Difference

Date 10-31-2007 16:15

Hello labib, I'll take a stab at that for you, others may have a different interpretation. Toughness and Hardness: toughness is basically the ability of a material to withstand stresses and pressures without compromising it's basic structure, hardness is determined by the degree of penetration a material will allow to it's surface when tested according to Brinnel scale or other means, it can also mean that the material might be suseptible to breakage and cracking when exposed to excessive pressures and stresses. Ductility generally covers a materials ability to be worked and formed without cracking or tearing and Elongation is generally the amount of stretch that a specific material will distort when subjected to a specific bending regimen, it can also be measured as the amount of stretch before fracture and separation under specific conditions. My $.02 Regards, aevald

By Kix

Date 10-31-2007 17:46

Well said aevald. I look at ductility as a materials ability to return to its natural state after subjected to some sort of stress. For example if you start to bend 2 pieces of 2 different metals and then let go see witch one returns to its natural state. The one that returns is ductile and the one that breaks or doesn't come back is not very ductile. Elongation is when you put a piece of metal into tension and try and pull it apart until it breaks and they can measure the % elongation. Then you have elasticity kind of like ductility, pretty much the same thing except you put 2 different pieces of metal into tension and try to pull them apart and see how far you can pull them apart and still get them to return to there original shape. Take two different steel and pull on them a set amount and let go and the one that goes back to it's normal shape is more elastic then one that does not return to it's original shape.
Some examples of tough steels Vs hard steels would be like a bridge and a tooth on a cutting bit. A bridge would require a steel that is going to be tough and a cutting bit would require a steel that is very hard. Have you ever sat on a bridge in traffic and felt how much it moved? They line the beds of the big CAT mining trucks with a very hard abrasive resistant steel so it will hold up to the rock hitting and grinding on it for a very long time.

By Lawrence (*****)

Date 10-31-2007 18:15 Edited 10-31-2007 18:17

Here are some terms I've paraphrased from Hobart Institute weld quality training guide

Ductility:
The ability of metals to be drawn, stretch or twisted without breaking.
The ductility of a material can be expressed as a percentage of elongation.
The percentage is based on the difference between the original length of the material and its final length after subjection to a pulling stress.
To Calculate the percentage of elongation: subtract the original length from the final length; divide the difference by the originl length; then multiply by 100

Elasticity:
Is the ability of a material to return to it's original shape after deformation.

Tensile Strength:
The resistance to breaking offered by metals when subjected to a pulling stress.

Yield strength:
The maximum load per unit area that a material can withstand without being permanently deformed.

Toughness (or Impact Strength):
The ability of a meterial to withstand a sudden, high-load shock at varying material temperatures without failing.

By aevald

Date 10-31-2007 18:39

Hello Lawrence, very nicely put, or "paraphrased" Regards, Allan

By 803056

Date 10-31-2007 21:29 Edited 10-31-2007 21:41

Malleability: ability to be deformed (without fracture).
Ductility: ability to be drawn through a die (as in a wire drawing die)
Elongation: ability to be stretched under a tensile load
Tensile strength: ability to sustain a tensile load (pulling force)
Elasticity: ability to return to the original length after a force has been removed (could be tensile or compressive force).
Toughness: ability to absorb energy. There is dynamic toughness which is measured by the Charpy and Izod tests, and there is static toughness which is the area under the stress strain curve as determined by a reduced section tensile test.
Hardness: the resistance to indentation.

Hard materials are strong materials. The relationship between hardness and tensile strength is a direct relationship, i.e., as the hardness goes up, tensile strength goes up, but the relationship between hardness and ductility is an inverse relationship, i.e., as hardness goes up, ductility goes down. So, As hardness and strength goes up, ductility goes down.

A ductile material typically has good toughness, that is, a ductile material will absorb more energy and fail in a ductile manner, i.e., it displays visible distress before failure. Whereas a hard material that is strong may fail in a brittle manner in that it will not absorb much energy before failing without visible signs of distress. While a malleable material such as lead will not absorb much energy because it isn't ductile as copper or iron in the metallurgical sense.

These are paraphrased definitions as I remember them. I'm on the road and I can't look them up, but you should be able to google the terms as easily as I can. With my memory, I would advise you to google them. ;)

Best regards -Al

By DaveBoyer (*****)

Date 11-01-2007 04:10 Edited 11-01-2007 04:12

Allen's, Lawrence's and Al's definitions are pretty good. "Toughness" can be a little harder to clarify. If starting from dead soft You can increase "toughness" by increasing hardness, as, long as You don't go too far. Like a crowbar is "tougher" than a same size and section of mild steel. After increasing hardness to a point where You are starting to worry about brittle failure, "toughness" increases with a decrease in hardness [tempering hardened material] Impact resistance is like this allso, it depends which end of the spectrum You are looking from.

By js55

Date 11-01-2007 15:21

Not really intending to muddy the waters even more because the definitions offered are very good, but, the very diversity of offerings in this thread demonstrate the problem with definitions of material properties. Verbal definitions allow us to communicate to a limited extent but when it gets right down to it terms such as toughness, tensile strength, ductility, hardness etc., are really just tags identifying the results of a specific mechanical test. Or what science would call an operational definition. Toughness is this because we have devised this particualr test and said that this is the measure of what we call toughness. This can be supported by the fact that the Charpy test has come under recent criticism (or not so recent) as not being indicative of real material properties. And CTOD's are often specified instead. Though I've read where some think CTOD's suffer from the same limitation though they are closer.