Simulation and Analysis of the Uniaxial Compression test

This section provides instructions for running a uniaxial compression test simulation in EDEM and post-processing the results using the files provided. The Freeman Uniaxial Powder Tester (UPT) was chosen as a case study.

Introduction

During the test, a powder sample confined in a rigid cylinder undergoes uniaxial compression under a known vertical stress and is subsequently crushed in the unconfined state as shown in Figure 1. The physical responses of interest are the initial packing state, the stress-strain response during confined compression, and unconfined compression strength.



Figure 1. DEM simulation of the Freeman Uniaxial Powder Tester

Prerequisites

The simulation and analysis procedure described in this section requires EDEM version 2022 or later. The Calibration Kit examples are installed in the Altair installation folder > EDEM (version) > examples > Calibration Kits. Copy the Calibration kit and examples to a processing folder before they are configured and run.

The analysis described in this section uses EDEMpy. For more information about EDEMpy, see the EDEM Help documents.

Running Simulations

An EDEM deck is provided for the standard test procedure of the Freeman Uniaxial Powder Tester. Run the deck provided in EDEM and do the following:
  1. Run the simulation till the end.
    The stages of the test described in Figure 1 are modeled using EDEM kinematics controllers as shown in Figure 2.


    Figure 2. Uniaxial compression test piston kinematics

Uniaxial compression tests produce measurements in the quasi-static flow regime where the macro-mechanical behavior of granular materials is independent of the strain rate . Therefore, the compression rate in the provided EDEM deck is accelerated to leverage computational efficiency. If the particle properties or the applied normal stresses in the model change significantly, the compression rate may need to be adjusted to ensure the quasi-static flow regime is maintained. This can be achieved by changing the piston vertical velocity as shown in Figure 2.

Automatic post-processing of results with EDEMpy

You can calculate the physical responses of interest in the uniaxial compression test from the EDEM simulation data using the UCT_analyst_v3.py script provided.

The post-processing script utilizes the EDEMpy library to locate all EDEM decks in the folder containing the script and subfolders. Finally, it generates reports and figures with all the relevant data. The analysis settings for the script are defined in the UCT_analyst_settings.txt file, as shown in Figure 3.


Figure 3. Contents of the UCT_analyst Preference file
You can post-process multiple simulation decks with the script by arranging the files into one of the two configurations as shown in Figure 4. The second configuration is recommended, as it allows for individual settings files for each EDEM deck, and therefore post-processing of different types of tests can be done simultaneously. In the first configuration, a single settings file is read for post-processing all decks.


Figure 4. File configuration for post-processing multiple simulations
To run the UCT_analyst_v3.py script:
  1. Arrange the files as shown in Figure 4.
  2. Open a blank or existing EDEM simulation file, and go to EDEM Analyst > Run > EDEMpy Script.
  3. Go to Select File > Run Script and then select the UCT_analyst_v3.py script.

    Reports and graphs will be generated in the master folder. Individual reports will contain all the relevant data and the summary report will contain only time-averaged results.

    Only complete simulations with the corresponding settings files will be post-processed. Otherwise the script will produce error messages as shown in Figure 5, and then move to the next simulation in the folder tree.
    Note: All simulation files must have unique folder names and simulation names. If the simulation names are identical, the results report will be overwritten.


    Figure 5. Possible error messages

Script Version changes

Version 3 of the UCT analyst script is designed to work with EDEM version 2022.0 (and later) and EDEMpy. This EDEMpy version includes a change where creatordata is indexable, and all references to creatordata have been replaced with creatordata[0].