Mechanical properties of steel 14: theoretical strength

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Mechanical properties of steel 14: theoretical strength
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The 14th in a series of lectures given by Professor Bruno de Cooman of the Graduate Institute of Ferrous Technology, POSTECH, South Korea. Deals with the theoretical strength of iron.
Keywords The Graduate Institute of Ferrous Technology (GIFT)
Typesetting Wood Cartridge (firearms) Slip (ceramics) Plane (tool) Gas turbine Single-cylinder engine Engine displacement
Steel Schubvektorsteuerung Ink Wire Shake (shingle) Cartridge (firearms) Spare part Digging stick Backpack Single-cylinder engine Ship of the line Engine displacement Engine displacement Striking clock Snips
Typesetting Surfing Piping Schubvektorsteuerung Machine Singing Casting defect Überschallstaustrahltriebwerk Cartridge (firearms) Azimuth thruster Screw Spare part Food storage Ship of the line Ship of the line Model building International Space Station Flatcar
MP5 Commodore MAX Machine Spare part Slip (ceramics) Plane (tool) Spare part Forging Firearm
Typesetting Off-road vehicle Hang gliding Steel Scouting Slip (ceramics) MP5 Mechanic Melting Cartridge (firearms) Spare part Commodore MAX Machine Slip (ceramics) Plane (tool) Spare part Ship of the line
Typesetting Depth sounding Tin can Schubvektorsteuerung Slip (ceramics) Mahindra & Mahindra Angle of attack Alcohol proof Cartridge (firearms) Gentleman Slip (ceramics) Single-cylinder engine Caliber Single-cylinder engine
Capital ship Slip (ceramics) Couch Weapon Finger protocol Angle of attack Angle of attack Cartridge (firearms) Gentleman Commodore MAX Machine Slip (ceramics) Plane (tool) Musical ensemble Plane (tool) Single-cylinder engine Firearm Strapping
Angle of attack Typesetting Finger protocol Plating Plane (tool) Slip (ceramics) Slip (ceramics) International Space Station Van
Typesetting Typesetting Buick Century Schubvektorsteuerung Presspassung Slip (ceramics) Cougar Angle of attack Angle of attack Cartridge (firearms) Gentleman Plane (tool) Slip (ceramics) Screw Plane (tool) Single-cylinder engine Engine Ship of the line Firearm Gun
Typesetting Die proof (philately) Temperature coefficient Mixing (process engineering) Couch Angle of attack Überschallstaustrahltriebwerk Volumetric flow rate Alcohol proof Gentleman Commodore MAX Machine Finger protocol Slip (ceramics) Plane (tool) Negation Kardieren Firearm Sheet metal Schubvektorsteuerung Slip (ceramics) Planer (metalworking) Hot isostatic pressing Cartridge (firearms) Screw Single-cylinder engine Gun
Typesetting Engine-generator Wire Game Mechanical watch Plane (tool) Spare part Firearm Pelzware International Space Station Typesetting Steel Hüttenindustrie Wire Mechanic Cartridge (firearms) Screw Plane (tool) Piston ring Remotely operated underwater vehicle Single-cylinder engine Goldsmith Ship of the line Glider (sailplane) Disc brake
Die proof (philately) Screw Screw Plane (tool) Spare part Slip (ceramics) Forging Ship of the line Firearm
Tin can Disc brake Screw Plane (tool)
it so we are moving on 1 of the things we're going to have to look at now is so basic basic strength of also siren pandemic In terms of plastic deformation so of Woods what would be distress you have to To get the the crystal to deformed for agreeing to deform I think so and then will come to this concept of what's called trials Forbes that I would have its 1st level look at the theoretical shared that stresses let's computer very simple idea would have an edge dislocation here so like this 1 and then this edge dislocation Mossad this this position here and so on so the but as it does this year as it goes through you have to go through a potential energy barrier and this is shown here In and we have an energy barrier and we take derivative of this year's but we get a distressingly Canadian distressed barrier candidate looks like this and and then got and to you we can see here that if this is the period the city has to be the the distance between those 2 equilibrium positions as that is equal to be then the maximum of the shares stressed in this case because we have to share the crystal to get dislocations to advance but is given by this scent of it total T and that occurs at a distance be over fall it is happy dismissed quarter because correct so far what we do here will
continue here it is is so well we will get this distressed variation here yes will assume it had is this the sign function sold this is a sign function has the maximum here pie over to Reagan's and so if I want to translate this In 2 no stress versus position in this fight the right time 2 I'm signing pie over 2 times next distance divided by the news this distance here b Over 4 good and and so would l do now is assume that the do the the displacements we we have or are not very large has ended in that week and replaced assigned function simply by dysfunction the fight over it's over 2 times X be over for and that's so that's that's this function here and as was said this is equal to hoax law for sheer Sears trust to shear modulus times this year and the sheer in this case is of course if this is a slip planes this is the next slip planes then the sheer idiocy what is this article here Worcestershire and there so that is equal to X's distance 6 divided by the Adidas linking the interplanetary space so I certify assume that these 2 things that hoops law applies that uh that I can simplified assigned function simply by the argument I find this this this tells me what is the sheer strength of the world that approximates the sheer strength Rentokil's share strength for firing here so what is important here it's dependent on the ratio of be over do so it means that the the this theoretical sheer strength will be proportional to the bird respected the larger the Burgers vector is large the this sheer strength at the the larger the interplay near spacing is the law the theoretical shear this let's just what plug-in some typical data points here right so that we know what the sheer much of this is bird we use 64 here we know what the interplay in spacing is .period tune animators and we know what a burger Specter's . 