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  • kf2qd
    replied
    Metal Compression. Flame Hardening brake dies. The flame hardening process is to take a torch(or several) and while moving, heat a section of die to red hot while right behind the heat supply a good flow of water to quench it. A 12ft long die 6"high curled up 3 feet on each end. What i interpret that as is this, the heated area was unable to expand but wound up shrinking when it was cooled. The heat treated are must have had a higher density and shorter length than it did in the original bar.

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  • Noitoen
    replied
    Originally posted by strokersix View Post
    Hot Isostatic Pressing sounds similar?

    Hot Isostatic Pressing is the Application of High Temperature & Pressure to Materials to Enhance Mechanical Properties & Service Reliability. Learn More!

    No, that wasn't it. It was a cube of about 1000mm of aluminium that was removed from a oven that was moved without any special care onto the press and you could see the sides "fattening" up, rotated on one side to press in another direction and again on the remaining side. It was a little deformed when it went into the machine.

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  • strokersix
    replied
    Hot Isostatic Pressing sounds similar?

    Hot Isostatic Pressing is the Application of High Temperature & Pressure to Materials to Enhance Mechanical Properties & Service Reliability. Learn More!


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  • Noitoen
    replied
    A long tome ago, I saw a video on TV that I tried to find online about the building of a Atmospheric Diving Suit. The main portion was machined out of a huge block of aluminium that was removed from an oven and put in a giant hydraulic press and squeezed on all 3 axis before being loaded into and ancient CNC mill to carve the main body of the suit. I don't recall they mentioning a reason for the press procedure but I could clearly see the difference in shape of the block before and after the pressing.

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  • Paul Alciatore
    replied
    Well, YES.

    From my post Albums above;

    The compression of a metal (uranium 235) is one of the mechanisms for triggering an atomic explosion. To achieve that actual compression explosive charges completely surround a spherical, uranium core and a large number of detonators are simultaneously triggered on the outside of these explosive charges to produce a very symmetric shock wave toward that inner uranium core. That compression of the U235 raises the number of neutrons per unit volume above the critical point and fission proceeds. The number of neutrons flying around inside the U235 remains the same but the volume is reduced. BTW, those charges and the trigger circuitry are the hard parts of building an A-bomb after the U235 isotope is produced.
    It also works with plutonium.

    The point is, metals can be and actually are compressed. Sometimes with spectacular results.



    Originally posted by fjk View Post
    FWIW I seem to recall that nuclear bombs compress their nuclear fuel (blobs of uranium or plutonium) to make it reach critical mass/density/etc…

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  • fjk
    replied
    FWIW I seem to recall that nuclear bombs compress their nuclear fuel (blobs of uranium or plutonium) to make it reach critical mass/density/etc…

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  • Paul Alciatore
    replied
    Picky, picky, picky!

    I am not going to go back and edit my post yet again. I think everybody got the idea.



    Originally posted by Lee Cordochorea View Post

    Friendly reminder: there are no molecules in a pure metal, only atoms. Steel will have carbides and inclusions, but the iron atoms are in a crystal lattice, not a molecule.

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  • J Tiers
    replied
    Originally posted by tomato coupe View Post

    It won't shrink. It will get stretched out and pulled apart by the gravitational gradient.
    From what I have read about "black holes", that's true with regard to the process of entering one. But the bits and pieces would seem to have to end up occupying less space and being denser........... At least "space" as measured out here, which does not seem to translate well.........

    That was going to be the argument..... that since density is huge in a black hole, everything is compressible, and so there would seem to be a mix of compression and deformation in the original question.

    The counter argument is that "structure" is changed on the way in, so no material makes it in as what it originally was.
    Last edited by J Tiers; 05-31-2022, 11:55 PM.

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  • Lee Cordochorea
    replied
    Originally posted by boslab View Post
    What if your micrometer were sucked into a black hole, I reckon it would shrink, I jest btw
    mark
    That happens every time I clean the shop.

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  • tomato coupe
    replied
    Originally posted by boslab View Post
    What if your micrometer were sucked into a black hole, I reckon it would shrink, I jest btw
    mark
    It won't shrink. It will get stretched out and pulled apart by the gravitational gradient.

