Fatigue for Combined Loading & Estimating Number of Cycles Until Failure

Here some conceptual approaches are presented for evaluating questions of fatigue in various modes in which a mechanical component may experience dynamic loading. When stress peaks from all of the types of stress (i.e. bending, torsion, axial) align in-phase and at the same frequency, a method based on von-Mises stress is particularly useful. An example problem is solved for a component loaded in such a way. Equivalent midrange and alternating stresses are computed for this example, and the ASME Elliptic criterion is used to evaluate a fatigue factor of safety. When it is discovered that this factor of safety is less than 1 (implying a finite predicted life) the number of cycles expected before failure is estimated.
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 February 16, 2018. All retainable rights are claimed by Michael Swanbom.
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[@giorgos_mark8401]

Im in uni right now and you are 100x better than my professor on explaining the solutions. Thank you so much.

[@TheBomPE]

I'm glad you are finding my videos helpful! Best of luck in your studies!

[@theitandthem]

Flawless transition Dr. Swanbom. Flawless.

[@Simulit]

I learned Fatigue by ONLY your Tutorials. Greatly appreciate you...

[@joesaad3089]

Your classes are epic Dr thank you for downloading these lectures on KZbin

[@TheBomPE]

Thanks for the positive review! I'm glad you like them! In case you haven't seen them yet, you might be interested in these playlists: ENGR122 (Statics & Engr Econ Intros): kzbin.info/aero/PL1IHA35xY5H52IKu6TVfFW-BDqAt_aZyg ENGR220 (Statics & Mech of Mat): kzbin.info/aero/PL1IHA35xY5H5sjfjibqn_XFFxk3-pFiaX MEMT203 (Dynamics): kzbin.info/aero/PL1IHA35xY5H6G64khh8fcNkjVJDGMqrHo MEEN361 (Adv. Mech of Mat): kzbin.info/aero/PL1IHA35xY5H5AJpRrM2lkF7Qu2WnbQLvS MEEN462 (Machine Design): kzbin.info/aero/PL1IHA35xY5H5KqySx6n09jaJLUukbvJvB (MEEN 361 & 462 are taught from Shigley's Mechanical Engineering Design) Thanks for watching!

[@StenCheesemonger]

Nice, I'm doing it right... now I need to do it within the test's allowed time.

[@TheBomPE]

Ah yes, that is another success parameter isn't it? :)

[@StenCheesemonger]

@@TheBomPE Well yes. First time I'm doing the subject and the first test already taught me that knowing the theory and steps is not enough, guess it's a bit like calculus, sit my butt in a chair and train until I "Get "it"" and manage to do it enough speed. A bit of a daunting task when you need neat drawn free-body diagram for each section of an axle, and a neat drawn mohr's circle and figure for the state of plane-stress... before you get the actual fatigue problem. Anyways nice thorough lesson

[@TheWuZhao]

Wow, we did it. It was a marathon; it was beautiful. Well, you did the engineering and I did the learning. It took you two days to present and it took me two days to watch. It was fantastic. The theoretical has been satiated, but the practical is hungry for more. If we built this machine, how close to the life would it fail? Is Where does Shiggley come up with these devices? Is it machined from one piece, a bent rod welded to a plate, cast, maybe 3D printed? Thank you, keep the quality videos coming. Looking forward to Gerber & ASME Elliptic Fatigue Failure Criteria.

[@TheBomPE]

I do my own example problems and apply Shigley's methods to them. I'm glad you found the video helpful! I wasn't focused so much in this video on how the parts would be made, but it is true that those considerations should generally be thought through. Thanks for your encouragement!

[@miladrad5901]

Thank you Mr. Michael Swanbom., your videos are so awesome . Would you please share the handouts as well? tanx in advance

[@TheBomPE]

Thanks for the positive review! I don't really make handouts for my lectures necessarily, but I don't mind sharing my notes if there are particular lectures you are interested in. Thanks for watching!

