Derivation of Griffith Fracture Theory

Once we realize that stress concentrators exist, the next step is to consider how they may exist in a material and how these will influence fracture. A. A. Griffith did some of the pioneering work in this area, alongside others. A key thing to recognize is that all materials have flaws and that the most severe flaw will govern failure if the maximum stress at the crack tip exceeds the yield strength of the material. The next point is that stress on a material causes two considerations. First, lattice strain occurs raising the energy of the system. This could be relieved by crack growth since it would return lattice to normal as crack separates the strained material. Second, the crack propagation will create a surface with some associated energy. Whether a crack propagates depends on the balance of strain energy release vs surface energy formation. We can observe a critical stress intensity factor that is equal to a dimensionless shape parameter, Y, the applied stress, and the square root of pi times the half-crack length, a.

[@Gfaitcoco]

Great explanation for a such important topic!

[@simonfritz9252]

Hello Taylor, First, I must say that I'm a huge fan of your videos! I think there is a little confusion between the stress intensity factor K (which has dimension Stress.length^1/2) and the stress concentration factor K_t which is Sigma_m/Sigma_0 which has no unit. [according to several Materials book and wikipedia pages] Both are connected but not exactly the same! Correct me if I'm wrong, Greetings from France, Simon

[@TaylorSparks]

Hmmm.... You are absolutely right and I'm at a loss for the discrepancy at the moment.

[@IshanKakad]

can i get the onenote notebook link please to prepare for my exams

[@ytneedsanameliu2468]

coming from MEch1280. it's helpful!

[@HopeHumorRelaxation]

Hi Taylor, Thank You for the informative videos, especially on fractography and materialism. Can you study the following two scenario: 1- If there is a transverse crack in a weld say it's a pressure vessel, and we weld a patch plate over the external surface ( as per design thickness) would the crack growth retard? We have practical experience of the same. 2- If there is a thru crack with leakage, and we weld a plate over it, after welding the leaking pressure on the patch plate will equalize the internal pressure, would the pressure balancing of both sides of the crack would retard the crack? In both 1 and 2 cases the base metal is healthy and there is only a flaw in the weldment. No circumferential cracks only transverse cracks. i have posted some detail in my blog if you want to see I will share them.

[@YunKai-ch8jl]

Great explanation and great lecturing style. My only problem with the lecture is that it is too fragmented. Maybe combining a few smaller videos into a medium size one can make a better flow.

[@TaylorSparks]

Not a bad idea. You can find all of the videos in my materials science 101 playlist

[@shivankkumar7185]

which book you take pictures

[@TaylorSparks]

Callister's intro to mse

[@jour154]

Love ur work hope I should do any reasearch paper with you sir

[@TaylorSparks]

Nice

[@amirkhatami5229]

Hi; tanks for a fantastic lecture great work

[@TaylorSparks]

Thanks so much. Feedback like this what keeps me going. You might like our materialism podcast. It is really awesome and you can find it on every platform including KZbin.

[@louiseyang2684]

what's ‘a’

[@louiseyang2684]

I got it