Years ago this test data was donated by a university student who tested this material as part of a class in materials.  It is representative of a broad class of low-carbon, or mild-carbon steels. It is also representative of something that happens quite often in testing - as the test just begins there is some slack in the fixturing, or the test machine. In the image below, we've zoomed in to the origin to better see this slack.  The first few data points are not correct, not representative of the actual stiffness of steel.  Before calibrating this test data, one wants to remove those incorrect data points ("slack removal") and perform a "zero-shift" on the rest of the test data. One major assumption often used is that the load cell can be believed, so no vertical shift of the the data is performed, only a horizontal shifted is performed. 

Our new calibration app in 3DX has a zero-shift capability, and the video below performs this correction for this 1018 steel test data.  Sometimes in the test lab, to avoid this issue of slack in the test system, the operator will impart a small amount of pre-load on the test specimen before zeroing the strain measuring device. This can lead to a related problem in which you want to perform a zero-shift to remove that pre-load.  In either case, the zero-shift tool back-extrapolates from a trusted region of test data points, then performs a strain shift on all of the test data. 
 

The video below was created using a beta version of 2020x FD04.  It shows how to import the test data, use the test data processing tool to clean up the data, and then to perform an elastic-plastic Johnson-Cook calibration.

Here is the raw test data in Excel:

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