Dislocation motion

Dislocation motion

[@BABBYz]

Better than what my professor teaching. Thanks ! you're the best

[@larissanuneshirata8221]

Thank you so much for the dislocation climb explanation!

[@JobayerJisan]

The best teacher in this area

[@mussagan]

20:20 , shouldn't it become a JOG as remaining dislocation ( into the plane of the screen will still keep lying in the same plane )?

[@introductiontomaterialsscience]

You are right. The single stem shown here will create a jog. For the entire dislocation to climb up all atoms along the edge have to move. It is unlikely that this will happen at the same instant. So several jogs will be created and dislocation will gradually climb up. I wanted to avoid bringing a further new concept of jogs here. But thanks for asking.

[@Harshgupta-bu6jl]

sir in 3d vacancy will not extend for the whole edge line then how will the step be created?

[@rajeshprasadlectures]

A good question. So in fact, one vacancy will lift only one small part of the dislocation. For the entire dislocation to climb up you require an entire row of vacancies. It is very unlikely that this will happen at the same instant, So dislocation line will climb up gradually by absorbing vacancy after vacancy. During the process, the dislocation line will not remain straight but will acquire several vertical steps called jogs.

[@xPaNzIxKinG]

You are fantastic! Thank you!

[@anooptiwari4098]

You are great. I love your way of teaching.

[@pedropalmeros8226]

Thank you so much! I was having trouble with this topic until i saw your video. Greetings from Mexico!

[@shivkumarojha9449]

Your teaching skills are very good

[@sivanuja8118]

How will the vacancy concentration increase or decrease? While climbing up, atoms leave the edge to occupy another vacancy, but it creates a vacant site at the edge itself, right?

[@introductiontomaterialsscience]

But a similar vacant site was there at the edge before the climb up as well. So there is no new vacant site created at the edge.

[@amychen2671]

If an edge dislocation is an extra half-plane of atoms, how can it be that the entire dislocation has climbed by simply shortening its front side by one atom?

[@introductiontomaterialsscience]

Your doubt is valid. By the movement of just one atom on the front face, the entire dislocation cannot climb up. All the atoms of the bottom edge of the half plane have to move.

[@amychen2671]

@@introductiontomaterialsscience Thank you for your response sir! So all of the atoms at the bottom edge of the half plane must exchange places with vacancies for the dislocation to climb? Would that make climbing an uncommon event?

[@introductiontomaterialsscience]

@@amychen2671 Climbing is indeed uncommon. First of all, it requires atomic diffusion. So it is a high temperature process. It does not happen at low temperatures. However, all atoms along the edge do not have to jump in one instant. It can happen one by one. So the dislocation line will climb in a gradual process. Some part of it may have climbed while other parts are still waiting to climb.

[@amychen2671]

@@introductiontomaterialsscience Thank you very much again for the clarification!

[@nickosborne5822]

Always clear explanations - thank you very much!

[@Vinay192]

We know that dislocation motion cause plastic deformation in a material. So if their is a crack propogation in a particular direction and suddenly changes its direction to another side, is it due to the obstacle that the dislocation line changes its direction? And second, How dislocation motion can be used to differentiate between a ductile and brittle fracture?

[@introductiontomaterialsscience]

Plastic deformation and fracture are different processes. Plastic deformation happens by dislocation motion. Fracture happens by crack propagation. So crack changing its direction is not necessarily related to the motion of dislocation.

[@vinaythakur4805]

@@introductiontomaterialsscience Okay sir...but I have still doubt that is there any relationship between the dislocation motion and crack propagation as I study in most of the research papers that dislocation emission from crack tip is responsible for the crack propagation in a material.

[@introductiontomaterialsscience]

@@vinaythakur4805 You could be right. This is an advanced topic on which I am unable to comment. That's why tried to play safe by putting in the phrase' not necessarily related' in my reply. If you wish, you can tell me more about it. I would be happy to learn.

[@vinaythakur4805]

@@introductiontomaterialsscience You are awesome Sir.... Reminds me the humour of Dr APJ Abdul Kalam.... Although this is the problem where I'm studying hydrogen embrittlmemt effect on crack propagation in nickel and aluminium using molecular simulation...And the reason for crack propagation is the dislocation nucleation and motion that has been discussed in most of the experimental research papers.

[@introductiontomaterialsscience]

@@vinaythakur4805 Best wishes for your study and research. Keep me updated.

[@ilyashamid2860]

Thanks for enlightening us with Knowledge

[@yongchaojia4610]

it is not vacancy, but the line of vancancies?

[@sunilugadi3653]

at 14.06, If it is a edge dislocation what will be the scenario ?

