Are metals and metal alloys practically incompressible?
Are metals and metal alloys practically incompressible?
(OP)
I am thinking this is an important concept when it comes to cold forming.
If I bend a piece of sheet stock on a small radius it seems to flow out along the bend axis.
If I do a hardness test on a piece of metal, the ball penetrator forms a crator with some metal flowing up and forming a crater rim. If I do several hardness tests on a small strip, the strip seems to change length and width.
What is the hive consensus on this question?
If I bend a piece of sheet stock on a small radius it seems to flow out along the bend axis.
If I do a hardness test on a piece of metal, the ball penetrator forms a crator with some metal flowing up and forming a crater rim. If I do several hardness tests on a small strip, the strip seems to change length and width.
What is the hive consensus on this question?





RE: Are metals and metal alloys practically incompressible?
Think about it this way: can you change the density of the metal workpiece, no matter what you do with it (temp. changes not included)?
RE: Are metals and metal alloys practically incompressible?
Aaron Tanzer
www.lehightesting.com
RE: Are metals and metal alloys practically incompressible?
Atomic-scale: the atoms in a lattice arrange ideally* in a close packed orientation, and in a best case will occupy a FCC or CCP formation at an efficiency ~74%(occupying as much space as possible)
*single crystal with no defects(ha)
Macro-scale: If you compare metals to other "solids" like a ceramic column or some other porous solid there are clear gaps between the agglomerates making up this solid (ie water on a sidewalk), this would allow for compression, you are not compressing the solid, you are simply pushing the air out.
RE: Are metals and metal alloys practically incompressible?
But the metal still has elastic compressibility...otherwise certain nuclular weapons would not work the way they do.
RE: Are metals and metal alloys practically incompressible?
Solids are compressible to the extent of their Bulk Modulus.
Metalhead
RE: Are metals and metal alloys practically incompressible?
RE: Are metals and metal alloys practically incompressible?
Anyway, thanks for the tips. You guys, as usual, very helpful.
RE: Are metals and metal alloys practically incompressible?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Are metals and metal alloys practically incompressible?
Aaron Tanzer
www.lehightesting.com
RE: Are metals and metal alloys practically incompressible?
RE: Are metals and metal alloys practically incompressible?
Plastic material is generally modeled as incompressible fluid; for incompressibility, Poisson's ratio v = 0.5
But for most metals in the elastic stress range, v = 0.3 or so, indicating that the elastic deformations do not conserve volume.
Not a big deal, but helps account for some funny behavior (like springback, maybe, but we digress, and I've been told that it's a forbidden subject especially if you are just a student) - when you realize that plastic deformations leave residual stresses, which cause the material to be in an elastically deformed state from that residual stress field.
Interestingly, rubber materials generally do behave incompressibly, ie. they are best modelled with v=0.5.
RE: Are metals and metal alloys practically incompressible?
In terms of plastic deformation, unless a change in microstructural phase is induced by that deformation (which can happen with some grades of austenitic stainless steels, for example) the concept of constant volume can be applied in most cases as a good approximation.
Maui
www.EngineeringMetallurgy.com