Strain Rate (Adaptive)

Metals test type only. Outer loop strain rate control while in position control. It is a strain pacing technique that remains active throughout the ramp in which it applies. An outer loop software algorithm monitors the current data stream within Bluehill and alters the position rate to achieve a user defined tensile strain rate as determined from the tensile strain sensor in Bluehill.

Strain rate (Adaptive) requires an extensometer attached to the specimen throughout the ramp in which the mode is specified. In the event that the strain exceeds the maximum limit of the extensometer during the test, the mode defaults to Straining rate and uses a fixed crosshead speed. Strain rate (Adaptive) mode of control differs from Straining rate in that the crosshead speed constantly updates to maintain the demanded strain rate. Straining rate calculates a single position rate based on the target strain rate and the gauge (parallel) length of the specimen. This rate remains constant throughout the entire ramp.

Strain rate (Adaptive) mode differs from Straining Rate in that you enter the target strain rate directly, rather than having Bluehill calculate the target strain rate. However, the standards often require that metals testing operate within specified stress rate limits. As a result, you must manually calculate the stress rate after testing to verify that the test(s) complied with the standard requirements.

Since Strain rate (Adaptive) uses a strain pacing algorithm, it is not a true strain control mode (i.e. responding directly to feedback from the strain device) and thus you should check your data to confirm that it complies with the stress requirements of the standard to which you are testing. Determine the stress/time curve and calculate the linear portion of the curve to verify that the test(s) stayed within the stress rate requirements of the standard.

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