Hard, Soft, Strong, and Tough in material science Watch

Aldian
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Anyone can help me to differentiate between hard, soft, brittle, strong, and tough, in material science. I hope you can give me relationship of that character with yield strength, tensile strength or another specific data. or maybe from stress-strain curve.
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lerjj
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(Original post by Aldian)
Anyone can help me to differentiate between hard, soft, brittle, strong, and tough, in material science. I hope you can give me relationship of that character with yield strength, tensile strength or another specific data. or maybe from stress-strain curve.
I don't do materials science or engineering, so this is probably unhelpful if you're taking a degree in this stuff and open to correction, but:

hard - resistant to scratching and breaking apart. Tested on a scale called the Vickers hardness scale (also more informally on the Mohs scale which compares the hardness of minerals based on what can scratch what)

Soft - opposite of hard

Brittle - how easily something snaps under tensile forces (stretching). Specifically, something is brittle if it's ultimate tensile strength (breaking point) is very close to it's yield point (point at which the material starts stretching a lot)

Strong - generally refers to UTS, or ultimate tensile strength. The amount of stress (force/area) that a material can handle before breaking. In a different context though it might refer to the Young Modulus (how much it stretches) or bulk modulus (same for compression). I'm not sure what this standardly refers to tbh, but it seems most often to imply UTS

Toughness - Not sure. Probably one of UTS, Young Modulus, Bulk modulus, ultimate compressive stress (?) or shear strength maybe.

These qualities are typically correlated because they are all affected by the cohesive forces of a material, but they don't have to be and can be due to other factors such as grain size which won't (I think) affect all of these equally.

Again, not a university student, this might not be very helpful unless you're just interested for the sake of it.
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jimmarshall
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Hardness - Resistance to scratching and pressure. Hardwood does not mark as easily as softwood. Hardness describes how much energy it takes to deform (stretch, compress, bend, etc.) a material.
Strength - Amount of force needed to break a material usually by pushing or pulling down.
Toughness - Resistance to breaking by cracking, opposite to ‘brittle’.
Stiffness - Amount of force needed to change the shape of a material, opposite to flexible.

Hardness is usually defined as resistance to any one of a set of tests, with the most significant one being a scratch test. A substance's brittleness, on the other hand, measures how it reacts to stress, the key property being the degree to which the material can flex in response to applied force - a common test is a three-point bend. A brittle material catastrophically fails with little to no flexure. The force required to bend something a given displacement is a measure of its rigidity.

Hardness is the indenter force divided by projected area of indent and approximately equals 3(strength). Toughness and Fracture toughness measure the resistance of a material to the propagation of a crack. [In Mike Ashby's words]

I looked up the numbers and this is what I found:

Strength and therefore Hardness of-
Diamond- GPa
Glass- MPa

Fracture toughness of-
Natural Diamond: 2 MPa(m)^1/2
Glass(including glass ceramics): 0.5-1.7MPa(m)^1/2
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Aldian
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(Original post by jimmarshall)
Hardness - Resistance to scratching and pressure. Hardwood does not mark as easily as softwood. Hardness describes how much energy it takes to deform (stretch, compress, bend, etc.) a material.
Strength - Amount of force needed to break a material usually by pushing or pulling down.
Toughness - Resistance to breaking by cracking, opposite to ‘brittle’.
Stiffness - Amount of force needed to change the shape of a material, opposite to flexible.

Hardness is usually defined as resistance to any one of a set of tests, with the most significant one being a scratch test. A substance's brittleness, on the other hand, measures how it reacts to stress, the key property being the degree to which the material can flex in response to applied force - a common test is a three-point bend. A brittle material catastrophically fails with little to no flexure. The force required to bend something a given displacement is a measure of its rigidity.

Hardness is the indenter force divided by projected area of indent and approximately equals 3(strength). Toughness and Fracture toughness measure the resistance of a material to the propagation of a crack. [In Mike Ashby's words]

I looked up the numbers and this is what I found:

Strength and therefore Hardness of-
Diamond- GPa
Glass- MPa

Fracture toughness of-
Natural Diamond: 2 MPa(m)^1/2
Glass(including glass ceramics): 0.5-1.7MPa(m)^1/2
Thank You So Much...
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Aldian
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(Original post by lerjj)
I don't do materials science or engineering, so this is probably unhelpful if you're taking a degree in this stuff and open to correction, but:

hard - resistant to scratching and breaking apart. Tested on a scale called the Vickers hardness scale (also more informally on the Mohs scale which compares the hardness of minerals based on what can scratch what)

Soft - opposite of hard

Brittle - how easily something snaps under tensile forces (stretching). Specifically, something is brittle if it's ultimate tensile strength (breaking point) is very close to it's yield point (point at which the material starts stretching a lot)

Strong - generally refers to UTS, or ultimate tensile strength. The amount of stress (force/area) that a material can handle before breaking. In a different context though it might refer to the Young Modulus (how much it stretches) or bulk modulus (same for compression). I'm not sure what this standardly refers to tbh, but it seems most often to imply UTS

Toughness - Not sure. Probably one of UTS, Young Modulus, Bulk modulus, ultimate compressive stress (?) or shear strength maybe.

These qualities are typically correlated because they are all affected by the cohesive forces of a material, but they don't have to be and can be due to other factors such as grain size which won't (I think) affect all of these equally.

Again, not a university student, this might not be very helpful unless you're just interested for the sake of it.
Thank You So Much Mabroo...
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