In engineering strain we are consdering total or intial cross section area while in true strain it is instantaneous one.soif we measure strain using strain gauge then is it a true or engineering strain?
Normally primary data of strain gage ( electric resistance, inductivity or other physical response) are converted in the Relative (engin) strain by the so called strain factor. However, even in real time, it is easy to recalculate in true strain.
It is the engineering strain.
True strain = ln(1 + engineering strain) where ln designates the natural log.
Yes I do agree with Alberta and Mohan, as the true strain is ln(1+engineering strain), no doubt about it.
To extend it further, True stress= (engineering stress) * exp(true strain) = (engineering stress) * (1 + engineering strain)
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Engineering measurements of the attributes of materials are achieved by measuring something else; the results are approximated representations of the phenomenon, stress, strain, torque, pressure, etc. For example, to measure the resistance of a body you apply a force to the body and study its response to the force. Such results lead to speculations on the properties of the body. The results are purely enginerring as Ayob, Mohan, Albert ... have mentioned. In fact, some measurements are valid only for the experimental conditions governing them as real stress or strain depend on physical dimensions, chemical properties ... of the body subjected to the test. The book Materials Under Stress by Gillam (1969) may be helpful. There are certainly newer editions but the principle is the same.
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