Introduction to Fatigue: Stress-Life Method, S-N Curve

Here the concept of fatigue is introduced and described. A rotating-bending material test is described, and typical results for steel are shown. The fatigue stress - number of cycles (S-N) curve is used to establish a technique of predicting the number of stress cycles that stressed parts can withstand, even in situations when the only material data available is ultimate strength. An example problem is completed demonstrating the use of this method on a polished rotating shaft with an overhanging load (flywheel).
Playlist for MEEN361 (Advanced Mechanics of Materials):
• MEEN 361: Advanced Mec...
Playlist for MEEN462 (Machine Element Design):
• MEEN 462: Machine Elem...
This lecture was presented on January 26, 2018. All retainable rights are claimed by Michael Swanbom.
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Your lectures are so good that I'm watching them for entertainment at this point

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You mean most people aren't just watching them for pure entertainment anyway?!? Ha ha. I'm glad you are enjoying them! Thank you for watching!

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This is the kind of teaching that produces capable and passionate students. I wish I had you as a teacher in my university. Thank you!

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Thanks for the positive review! Come on over to Louisiana Tech University, and sign up for my class! Ha ha. Thanks for watching!

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Wish I could… Too far , from Melbourne Australia 🇦🇺

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Much obliged for this lesson! I was trying to refresh my FEA after 30+ years from college and found this video, very helpful.

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Glad it helped!

[@corrdude]

Puts Shigley, "M.E. Design" 4th edition, pg. 286 to shame. Really strong and clear for the first time since 1988 when I had to do this for a grade at UC Berkeley. Thanks.

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I'm glad you found it clear! Thanks for watching!

[@littleakku2799]

Great lectures for professional engineers like me to refresh concepts and use in our day to day work.

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I'm glad I could help! Thanks for watching!

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It’s like music to my ears. Absolutely interesting to listen and maturing of explaining techniques and communication is another level. Fantastic 🧠 Was a FnDT engineer for 4 years… feels stupid being a robot without a deep understanding after listening to you .. Bless this lecturer. 🙏🙏🙏

[@soronemus8815]

I have a BSME/MSME but chose to focus on robotics/electromechanical. 6 years out of grad school, I am stumbling upon your videos. It is really nice being able to re-live the lectures that I once sat through, explained in a slightly different way. It's like all of this knowledge that I haven't used since the final exam rushes back to me at once! Almost makes me wish I had pursued a career in machine design. Thanks for recording/releasing this extremely well done lecture! It was a pleasure to watch.

[@TheBomPE]

I'm glad you enjoyed it! All the best to you in your career!

[@nave2n]

I am refreshing my entire mechanical engineering. Thanks to you. Your videos are much helpful.

[@TheBomPE]

I'm glad I can help! Thanks for watching!

[@dogansahutoglu2073]

that was the most interesting video. I was always scared from fatigue loading, now that I watch this video I am good to go.

[@TheBomPE]

I'm glad it helped! Thank you for watching!

[@RaulGerardoHuertasPaiva]

I had to watch this three times, but I finally have my mathematica routines working. Thanks!!!!!

[@TheBomPE]

I'm glad I could help! Thanks for watching!

[@infinite-journey]

Have 2 Masters, but never understood concepts clearly then. Watching your videos and relearning again. Thank you for giving me another opportunity at learning. Really grateful 🙏

[@TheBomPE]

I'm glad I could be of some help!

[@frederickschulze8014]

I'm an aero major and I'm learning this stress analysis stuff for my job because I didn't learn it in my major. I remember in those undergrad classes, I probably only truly paid attention to less than half of what the professor said in class. Yet, watching this video, I'm surprised that I found myself completely focused throughout the whole thing. Whatever you're doing, it works!

[@TheBomPE]

I'm glad you like the videos! Thanks for watching!

[@b3dubbs72]

I watched 5 minutes of your video and you're way better than my materials engineering prof. I'm going to watch your vids over the summer so I'm not a shitty engineer.

[@TheBomPE]

They will be there! I'm glad they are helpful!

[@b3dubbs72]

Came back for Machine element design. Didn’t know you covered Shigley’s ❤️

[@victoriavictoria7825]

Thank you so much for these videos, Sir. Your help and providing these lectures for free is beyond appreciated!

