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Strain Rate in Tensile Testing
2

Strain Rate in Tensile Testing

Strain Rate in Tensile Testing

(OP)
I am looking information on how to calculate strain rate in tensile testing if I only can control crosshead speed.
Thanks

RE: Strain Rate in Tensile Testing

If you can determine the crosshead velocity (v) in/sec, the engineering strain rate for a tensile test is

v/Lo

where Lo is the initial gage length of the specimen.

RE: Strain Rate in Tensile Testing

(OP)
Thanks for your answer but I am looking for a formula that consider the machine stiffness, for example, in order to obtain the actual strain rate over the material

RE: Strain Rate in Tensile Testing

If the machine isn't a few orders of magnitude stiffer than the sample then it isn't suitable.
You should be able to ignore it and consider the frame infinitely stiff.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Strain Rate in Tensile Testing

What ED is saying is true for strain rate. However, for actual strain measurements an extensometer on the specimen is used to eliminate the errors of machine stretch.

RE: Strain Rate in Tensile Testing

Quote (EdStainless)

If the machine isn't a few orders of magnitude stiffer than the sample then it isn't suitable.
You should be able to ignore it and consider the frame infinitely stiff.

What you say may be valid for a standard tensile test, but doesn't apply to all cases. Slow strain rate tensile tests are corrected for machine compliance, as specified in NACE TM0198.

RE: Strain Rate in Tensile Testing

In my slow strain rate experience we monitored the sample optically, so we had actual direct reading of both strain rate and elongation. It was more an issue with the fixtures than the frame.
This is also true in tensile work. The frame should be 1000x as stiff as anything else in the system, but the extensions and grips are another issue.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

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