Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Footkerchief]

It has a meaning in colloquial language.  This is like you walking up to someone speaking Portuguese and telling them their English sucks.

The meaning you are referring to isn't correct in any language.

strength   /str'eŋθ/

3. The strength of an object or material is its ability to be treated roughly, or to carry heavy weights, without being damaged or destroyed. N-UNCOUNT also N in pl
          * He checked the strength of the cables. + 'of'
          * ...the properties of a material, such as strength or electrical conductivity.

[Aachen]

English : Portuguese :: Jargon English : English

roughly?

[Noble Digger]

Please friends, worry less about the little quibble over the usage of the word strength, everyone except one person understood what I meant (I suspect he understood just fine as well) and didn't feel the need to dangle their degree and diction about like a limp pecker. I'm more interested in continuing the discussion, especially since some people in this thread seem to know what they're talking about.

[Arrkhal]

my question is basically "what combination of properties make folded steel better for weapons than homogeneous steels?" and does this hold true for all weapons or only swords and knives which must be ductile enough to bend slightly under stress without breaking while still being hard enough to hold an edge and win hardness competitions vs. armor materials?

I suspect the folded steel issue is a real boon for things like swords, maybe not so necessary for hammers.

Folded steel isn't like a cable, or a folded piece of aluminum foil.  Historical metal folding took place at a high enough temperature that the layers would be forge-welded together, becoming a single piece of steel, the layers no more seperable than a more homogenous piece of steel.

Historically, this was done for numerous reasons.  The number one reason probably is, it was a holdover from making iron in a bloomery, as opposed to a crucible technique, like a blast furnace.  Bloomery iron has an enormous amount of silicon slag (strands of sand/glass), which must be removed; the easiest way to do that, if you don't have the technology to melt the iron completely (Europeans didn't until after the 10th century AD, IIRC), is to heat up the iron until it's soft, then hammer it out and fold it repeatedly, eventually driving out most of the slag, though even the purest "wrought iron" (wrought meaning beaten) would have about 1-2% slag by weight.

The carbon in steel makes it possible to drive out even more slag, until you have practically none.  Slag makes wrought iron a bit stronger than mild steel, but in high-carbon steel, it weakens it, so folding steel would be important to get that last little bit of slag out.

Folding will also homogenize the carbon content.  This is particularly important in blister steel, which is pretty much the only way to make steel out of iron without a complete melt.  Bars of wrought iron are put in sealed, airtight containers with charcoal, and heated to a high temperature for weeks at a time, much like case-hardening, but hotter and longer.  That results in metal with a lot of carbon on the outside, very little on the inside, and lots of slag still; obviously in need of folding before it's usable for anything.

The folding together of different types of steel, on the other hand, was generally done to conserve metal and/or to change the properties by blending different steels, or steel with iron.

The Vikings, IIRC, would use pure folded steel for the edges of their swords, while the center section would be steel folded together with iron, then the 3 sections would be forge-welded together.  End result was a stronger sword than monosteel construction, with hard cutting edges, and a soft, springy inner core.  This strength boost was mainly necessary because of the very poor quality ores that they used, however.  Mainland European, Chinese, Indian, etc., swords were more often monosteel, because the metal was stronger to begin with.

Folding different steels together could also "stretch" your supplies of good quality steel.  A relatively small amount of "good" steel with a high carbon content, blended with a large amount of poorer stuff with a low-ish carbon content, could result in a decent quantity of reasonable quality steel.  The Japanese did that pretty often, once again due to rather poor quality ore.

Finally, on casting vs. forging vs. machining, it's usually much ado about nothing.  Actually, casting can theoretically produce the strongest results; the problem is air inclusions, and the use of inferior strength alloys because they're the easiest to cast.

Machining, you've generally got a distinct "grain" in the metal (like wood grain) left over from the manufacturing process of making bar stock, which is rolled, drawn, or otherwise extruded.  That also usually means a weaker alloy, one chosen because it's easier to roll/draw, and also to be more machinable.  A lot of the machining alloys have just a touch of sulphur, which makes the steel a little bit "crumbly" (especially at high temperatures).  Obviously of benefit when you're machining, but not so much when you're actually using the end result.  Machinists usually hate working with the really strong steels, because they wear out bits faster.

Forging lets you pick whatever the heck steel you want, and will generally let you control how much of a "grain" the steel picks up, what direction it goes, etc.  But then the problem is it's the most labor-intensive and time-consuming.

[PencilinHand]

Arrkhal typed his response while I was typing mine so there is probably some overlap.

