Test Phases: The Smallest Unit Of Testing; Control Modes; Control Functions - CellScale UniVert User Manual

Test Phases: The Smallest Unit of Testing

The test phase is the smallest unit of the test specification. There are five phases within a cycle.
Each phase serves a specific purpose:
Preloading- Preloads are applied to bring a test
to a well-defined starting point. Because the
dimensions of a specimen may change as a
result of a loading cycle (stretching of fibers,
viscoelastic effects, plastic deformation, or
localized material failure at the attachment
points), the preload adjustment compensates for
any of these changes in specimen geometry.
Stretching - During the stretch phase, a
deformation is applied to the specimen. The
deformation can be specified either in terms of
force applied or displacement achieved.
Holding - The deformation can be held for a given duration. The duration for which it is
held is dependent on the nature of the testing.
Recovering - The recovery phase is the time during which the force being applied to
the specimen is removed. The duration of the recovery time is configurable and
dependent on the nature of the testing.
Resting - Finally, the rest phase is the time between the end of one cycle and the
beginning of the next. Some tests may specify a short recover time, while others may
specify a longer time. The duration is configurable and dependent on the nature of the
testing.

Control Modes

There are two control modes which define the basic approach to a given test: displacement
control and force control:
Under displacement control, the displacement of the specimen is predefined. The
UniVert stretches or compresses the specimen until the predefined displacement is
achieved. The force required to achieve the displacement is an output of the test.
Under force control, the force applied to the specimen is predefined. The UniVert
stretches or compresses the specimen until the predefined force is achieved. The
displacement required to achieve the force is an output of the test.

Control Functions

The UniVert makes it possible to test specimens under several control functions:
Under displacement control:
The true strain function applies the displacement at a true strain rate, which accounts
for the current specimen length while the specimen is being stretched. The UniVert
system approximates this with a series of linear segments (default = 10).
The ramp function applies the displacement at a constant nominal rate. This is
equivalent to engineering strain or constant velocity.
The sine function applies the displacement according to a sinusoid with the desired
displacement magnitude and duration. The UniVert system approximates this with a
series of linear segments.
UniVert User Manual
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