[@rajeshprasad101]

Edge dislocation cannot cross slip to an inclined slip plane. But it can climb up or down to a parallel slip plane.

[@ShuvamNayak]

Sir, I could not understand how the screw dislocation has infinite slip plane while edge dislocation has a unique slip plane?

[@vittoriopiaser9233]

Shuvam Nayak it’s because the vectors t and b define the plane where the dislocation moves. A plane is uniquely defined by two vectors, if those ones are not parallel; this is the case of the screw dislocation, thereby its got an infinite number of planes where the dislocation can move. All this planes have in common that line which is the linear span of the vectors b and t (or even of just one of them, it’s equivalent since they’re parallel).

[@ajayjoshi9256]

bhai , you can understand in simple vector terms that one a unique plane can contain two perpendicular vectors . jaise ek vector x axis ke along hai n ek y ke along hai to only xy plane will contain both the vectors , whereas two paraller vectors be contained by multiple planes. watch 15:22 in the video both b and t vector are parallel to both plane 1 and 2

[@ducky4185]

So damn good

[@upoldezfranky8118]

Sir, what is dislocation punching mechanism?

[@introductiontomaterialsscience]

I have not touched this topic in this course. This is a mechanism for nucleation of dislocation, i.e. creation of new dislocation in a crystal. If you have a precipitate or an inclusion then stresses develop due to differential thermal expansion or contraction of precipitate and matrix during a temperature change. These stresses generate a prismatic dislocation loop around the inclusion. For details see
Hull, D and Bacon, D.J. Introduction to Dislocations.

[@user-bw3zd9px9s]

13:56 sir I donot realize the non uniqueness of slip plane for screw disloction , having many slip plane. How i imagine it in my mind real lattices?

[@introductiontomaterialsscience]

Slip plane by definition is a plane which contains both the dislocation line vector and the Burgers vector. For screw dislocation both these vectors are along the line of the dislocation. So only one line and not a unique plane is defined by these two vectors. Thus, there are many slip planes possible in this case.

[@user-bw3zd9px9s]

​@@introductiontomaterialssciencesir, I am agree with your statement, But we know that slip plane having slip and no slip region also. If we know that above this slip region ,slip happened in atomic model of screw dislocation, then this plane is unique? Sir, I request you to explain using atomic model of screw dislocation.

[@DiegoLopez-br4po]

So if there is no vancancy, the climb up wont be able to happen?

[@rajeshprasadlectures]

That's right. Climb motion is linked to the interaction of dislocation with vacancy.

[@akithjabed553]

can we by our wish shift the dislocation line ? what you ahve shown sir ??

[@SANDEEP_Kumar138]

Thankyou sir

[@akashtiwari78059]

better yhsn then my proffesor

[@aravindkumar6631]

Sir what is pierls strees is it different from crss if it is how

[@pouraliakbar]

Wonderful lecture - Thanks!

[@hustler6685]

amazing

[@prakhartiwari6433]

Sir , is dislocation effect happens in polymer material ..

[@introductiontomaterialsscience]

I had not thought about it. But to answer your question I googled and found this.
www.ncbi.nlm.nih.gov/pmc/articles/PMC6628581/

[@prakhartiwari6433]

@@introductiontomaterialsscience Thank you so much sir...

[@jidapa2969]

Thank you so much

[@smarajitpunaykanti6463]

Sir in a research paper I came across the term: Non basal (a+c) dislocation . Unable to understand what it is. Can you pls throw some light on it

[@introductiontomaterialsscience]

This is for hcp crystals. Here the most common Burgers vector for dislocations is the {a} type, which means that the Burgers vector is along the edge length of the unit cell and its magnitude is equal to the lattice parameter a. If you now add a c vector (which is perpendicular to the basal plane) to the {a} vector you get {a+c} vector which is a less common but possible Burgers vector. It will not lie in the basal plane so it is called nonbasal.

[@smarajitpunaykanti6463]

@@introductiontomaterialsscience yes sir HCP. Magnesium crystal. Where can I get some more theory on it
Thanks and regards

[@arjunaravind1931]

Split portions into 3 separate videos

[@introductiontomaterialsscience]

Thanks. I think it is a nice suggestion.

[@user-xv9yi9ti7v]

Thankyou sooooo much

[@kingalpha2006]

😊

[@sarthakroy5292]

11:45 dislocation line moves perpendicu;lar ti itself
what it means

[@introductiontomaterialsscience]

The direction of motion of the dislocation line is perpendicular to the line.

[@watchit620]

Please upload kinks and jogs vedio