---

EDIT:My apologies to posters mendonca and PMantix as, in the process of reading the thread, grabbing quotes, and constructing this post and then rewriting it(it took me a couple hours) I confused which posts were attributed to which authors.  I have put it in a spoiler so as to remove it from plain sight while preserving it for posterity.  Again, I apologize for words said in error.

Spoiler (click to show/hide)

....
Not sure if this really makes sense or represents fact, but these are my musings. So take them as you will.

...
This is a basic fundamental idea of mechanical engineering (which I happen to have a degree in, btw  )
...

You should be more careful as an engineer.  If you are going to try to lay it out for somebody as an engineer then don't hedge like you know nothing. Give an accurate representation of the facts or say nothing at all to begin with.

...Since weaponry is commonly made of a non-homogeneous material (folded steel)...

Folded steel is homogeneous because the composition is uniform throughout relative to the macroscale(scales relevant to our daily experience).  At very small scales, sub-micrometer scales, almost nothing we deal with on a daily basis is truly homogeneous throughout, but we can ignore this because it only rarely matters.  Wood and fiberglass are not homogeneous on scales that matter to us.  Something like concrete, which isn't strictly speaking homogeneous, can generally be thought of as homogeneous if the mixture is good and the internal aggregate is relatively small compared to the geometry of whatever it is used in, though there are application dependent exceptions.  Fiber reinforced rubber is another example of this.  Note that I am assuming the geometry isn't very complicated because that can open whole other cans of worms.  Practically speaking, for our purposes all metals, stone, and most other materials in DF are homogeneous with the noteworthy exceptions of wood, cloth, silk, and bone(or similar) and in those cases hand waving can be involved.  Bone as a material tends to be very complicated, doctorates have been done on the composition of bone as a material and I am not in any position to elaborate beyond saying it is complicated.

"what combination of properties make folded steel better for weapons than homogeneous steels?" and does this hold true for all weapons

To answer your question about why hand forged steel was used for weapons, it is because steel has a good combination of hardness and strength and the methods of manufacturing steel were conducive to making a blade.  Material selection is often dominated by the ease of manufacture with the properties of a material playing second fiddle.  If you can't make something out of a given material, either because you can't get enough of the material or you can't make it into the shape, then there is little point.

In the specific case of the katana, which I assume you are intending to refer to with your reference to folded steel, the answer is less simple.  For that case I need to split hairs and it will require a little explanation.

The composition of, how it was treated with heat, and how it was forged will all affect the properties of a material like steel.  That is, we call a very wide variety of carbon infused ferrous alloys "steel" but not all of them have exactly the same trace amounts of additives like beryllium, nickle, chromium, to name a few.  This much you know.  But the rate at which a given steel is cooled, reheated, cooled again, and the annealed(kept in a specific temperature range) will cause dramatic changes to the microscopic crystalline structure(not crystaline like this, but like this and this).  Lastly, how steel is worked into its final shape has a similar impact on its properties, this is why many tools, like pliers and wrenches, are made of drop-forged or cold forged steel.  The act of shaping the virgin metal actually "strengthens" the material, to a point.  This page is a pretty good primer for the subject.

For a katana, the steel at the cutting edge of the blade was cooled more quicker so it is harder and takes an edge better but is a little brittle.  While the steel at the back of the blade was cooled a little more slowly so it is softer and capable of absorbing more energy.  Admittedly, I am leaving a lot of stuff out because people literally write books on this and have been for hundreds of years, but I hope this was at least a little enlightening.  If you want to know more, then I suggest you consider getting a degree in metallurgy.

The image you attached shows really nicely how the material stress is affected by a fracture, that white area in the middle is entirely disconnected (by appearances, due to tensile forces, though since it's an intra-substance fracture rather than at the edges, I'm not sure) ...

The fracture size is exaggerated in the example picture given.  The important feature in any fracture(as oppose to a break, a stress fracture, a shear, a puncture, or any other type of failure) is the "radius of curvature" which is a fancy way of saying how angled or sharp the fracture appears.  The smaller and sharper the fracture the higher the stress concentration, though all fractures tend to propagate with cyclic loading.  This can most easily be shown and appreciated by examination of the fracture face.  Smaller defects are a bigger concern than large fractures because major fractures are obvious and it is easy to predict how much load it can take while an initially small fracture will be nearly undetectable until it is too late.  Brittle materials, including some steel alloys, are much more prone to this kind of behavior than more elastic materials.

...or only swords and knives which must be ductile enough to bend slightly under stress without breaking ...

This is...all wrong. 

