5 ms·

Toughness is a new term for me. From [1]: Hardness is a characteristic of a solid material expressing its resistance to permanent deformation. The Rockwell or

by pcl 10y ago

Toughness is a new term for me. From [1]: Hardness is a characteristic of a solid material expressing its resistance to permanent deformation. The Rockwell or Vickers hardness scales are most commonly used in the industrial blade industry. Toughness on the other hand is the maximum amount of energy a material can absorb before fracturing, which is different than the amount of force that can be applied. Toughness tends to be small for brittle materials, because it is elastic and plastic deformations that allow materials to absorb large amounts of energy. [1] http://americancuttingedge.com/hardness-vs-toughness/ http://americancuttingedge.com/hardness-vs-toughness/

dexwiz 10y ago
There are several material property terms that get mixed around when converting to layman's. Toughness and hardness are two of them. Another set is Plasticity and Elasticity which measure tension properties. Elasticity is how much you can deform (stretch) an object, before the deformation is no longer reversible. Think of a rubber band, you can stretch it a little, and it returns to its original shape. Stretch it a lot, and it breaks down and does not return to its original shape. Plasticity is how much you can deform an object before it breaks. This is the snapping point in the rubber band, where it completely breaks. These two properties are different, and have to do with how the material is deforming on an atomic level. During elastic deformation, the individual bonds stretch. During plastic deformation, regions, layers, or fibers of the material slip. The relationship is best described by the stress-strain curve [1]. This plots deformation versus the pressure required. Hardness and Toughness are the compression version of Elasticity and Plasticity. These properties are often found experimentally, because they are a summation of many different atomic level interactions. Infact most materials are anisotropic, meaning if I measured the toughness of a material along two axises, I would get two different values. [1] https://en.wikipedia.org/wiki/Stress%E2%80%93strain_curve https://en.wikipedia.org/wiki/Stress%E2%80%93strain_curve
- rattray 10y ago
  Thank you for a terrific description! I learned something today.
- 00098345 10y ago
  > Elasticity is how much you can deform (stretch) an object, before the deformation is no longer reversible. Think of a rubber band, you can stretch it a little, and it returns to its original shape. Stretch it a lot, and it breaks down and does not return to its original shape. > Plasticity is how much you can deform an object before it breaks. This is the snapping point in the rubber band, where it completely breaks. These both are completely false. Elasticity is the idealistic property of a solid material to get back to it's original shape after a deformation force is retracted. (property of most solid metals where stress is much below the yield point) Plasticity is the idealistic property of a solid material to stay in the deformed shape after a deformation force is retracted. (Plasticine)
  - ehsanu1 10y ago
    You are correct, but the statement you're quoting can be easily corrected: replace "elasticity" with "The elastic limit of a material". The elastic limit is also conventionally called the "yield strength". "Plastic limit" is not a real term, but if it were, it might be a synonym for "ultimate tensile strength". There's also compressive strength and shear strength.
StavrosK 10y ago
Does this mean that plastic is very tough and hard? Edit: Sorry, not plastic. I meant rubber.
- bearbin 10y ago
  No, plastic can be very tough, but is not generally very hard (although there are exceptions to both). Since plastic can stretch a large amount before breaking it absorbs more energy than a (inverse of tough) object, so it is tough. Since it is easy to stretch inelastically, it is not hard.
  - dragontamer 10y ago
    Plastics are... plastic. Uggghhhhh.... https://en.wikipedia.org/wiki/Plasticity_(physics) https://en.wikipedia.org/wiki/Plasticity_(physics) Usually anyway. IIRC, Acrylic is a plastic that shatters instead of deforming. But most plastics (ABS (aka Legos), polypropylene (PP, #5 Plastic), Pete (most bottles), HDPE (aka cutting boards)) all are "plastic", as in having high plasticity. IIRC, metals are actually more "plastic" (deform more before breaking) than erm... plastics. See iPhone aluminum bending issue for details.
    - jrapdx3 10y ago
      I recall that "plastic" was so named because of the material's formability. Thermoplastics soften or liquefy when heated, becoming malleable and can be molded or extruded, retaining shape when cooled. Thermosetting types are products that are cured by heat, UV or chemical reaction, having high plasticity before curing but irreversible rigidity after. "Plastics" are mostly petrochemical derived organic polymers. Properties of some, like acrylic glazing are relatively hard and brittle, others quite elastic and soft, e.g., foam rubber. Obviously modern life is utterly dependent on these materials which are employed in virtually everything we use from food to space probes. There are good reasons to believe that production of "plastics" is among the highest and best use of petroleum resources, it's a shame we continue burning it up at a prodigious rate. Trends to find alternative energy sources would have benefit in this respect too.
abakker 10y ago
A relevant test for toughness is called the Charpy impact test. It uses a fixed size piece of material and a fixed weight pendulum to snap the material. The amount of force needed to snap the material becomes a score for toughness.
- deleted 10y ago
  [deleted]
- abakker 10y ago
  According to the ASM manual in front of me, toughness is the ability of metal to absorb energy and deform plastic ally before fracturing. The Charpy test is a test of absorbed energy, not force. I misspoke earlier when I said force. I was inadvertently sloppy in my writing.