[@KK-it1ts]

Crystal Clear

[@TheBomPE]

Thanks! Glad you liked it!

[@adrianalbertomunozcruz4024]

Thank you so much for this professor. This really helped me to understand this subjects. I just have a question, and that is: what could we do if we were asked to calculate the diameter of the rod to have an infinite life?

[@gabewebb8936]

You would ideally know your forces so your stress varies based on the area. You would then based on your criteria make sure that the stresses fall below your curve. IE. Find your stress in terms of diameter plug into your equation for failure criteria and solve for d so that the equation is satisfied

[@MrJohanh80]

Greetings from Colombia professor. I'm so glad with this kind of videos. How do I calculate the notch sensitivity of a keyway shaft? I hope you can help.

[@jandroinspace]

thank you so much for posting this!

[@TheBomPE]

I'm glad it helped, thanks for watching! You might also find the lectures from my other Shigley-based courses helpful...see these playlists: MEEN361: kzbin.info/aero/PL1IHA35xY5H5AJpRrM2lkF7Qu2WnbQLvS and MEEN462: kzbin.info/aero/PL1IHA35xY5H5KqySx6n09jaJLUukbvJvB

[@speedbird7587]

thanks sir, neat explanation!

[@estoylopez]

Why do you calculate the theoretical stress concentrator if you dont use them? you only use the fatigue stress concentrator to calculate the von mises. Thanks

[@gerard-nagle]

Great videos. What software do you use for the scrolling background?

[@TheBomPE]

Thanks! I use Microsoft Onenote 2007. (Last version with customizable toolbars :)

[@sameterkan3892]

Thanks much professor, I have a question, do you square part example not rod :) how can we find Kt, Kf?

[@xiahua3811]

Did we forgot the normal shear stress?

[@jitongduan5960]

Hello Professor, the class was super clear, thanks a lot. I kinda have a question regarding the equivalent mean bending stress. In the Juvinall textbook, it was denoted as the max principal stress resulting from the superposition of all existing static mean stress; like Sem = Sm/2 + sqrt(Tao_m^ 2 + (Sm/2)^2). I am wondering that how much difference between this equation and the Von Moses equation you mentioned in the video to calculate equivalent mean bending stress?

[@jjalgu8696]

thank you it was great help to me! what was the textbook of this class?

[@TheBomPE]

We use Shigley, 10th ed. Glad you liked it!

[@oneofyk]

Hello Dr. I used Goodman's to find number of cycles. Was much lower.. 185.28. Is Goodman's much more conservative when used on fluctuating stress?

[@CrisDFF30917]

Hello Mr. Swanbom what is the name of the book you are using on this course?

[@TheBomPE]

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

[@CrisDFF30917]

@@TheBomPE thank you, I just have a doubt when Loads are same frequency but out of phase the method consists in finding the stress of each load in function of time and then combine them with Von-Mises (which also will be in function of time)? And if so, my Alternating and Mean Stress are those of that time-function-Von Mises (max and min)?

[@cyrusIIIII]

How did you change your shirt during class? :)

[@TheBomPE]

Ha ha, I wish that was the worst of the production foibles I have out there! :)

[@ahmadelbliwi5626]

What is the name of app you r using

[@TheBomPE]

I do the notes in Microsoft Onenote. Thanks for watching!

[@ahmadelbliwi5626]

@@TheBomPE u r thanked for doing this lectures ver very useful May (allah) bless you ❤

[@ahmetkulaksiz5674]

Hello Sir, Your class is amazing. I am studying LCF using FE model. But i have some questions about it. Could you share your e-mail for me to contact?

[@TheBomPE]

I teach Mechanical Engineering at Louisiana Tech University. Please find my contact information on that website; my name is Michael Swanbom. I always try to help as much as I can, while trying to balance it against my other duties as well. Good luck!

[@fatimaal-zahraa5016]

hello can you learn me how you use model to study !