4 8 2 4 8 9 0 meters with blood this we find 3 8 . 3 dig a pastel is is rather it we dig Pascal this is a large value but we we can make steals technically wait close to 4 the bigger Pascal we can make you can actually buy why With strengths of the order of a 3 to 5 Figure Pascal if you make up the so-called In a very very fine wires so-called whispers of Byron you can get pretty close to but these values and that this value and an even higher if the wire did whiskers small enough but it's an excessively hot high value still and as I have this theory it has been refined
yes but Over the years we have some better formulas To compute with which we call the at the Pyros stressed so when you do for for Riddick steals in the dislocations will move through grains and his greater single crystals and the dislocations will encounter would would we call it potential energy landscape basically because they run into product arrangement of atoms yes if their their potential energy will go up and down if they remain straight and go from 1 little a potential the energy channeled to the next 1 to you you you've got to see this energy here and the base energy the minimum energy is the the line energy of our the dislocation we have introduced more and than you know that's related as to the wide attention but so and it would end and have we call this there we define a EPA's Energy visited the city shear stress of the results here stress which is required to move a dislocation from potential Valley to the next potential Valley and In the process as it does is it remains strike because as a whole from 1 potential Valley to the next 1 and and and so the shear stress variation has has this part of the shake us as we discussed previous life are so so what you end
up with with a theory yes but which which gives you function which gets the 2 the so-called Paris share stressed in which actually looks a little bit similar to the the former lose not much more complicated than to the deformities we've just derived from a very simple model the the Pyros shear stresses G over 1 one-liners that was somewhat less than exponential minus to pile over one-liners for storage of types the Overby and it basically expressed the same thing is that the the primary that influences parameters that influence the at the par also stress art the modulus sure modulus the personal qualifications and then the the ratio of the burgers factor to the Inter planar space the declined .period and again it's the same story you have a smaller Burgers factor the past stress goes up you have a larger displayed laying spacing the 1 that the pirates there's the stress goes down so that you can block dispute you can plot this and function it Paris the Spanish EU stress divided by the shear modulus I am a new plot of the log of this function as a function of the over B yes when and in what you find is that it goes down as d increases or as the Berbers factor increased and there is a difference between a screw dislocations legislatures the color of week but if we indicated the deal for Bure a show for fire which is about here at 0 . 8 and a D over ratio for gamma scientists a little but less than 1 . 2 years we see that's 1st of all the policy stresses in the case of Al-Faran always higher than than those of Kamiah and the pod stresses for screw dislocations are higher than for edge dislocations and right that this but the ratio of the Overby temperature independent because of when you were when the crystal and expressed due to thermal expansion of both the it is the lattice parameter increases health just as an insult to deal in the deal from the ratio but that gets canceled out right so so so it do the temperature dependence of the parcels of of this style will come from the temperature dependence of cheap and the possible ratio income but so let's just just so we get the feeling of the the differences here let's put in numbers so we have to the functions just simple functions simple exponential functions so if we know the before all fire and what the interplay the spacing is what do Burger struck a length it's but we can easily calculate with the the Overby ratio as and and if we take a reasonable values for the modulus shear modulus and Wessels ratio we complied all this data into the formulas for instance for Alpha we find 75 maker Pascal for edge dislocations and 400 pence 73 make possible for the screw dislocations and if we do the same thing for gamma yes we find that edge dislocation free remake Pascal and screw dislocations 52 made pass adjusted a note of caution here yes if you look at these values it said you know these are really heists values as of the end these only applies at 0 OK yes 0 this equations of their applied 0 so that the values we measure at room temperatures will be small but you very important here around it's harder to move screw dislocations yes an edge dislocations yes and this look regionals in general yes b have a higher carols stress shear stress in Alpha Arun infotech since then in Boston it sticks to its hard to move a dislocation from 1 part as well into another EPA's Valley Inc In a taken C C L 5 iron structure that's important to