Ductility, the ability to draw a material out into a wire or deform permanently under tensile stress, has little to do with with the manufacture or use of a bladed weapon.  With regards to manufacturing you are probably thinking of malleability which is the ability of a material to be beaten into a flat sheet or deform permanently under tensile stress, is of relevance but is not unique to steel.  I suspect that what you are thinking of is actually two things young's modulus and the yield strength. 

while still being hard enough to hold an edge and win hardness competitions vs. armor materials?

Hardness is complicated.  Any kind of absolute scale is derived empirically using specific tests, and not from any one fundamental material property.  Furthermore, you can't accurately transform one type of hardness test to another and because of this hardness is relative.  For our purposes we can just say that the hardness of steel is almost ideal for use as a blade.  Any way that Toady decides to work the material property balance in DF for both real and imaginary materials is up to him but I would shy away from a truly accurate real world model.

my expectation is that the layers, having different levels of strength vs various types of destructive force, ought to fare poorly at any specific finite test compared to a weapon made of a homogeneous material specifically suited for that purpose

Force is force.  How it is applied is important.  Generally, a composite material is actually better than any of the component materials by themselves because they were designed to be used for whatever purpose they are functioning in.  See my previous comments about homogeneous materials for other considerations.

(for example, a support cable ought to have tensile and shear strength whereas structural steel needs compression strength and whichever it is that prevents a beam from bowing out sideways due to compression forces)

Comparing a cable to a beam or a column--and yes the distinction is very important--is just not done.  For one thing a cable or rope has no compressive strength to speak of along its axis of use.
Most materials have very similar tensile and compressive strengths with the exception of brittle materials like ceramics which have a higher compressive strength. 

A given beam is almost certain to have equal use for both tensile and compressive strength.  For a simply supported beam, a force down on the top with two supports underneath at either end of the beam,  the top of the beam will be under compression and the bottom will be under tension.  A similar situation will occur if it is a cantilever beam.

A two force member is a member only in tension, such as a rope, chain, cable, or bracket.  These tend to be very strong because when a two force member deflects(is stretched) it tends to get correct any eccentricity in loading. 

A column on the other hand is almost entirely under compressive force which will exaggerate loading eccentricity when it deflects leading to buckling unless the length to width ratio is very very low(3 or 4 to 1).  I can elaborate more if need be.


---
Arrkhal typed his response while I was typing mine so there is probably some overlap.
-------

EDIT: Spelling and what grammar I could find.
Also, given the length of my and Arrkahl's responses I hope everyone can appreciate the complexities of these subjects.

[Arrkhal]

The composition of, how it was treated with heat, and how it was forged will all affect the properties of a material like steel.  That is, we call a very wide variety of carbon infused ferrous alloys "steel" but not all of them have exactly the same trace amounts of additives like beryllium, nickle, chromium, to name a few.  This much you know.

Do you happen to know which elements will migrate between layers when forge-folding?  All's I know is the generalization that of the common alloying elements in modern steels, only carbon will actually migrate and homogenize, the others will stay put (which, as you probably know, is why forge-folded steels can be etched to show a pattern; and the relative ease with which carbon migrates is also what makes blistering and case hardening possible).  But there may be crazy stuff that's generally not present or desirable in modern steels, that does migrate.  I'm fairly sure that phosphorous migrates easily, but that makes steel brittle at low temperatures.

Historically, anyway, the only culture I'm aware of that actually used blending of metal for alloying elements other than carbon, is the Indians.  They figured out eventually that there was something special in their white hematite deposits, and would always include a minimum amount of either that ore, or a piece of old wootz, when making wootz steel.  And as you probably already know, wootz was a fluxed crucible steel, thus it would pretty much never be folded.  No reason to.

The Japanese, on the other hand, folded steel to "purify" it (getting rid of slag), to homogenize the carbon content, and to stretch their supplies of good quality steel.  There's a pretty sharp transition between 0.50% and 0.55% carbon IIRC, so it doesn't take much of an addition to get an enormously better quality blade.

[Noble Digger]

Damn, you're awesome. I'll do my best to respond with my thoughts as I read and pose more questions. Expect meandering.

For starters, I actually studied Katana forging up-down-and-sideways when I was younger and did two research projects in HS. In this case I was more referring to spring- and damascus-style steels which are really just beaten and folded a lot, while not being treated with clay, acid, etc. as the hamon of a Katana would be, or given well-controlled heating and quenching at appropriate times. If a piece were to snap in two, you could look at the grain of the steel and clearly see that there are alternating bands of dissimilar metal in its structure, indicating a hand-folding process repeated fewer than a half-dozen times or whatever.