[@TheBomPE]

I'm glad they are helpful! Thanks for watching!

[@user-zf5qn9cf2t]

This is perfectly on point, just about the best teaching I've ever seen on the topic

[@babajungLA]

Good refresher...everyone at the refinery talks about Fatigue. I needed a refresher course since its been a while and not much of an emphasis in Chemical Engineering.

[@kameronwilliams723]

Brings me back to the classroom. I can't imagine a better way to review for the MD&M exam.

[@Felipe-53]

Sir, you are a GOD. Pardon the expression, but you are saving a lot of asses like mine. You speak with clarity and in logical sequence and most importantly you are able to get us excited about the subjected you're lecturing. Thank you so much!

[@TheBomPE]

I'm glad you find it helpful, but no, I'm no deity. I'm not even that good as a person a lot of times! I do enjoy this material though, and I'm glad it is contagious!

[@Pauldyke]

Structural engineer with a civil engineering background 🖐. I do a lot of fatigue analysis.

[@TheBomPE]

My apologies! I didn't mean to say or imply that civils never do fatigue analysis. I probably should have been more focused on saying that our ME program at Louisiana Tech features a lot more fatigue analysis than the civil program does. Thanks for the feedback!

[@Wand377]

very clear, and also the presentation is very good. the quality of the the video is well above the online classes of my university and I paid like $5000 for each course

[@TheBomPE]

Thanks for the review! I'm glad you liked it! Thanks for watching!

[@saiprakash04]

Great lectures. Learning so much from these video series. Very useful to refresh fundamental mechanical concepts.

[@Antuan2911]

So great lecture! As all your lectures. To learn new or to refresh some old knowledge. So helpful for engineers from other fields, Civil in my case. Thank you!

[@akhilsingh7917]

sir i really appreciate your effort to impart quality content through this channel.🙂thank you

[@TheBomPE]

I'm glad you are finding it helpful! Thanks for watching!

[@ravipasupuleti6974]

Thanks you so much for making these videos. They have been helping me in improving my technical knowledge.

[@TheBomPE]

Glad I could help! Thanks for watching!

[@tahy59]

Thanks Dr.I wont lie my professor at college is great but watching your video help me master concept.

[@Rino95]

Thank you very much for the excellent Explanation of fatigue, Greetings from Perú!

[@TheBomPE]

Greetings to you in Peru! I'm glad you enjoyed it! Thanks for watching!

[@heatherdisco1277]

I'm currently taking Design Machine Elements at the University of Connecticut and at this point I am no longer going/watching my professor's lecture videos. I wish I had found your channel at the beginning of the semester. Thank you for doing all of this, I will gladly share your channel with my classmates!

[@TheBomPE]

I'm glad you are finding my content useful! I appreciate that you are promoting it among your friends! Thanks for watching, and best of luck in your studies!

[@heatherdisco1277]

@@TheBomPE Thank you much. Hey I had a quick question in regard to the relationship you obtained for sigma_f^prime from the SAE handbook. I am using shigleys 11th addition and I cant find that information. Was curious to know if I can use that relationship in regard to a specimen that has a machined surface where I have already obtained the modified endurance limit? Also, do you always add 50 ksi to the specimen's ultimate tensile strength or does that value change with respect to different steels' ultimate tensile strengths?

[@TheBomPE]

Yes they made significant changes to the 11th edition. To understand all of the steps I took in this video, it helps to have a 10th edition to reference. The short answer is that yes, you just add 50ksi (constant).

[@watchyoutube1268]

Just found your channel - this is pretty incredible stuff

[@TheBomPE]

I'm glad you're enjoying it! Thanks for watching!

[@gamasb8222]

great lecturer. thanks for your time for teaching not only your class but the whole world.

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I'm glad to be able to help! Thanks for watching!

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Needed this bad! Thank you!

[@TheBomPE]

glad it helped!

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I like the new notes system. Looks really clean

[@TheBomPE]

Thanks! It seemed like it would be helpful.

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you are God sir, I'm seeing the lectures on every topic I search for. Infact the lectures are more than the topics I search for. How it is possible to be perfect in all fields like Civil, Mechanical and Electrical departments.

