CRACK PROPAGATION and Paris Equation in Under 10 Minutes

Crack Propagation; Fatigue; Crack Nucleation and Propagation; Number of Cycles to Failure
Linear-Elastic Fracture Mechanics Method
0:00 Original Fatigue Definition
1:07 Crack Nucleation
1:23 Propagation Stages
3:09 Crack Propagation Bases
4:45 Paris Equation
5:45 Crack Propagation Example
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[@LessBoringLectures]

Corrections: at minute 7 and a half, the integral should be [-2/sqrt(a)], not [-1/sqrt(a)]. Therefore, the final answer should be 203,132 for the number of cycles to fracture failure.

[@suleymansiverekli6839]

Great content and explanation. Thanks!

[@AbhishekVerma-il4or]

Awesome video. Thanks Sensei

[@LeaKoho]

very cool, thanks so much

[@lavanachary]

Thank you so Much....

[@gregbarnhouse8923]

What program are you using to present your lectures? They are pleasing to the eyes, but i also see how robust they can be as you shift from one area to another, use of the ruler, etc..

[@cookiemaria780]

Really great video!! Do you have any details on how the initial micro crack forms ? I have read things like that small amounts of dislocation movements happens near the surface (even if loading is below the yield strength), causing the surface to roughen and hence cause micro-notches, turning later into cracks. I just don't understand why we are having dislocation motion underneath the yield strength...?

[@elias5837]

good video sir

[@BravoBravoMike]

yeah..yeah....delicious... It took me a 3,14 centuries to understand this

[@SeracS354]

How useful is leaning fracture mechanics for the other loading modes? Or does using K_I vs K_IC and the Paris equation cover most cases?

[@LessBoringLectures]

They cover a good amount of real world cases. The other two modes are still important for other applications (brittle metals and ceramics), but their nature is more complex than that of K_I, generally relying on experimental results, and not just analytically derived models.

[@SeracS354]

@@LessBoringLectures Thanks

[@ismaelerroussi9704]

hello, I've a question, isn't the Beta coefficient supposed to vary with respect to a ? I don't understand why beta is a constant since it depends on a, when a grows, beta is supposed to vary ? thanks for reading

[@LessBoringLectures]

You are totally correct. ß does vary with a. The proper use of the Paris Equation requires you to write ß as a function of a, which can easily be done creating a regression from data-points in the ß plots that you find in textbooks (for whatever type of crack you have). HOWEVER, almost no instructor or textbook teaches it that way, and the big (and in my opinion, not-accurate-at-all assumption/simplification) is that ß doesn't vary much as the crack grows. So for this video, I stuck to explaining it the basic, most-commonly-used way. But again, you are indeed right.

[@ismaelerroussi9704]

@@LessBoringLectures thank you so much for you reply, it's much more clear now :)

[@ulaserden1508]

Isn’t the solution to the integral -2x^(-1/2) in 7:35?

[@MochChamim]

How to get KIc steel and C? at 6:01

[@LessBoringLectures]

These are usually included in textbook tables, around the crack propagation chapters, but you can also look them up online as the fracture strength (KIC) and the crack propagation coefficients of steel (or any other material).

[@MochChamim]

@@LessBoringLectures Thank for yours explanation, its very helpfull, but maybe I have another question, can I ask you some day?

[@geoffgeoff143]

Why doesn't a crack always go in a straight line?

[@anuragchakraborty8766]

because a crack always follows the path of least resistance as defined by the local microstructure of the material and it's imperfections