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I'm trying to figure out how to remember that

  • hardness: how resistant it is to deformation
  • toughness: how resistant it is to brittle failures
  • stress: force on a surface area
  • strength: ability to withstand stress without failure
  • strain: measurement of deformation of a material

Does anyone know of a mnemonic or easy way? I only know these from googling them, and I'm finding it tricky to remember them.

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Note that this is really language dependent, without your definitions I would not be able to translate and understand them, even tough I know the differences (in French) :p –  Cedric H. Nov 2 '10 at 23:11
    
Yes I suppose, I'm looking for English definitions. I speak a tiny bit of German, but not enough to understand or translate these definitions. –  Thomas O Nov 2 '10 at 23:27
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2 Answers

up vote 2 down vote accepted

I always used to confuse stress and strain: most of my mnemonics involved making words out of initial letters.

When you're stressed, you show the strain.

Stress is what is applied to the material, strain is what it does in response - I always used to get these the wrong way around.

E equals Fl/ea

Young's Modulus = (force × length) / (extension × area)

Good luck with the others: I suggest imagining a hard man (grizzled veteran) who is actually secretly limp wristed and camp (he bends unlike hard materials), a tough guy (showy, probably with twin pistols) who literally goes to pieces in difficult situations (imagine his brittle bones snapping) and a strong man (lifting a dumbbell) who is crushed to a pancake by the weight.

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I would suggest learning about some of the formulas relating them - that way you're not just memorizing things but actually have some grasp of what goes into them. In particular, I only really know about stress and strain, and it's because I think of them as being the analogue in linear elasticity theory of "force" and "displacement" in Hooke's law.

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