To give you some background, I've been through metal shop and worked with all manner of cutting tools and different steel and iron alloys, aluminum, titanium, diamond and carbide lathe cutting tools, etc. I have a good sense for how cutting speed affects heat generation and how excess heat can cause discoloration and undesirable work hardening or other undesirable effects. Most of the time you're supposed to take cuts of 2-4 thousandths of an inch and bathe the part in coolant when you're doing machining work, this keeps the part cool--and thus less ductile or malleable--and makes it easier for the cutting tool to chip off a tiny, finite, geometric piece of the metal rather than gashing out a huge gummy chip and leaving blue-and-purple-stained steel behind.

These are effects of how temperature affects the balance between malleability\ductility and "strength" and it's very easy to put this in a macroscopic context: if a piece of thermal plastic is very cold it behaves as a solid, it can shatter and fracture and break and you can etch it with a hard tool very easily. Case in point, bakelite (used for example to make old rotary phones, the ones that can function as a +1 melee weapon). Metals seem to act very much like plastics, or vice-versa. There is a sweet spot in termperature where they have a nice balance between fluidity and strength such that they aren't at excessive risk of breaking but aren't too malleable either. On a macroscopic level this makes perfect sense. It's on the microscopic level where metal bonding takes place that I'm not really sure what is going on. I understand valence, valence electrons, covalent bonding, ionic bonding, electronegativity, etc. but I still can't make sense of what has become of all the electrons in a large chunk of metal, let alone what has become of the electrons shared by two individual metal atoms that are metallically bonded to each other. If I managed to isolate a 2-atom sample of Iron, how might be best to represent them with a diagram?

So... by and by.. I understand it like this, on a microscopic level. One of the nuclear forces is responsible for metal atoms "bonding" to each other and thus, creates a propensity for them to remain in close proximity to one another despite the action of forces that would otherwise separate them if they were not "bonded" (basically, the energy is absorbed by the bonds which flex without breaking) even though they do not share covalent or ionic bonds, they share metallic bonds. However, if the distance between two bonded atoms increases enough, that metal bond is broken and stresses are no longer shared by these two atoms, and this broken bond requires both heat and pressure to re-form, and thus a sword can be re-forged to fix microscopic "tears" like these.


Now I'm gonna go off the wall for a sec, stay with me and even if I'm not using the proper semantics to describe ANY of this, please tell me if my UNDERSTANDING is correct or not. Temperature is a measure of the average energy level of a sample of matter, and isn't measured on a per-atom level, we have no way of doing this and Heisenberg says such an observation would modify the temperature anyway. However, the "temperature" of a single atom can still be thought of as, literally, how energized it is, or how quickly it is spinning. With faster rotation, the atom's effective "size" increases (thermal expansion) as it is rotating faster and its electron field, which acts as the finite boundary at the edge of an atom, is further away from its nucleus. When the atom begins to spin less quickly, the attractive force between its electrons and protons causes the overall "size" of the atom to decrease again, its radius is reduced to a point where its attraction and the centripetal acceleration of its spinning electrons are in relative equilibrium. If attraction and spin forces are in equilibrium the atom simply spins at a fixed size\radius and may be said to be at rest and not experiencing changes. Mostly sound correct?

So, my thought is that the strength of this proton-electron attractive force must not vary with the square of the "distance" between them, as it does in the case of gravitational force. If it did, atoms would reach a certain point in temperature at which it would be impossible for them to cool down, their centripetal acceleration would cause their electrons to fly off and away and the attractive force would grow weaker in response and never have any hope of drawing them back together. Isn't that what's happening in the case of plasma, though? And if so, just what the hell is a metallic bond that it can allow a sample of matter to store SO MUCH ENERGY before undergoing any sort of deformation? If all those atoms are rotating and vibrating, yet the sample maintains a fixed appearance aside from thermal expansion which can be visible, whats going on between them that they almost seem to be attached to each other by springs?

Sorry for my haste in writing these posts and for any perceived "naivety" --I'm very smart but very lazy and had very little patience for the slow pace of Uni when I went. Classes don't give me the chance to stop everyone and ask for clarification when I'm particularly interested or desire a more thorough understanding and I fear this sort of thing--aside from the money part--will keep me out of Uni for as long as I live. Despite this, I never stop craving knowledge and I try to ask as many different people as possible to check for contradictions or parallel understanings with different verbal descriptions!

[Arrkhal]

I think you're confusing how microwaves heat water specifically, with how normal heat/temperature works.

Microwave radiation makes water molecules rotate, which then gets changed into vibration and heat.

