peter tilbury Posted October 29, 2009 Share Posted October 29, 2009 Could anybody tell me the difference between plasticity and malleability? The books I have compare elasticity with plasticity and malleability with ductility, but plasticity seems, for a non-engineer like me, to have a lot in common with malleability, so what is the difference. Thanks in advance for any help. 0 Quote Link to comment Share on other sites More sharing options...
JonS Posted October 29, 2009 Share Posted October 29, 2009 Plasticity is a measure of how readily something can be deformed and then will return to it's rest state without damage. For example, squeeze a rubber ball, it will deform, then spring back when the applied force is released. Malleability is a measure of how readily something can be bent without damage. For example, if you have a lump of BluTack and squeeze (or bend) it, it will accept that deformation without breaking. It will not return to it's original state once the force is released. That rubber ball, though, will bounce back to its original shape so therefore it has low malleability. Ductility is a measure of how well a material can be drawn. The usual example is copper, which can be drawn into long thin wires quite readily. If we go back to the BluTack example, you can see that it - too - can be drawn quite readily, and will not return to its original shape once the drawing force is released. Hence Malleability ~ Ductility. Elasticity is a measure of how much something can be stretched and return to its original state. Obviously an elastic band has good elasticity - mount it taut between two fixed points, then stretch it, and it will return to where it was. However, elastic has low ductility because while it can quite easily be drawn, it will snap back to it's original dimensions once the force is released. In summary, BluTack has: Low plasticity (and low elasticity) High Malleability (and high ductility) while Rubber has: High plasticity (and high elasticity) Low malleability ( and low ductility) 0 Quote Link to comment Share on other sites More sharing options...
dieseltaylor Posted October 29, 2009 Share Posted October 29, 2009 Good answer - liked it a lot. 0 Quote Link to comment Share on other sites More sharing options...
peter tilbury Posted October 29, 2009 Author Share Posted October 29, 2009 quote: Plasticity is a measure of how readily something can be deformed and then will return to it's rest state without damage. For example, squeeze a rubber ball, it will deform, then spring back when the applied force is released. Isn't this a definition of elasticity? I've been thinking about this; aren't malleability and ductility merely forms of plasticity? Each taking a different take on the forces involved, compressive for malleability and tensile for ductility? 0 Quote Link to comment Share on other sites More sharing options...
hcrof Posted October 29, 2009 Share Posted October 29, 2009 Plasticity is the ability to be shaped or formed. The rubber ball analogy is perhaps a bit unclear but imagine a coathanger. You can bend it a bit and it will spring back to shape (elastic deformation) or you could bend it a lot and it will stay in the new shape (plastic deformation). The steel is plastic because you can cause lots of plastic deformation without damaging it, indeed you can simply bend it back to its orginal shape should you wish (with some work hardening etc that isnt very relevent here). It is not very maleable because it is not that easy to bend it. The steel is slightly elastic because it will take a little elastic deformation before going plastic. The opposite of plastic is brittle. You can't stretch or bend glass! As mentioned above, malleablity is how easy it is to cause plastic deformation, bluetack is very malleable, steel is not but both exibit plastic properties. Ductility is slightly different because it relates to how easily atoms slide over each other within the metal but I am not such an expert at wires etc so I am sure someone else could give a better answer 0 Quote Link to comment Share on other sites More sharing options...
peter tilbury Posted October 29, 2009 Author Share Posted October 29, 2009 I think the rubber ball analogy is simply wrong. Plasticity as far as I am aware is the ability of a material to undergo deformation when subject to force and to remain in its new shape after the force is removed. That is not the rubber ball. I'm perfectly clear on what ductility and malleability are; it is the relationship with plasticity that concerns me. I think, in fact, I have answered my own question, as malleability and ductility seem to be subdivisions of plasticity. As far as I know, the opposite of brittle is toughness. 0 Quote Link to comment Share on other sites More sharing options...
Thomm Posted October 29, 2009 Share Posted October 29, 2009 IThe opposite of brittle is toughness. The opposite of brittle is ductile. Example: brittle fracture / ductile fracture. Best regards, Thomm 0 Quote Link to comment Share on other sites More sharing options...
Thomm Posted October 29, 2009 Share Posted October 29, 2009 I think the rubber ball analogy is simply wrong. Plasticity as far as I am aware is the ability of a material to undergo deformation when subject to force and to remain in its new shape after the force is removed. That is not the rubber ball. I'm perfectly clear on what ductility and malleability are; it is the relationship with plasticity that concerns me. I think, in fact, I have answered my own question, as malleability and ductility seem to be subdivisions of plasticity. Everything you wrote above is correct. A ductile material can undergo a lot of plastic deformation before it fails. I have never heard or used the word "malleability" in 10 years of academic work, by the way, as opposed to "ductility". Best regards, Thomm 0 Quote Link to comment Share on other sites More sharing options...
peter tilbury Posted October 29, 2009 Author Share Posted October 29, 2009 A ductile material can undergo a lot of plastic deformation before it fails. I have never heard or used the word "malleability" in 10 years of academic work, by the way, as opposed to "ductility". Best regards, Thomm 0 Quote Link to comment Share on other sites More sharing options...
costard Posted October 29, 2009 Share Posted October 29, 2009 snip The opposite of plastic is brittle. You can't stretch or bend glass! snip Glass is a fluid - if you are prepared to wait long enough, it will slump and/or bend. 0 Quote Link to comment Share on other sites More sharing options...
hcrof Posted October 29, 2009 Share Posted October 29, 2009 Glass is a fluid - if you are prepared to wait long enough, it will slump and/or bend. Apparently that is a myth cause by poor glass manufacturing techniques in old buildings. I have no facts or sources apart from wikipedia though I'm afraid. http://en.wikipedia.org/wiki/Glass#Glass_versus_a_supercooled_liquid 0 Quote Link to comment Share on other sites More sharing options...
dieseltaylor Posted October 29, 2009 Share Posted October 29, 2009 Thats the trouble with Wiki - just a quick mention and thats it .... : ) 0 Quote Link to comment Share on other sites More sharing options...
