Use True or Engineering Strain to calculation Young's E for FEA ?

[SAK123]

Hello,

I am presently involved with measuring the stress strain relationship of a pretensioned sample of fabric material. Needless to say, the strains that I measuring are much larger than typically seen for aluminum and steel.

Since the strains are "larger", it occurred to me that possibly I should be using "true strain" versus stress to calculate Young's modulus. The strains are typically on the order of 3-4%.

Some time ago I recall a person quite knowledgeable in structural mechanics telling me that for large strain measurements the true strain should be used to determine Young's modulus when the modulus is to be used in a large nonlinear finite element computer program such as ABAQUS. I would like a second opinion.

Does anyone have any guidelines as to whether strains of 3-4% are considered large" and require the use of "true strain" measurements versus "engineering strain" measurements?

Thank you for any input.

 

[PamCrash]

Never heard of true strain. What you mean is true stress, force divided by the current section area.

If you are working on a material law and the material experiences 4% you should think about using true stress

 

[Drej]

The (elastic) modulus will be the same regardless. For most metallic materials, if your strains are above 5% (plastic or total strain, it doesn't really matter) then consider converting your curve from engineering stress/strain to true stress/strain. Otherwise, there will be very little difference generally speaking.


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