Brittle Materials: Bending Yield Strength

[1350-F]

It seems to me that the ultimate strength of a brittle material can be easily determined by a bending test, but what about the yield? In the brittle regime, I can see how you couldn't, since the sample would fail before it would flow significantly. However, brittle materials can be made to flow a little bit by heating, confining pressure etc. In a hot bending test for example, is there a measure of the yield?

 

[Chestermiller]

Isn't the measure of yield: If you release the loading on the body, it returns to its original shape.

Chet

 

[1350-F]

Isn't the measure of yield: If you release the loading on the body, it returns to its original shape.

Chet

Hmm. I suppose you could do an incremental bending test. ASTM C1161 calls for a constant loading rate. I'll go looking for a standard that includes it.

Thanks.

 

[Astronuc]

It seems to me that the ultimate strength of a brittle material can be easily determined by a bending test, but what about the yield? In the brittle regime, I can see how you couldn't, since the sample would fail before it would flow significantly. However, brittle materials can be made to flow a little bit by heating, confining pressure etc. In a hot bending test for example, is there a measure of the yield?

Most often tensile tests are uniaxial, or biaxial. Heating (increase in temperature) reduces yield strength.

Bend tests are usually performed to assure a certain level of ductility (usually for reasons of formability or performance). What is the purpose of ASTM C1161?

Measurement of yield stress in a bend test can be done, but it is rather complicated compared to a uniaxial test.
http://en.wikipedia.org/wiki/Flexural_strength

 

[1350-F]

Most often tensile tests are uniaxial, or biaxial. Heating (increase in temperature) reduces yield strength.

Bend tests are usually performed to assure a certain level of ductility (usually for reasons of formability or performance). What is the purpose of ASTM C1161?

Measurement of yield stress in a bend test can be done, but it is rather complicated compared to a uniaxial test.
http://en.wikipedia.org/wiki/Flexural_strength

Taking another look at C1161, there's no provision for hot tests. I can see also how finding the yield wouldn't be the point. At the root of my question was: How can I evaluate a yield estimate for a brittle material? I am, like you say, interested in a yield at high temperature which will be lower and at enough confining pressure that the material is likely to flow. I thought there would be some info from the bending test (if it did become ductile at that temp alone) since its fairly common compared to the uniaxial test. Otherwise I thought a hot triaxial test would be appropriate, a sort of creep test under confining pressure.