Why Is Proof Stress Important in Material Science?

[uzman1243]

I don't really understand why use proof of stress.

One reason I can come up with is: For materials without a clear distinct yield point, yield strength is stated as stress at which permanent deformation of 0.2% of original dimension will result. (a dictionary definition)

Other than that, why we use proof stress as a measure of yielding in the case of some materials? and how well does it show the material's yielding behavior?

 

[Astronuc]

Yield strength/stress or 'proof stress' allows for some uncertainty in testing. The uncertainty arises from some variation in composition (various elements have a range of content), microstructure, metallurgical state, and testing method.

Many materials are used in their elastic range, well below the elastic limit or yield point.


For more information, see - http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Mechanical/Tensile.htm

Hopefully, I'll be able to dig up some more resources, or others may contribute from their experience.

 

[AlephZero]

For materials that do not have a clear yield point, the idea of "proof stress" is a simple way to test samples of material to check their properties. You apply a load that generates the correct stress level, remove the load, and measure the change in length of the test piece. If it is bigger than 0.2%, the test failed.

That sort of testing was done before there was any mathematical theory of stress and strain. In fact one meaning of "to prove" in English is "to test". For example, guns are tested by firing a "proof charge" which is bigger than the normal amount of explosive, and then checking the dimensions of the gun barrel. This may also create some locked-in plastic stresses in the barrel which improve its resistance to the loads in normal use.

A bit of British history: http://www.gunproof.com/

A similar type of "proof testing" is sometimes done on rotating machinery, where it is deliberately run above its normal operating speed and then checked for the amount of permanent deformation.

 

[satchurated]

The 0.2% yield is a usefull value in maritime industry because allows you to understand how much energy a hull ship or a platform leg can withstand without permanent damage

 

[alphy]

I can understand your confusion about the use of proof stress. Proof stress is a measure of a material's resistance to deformation under stress and is often used to determine the yield strength of a material. This is important because it helps us understand how a material will behave under different levels of stress and can inform decisions about its use in various applications.

One of the main reasons for using proof stress is that it provides a more accurate measure of a material's yielding behavior than simply looking at its yield point. The yield point is the stress at which a material begins to deform permanently, but this can be difficult to determine precisely, especially for materials without a distinct yield point. In contrast, proof stress is defined as the stress at which a specific amount of permanent deformation (usually 0.2% of the original dimension) occurs. This allows for a more consistent and reliable measurement of a material's yielding behavior.

Moreover, proof stress is often used in materials testing and quality control processes to ensure that materials meet certain standards and specifications. By determining the proof stress of a material, we can assess its strength and determine if it is suitable for a particular use.

In summary, proof stress is an important measure in materials science as it provides a more precise and consistent way to determine a material's yielding behavior. Its use allows us to better understand the properties of materials and make informed decisions about their use in various applications.