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Great video my uni professors suggested your chanel :))

[@TheBomPE]

Wonderful! I'm glad you liked it! Are you in the US or elsewhere?

[@anuragkumar1015]

You are amazing Professor, Thank you very much for the video

[@TheBomPE]

I'm glad you liked it! Thanks for watching!

[@hardiknasit6296]

Thanks for making video of about fatigue as it will be very help for me in my study. I would like to request you to please explain little bit about Basquin’s law

[@jordanporche3707]

Greatest Professor. TheBom

[@TheBomPE]

I'm glad you are enjoying the class! Good luck on Tuesday!

[@fufutem4679]

U r just one genius teacher

[@TheBomPE]

You are very kind! Thanks for watching!

[@prashantshinde4479]

very good presentation format

[@TheBomPE]

Thank you! I'm glad you enjoyed it! I have two courses that I teach out of this text (Shigley), and I have a good number of videos presenting this material, organized into these playlists: MEEN361: kzbin.info/aero/PL1IHA35xY5H5AJpRrM2lkF7Qu2WnbQLvS and MEEN462: kzbin.info/aero/PL1IHA35xY5H5KqySx6n09jaJLUukbvJvB Check them out if you are interested! Thanks for watching!

[@thismatters7498]

Every Engineering prof makes the face at 28:42 when they reference a handbook.

[@TheBomPE]

I love this comment!

[@protonwind]

Great presentation, thank you! I've followed the methodology for my case (a load monitoring pin made of 17/4PH to condition H1150D) and I used the maximum calculated stress as the Von Mises stress (in my loading case). Sf(prime)1000 is far bigger than my calculated stress, which would take me into the high cycle region. The formula for "a" (high cycle) contains Se (fully corrected). Where do I take that one from? I couldn't find anywhere the S-N curve for that material and condition. Am I on the right path? Many thanks for your support.

[@longBowHunterII]

Very Well Done Video, Thank you, Question is there a Handbook out there with Common American Steels SN Curves with Carburizing Steels?

[@TheBomPE]

I'm glad you enjoyed it! Have you tried the Atlas of Fatigue Curves?

[@Iplayforhim16]

Thank you!

[@TheBomPE]

Glad you liked it! I hope you're ready for this quarter!

[@longBowHunterII]

Thank you Professor

[@TheBomPE]

Glad you find it useful! All the best!

[@mintesenotjakamo3629]

Good job!

[@TheBomPE]

Glad you liked it! Thanks for watching!

[@mahiraliyev7435]

Hello Sir. Many thanks for your valuable video. Could you please advise which book can be useful for plastic/non linear analysis?

[@pseudorealityisreal]

Tom Selleck traveled back in time to teach Mechanics of Materials...::grabs popcorn and starts watching::

[@TheBomPE]

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[@lengockhanh4018]

thank you sir !!

[@TheBomPE]

I'm glad you liked it! Thanks for watching!

[@ramiroarieldelsolarsandova5873]

Thanks!!

[@TheBomPE]

I'm glad I could help! Thanks for watching!

[@powerparashuram]

Very much interesting

[@TheBomPE]

I'm glad you liked it! Thanks for watching!

[@mirariham3645]

merci

[@TheBomPE]

You're welcome, thanks for watching!

[@zlatanibrahimovic3425]

Fantastic Lecture!! can you share me what are using to draw all these lines and write equation? is it a tab or something else cause i am also planning to give lecture to undergraduate students.Thankyou

[@TheBomPE]

I use a Fujitsu tablet PC running onenote 2007 and Camtasia 9. The tablet is a T901 that has good specs (Gen2 i7, 16GB ram, NVIDIA graphics, wacom digitizer). Best of luck with your class!

[@rajanikshithkatta9802]

Wow that's great Please make another one or two videos and explain different problems based on this

[@pranavkulkarni150]

Great Explanation! Thank you so much sir👌 Could you please tell which book has been referred here? That would really help a lot

[@TheBomPE]

I'm glad you liked it! I use Shigley's Mechanical Engineering Design, 10th edition. Thanks for watching!

[@pranavkulkarni150]

@@TheBomPE Thanks for the reply, sir🙏🙏

[@pisolo86]

Question from a young colleague, which software do you use during your lectures? PS You are a great lecturer!

