HOME  |  NEWS  |  BLOGS  |  MESSAGES  |  FEATURES  |  VIDEOS  |  WEBINARS  |  INDUSTRIES  |  FOCUS ON FUNDAMENTALS
  |  REGISTER  |  LOGIN  |  HELP
Comments
View Comments: Newest First|Oldest First|Threaded View
Page 1/3  >  >>
David12345
User Rank
Platinum
Re: Mastering the art of designing for fatigue
David12345   4/17/2012 6:06:41 PM
NO RATINGS
Yes, we work with ultrasonically driven dental tool manufacturing.  You can quickly reach a fatigue failure at 30KHz if you have a surface finish that can initiate crack propagation.  Excellent article.

I used to get frustrated by friends in my car hobbies discussing bolt failures of rperformance cars. Classic examples were the failures of the Corvette suspension bolts at the ends of the leaf springs. In many cases these were fatigue failures and the friends reactions were to the effect that "these are grade 8 bolts with very high tensile strength, you cannot get better than that!"  Often these high strength bolts failed from brittle crack propagation from fatigue not from gross overstress. Salt pitting corrosion was often the culprit. The strength was less importent than corrosion resistance and anodic zinc plating. Sometimes aircraft hardware with controlled geometry under the head, good thread root shape, and good hole preparation was also helpful.

Scott Orlosky
User Rank
Platinum
Re: Mastering the art of designing for fatigue
Scott Orlosky   4/14/2012 7:11:19 PM
NO RATINGS
Thanks for highlighting the fatigue failure mechanism in an new way.  Interestingly enough the same design approaches that reduce stress risers for fatigue failure generally also improve the performance of a part in heavily loaded, non-cyclical stress situations.  Good design practice often yields multiple performance benefits.

Ann R. Thryft
User Rank
Blogger
Re: Mastering the art of designing for fatigue
Ann R. Thryft   4/11/2012 12:57:12 PM
NO RATINGS

Dave, thanks for that input. The attitude is one that is, unfortunately, prevalent in several industries. Glad to hear that there are movements to open up things more in materials engineering. Industry associations can play a big part in such efforts.


vimalkumarp
User Rank
Gold
understanding fatigue failures
vimalkumarp   4/11/2012 11:43:11 AM
NO RATINGS
i am sure you will find the book cradle to cradle very interesting. It is really an eyes opener

Beth Stackpole
User Rank
Blogger
Re: Understanding fatigue failure.
Beth Stackpole   4/11/2012 6:58:09 AM
NO RATINGS
If the Made for Monkeys column is any indication, there are a ton of folks out there that are well willing to juryrig products or trouble shoot issues just to get a longer product life span. Interesting, often those older products have failure points that don't necessary have to do with fatigue of parts, but rather quirky design choices that lead to issues.

Dave Palmer
User Rank
Platinum
Re: Mastering the art of designing for fatigue
Dave Palmer   4/10/2012 6:08:12 PM
NO RATINGS
@kenish: You are absolutely right; any interruption to the surface is a potential site for initiation of a fatigue crack.  This might mean nicks or dings which occur either during manufacturing or during use.

Fatigue testing is usually done on highly polished samples.  Broadly speaking, the rougher the surface, the lower the effective fatigue strength.  Surface finish is a very important parameter, which unfortunately is very difficult to incorporate into a FEA model.

Dave Palmer
User Rank
Platinum
Re: Mastering the art of designing for fatigue
Dave Palmer   4/10/2012 6:03:25 PM
NO RATINGS
@Ann: I think it would be great if there were more cooperation between companies with this type of data.  There are already some industry efforts in this direction.  The American Iron and Steel Institute's Bar Steel Fatigue Database, which I linked to before, is a good example.  The American Foundry Society has a database of fatigue properties for cast irons.  USCAR and the Department of Energy have developed, or are developing, a similar but much larger database for light metals (aluminum, magnesium, etc.) -- I don't know much about this database, but I'd like to.  Ultimately, assembling these databases is just one part of an much more ambitious project called integrated computational materials engineering.

However, in order for this to work, companies have to shed their old mentality of holding this kind of information closely.  Industry associations and government can help to facilitate this.

Shelly
User Rank
Iron
Re: Mastering the art of designing for fatigue
Shelly   4/10/2012 4:50:37 PM
NO RATINGS
Ncode/Somat has a good fatigue calculator, designed by Daryll Socie from the University of Illinois, Champaign.  He also offers seminars/short courses for engineers who need to know more about designing for fatigue.

Using the NCode/Somat software to perform the calculations works fine, but you still have to know all of the properties of the materials in each situation to plug into the software in order to get accurate results.

William K.
User Rank
Platinum
Understanding fatigue failure.
William K.   4/10/2012 3:52:32 PM
NO RATINGS
If "overdesign" is the term for a design that includes only just barely enough to last until the warranty expires, possibly, then it is a very good attribute. The reality is that many products are sometimes used beyond the "typical" levels, and so they do need to be stronger than only enough to handle "typical". Designing only to the lower boundry of typical is why such a large portion of consumer goods are trash at the very instant that they are made. 

Fatigue failure is indeed a whole lot more subtle than the other kinds, such as yield and wear failure, but it is avery important consideration in a lot of places. The article was both useful and needed.

kenish
User Rank
Platinum
Re: Mastering the art of designing for fatigue
kenish   4/10/2012 3:45:28 PM
NO RATINGS
Dave, great article.  I'm a EE and this helped me visualize fatigue in a different way.  Even I understood it!  You mention design, manufacturing, and materials as sources of fatigue cracks.  Aren't they also important to prevent minor damage in-service from turning into a fatigue site (along with periodic inspection of critical areas...I'm thinking about aircraft skins)?

Page 1/3  >  >>


Partner Zone
Latest Analysis
Ever wanted your own giant robot? Three engineers did, and now they want to make 15-ft, fighting MegaBots a household name.
Here are 10 examples of the wide range of new technology on display at Pack Expo in Chicago earlier this month.
For decades, engineers have worked to combat erosion by developing high-strength alloys, composites, and surface coatings. However, in a new paper, a team at Jilin University in China turned to one of the most deadly animals in the world for inspiration -- the yellow fat-backed scorpion.
Freescale Semiconductor has rolled out a development system that aims to help automotive engineers create Ethernet-based multimedia hubs inside the vehicle.
Green energy is being billed as a way to make communities that are energy deprived more self-sustaining. So it makes sense to use natural materials to create devices that harvest this type of energy. That’s the idea behind a hybrid wind/solar energy harvester made of bamboo that’s been developed by UVM researchers.
More:Blogs|News
Design News Webinar Series
11/19/2014 11:00 a.m. California / 2:00 p.m. New York
11/6/2014 11:00 a.m. California / 2:00 p.m. New York
10/7/2014 8:00 a.m. California / 11:00 a.m. New York
12/11/2014 8:00 a.m. California / 11:00 a.m. New York
Quick Poll
The Continuing Education Center offers engineers an entirely new way to get the education they need to formulate next-generation solutions.
Nov 17 - 21, Analog Design for the Digital World
SEMESTERS: 1  |  2  |  3  |  4  |  5  |  6


Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.
Last Archived Class
Sponsored by Littelfuse
Learn More   |   Login   |   Archived Classes
Twitter Feed
Design News Twitter Feed
Like Us on Facebook

Sponsored Content

Technology Marketplace

Copyright © 2014 UBM Canon, A UBM company, All rights reserved. Privacy Policy | Terms of Service