know if not of course the equations there and in the calculation of the policy energy but force sheer force that I just showed you a is 0 OK we're not really interested not many applications of 0 OK applications were interested images showing you here on this the temperature Skilling Calvin and Inc deg C with typical the application temperatures are there are applications which are very close to all of 2 0 OK but they're not really is OK that's that's when we found that we work with liquid the liquid gasses argon helium hydrogen gas very close but there are technical applications such as LNG gasses LPG gas and liquid gasses yes but not so in general line pipe situations will be used for instance in Arctic conditions but you know most of the applications were looking at will be room temperature and of course there will be machinery applications and exhaust systems of power generations where would the temperatures can go as high as the 900 deg C in service and perhaps higher so we're kind of in will not really interested in the very cold temperatures this is so it is in that case it so you
can actually extend the theory that too To compute what uh the Pyros energy would be at higher temperatures we were not going to go into the theory but because this formula is quite conveniently simple 1 I'm giving it to you so basically tells you what what is deposit energy of an edge looking at higher temperatures and and the only thing you need to know is calculated the parts energy 0 Calvin yes and a no basically with the melting temperature is of our and rent so if we if we do this for again and we do this well for our hands but we and we know what the melting temperature is 1535 we know that we have 75 mega Pascal as pearls the stress for Al-Faran 82 make Pascal forwarded the shear modulus and also the was so ratio of 1 . 3 so if we plug this and this formula the original 75 the major Pascal dues 75 make skull show the policy of stressed that we get at 0 OK this is reduced to 67 it's a bit of a law professor kenyan and we can calculate this using are
so so we know the the theoretically what it would take to shared a crystal so that it jumps From 1 valley to another Valley the goal potential energy valid again theoretically and screw dislocations this around 400 make a pastor let's let's but I think the let's this value
here Canada's
473 may have passed and what will actually
see is that it's it's
not far from reality check but let's now see at 2 what we can do In experimentally to measure this the shear stress it takes to move dislocations in L siren and gamma irony L and then also seeing that led the dislocations the experimentally do not moved from the in 1 From apart Valley to the next part of the other mechanism that that controls the motion of the dislocations From from 1 equilibrium position to the next delivery are so well but most of us have heard about Smith's in In our undergraduate studies so our take singles you have know that this experimental determine way you did it experimentally measures what what the level is of shear stress that you need to initiate plastic deformation and you can do this at any temperature you want to for instance it and you can do this for I don't know how far gamma irony as to the here you have a single crystals it's a single crystal of the steel in this case it's an Austin Texas deal yes and I'm so it's so oriented and it's compressed it's been compressed slightly and you can see it there you can see that there is supply light only 1 slip system activated yes in this particular case not so there the shear stress at which the plastic deformation it starts can be used as part of the we we don't call it an animal see why we don't call it the Pyros stress because the mechanism by which this location is not the perils jumping mechanism recalled that the critical resolved shear stress important parameter uh that we certainly want to know for pure irony fire and when we do computations of strengths are so this did the geometry is very simple of this test in an hour and a half again as you probably know and that if you compress your crystal this is an example here the example I just show you it's been magnified as to which you have you have you know forced to apply princess along the A 1 0 0 direction yes on this cross-section here this slip plane section is of course different from the cross section of your physical Crystal wanted to the cross section considering the on on the blight playing against this the likely this month of the year actual if you want computer shear stress on this on Monday the glide playing you have to use the prime here there's and which is the same as they divided by the coastline of firefight being the bungled between the applied external forces and the normal too your slip planes and then you also have to resolve they but I sheer force get the sheer force the component of the sheer force along the glide direction that's and that's the bird respect so and and that is given by b 1 of the co-signer of this article the lander which is the ongoing between applied for standard direction of the set With 7 if you do this the
