DHR/AR Rheometer: Setting Up an Axial Test

In this topic
Overview
Test Setup

Overview

An Axial test deforms the sample while controlling the vertical motion of the slide. The dynamics of the Axial tests depend on the performance of the motor for the slide motion. Only the speed of the vertical displacement is controlled.

Typical applications for the Axial test are the tack test and strain/stress curves measurements on films and fibers, etc. In a tack test (special probes are available), a constant force (axial force control) is applied to the sample prior to test. Then the sample is deformed by separating the probes at constant speed. The force, as a function of displacement, is measured. Maximum force and adhesion energies can be determined from this test procedure.

Test Setup

To select an Axial test, select Other > Axial from the Procedure tab option. See Using Experimental Procedures for detailed instructions.

When you perform an Axial test, the following parameters need to be chosen.

Environmental Control

Select the following environmental control parameters:

Temperature: The temperature selection to maintain throughout the test. Enter the desired test temperature, or select Inherit set point to maintain the previously-specified temperature at the start of this step. The temperature range is dependent on the configuration of your instrument and the installed environment control system.
Soak time: The amount of time to delay data acquisition at the start of the step, typically to allow for temperature equilibration. This time is measured from the start of the step if Wait for temperature is not selected, or from the point at which the measured temperature becomes stabilized at the specified Temperature, if Wait for temperature is selected. Because of the mass of the sample, test fixtures, and environmental control systems a "soak time" (i.e., time to equilibrate at temperature) is recommended, particularly when starting steps at different temperatures. A five-minute soak time is sufficient for most samples in cases where the change in temperature is not too large. This time is also used at each increment temperature.
Wait for temperature: Select this option to wait until the measured sample temperature reaches the specified temperature before beginning data acquisition. If you wish to begin data collection without waiting for the sample temperature to reach the specified value, disable this option.

Test Parameters

Set up the following test parameters:

Enter the Distance (in µm) or Duration (in seconds) for your experiment.
Select the head direction (Tension or Compression).
Enter the Gap speed. This is the displacement speed of the head in m/s
Enter the Angular velocity. This is the velocity at which the geometry will rotate during the test. NOTE: To keep the geometry stationary, enter a value of zero.

Data Acquisition

Save the image using one of the following options:
1. Save image: Select to store images of the test within the data file for future recall when using the Camera accessory.
2. Save image every: Specify the collection rate for time-based experiments. Select the minimum time in seconds between images. An image is stored with the next test point when the time between images has elapsed.
Select the Fast sampling option, or manually set the data sampling conditions. In the fast sampling mode, data acquisition decreases logarithmically with time.
If fast sampling is not set, data are acquired linearly.
1. Enter the Initial time between samples.
2. If Adjust time between points is selected, the linear sampling rate is adjusted (and time between data points is doubled) after a given number of data points.
3. Enter the Number of points before time changes.

Step Termination

TRIOS Software allows you to define conditions in which a step is halted ahead of its normal termination conditions (Limit checking). You can use this to ensure that, for instance, the instrument does not over speed or apply excessive strains.

Rather than running a step for a certain amount of time, you may wish to run it until stable data is obtained. You can set an Equilibrium limit (such as the viscosity value becoming constant when running a single shear with time) that will stop the currently active test.