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DHR/AR Rheometer: Setting Up an Oscillation Temperature Ramp

In this topic
Overview
Suggested Use
Test Setup

Overview

The oscillation temperature ramp provides information of how a material changes with temperature. In a temperature ramp the temperature is varied continuously. Typically the frequency is a constant, however, multiple frequencies are possible. In this case the different frequencies are executed consecutively. For simultaneous frequency applications, the Multiwave test mode has to be used since the raw data for all are measured at the same time and temperature. Strain, stress amplitude, and phase shift are recorded. The most important application of the temperature ramp test is the measurement of thermal transition in materials or to simulate cure cycles of thermosetting materials such as structural adhesives, powder coatings, etc.

The most characteristic and important thermal transition in amorphous materials is the glass transition. The glass temperature defines the transition from a solid to a melt. The modulus G* can drop by several decades at Tg. At the glass transition, the thermal expansion coefficient changes dramatically. To compensate for the change in sample shape the Axial Force feature needs to be set in a preceding conditioning step.

Suggested Use

Evolving materials are usually characterized under isothermal condition in the time sweep test, however, industrial processes often operate under non-isothermal conditions. In the temperature ramp, the temperature is ramped up and down to simulate cure operations. Important processing parameters to be determined are the viscosity minimum and the gel point. Both parameters are strongly material and process dependent, and are used for material control as well as for process evaluation.

Similar to the time sweep, the Axial Force function adjusts the sample gap to compensate for volume changes due to temperature. Care has to be taken while selecting the strain. Most reactive systems are complex and transition to non-linear behavior at small total strains already.

Test Setup 

To select an Oscillation Temperature Ramp test, see Using Experimental Procedures for detailed instructions.

When you perform an Oscillation Temperature Ramp test, the following parameters need to be chosen.

Environmental Control 

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Test Parameters

Set up the following test parameters:

  1. Select the desired method used to collect your data.
  1. Select between Torque, Stress, Displacement, Strain, or Strain%. This test can be run using either torque/stress or displacement/strain as the controlling variable.

Frequency Sweep Parameters

Four types of frequency sweeps can be run. Choose the desired method from the list below. The available frequency range is dependent on your instrument type and configuration. 

If you want to edit the values already displayed in the table, place the cursor in the table at the desired point and make your editing changes. The entries will be used in order until the first 0.00 entry is encountered, which is recognized as the end of the table.

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Controlled Stress/Strain Advanced

Data Acquisition

There are additional data collection options that can be adjusted to control how data is obtained and what additional information is collected during the measurement. To access these options, click on the “arrow” to display these test fields.  

  1. Select the desired Split data: You can decide how data is to be split during acquisition. This option becomes available if the frequency is to be swept during the test.

  2. Save waveform (point display): Select this option to store a snapshot of the data correlation buffer used for the calculation of the oscillatory data, along within the data file, for future recall. Note that this waveform snapshot is a small subset of the actual data used in the calculation, and can be used to provide insight into the quality of the stress and strain signals used based on the shape of the waveforms and noise levels present.

See Also
Viewing the Point Display

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Controlled Flow

 This is used to superpose a continuous flow onto the oscillation signal (parallel superposition). This option is not available for continuous oscillation in controlled stress and strain mode. Select the flow control below: 

 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.


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