results here stressed is the forest divided by the area resolved on the sheer playing of and in the sheer direction and you find basically is to be externally applied force over the cross section of your sample times costs for sci-fi and coastline wonder intent and so on and this of course is the externally applied force 6 so I if you measure yes and you know the geometry of the test as which are right you know the final certified and land you can basically cited Sigma externally applied force at which you have yield is 10 times the critical results here stressed at types due to the factor M & M is so-called Schmidt factor 1 over "quotation mark fight "quotation mark wonder and the maximum value of this that is when fight and land 45 degrees and and the value of them is then too meant so if you if you measure a certain shares stress and the the value of the Sigma happens to be too In that particular test the distressed appliances be twice the critical resolved Chester Kent so
that's sound look at for example here said so you have alpha iron crystal and it's oriented with 4 minus 1 8 axis parallel to the tensile directions are you are you wonder why why users want you know because that's the best direction orientation directions To get single slip notes In this case but this subsystem is given by the age 1 1 1 the direction of the Burgers vector direction and siblings 1 bar 1 1 so we we can directly calculate what land that is by making the dock products between the time so axis and the Burgers vector yes and we can also calculate the angle but we can calculate the co-signed fly by making the dock products between the the direction of the externally he applied for spanned the normal to the slipway so we find here about 0 . 7 0 . 7 4 land and and "quotation mark fine and of course that means that their land and firepower 45 degrees and in other words the cement factory is is 1 over "quotation mark landed times fire stew and segment is 2 times the the shares structures so and and that's
usually where an undergraduate that information about critical resolved shear stress applies and kind and we all usually assume that Schmitz law this Nunavut applies universally well this there are it there were many more Crystal systems where the Smits law does not apply and I said does not apply and most people think that actually Smits law is a universal wall yes and will end in 1 of the big bang exceptions to Smits small most of the BCC metals yes was a visit including elsewhere including so in steals now Swiss switzerland's actually does not apply well so 1st of all and what what does Smits lost sight of it and and then here I'm going to assume that you know I don't know familiar enough with Chris Tolles and and and Sderot graphic projections that they don't have to explain it to you but saying you know that you take a single crystal yes so you can represent the orientation of that single crystals using exterior graphic projection and any specific the orientation can be on any specific orientation can be represented in it what we call the basic triangle in that 0 graphic projection and this is this is the old 1 0 Graf protest so this is a great got here is a a specific orientation specific crystal orientation but when you have an orientation in this Crystal Smith but the Smits law says that you will have is single the single slid direction and a single slipped playing and this this the blame will be this particular that will be 1 1 1 in the same direction been we 0 BA 1 wants it doesn't matter where we are and what he orientation is both my single crystal these will always be the 2 the 2 defining parameters of the Switzer once the plane and once slip system right in the case of elsewhere are and it's not like this if you if I have crystals with then with orientations given by any of these points here the only thing I know for sure Is that the 1 1 1 direction this 1 1 direction will be the slip direction when it comes to slip playing well in the past year 1 of the things you we find is that this sled is on the plane of the maximum resolved shear stress was so normally if if the the if Smits law would apply 0 1 1 would always be the slick plan answer as it is it will depend on it it will be origin should be the maximum results here shipments of that's a plane that's on this trace and and so if I make but if I connect this trays the strongest trace that that is the playing of maximum results you stressed right and it's so displaying depends 100 per cent on the choice of the tensile access here and so I don't only have to take into account the angle Lambda and fight as in the case of gamma iron lender 5 His but also an on goal the next round will try yes away from what what the the slip planes if Smits law would apply content but case so
just note on the Greek alphabet In the tongue-in-cheek joke here to lend Islam verifies fact this is the angle kinds of this this sunless Chi Minh is another on goal this bundle side capital side and for the Korean music it's iron oxide can the presence of so in addition to London fight you have to do these 2 extra uncles that play a role in that and so so so you have Thai here yes but normally if if it was simple the indeed you would have D plane of maximum shear stress would be the guy like this and you only have this on goal Kite to worry about but in practice it turns out that you get the actually observed go wide system macroscopic is it is also not this Xiu but this deplane given by disputes but up slightly away from it the plane are yes and the fact is you 2 Cross the frequent change of the the lied playing in the C C R so and that's where there is there is a need to define this 4th on goal side and where were we say a would is a convention to say Well if we measure aside from this claimed pole of this plane to bar 2 1 1 in we we say size positive and its negative if you can room rates 10 by the end of yes and so
