Extensometer data vs. tensile strain

[salma424]

I have been trying to use an axial extensometer on instron 5560. The data that I get from using the extensometer shows as "strain 1%" is 20 times more than the actual data that I expect ( the data from crossheads moving which is "tensile strain").
How can I change that?
The gauge length of extensometer is 1 inch. The gauge length of the crossheads is about 1.5-2 inches.

 

[TVP]

Did you calibrate the extensometer? It sounds like the signal for turning voltage in the extensometer into specimen displacement/strain is not calibrated properly.

 

[EdStainless]

What type of extensometer is it?
Is it really meant for these long extensions?

2" is a very short distance between the grips. In elastomers there is very non-uniform deformation near the grips.
Are these straight uniform cross section samples?
Try a longer sample, say 8" between grips to start and see if the two values agree closer.

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Plymouth Tube

 

[blacksmith37]

Not my expertise but; it sounds like mixing crosshead movement with extensometer data. And "gage length" applies to test coupon , not crosshead.