[@TheBomPE]

I use Microsoft Office Onenote 2007. That is the last version where you can customize your toolbars. Thanks for the encouragement, and all the best to you!

[@pisolo86]

TheBom_PE many thanks, I think I will switch to surface, since I tried and it is really amazing. I am a paper guy and always need to write to explain and it is at the moment the only device that gave me that feeling. Thanks for sharing your experience!

[@HolyDiver22]

Is this considered the stress-life method? My lectures only covered applying Goodman's Criterion with adjusted endurance limit right out of the gate, and I am a bit confused at this point. My textbook(Shigley's 11th ed.) does not solve in this way, rather applies an adjusted von-mises stress without great detail of any underlying development of the equations. It is extremely hard to find supplement for this topic. Your lecture helped me tremendously, but there are gaps in connecting the relation with Von-Mises stresses.

[@gazzzada]

It seems that the gyroscopic effect was completely ignored in the loading model in the last example ... In the classic fatigue setting of Völler, the model is different and includes a steady mass that creates a bending moment for a rotating shaft.

[@cyrusIIIII]

What software is this that you easily write things on it?

[@TheBomPE]

I use Microsoft Onenote 2007. Thanks for watching!

[@markwilliammendoza]

should we iterate for fatigue strength coefficient so the value of b will be the same?

[@balkdermins1528]

nice vid,what device are you using sir ??

[@TheBomPE]

I use a Fujitsu T901 with a gen 2 i7, 16GB of ram, an nvidia graphics chip, and a wacom digitizer. I use Microsoft onenote 2007 for inking and camtasia for capture and editing. Thanks for watching!

[@balkdermins1528]

@@TheBomPE thank you sir

[@chutwinamree4508]

Thk

[@TheBomPE]

👍

[@rojmarahatta5560]

Where do you necessarily cut the beam to find the max stress or moment?

[@sumans5623]

Dear professor is there a formula to find fatigue stress coefficient?? Thank you

[@TheBomPE]

There are fatigue strength coefficients listed for several types of materials in table A-23 in Shigley. If you are dealing with steel and you do not have specific data available for fatigue strength coefficient, you can use the SAE estimations cited in equation 6-11 in Shigley (as I did in the example in this video). If you have an experimental SN curve for the specific type of material in question, you can use equation 6-9 in Shigley as a model and do a curve fit to find the fatigue strength coefficient and the fatigue strength exponent. I'm not sure what you are starting with, but these are some possible answers. Thanks for watching!

[@sudhansugrahacharya7094]

Hi, should we consider the marin factors for calculating the stress at 1000 cycles, as we are considering it at the million cycle. also for the Ultimate stress. while drawing the SN curve for a part. in other words the curve will shift down by the factor of product of all the marin factors. Please clarify.

[@sdsssdd1987]

I'm a student studing mechanical eng. then I have a question about fatigue life. For example, when predicting the fatigue life of a rubber in a rubber mount, does the change in the mass of the cradle affect the fatigue life? (cradle is base frame and it is connected rubber mount) otherwise this video was GOOD

[@user-tc1kj8lj9r]

Thanks, doctor I have a question ? When analyzing metal fatigue, should we prioritize the first plastic strain or the equivalent plastic strain? How might this choice impact the accuracy and efficiency of our results?

[@ambasinha4993]

Sir! I am solving one fatigue analysis problem in Hypermesh using S-N method. So I needed S-N curve data so could you suggest where can I get all these data for different materials?

[@yuzhuwang4819]

Try ncode matrial data

[@ambasinha4993]

@@yuzhuwang4819 thank you

[@ambasinha4993]

@@yuzhuwang4819 do you have any link for that?

[@yuzhuwang4819]

@@ambasinha4993 I have this data but unless you have this software, you can't open it

[@ambasinha4993]

@@yuzhuwang4819 OK.. No problem

[@dogansahutoglu2073]

Sir, have you solved a beam with two end fixed , support at any point in the middle and loaded at multi points with 3 reactions yet? This could be a statically indeterminate problem.