by pcl 10y ago

dexwiz 10y ago

There are several material property terms that get mixed around when converting to layman's. Toughness and hardness are two of them. Another set is Plasticity and Elasticity which measure tension properties. Elasticity is how much you can deform (stretch) an object, before the deformation is no longer reversible. Think of a rubber band, you can stretch it a little, and it returns to its original shape. Stretch it a lot, and it breaks down and does not return to its original shape. Plasticity is how much you can deform an object before it breaks. This is the snapping point in the rubber band, where it completely breaks. These two properties are different, and have to do with how the material is deforming on an atomic level. During elastic deformation, the individual bonds stretch. During plastic deformation, regions, layers, or fibers of the material slip. The relationship is best described by the stress-strain curve [1]. This plots deformation versus the pressure required. Hardness and Toughness are the compression version of Elasticity and Plasticity. These properties are often found experimentally, because they are a summation of many different atomic level interactions. Infact most materials are anisotropic, meaning if I measured the toughness of a material along two axises, I would get two different values. [1] https://en.wikipedia.org/wiki/Stress%E2%80%93strain_curve https://en.wikipedia.org/wiki/Stress%E2%80%93strain_curve

rattray 10y ago
Thank you for a terrific description! I learned something today.
00098345 10y ago
> Elasticity is how much you can deform (stretch) an object, before the deformation is no longer reversible. Think of a rubber band, you can stretch it a little, and it returns to its original shape. Stretch it a lot, and it breaks down and does not return to its original shape. > Plasticity is how much you can deform an object before it breaks. This is the snapping point in the rubber band, where it completely breaks. These both are completely false. Elasticity is the idealistic property of a solid material to get back to it's original shape after a deformation force is retracted. (property of most solid metals where stress is much below the yield point) Plasticity is the idealistic property of a solid material to stay in the deformed shape after a deformation force is retracted. (Plasticine)
- ehsanu1 10y ago
  You are correct, but the statement you're quoting can be easily corrected: replace "elasticity" with "The elastic limit of a material". The elastic limit is also conventionally called the "yield strength". "Plastic limit" is not a real term, but if it were, it might be a synonym for "ultimate tensile strength". There's also compressive strength and shear strength.

StavrosK 10y ago

Does this mean that plastic is very tough and hard? Edit: Sorry, not plastic. I meant rubber.

bearbin 10y ago
No, plastic can be very tough, but is not generally very hard (although there are exceptions to both). Since plastic can stretch a large amount before breaking it absorbs more energy than a (inverse of tough) object, so it is tough. Since it is easy to stretch inelastically, it is not hard.
- dragontamer 10y ago
  Plastics are... plastic. Uggghhhhh.... https://en.wikipedia.org/wiki/Plasticity_(physics) https://en.wikipedia.org/wiki/Plasticity_(physics) Usually anyway. IIRC, Acrylic is a plastic that shatters instead of deforming. But most plastics (ABS (aka Legos), polypropylene (PP, #5 Plastic), Pete (most bottles), HDPE (aka cutting boards)) all are "plastic", as in having high plasticity. IIRC, metals are actually more "plastic" (deform more before breaking) than erm... plastics. See iPhone aluminum bending issue for details.
  - jrapdx3 10y ago
    I recall that "plastic" was so named because of the material's formability. Thermoplastics soften or liquefy when heated, becoming malleable and can be molded or extruded, retaining shape when cooled. Thermosetting types are products that are cured by heat, UV or chemical reaction, having high plasticity before curing but irreversible rigidity after. "Plastics" are mostly petrochemical derived organic polymers. Properties of some, like acrylic glazing are relatively hard and brittle, others quite elastic and soft, e.g., foam rubber. Obviously modern life is utterly dependent on these materials which are employed in virtually everything we use from food to space probes. There are good reasons to believe that production of "plastics" is among the highest and best use of petroleum resources, it's a shame we continue burning it up at a prodigious rate. Trends to find alternative energy sources would have benefit in this respect too.

abakker 10y ago

A relevant test for toughness is called the Charpy impact test. It uses a fixed size piece of material and a fixed weight pendulum to snap the material. The amount of force needed to snap the material becomes a score for toughness.

deleted 10y ago
[deleted]
abakker 10y ago
According to the ASM manual in front of me, toughness is the ability of metal to absorb energy and deform plastic ally before fracturing. The Charpy test is a test of absorbed energy, not force. I misspoke earlier when I said force. I was inadvertently sloppy in my writing.