An article by P. Davoli and K. Michaelis entitled "Recognizing gear failures" with 14 photographs appeared in the June 21, 2007 issue of Machine Design magazine. It can be viewed on their web site by clicking on the current issue button and selecting the title at:
http://www.machinedesign.com/ASP/viewSelectedArticle.asp?strArticleId=62746&strSite=MDSite&Screen=CURRENTISSUE&CatID=3
Sunday, July 8, 2007
Wednesday, May 30, 2007
Laws of failure analysis III: Grange’s law (Make sure you see the forest before you start looking at the leaves on the trees)
Grange's law of visual examination also is from about thirty years ago. It states that you should: "First take a look at the failure at 10Xwith a magnifier, and then look again and think harder".
A lot can be learned from most mechanical failures by careful visual examination aided by a magnifier, or preferably a stereo microscope.
A couple times I have seen people claim that a failure had not occurred progressively via fatigue cracking because they could not find striations at high magnifications (~8000X) in the scanning electron microscope (SEM). However, there were concentric crack arrest markings ("beach marks") visible at low (~8X) magnifications.
Ray Grange was a metallurgist at the US Steel Research Lab. You can still find some of Ray’s 1956 work on tempering of carbon steel referenced in the Heat Treating volume 4 of the current ASM Handbook.
A lot can be learned from most mechanical failures by careful visual examination aided by a magnifier, or preferably a stereo microscope.
A couple times I have seen people claim that a failure had not occurred progressively via fatigue cracking because they could not find striations at high magnifications (~8000X) in the scanning electron microscope (SEM). However, there were concentric crack arrest markings ("beach marks") visible at low (~8X) magnifications.
Ray Grange was a metallurgist at the US Steel Research Lab. You can still find some of Ray’s 1956 work on tempering of carbon steel referenced in the Heat Treating volume 4 of the current ASM Handbook.
Thursday, May 3, 2007
Laws of failure analysis II: Sloter’s law (Have a plethora of pictures)
Sloter’s law of photography is from about thirty years ago and says that the difference between an amateur photographer and a professional is that the pro uses a lot more film (and thus makes sure that he gets all the relevant pictures).
In the initial visual examination of a failure it is tempting to take just a few pictures of the "as-received" product or component, and then to rush into cleaning or cutting. This temptation should be resisted.
It is far better to have an excess of pictures showing all orientations than to later realize (perhaps even at the report writing stage) that something relevant may have been missed.
For a litigation case I once photographed a trailer hitch coupler that allegedly had a manufacturing defect leading to an accident. Examination of the top surface revealed impressions of the heads of vertically oriented carriage bolts used to attach the coupler to the trailer tongue. These impressions were carefully photographed using oblique lighting.
An important witness for one party claimed that the coupler had only been used on one trailer, where it had been attached via horizontally oriented bolts. I never testified, but my enlarged photos raised considerable doubt in court regarding the credibility of that witness and his version of the service history of the coupler.
Lewis Sloter currently is Associate Director for Materials and Structures in the Office of the Deputy Under Secretary of Defense for Science and Technology. He was recently interviewed:
http://www.dodcorrosionexchange.org/CorrDefense/Spring-2006/other_news1.htm
In the initial visual examination of a failure it is tempting to take just a few pictures of the "as-received" product or component, and then to rush into cleaning or cutting. This temptation should be resisted.
It is far better to have an excess of pictures showing all orientations than to later realize (perhaps even at the report writing stage) that something relevant may have been missed.
For a litigation case I once photographed a trailer hitch coupler that allegedly had a manufacturing defect leading to an accident. Examination of the top surface revealed impressions of the heads of vertically oriented carriage bolts used to attach the coupler to the trailer tongue. These impressions were carefully photographed using oblique lighting.
An important witness for one party claimed that the coupler had only been used on one trailer, where it had been attached via horizontally oriented bolts. I never testified, but my enlarged photos raised considerable doubt in court regarding the credibility of that witness and his version of the service history of the coupler.
Lewis Sloter currently is Associate Director for Materials and Structures in the Office of the Deputy Under Secretary of Defense for Science and Technology. He was recently interviewed:
http://www.dodcorrosionexchange.org/CorrDefense/Spring-2006/other_news1.htm
Wednesday, February 28, 2007
Laws of failure analysis I: Pelloux’s law
Pelloux’s law of metal failure states that: "It always breaks where it’s welded".
Why?
The filler metal used for welding may have a different composition and be softer or harder than the adjacent base metal. Also, the surrounding heat affected zone (HAZ) may be is softer than base metal due to phenomena such as tempering or recrystallization. Conversely in steels, due to a high cooling rate, some regions of the HAZ also may be harder than the base metal.
The welding process may introduce discontinuities. See "Understanding weld discontinuities" The Fabricator, June 12, 2003:
http://www.thefabricator.com/WeldingInspection/WeldingInspection_Article.cfm?ID=603
For a discussion of weld cracking also see:
http://content.lincolnelectric.com/pdfs/knowledge/articles/content/weldcracking.pdf
Ken Russell has quoted Pelloux’s law in two of his dozens of brief case histories published in Design News magazine. See "The case of the wayward weld", Design News, September 22, 2003: http://www.designnews.com/article/ca321648.html
Russell is an emeritus professor at MIT, as is Pelloux. Pelloux received ASM’s Albert Sauver Achievement Award "for pioneering contributions in the areas of fatigue crack propagation, micromechanisms of deformation and fracture, and quantitative microscopic analysis of fracture processes in structural engineering alloys."
Why?