[@TheBomPE]

No, I don't have a problem like that recorded yet. It looks likely that I will be teaching a course here at Louisiana Tech University that covers statically indeterminate problems like that within the next year or so, so I'll probably get to it sometime relatively soon!

[@dogansahutoglu2073]

Thank you sir. looking forward to it.

[@maxrkmrose]

What is the textbook for MEEN 361? thanks.

[@TheBomPE]

I use Shigley's Mechanical Engineering Design, 10th edition. Thanks for watching!

[@maxrkmrose]

Thank you very much for your work and placing it on KZbin!

[@GideonEbelebe]

Please, what is the title of the material (textbook) you used in this lecture? Thanks.

[@TheBomPE]

I use Shigley's Mechanical Engineering Design, 10th edition. Thanks for watching!

[@GideonEbelebe]

@@TheBomPE kindly give me your email. Mine is [e-mail].

[@technicalknowledgesharing6701]

Thank you very much for this great lecturer. Please provide some more insight on fatigue analysis such as real time fatigue analysis as per international codes.

[@mahiraliyev2296]

Hello Mr. Could you please share name of the book which you refer?

[@TheBomPE]

I use Shigley's Mechanical Engineering Design, 10th ed. Thanks for watching!

[@mahiraliyev7435]

@@TheBomPE Thanks a lot Mr.

[@mahiraliyev7435]

Hello Sir. Many thanks for your pricless support! Could you please advise which book can be usefull for plastic/non linear analysis?

[@user-vv2yc9vo5k]

Can you please suggest a reference book?

[@TheBomPE]

On this material I am teaching out of Shigley's Mechanical Engineering Design, 10th edition. Thanks for watching!

[@michaelswanbom6023]

If you found this video useful, consider helping me upgrade the old tablet PC I use to create these videos! Thanks! www.gofundme.com/help-replace-my-2011-tablet-pc

[@saidnahi6540]

Hello, i have a question that came up in my mechanical exam and it was 'Explain how fatigue affects the behavior of engineering materials, then explain how and why fatigue affects the stated behavior'. I'm confused

[@TheBomPE]

The second question seems to repeat half of the first question. Who wrote the question?

[@basavdotikal1415]

Sir , you ignored direct shear caused by the Flywheel, in the example!!! Thank u for the video

[@TheBomPE]

You're right, I did neglect direct shear. Fortunately direct shear would only add about 1.34ksi of shearing stress. Combining that with bending stress using DE theory would bring the von-mises stress to about 107.46ksi as opposed to the 107.43ksi I used in the example. I think it is OK to neglect direct shear in this case. Thanks for watching!

[@fdta2536]

S-N curve is main source of analysis incorrnectnes

[@fdta2536]

S is one more source of incorrectness.

[@balajirajendran5139]

I couldn't follow up your next video (say your 20th lecture).

[@TheBomPE]

I'm not sure I understand. Are you having trouble viewing one of my videos?

[@balajirajendran5139]

@@TheBomPE Dear Professor, I couldn't trace your next video, since you didn't mention any module numbers. I just skipped lecture 20, 21 and watching 22 Marin Factor and Stress Concentration.

[@TheBomPE]

Ah, I understand now. There aren't any videos between this one and the one about Marin factors. You probably saw the numbering at the top of my notes... these are the meeting numbers where I began those lectures in the term when I recorded them. Don't worry about the numbers too much, I have everything put in the proper sequence in the playlist.

[@balajirajendran5139]

@@TheBomPE Thank you professor, Love your way of lecturing.

[@TheBomPE]

I'm glad you find it helpful! Thanks for watching!

[@gazzzada]

Thank you! kzbin.info/www/bejne/kKSsqHimapxnntE Can not understand how Sigma F can be bigger than Sut (+50ksi)? IMHO Sigma ultimate is always have to be biggest value of all as it is a result of shortest test of all discussed here... (only one loading)

[@TheBomPE]

Sigma F is just a coefficient that happens to have stress units. It is not a material strength value all by itself.

[@gazzzada]

@@TheBomPE Thank you. Well, i one couldn't tell value from coefficient... I think I have to listen the webinar again from beginning:)

[@raviashokiyer7238]

can you let us know your email id

[@TheBomPE]

I teach at Louisiana Tech University. You can likely find me through that website if you need to contact me.