What if extensometer is not attached directly to gauge length of a tensile specimen instead it is applied at cross head position? What about the accuracy and reliability of yield strength & ultimate tensile strength. Could anyone please provide some references which show the difference in % elongation depending upon the position of extensometer i.e at the guage length or somewhere else?
I think you can reliably determine yield strength, tensile strength and elongation. You may have to analyze the load-displacement data to determine whether load and displacement start increasing linearly from the start or whether the linear regime is delayed. If they do not change linearly feom the beginning, you will have to do regression in the linear region to extrapolate backwards to the initial displacement and then add the x-axis intercept to your displacement data. Tensile strength is easy. You can esti.ate elongation from the data but I would double check by using the old method of bringing the two pieces together and measure the dinal length. A lot of additional work. I hope this helps.
Extensometer position does not influence yield strength and ultimate strength. If fracture occurs outside the position of extensometer, a drop in elongation may occur.
Dear Pardeep Saini
I think the position does not influence your reading. However, you can make a check for the reading at the beginning of the test (must be linear) and the length of the two pieces of the specimen (comparing the elongation with the recorded by the extensometer)
Ultimate Tensile Strength and percentage elongation of the material is not affected by the position of the extensometer .
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