Rotation plays some part in temperature, but the vast majority of thermal energy in a solid is in the form of vibration (flexing atomic bonds back and forth), not rotation.  So it's pretty easy to understand why things usually soften at high temperatures.  A chemical bond requires a certain amount of energy to shift or break.  The vibrational energy caused by heat makes the bonds "wiggle," so they're much easier to break or shift by other means.

[mendonca]

http://en.wikipedia.org/wiki/File:Phase_diag_iron_carbon.PNG

You should be more careful as an engineer.  If you are going to try to lay it out for somebody as an engineer then don't hedge like you know nothing. Give an accurate representation of the facts or say nothing at all to begin with.

I'm not sure if this was directed at me, but if so I should apologise.

My wording should have been better, in that I had some schooling some time ago in this subject, however I didn't want to come across as a complete expert as it is possible my understanding had faltered with time.

I take some exception to the statement 'or say nothing at all', whoever it was directed at. The purposes of this forum is discussion. Not statement of scientific fact. Discussion in this respect is a many-way process, in which people on either side are entitled to be wrong or speculative.

[Noble Digger]

Mendocna, he was referring to the 2nd poster who wanted to focus on my use of the word "strength" to refer to the ... strength... of the object. Which is not appropriate in engineering jargon, I believe.

On that note, despite that i dislike quibbles, the fact is that nobody contains within themself a 100.00% accurate picture of the entire universal truth and as such, while some of us are better-equipped than others, we must all admit that we work with our available knowledge and naught else and thus I agree with you that even the very ignorant must converse if they're to improve. The mechanism hereby is in comparing notes with other people, my favorite way of chipping the rock of ignorance away a bit at a time.

Saying something foolish gives others an opportunity to make corrections or adjustments which generally benefits everyone

[mendonca]

Thanks Noble Digger for the clarification. I see now, yes.

Unfortunately as a typical self-centred man the world DOES tend to revolve around me ... but that's a gravity issue not relevant to this thread.

And I like that second paragraph, thems are wise words right there.

[PencilinHand]

Thanks Noble Digger for the clarification. I see now, yes.

Unfortunately as a typical self-centred man the world DOES tend to revolve around me ... but that's a gravity issue not relevant to this thread.

And I like that second paragraph, thems are wise words right there.

My apologies, mendonca.  I will review what I was thinking when I have more time, for the moment I know I did something in error and have put it inside a spoiler tag. 

Noble Digger, I will try to answer/correct your question(s) later.

Arrkhal, as I recall there is an exchange of atoms by diffusion for any two materials regardless of temperature, provided that they are actually in contact with one another.  Generally, though, at room temperatures the rate of exchange is not appreciable for most materials.  I will see if I can elaborate more when I have more time.  For those who are interested there is a good book for this sort of thing, the first 11 chapters should answer most peoples questions.

[Noble Digger]

Hehe, $75 in paperback, I generally spend that much on food over the course of two weeks It must be a very thick volume.

[Kilo24]

So, my thought is that the strength of this proton-electron attractive force must not vary with the square of the "distance" between them, as it does in the case of gravitational force. If it did, atoms would reach a certain point in temperature at which it would be impossible for them to cool down, their centripetal acceleration would cause their electrons to fly off and away and the attractive force would grow weaker in response and never have any hope of drawing them back together. Isn't that what's happening in the case of plasma, though? And if so, just what the hell is a metallic bond that it can allow a sample of matter to store SO MUCH ENERGY before undergoing any sort of deformation? If all those atoms are rotating and vibrating, yet the sample maintains a fixed appearance aside from thermal expansion which can be visible, whats going on between them that they almost seem to be attached to each other by springs?

That's the basics of energy levels on electrons.  The notion that the electrons need no additional energy to stay orbiting at a certain level, else they'd simply collapse into the atom - it's not the traditional gravitational model.

Meh.  I'd be more specific, but I fear that I'm already stretching my memory of the AP Chemistry class that I had ~5 years ago beyond tolerable limits.

Interesting discussion, btw.  Though I'm hardly equipped with the knowledge to comment on it.  If it diversifies into psychology or computer science, I'd be happy to join in.

Hehe, $75 in paperback, I generally spend that much on food over the course of two weeks It must be a very thick volume.

It's a college textbook; they know that, compared to the cost of college tuition, any sub-~$200 figure isn't a big deal for a book if it's required for a class.

[CaptainNitpick]

Unfortunately this phenomenon was believed to be part of the downfall of the titanic. Also as the hull was fully welded, the brittle behaviour of the steel led to a huge rip all the way down the side (the 'wing' of the hull acted like a continuous sheet).

RMS Titanic was riveted, not welded. The first ship with an all-welded hull was Fullagar, launched in 1920.