simple addition.
1 + 2 3
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Difficult inspection and repair conditions demand low failure probabilities.
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Large populations make matters worse.
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Intolerable failure consequences demand very small failure probabilities.
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Welded and non-welded components behave differently
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Pre
ssur
e
Cycles
Not all standards use the same catalogue of fatigue details
1000
Stre
ss
100 1.E+04 1.E+05 1.E+06 1.E+07
Cycle s
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Different standards adopt different failure probabilities
AS 4100, EN1993 5% probability of failure
BS7608 (default) 2.3% probability of failure
BS7608 (user defined) ?% probability of failure
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Assess your available remedial options.
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Trend do you have a problem?
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Repair
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Replace
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Quantify & Analyse what causes the most damage? can it be eliminated or minimised?
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Minimise the Worst Contributions
Can the peaks be clipped?
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Operator Training
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Different Material
Material Strength = Fatigue Life Toughness = Critical Crack Length
But not for welded components Welded and non-welded components
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Pr
essu
re
Cycles
Pres
sure
Cycles
1000
Different Detail St
ress
Stre
ss
100 1.E+04 1.E+05 1.E+06 1.E+07
1000
100 1.E+04 1.E+05 1.E+06 1.E+07
Cycles Cycles
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Different Owner
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Acknowledge Wrong to Make it Right - Staples
Spring Steel 420 Stainless
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Acknowledge Wrong to make it Right - Sample Size
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Acknowledge Wrong to Make it Right Leg Cylinders
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THANK YOU - THE END
Russell Smith Daniel Carpenter
Managing Fatigue Failures of Longwall Hydraulic EquipmentYour Machinery has been performing flawlessly for yearsYour Job is to keep the machinery runningSuddenly, your key machine starts failing, and no one seems to know whyYou find the failures are due to fatigue, and design effective remedial strategies.Learn about fatigue and how to manage itFamiliarise yourself with the causes and characteristics of fatigue failure.Fatigue failure requires repetitive loading and unloading Overload failures require just a single load application.Overload failure occurs at less than the theoretical bond strength.Dislocations can move at very low stresses, and pile-up at stress concentrations and form cracks.Fatigue failure requires repetitive loading and unloading Fatigue failures are different to overload failureOverload failures often display bend-before-break characteristicsFatigue failures often display ratchet marks, beach marks, and striations.80 - 90% of component fractures are due to fatigue.Fatigue failure requires repetitive loading and unloading Fatigue failures are different to overload failureFatigue lives scatter statistically within large component populationsNormal DistributionFatigue failures follow a lognormal distribution. Fatigue lives for identical components can vary by a factor of 10.Understand the key inputs needed for reliable fatigue design.Identify the repetitive loads of the applicationCycle counts are required for all repetitive events.Dynamic responses add to the planned behaviour.Fatigue damage from cycles of different magnitudes is not a simple addition.Identify the repetitive loads of the applicationEstablish your tolerable failure rateDifficult inspection and repair conditions demand low failure probabilities.Large populations make matters worse.Intolerable failure consequences demand very small failure probabilities.Identify the repetitive loads of the applicationAdopt your tolerable failure rateNot all fatigue design standards are equal choose carefullyWelded and non-welded components behave differently Not all standards use the same catalogue of fatigue details Different standards adopt different failure probabilities Assess your available remedial options.Do nothingTrend do you have a problem?RepairReplaceDo nothingChange the operationQuantify & Analyse what causes the most damage? can it be eliminated or minimised?Minimise the Worst ContributionsOperator TrainingDo nothingChange the operationChange the designDifferent MaterialDifferent DetailDifferent OwnerDo nothingChange the operationChange the designWatch out for trapsAcknowledge Wrong to Make it Right - StaplesAcknowledge Wrong to make it Right - Sample SizeAcknowledge Wrong to Make it Right Leg CylindersSuddenly, your key machine starts failing, and no one seems to know whyYou find the failures are due to fatigue, and design effective remedial strategies.Learn about fatigue and how to manage itSlide Number 53