Thomm Posted October 29, 2009 Share Posted October 29, 2009 That problem has been dealt with ... http://dwb.unl.edu/Teacher/NSF/C01/C01Links/www.ualberta.ca/~bderksen/florin.html Best regards, Thomm 0 Quote Link to comment Share on other sites More sharing options...
costard Posted October 30, 2009 Share Posted October 30, 2009 Apparently that is a myth cause by poor glass manufacturing techniques in old buildings. I have no facts or sources apart from wikipedia though I'm afraid. http://en.wikipedia.org/wiki/Glass#Glass_versus_a_supercooled_liquid University of Queensland has an experiment going on in one of the Engineering buidlings - one part is pitch making its way through a funnel, the other is a glass rod held horizontally in a vice. Both experiments have been going for more than fifty years. Both show the fluid nature of the materials. 0 Quote Link to comment Share on other sites More sharing options...
costard Posted October 30, 2009 Share Posted October 30, 2009 That Wikipedia article is factually incorrect: glass wasn't made by spinning the melt, it was floated on molten tin or lead. Spinning the melt is a relatively new idea used in the manufacture of parabolic lenses. 0 Quote Link to comment Share on other sites More sharing options...
Stalins Organ Posted October 30, 2009 Share Posted October 30, 2009 University of Queensland has an experiment going on in one of the Engineering buidlings - one part is pitch making its way through a funnel, the other is a glass rod held horizontally in a vice. Both experiments have been going for more than fifty years. Both show the fluid nature of the materials. And someone did an "art work" where they connected a dozen 50:1 reduction gearboxes (or some such number) in series, put 200 rpm into the 1st one and fixed the output of the last one into concrete... However the definition of a fluid is a state of matter that flows EASILY and readily.....glass does not fit! 0 Quote Link to comment Share on other sites More sharing options...
John Kettler Posted October 30, 2009 Share Posted October 30, 2009 peter tilbury, The definition I learned of malleability in high school science classes (am not an engineer, but my father was a EE, and I spent over a decade in Research & Engineering related military aerospace work) relates directly to its root word malleus, Latin for hammer. I was taught that malleability is the property which allows a metal to be hammered into thin sheets. There, gold is the hands down winner. I was also taught that ductility related to how well a metal could be drawn into thin wires. Here again, gold is a big winner. I particularly like the distinction the Wiki on ductility makes, where it notes that gold is both malleable and ductile, while lead is only malleable. http://en.wikipedia.org/wiki/Ductility This definition, taken from mechanical engineering, takes a somewhat different approach to the problem. http://www.engineersedge.com/material_science/malleability.htm Regards, John Kettler 0 Quote Link to comment Share on other sites More sharing options...
Wilhammer Posted October 30, 2009 Share Posted October 30, 2009 http://www.smp.uq.edu.au/pitch/ "The experiment demonstrates the fluidity and high viscosity of pitch, a derivative of tar once used for waterproofing boats." (I am not an engineer, but stayed at a Holiday Inn a few times!) 0 Quote Link to comment Share on other sites More sharing options...
Thomm Posted October 30, 2009 Share Posted October 30, 2009 Both show the fluid nature of the materials. The correct attribute would be viscous, not fluid, IMHO. Visco-plastic material behavior, e.g., describes a time dependency, even when loading or deformation is kept constant, leading to phenomena like creep (load kept constant, material keeps deforming) and relaxation (deformation kept constant, reaction force is decreasing over time). Best regards, Thomm 0 Quote Link to comment Share on other sites More sharing options...
peter tilbury Posted October 30, 2009 Author Share Posted October 30, 2009 peter tilbury, The definition I learned of malleability in high school science classes (am not an engineer, http://www.engineersedge.com/material_science/malleability.htm Regards, John Kettler Yeah, the link seems to suggest what I have slowly come up with myself. Ductility involves tensile forces and malleability involves compressive forces, but both demonstrate plasticity and therefore malleability is plasticity involving compresseive forces wheras ductility is plasticity involving tensile forces. 0 Quote Link to comment Share on other sites More sharing options...
costard Posted October 30, 2009 Share Posted October 30, 2009 The correct attribute would be viscous, not fluid, IMHO. Visco-plastic material behavior, e.g., describes a time dependency, even when loading or deformation is kept constant, leading to phenomena like creep (load kept constant, material keeps deforming) and relaxation (deformation kept constant, reaction force is decreasing over time). Best regards, Thomm Fair enough - I sit corrected. Thanks Thomm. 0 Quote Link to comment Share on other sites More sharing options...
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