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  • boslab
    replied
    What if your micrometer were sucked into a black hole, I reckon it would shrink, I jest btw
    mark

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  • Lee Cordochorea
    replied
    Molecules can rearrange themselves. And different arrangements can have different volumes.
    Friendly reminder: there are no molecules in a pure metal, only atoms. Steel will have carbides and inclusions, but the iron atoms are in a crystal lattice, not a molecule.

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  • J Tiers
    replied
    As far as I know, there is no material that does not compress, i.e. reduce in volume/increase in density if pressure is applied to it on all sides. People would be very interested in any material which truly did not compress at all, under any circumstance

    If it compresses at all, it compresses to some degree at essentially any pressure (although it may be impossible to measure at low pressures). If that is true, then when pressure is applied to the top and bottom of a solid sample, with the sides unconstrained, there must be a mixed effect with some displacement, and some volume reduction.
    Last edited by J Tiers; 05-31-2022, 10:44 AM.

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  • Paul Alciatore
    replied
    Molecules can rearrange themselves. And different arrangements can have different volumes. Take water as an example. Water's volume decreases (it's density increases) as the temperature is lowered until you reach 4 degrees C. Then, the molecules rearrange themselves and they suddenly start to take up MORE volume. This if while it is still a liquid. The density change has undergone a reversal and just before freezing at 0 degrees C it is back to about the same density it had at about 8 or 9 degrees C. But then when it reaches the freezing point there is another rearrangement of those molecules and the density drops by almost 10%. This not only explains why ice floats on the top of water, but it also explains why only the top of a lake or pond freezes while the water below that layer of ice stays in the liquid state. Then, as the temperature drops even more, the density, once again increases. All of this is at a pressure of about 1 atmosphere and pressure does have an effect on this.

    Perhaps carbon is a better example in that it can exist in different molecular arrangements at room temperature. Amorphous carbon has a density of about 1.8–2.1 g/cm3 while graphite is 2.267 g/cm3. But wait, diamond is way up there at 3.515 g/cm3, And pressure is one way to create diamond from the other forms of carbon. When the other forms of carbon become diamond, then the density increases and the volume DECREASES. So, YES, the volume can definitely decrease or increase depending on the molecular arrangement of the atoms and/or molecules.

    When you are talking about changes in density under different circumstances, there is more than one physical process going on. Thus a change in volume across the three dimensions is not a simple thing to explain or to write an equation for. And a first order approximation may be very useful for many purposes even if it is not the ultimate explanation.

    In contrast to what many people think, science is NEVER exact. There is always room for additional refinements. This is something that is often lost on many people and, strangely enough, that includes many scientists.



    Originally posted by Bob Engelhardt View Post
    The Poisson effect compression vs compression defined by the bulk modulus has me confused. The 0.001" strain on my 1" steel cube example produced a Poisson effect volume reduction of 0.0004 cu-in. That 0.001 strain would require (30 x 10^6) x 0.001/1.0 pounds stress (elastic modulus) = 30,000 lbf. To achieve a compression of 0.0004 cu-in with pressure on all sides, would require 25 x 10^6 psi (bulk modulus) x 0.0004/1.0 = 10,000 lbf.

    Well, I guess that pushing on all sides takes less force than pushing on one side is not that confusing. What is still confusing is how the Poisson effect causes a reduction in volume at all. The material is elastic and unconstrained in 2 axes - why doesn't it just spread out without compression? The forces resisting deformation are greater than the forces resisting compression?

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  • Paul Alciatore
    replied
    The math I am seeing on this subject definitely involves approximations. They are at least partially justified by the fact that more than one physical process is taking place and even the more correct volume calculations that you are urging will still not produce exact results.



    Originally posted by Bob Engelhardt View Post

    The fundamental problem here is that you are summing linear values and using the result as a cubic. Length PLUS width PLUS height does not equal volume.

    If L,W,H are the initial dimensions, "v" the P-R, and "s" the strain in the length axis, then the correct equation for the change in volume is:

    L x W x H - (L-s) x (W + v x s) x (H + v x s)

    which is really messy and will include terms with L x H, W x H, L x W, & L, W, H. Not just the 3 strains.

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