I think I've already exists and all the so end you would think at this
point and in the only thing you really have to remember is that it's this is the selection of the actual slip playing in bcc there is pretty much a headache but that would not that's not even enough it's even more complex 1st of all In but there are very interesting temperature effects then there is also another effect they are twinning and tight 20 the facts and there is something that is the result of the known playing their cost structure screw dislocations in in Alpha just to make things but personal it's the temperature effects well it turns out that In hellfire and I think already been introduced and elsewhere are the slip system the preferred subsystem system the preferred slip planes will change with temperature and so normally at really low temperatures in pure Alpha you have slept on 1 1 old play and as the temperature increases we get a change a gradual change at height of the situation at higher temperature we get 2 1 1 yes as normally you would think well in steals are slip systems because we work at room temperature yes it should be 1 1 2 points now turns out that would steals it's different you know the low-temperature situation gets extended to high temperatures and get 1 1 0 0 and light plates are preferred what is this twinning and tight winning symmetry well this week shear stress that's needed to share a crystal in the FCC in 1 direction it's the same as this year's stressed it takes to share the crystal in the other direction not like that In in bcc fire that meet said so you know what I mean
so and so the pile stress ordered to do as you call it the critical resources stress of dislocations deep enough and depends on the direction and the direction in which the dislocation moves yes but that's also the exists and the violation of Smits Longwood University say they're not an end but and it doesn't hold for gamma are in there could does matter where you go in this direction this directive saying that so any particular you can see this when you look at 2 1 1 2 glide planes but it so which we're looking at here is a 1 1 overview of Alpha because of this is the units in there yes we're looking down the 1 1 0 directions but the play those the Plains here yes the planes we see and on here 1 0 1 to play him it's up to you can have glide on this on these planes and and this is the burgers factor is a upon 2 1 1 1 this so that you can have blighted this or that if you glide in this direction there's this afternoon will have to move over this afternoon 2 reached this position In the other cases this afternoon most into this position 2 and it will continue them In Good was into this position and now these 2 the shares give rise to this aim yes the same Shearer you can see here the shame sheared crystal the shame sheer crystal you can see him at the act on the blight like this century crystal however and and you can see the sheer is that has resulted in a 20 in 1 direction yes this year this in this direction as the share was easy to achieve in this direction it was harder to achieve because in this correction the atom has to move over the hump created you due to the present of this act so there is a difference in so she stress required to get this twinning yes in 1 direction and and tight win yes then the other thing is the influence of this playing there cost structure of screw dislocations Will it it turns out that when you form a screw dislocations In the city the cost structure is not a very sharp line but the court extends Over all the Crystal Place 1 1 0 0 1 1 2 crystal planes it's not a stacking fault it's not the Crossland assist the core is slightly extended the into these directions and as a consequence forces forces normal to the slip play yes From now on sheer forces normal forces have an influence on the critical resolved shear stress and and again that's a violation of Smith's law which says that you only have to consider sheer forces so what do we mean 1 of them when we say the cost structure is uh it's bread out over it slip planes which share the same slipped direction this is this is basically what you have to consider it so it if we look down if we look down the screw dislocations the cost structure is not localized here but it's bred out all 4 yes it spreads out for instance in this case In the 6 directions or in these 3 directions and in this case it's the sets and this is real because it spreads out in in the the 6 directions and non degenerate structures and in this case we saved the general structure so it can if it is fits said that if he goes out on 1 1 1 1 2 3 1 1 planes as it can you can go in however generate structure by the like this like this the wide position or and Thai wife position it's important that the we realize that this is not a stacking fault right In but this is more a spreading of the dislocation call this is a brother but really complex people have spent a lot of time and trying to understand what was going on because it's not only characteristic for althought are these giant but also in other the BCC battles general and what is also for its is of importance is they the handedness both the the crystal structure of the new you can show that if you look down and 1 1 1 directions you will have channels where the the atoms 4 aid sport it's cool like succession of atoms in the friends in this case the atoms go like like this I performed the school type a succession of atoms this direction in the counterclockwise direction here it's in the clockwise direction so and of course everything happening at the atomic level computing the equilibrium structure of and the cost structure of a screw dislocations requires calculations right and Stickler so you do computational the use computational techniques to try to discover what the cost structure is that these are the school dislocation