The filler metal used for welding may have a different composition and be softer or harder than the adjacent base metal. Also, the surrounding heat affected zone (HAZ) may be is softer than base metal due to phenomena such as tempering or recrystallization. Conversely in steels, due to a high cooling rate, some regions of the HAZ also may be harder than the base metal.
The welding process may introduce discontinuities. See "Understanding weld discontinuities" The Fabricator, June 12, 2003:
http://www.thefabricator.com/WeldingInspection/WeldingInspection_Article.cfm?ID=603
For a discussion of weld cracking also see:
http://content.lincolnelectric.com/pdfs/knowledge/articles/content/weldcracking.pdf
Ken Russell has quoted Pelloux’s law in two of his dozens of brief case histories published in Design News magazine. See "The case of the wayward weld", Design News, September 22, 2003: http://www.designnews.com/article/ca321648.html
Russell is an emeritus professor at MIT, as is Pelloux. Pelloux received ASM’s Albert Sauver Achievement Award "for pioneering contributions in the areas of fatigue crack propagation, micromechanisms of deformation and fracture, and quantitative microscopic analysis of fracture processes in structural engineering alloys."
Wednesday, February 21, 2007
How to Analyze Gear Failures
There is an excellent tutorial article by Robert Errichello which appeared in the December 2002 issue of the journal Practical Failure Analysis that is published by ASM International. (The magazine has since been renamed the Journal of Failure Analysis and Prevention).
This and other articles from that magazine issue can be downloaded for free at www.ingentaconnect.com
Put "Practical Failure Analysis" in the search box, click in the "Journal or book title" circle, and then click on GO. Then point to the blue title Practical Failure Analysis and click. The F next to December 2002 denotes a free issue, so click on it to see the table of contents.
A very similar article also can be viewed on the web in html at: http://www.noria.com/learning_center/category_article.asp?articleid=150&relatedbookgroup=WearDebris
You know the mantra "Cheap Quick Good. Pick any two". When Quick and Good are important, then keep Ingentaconnect in mind. They can sell you a whole ocean of magazine articles.
If you want to learn a lot more about gear failure analysis, then, you can attend a two-day seminar that Robert Errichello presents for the American Gear Manufacturers Association (AGMA). See: http://www.agma.org/Content/NavigationMenu/EducationTraining/GearFailureAnalysisSeminar/default.htm
This and other articles from that magazine issue can be downloaded for free at www.ingentaconnect.com
Put "Practical Failure Analysis" in the search box, click in the "Journal or book title" circle, and then click on GO. Then point to the blue title Practical Failure Analysis and click. The F next to December 2002 denotes a free issue, so click on it to see the table of contents.
A very similar article also can be viewed on the web in html at: http://www.noria.com/learning_center/category_article.asp?articleid=150&relatedbookgroup=WearDebris
You know the mantra "Cheap Quick Good. Pick any two". When Quick and Good are important, then keep Ingentaconnect in mind. They can sell you a whole ocean of magazine articles.
If you want to learn a lot more about gear failure analysis, then, you can attend a two-day seminar that Robert Errichello presents for the American Gear Manufacturers Association (AGMA). See: http://www.agma.org/Content/NavigationMenu/EducationTraining/GearFailureAnalysisSeminar/default.htm
Tuesday, February 20, 2007
What organization best covers the topic of failure analysis?
ASM International is the best organization for learning more about failure analysis.
Their website is at www.asminternational.org
ASM sells several books, presents courses, and publishes a magazine called the Journal of Failure Analysis and Prevention.
Volume 11 of the ASM handbook is on Failure Analysis and Prevention. It was published in 2002 and updates their previous handbook volumes with the same title in the eighth and ninth editions of the Metals Handbook. ASM also has published a two volume Handbook of Case Histories in Failure Analysis.
One of ASM’s best selling books is Understanding How Components Fail. Donald J Wulpi wrote this book. The second edition is dated 1999. The book was preceded by a much shorter book (published back in 1966) called How Components Fail. The first chapter of Understanding How Components Fail is an excellent starting point for learning about the failure analysis process. A sneak preview Acrobat file of it can be downloaded from the ASM bookstore. Look up the book by its title, scroll to the bottom of the listing and click on "Preview of a chapter".
There also is an affiliate society, called the ASM Electronic Device Failure Analysis Society (EDFAS), which works for technology advancement and the improved performance and reliability of devices and materials for the electronic industry.
Their website is at www.asminternational.org
ASM sells several books, presents courses, and publishes a magazine called the Journal of Failure Analysis and Prevention.
Volume 11 of the ASM handbook is on Failure Analysis and Prevention. It was published in 2002 and updates their previous handbook volumes with the same title in the eighth and ninth editions of the Metals Handbook. ASM also has published a two volume Handbook of Case Histories in Failure Analysis.
One of ASM’s best selling books is Understanding How Components Fail. Donald J Wulpi wrote this book. The second edition is dated 1999. The book was preceded by a much shorter book (published back in 1966) called How Components Fail. The first chapter of Understanding How Components Fail is an excellent starting point for learning about the failure analysis process. A sneak preview Acrobat file of it can be downloaded from the ASM bookstore. Look up the book by its title, scroll to the bottom of the listing and click on "Preview of a chapter".
There also is an affiliate society, called the ASM Electronic Device Failure Analysis Society (EDFAS), which works for technology advancement and the improved performance and reliability of devices and materials for the electronic industry.
Welcome to the failure analysis blog!
Failure analysis is the logical, systematic examination of a product or component to identify the failure mode, determine the root cause, and recommend how to avoid future failures.
This web log was created to share information about this subject, including noting useful information scattered around the web. I also will point out useful magazine articles and books.
This web log was created to share information about this subject, including noting useful information scattered around the web. I also will point out useful magazine articles and books.
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