experimentally go back to experiment if you do very careful experiments with single crystal you can see these effects and in the 2 shown here for instance you have for instance of this would be the orientation of a single crystal Al-Faran years so this is this particular 1 4 8 orientation as if you do this you use squash dispersal you pull at the against the this system you you observe on the old 1 1 said plane and 1 bar 1 1 the direction that means that this is the burgers factor when you get this dislocation loops here on this but it was a like and if you measured this year stressed so you received pulled this crystal there you go but cost person will be elastic for a little bit and then you'll start plastic deformation engine you measure the critical resolved shear stress bonds 1 1 0 19 make capacity so really soft yes release off of it you can of course now change yes the on the slip system because there you can and you can changes by changing the goal kite that we just defies right that's and if you do this this allows you to so if your look I angle is is 0 it's back here so
you use way we're talking
about this is not so this article is 0 yes might slip plane is this 1 here right and
if we go back and then and so that's the 0 Laura 1 slip plane became 1 1 1 1 1 0 types of
so 1 Wilson Plame if so
so that's that's position here I can change within the there my basic ongoing Chris that I can change is on the cards and they can make it there it can make it up to 30 degrees positive or 30 degrees negative that I get another supplier if it's 30 degree positive I'm in the and tight winning orientation so there I'm undefined my slip is not anymore on the 1 1 opening but on 1 1 2 2 planes and in the other direction it's on a similar plane but with in the other direction and you and you can see that the sheer yes To start the this led the defamation will be higher to start with and 2nd that I will not be decided it will not be symmetric and this is definitely a proof that the Schmitz law does not hold for elsewhere that these differences are small and Kate it's important and I I want you to notices 23 and 26 of its only free make a pastels of different so you really need to be very careful experiments here and this is the actual Raul data knows this is the actual is that this the externally of measured flow for the yield strength on your on your press and then so why don't you remember that that we calculated it's for this specific case the uncles were 14 2 1 was were 45 degrees so the difference between the way we count was simply calculate the result shear stress from the measure applied the stress rights it would we actually measured here was not 19 make a Pascal of a few stress that we measured 38 Major Pascal "quotation mark yield stress right and that's what we measure and then we divided this by 2 To get the critical results stress of 19 I said this is
the other I think it's important for 4 ironies is the fact that you depending on the temperature you'll have a different set of planes review he plotted temperature thank you blocked which we call the effective stress that means you only plot the temperature dependent part Of of the of the stress all of the shares stressed that's why it looks here like that like the stress is this it's 0 at room temperature not hearing which is removed anything that was temperature in defense of the and and and so that you see outside are there were you can see that as we the temperature decreases the increase all of the critical results users with temperature goes over difference curves here and different in a different zones of of a blight that different temperatures ranges where the the the glide planes to declare In pure fire and you get 1 1 0 glide at at very low temperatures as in as you go higher this 1 was puerile fire once you alloyed this you going to Alloy Inc it's different the whole picture changes that which makes things In an even more difficult with steals because 1 of the fundamental data on Alpha Al-Faran got to really use steals because it's different because of the and that's what I I show here is set for alloys softened From the prairies but all that and will come back to that when when the Allied actually at a lower temperature we find that the following causes a softening of the Al-Faran but which are important for us now is that when we win win allies 1 1 0 such system is his favorite rather than 1 1 2 1 of the things I would like to mention you remember when we calculated the Pyros shear stress we found the value of 473 maker Pascal at 0 OK if you go if you look here the experimentally measured values at 0 OK 4 the critical results shear stress not very far away so it's around 400 made Pascal at 0 this graph also by the way we feel to be very strong temperature dependence the all of the factors stress or or the results stressed units and and will see that this is also known as an important as characteristic of lot of 1 of the things it's really important that and it's always been a challenging aspect of getting good data for for irony is the fact that even in extremely small amounts of alloy have an impact on what you measure yes and of princess in this case we have in the effect of carbon on the critical result shear stress and you can see that it is the only if you add 20 ppm of carbon and it's very very small amount you can already see almost you know doubling of a critical resolved shear stress you have to be really careful and there are not many extremely high purity single crystals which which allow you to use to measure do fundamental experiments can but rights so what does it mean for us because at the end of the day most of us are here to and not here to work on pure Alpha parents single crystals but what would stay influence will 1st of all week let's let's talk about this twinning and tight winning effect is that important while we're seeing in you know when you the measurements it's the difference between 23 mega Pascal and 26 megabytes Pascal's that's not really a very important difference from a technical point of view and I have a lot of these violations of Smith
floor we don't really have to and don't worry too much about them and their impact however 1 of the things we should remember is that a lot of these violations are results of the complex cost structure of screw dislocations knows and as a consequence of pronounced temperature dependence of the mechanical properties of Alpha and Alderfer at 60 that's something we is really important to remember so what is important is that we have In practice the low mobility of screw dislocations Al-Faran and in steel says that's a direct consequence of the disk degeneration clear 1 of the of the screw dislocations critics of his or not lines there they have their extended units so that makes it difficult for them to move him how they are extended is still a matter of discussion as well even today you people in solid-state physics and metal physics interested in this topic of it's not an old topic where are all the physics has been gone yet I said that the way the intervention you and you have the degeneration of the cost structure is still a matter of discretion isn't on 1 1 2 planes is that it is generators at number generator is it on 1 1 old planes and the importance with which important for us is it is degenerate and this has impact of the mobility of the screw dislocations varies very low and the low temperature so but you know what does that mean no mobility while using your cost structure yes looks like this the core not Bond the glide plane yes it's extended its it's 6 in other words it's extended I want Of the glide plane and this is the glider plane for instance the core is extended like this there's only 1 only this little part is in the glider planes there's so if if this dislocation needs to move on this glide plane it will tell you will 1st have to change the cost structure yes change the cost structure so it can glide as soon as it stops it will extend again turnover if it is safe to your your cost structure looks like this this is your blight playing the 1st thing that has to happen is these bets here I have to be removed yes then the dislocation can move in as soon as it stops yes it's extends again and of course because it's extended yes but you also get different ways of dislocations can move here they can move out of its glide way yes the show inferences and and this is where the the non shear stresses the stresses normal to the delight playing start playing a role the friends in this case but the distressed normal to the blight plane causes the dislocation these bets too I moved to the core and dislocation this way and this way so but a new conceded persuaded dislocation can move for a little bit along day 1 1 or direction but if it chooses to do go in a succession of these 2 1st steps they can go like this and then I think it looks like it's moving on a 1 1 2 directions on 1 1 2 to play yes but the thing is the dislocation just doesn't jump From 1 Charles Valley to the next wires Valley it 1st has to be constructed and then it can move this as it stops it expands again so and that is the reason the fundamental reason why this location screw dislocation mobility is so low because it doesn't happen on the edge dislocation so
maybe I can finish with this so but so would you get this the Powell stressed is very high to force screw dislocations in comparison to edge dislocation mainly it's about 20 times higher and that is a direct result of the non non-playing playing the structure of the Corsican dislocations and this gives them very low mobility and when you have this location so I have had dislocation loop like this and it expands because I applied an external force yes what am I going to if so this is the screw part and this is this group on and this is the edge parts what am I going to see in practice while the edge dislocations move very quickly they don't dare not extended the screw dislocations move very slowly well these guys don't move and these guys move very fast so let's make the move this way these guys don't move so my dislocations start to look like this yes the pieces that move very fast not many of them please that move very slowly you get to see a lot of them so when you when you make a TM sample of are all fire and it's been deformed in single slip that's what you see long along the dislocation lines that are in when the parallel to the line directions so they're all screw dislocations the best it is clear direct proof of the fact that and we have the this non-playing there glory structure of screw dislocations in health
workers will continue with this but subject to next
Monday if you for your attention


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