Cyclic Stress Strain

Tutorial Created with Software Release: 2026-1
Topics: Consumer Packaged Goods, Pharmaceutical Formulations, Polymeric Materials
Methodology: All-Atom Molecular Dynamics
Products Used: Desmond, MS Maestro

Tutorial files

64 MB
This tutorial is written for use with a 3-button mouse with a scroll wheel.
Words found in the Glossary of Terms are shown like this: Workspacethe 3D display area in the center of the main window, where molecular structures are displayed

 

Tip: You can hover over a glossary term to display its definition. You can click on an image to expand it in the page.
Abstract:

 

In this tutorial, you will learn how to use the stress strain calculations and viewer panels to run and analyze cyclic stress strain calculations on a crosslinked polymer.

 

Tutorial Content

  1. Introduction to Cyclic Stress Strain

  1. Creating Projects and Importing Structures

  1. Calculating Cyclic Stress Strain

  1. Analyzing Cyclic Stress Strain Calculations

  1. Performing Free Volume Analyses

  1. Conclusion and References

  1. Glossary of Terms

1. Introduction to Cyclic Stress Strain

Polymers are a critical class of materials central to applications from advanced carbon-fiber composites and structural organics, to semiconductor and electronics manufacture and packaging. Development of next generation polymer systems can be enabled by Schrödinger’s (MS) Materials Science Maestro Suite capabilities for in silico design and analysis of various polymer chemistries. A key characteristic of polymers, polymer fatigue through cyclic loading, can be investigated using the Cyclic Stress Strain feature provided in the Stress Strain panel in MS Maestro. Understanding polymer fatigue can expand the understanding of polymer performance.

The Stress Strain Calculations and Viewer panels allow for the simulation of a polymeric system under stress by applying a series of strains and measuring the resulting stress. ln Schrödinger’s Materials Science (MS) Maestro suite, we run and analyze the stress-strain of a polymeric material following a straightforward workflow as summarized here:

The stress-strain calculations are run as a series of MD simulations in the NVT or lateral NPT ensembles as the strain on the system is increased. The NVT Ensemble class will hold the volume constant and allow the pressure of the unit cell to change as strain is applied on the system. The lateral NPT ensemble class will hold the pressure constant in the lateral directions and allow the volume of the induced strain to change. Naturally pressure causes stress inside the polymer. The stress on a system is calculated as a function of strain. The strain is applied by changing the lattice parameters of the unit cell. Different types of strain can be applied and are defined by increments in the lengths of the unit cell in different directions. Different types of the strain relate the transverse strain increment 2 or 3 to the main axis strain increment =1 where = L/L0. In this definition L represents the main axis along which strain is applied. The main axis can be specified in the initial setting. If the initial length of the main axis is L0, then L is the small linear increment of that length as a result of the strain. It is assumed that the increment L << L0, i.e., it is much smaller compared to the initial length along that axis.

The strain type is defined in terms of parameter , that is known as Poisson’s ratio, according to the expression:

The choices are:

1. Volume conserving uniaxial strain (=0.5): 2=3=-1+1/√(1+1 )  (NVT MD)

2. Increased dilation strain (=0.33): 2=3=-1+1/(1+1 )0.33  (NVT MD)

3. Pure uniaxial strain (=0): 2=3=0 (NVT MD)

4. Isotropic expansion strain (=-1): 2=3= 1  (NVT MD)

5. Constant lateral pressure strain (=0.33): 2=3=-1+1/(1+1 )0.33 (lateral NPT MD)

6. A custom option is also available for -1 < < 0.5

For more information on strain types, please visit the help documentation.

In this tutorial, we investigate the fatigue of a thermoset composite polymeric material consisting of crosslinked N,N,N′,N′-tetraglycidyl-4,4'-diaminodiphenylmethane (TGDDM) and 3,3'-diaminodiphenyl sulfone (3,3-DDS) monomers by applying cyclic loading of the isotropic expansion of the unit cell. We will import an equilibrated crosslinked polymer system which was already built and equilibrated as described in the Crosslinking Polymers tutorial.

For an example of calculating yield point for the same crosslinked system under a non cyclic stress strain simulation, please see the Polymer Property Prediction tutorial.

2. Creating Projects and Importing Structures

At the start of the session, change the file path to your chosen Working Directorythe location where files are saved in MS Maestro to make file navigation easier. Each session in MS Maestro begins with a default Scratch Projecta temporary project in which work is not saved, closing a scratch project removes all current work and begins a new scratch project, which is not saved. An MS Maestro project stores all your data and has a .prj extension. A project may contain numerous entries corresponding to imported structures, as well as the output of modeling-related tasks. Once a project is created, the project is automatically saved each time a change is made.

Structures can be imported directly or from your Working Directorythe location where files are saved using File > Import Structures, and are added to the Entry Lista simplified view of the Project Table that allows you to perform basic operations such as selection and inclusion and Project Tabledisplays the contents of a project and is also an interface for performing operations on selected entries, viewing properties, and organizing structures and data. The Entry Lista simplified view of the Project Table that allows you to perform basic operations such as selection and inclusion is located to the left of the Workspacethe 3D display area in the center of the main window, where molecular structures are displayed. The Project Tabledisplays the contents of a project and is also an interface for performing operations on selected entries, viewing properties, and organizing structures and data can be accessed by Ctrl+T (Cmd+T) or Window > Project Table if you would like to see an expanded view of your project data.

  1. Double-click the Materials Science icon

Figure 2-1. Change Working Directory option.

  1. Go to File > Change Working Directory
  2. Find your directory, and click Choose
  3. Pre-generated files are included for running jobs or examining output. Download the zip file here: schrodinger.com/sites/default/files/s3/release/current/Tutorials/zip/cyclic_stress_strain.zip
  4. After downloading the zip file, unzip the contents in your Working Directorythe location where files are saved for ease of access throughout the tutorial

Figure 2-2. Save Project panel.

  1. Go to File > Save Project As
  2. Change the File name to cyclic_stress_strain_tutorial, click Save
    • The project is now named cyclic_stress_strain_tutorial.prj

Figure 2-3. Importing the crosslinked polymer.

  1. Go to File > Import Structures
  2. Navigate to where you downloaded the tutorial files (presumably your working directory) and choose initial_configuration.cms from the provided files
  3. Click Open
    • A new entry group is added to the entry list containing an entry titled disordered_system_TGDDM_33DDS_all_components_amorphous

Feel free to visualize and stylize the imported structure.

Note: This crosslinked polymer was prepared as detailed in the Crosslinking Polymers tutorial. For practice building crosslinked polymer systems, revisit that tutorial.

3. Calculating Cyclic Stress Strain

In this section, we will use the Stress Strain panel to calculate stress by applying a cyclic strain of the isotropic expansion type on a crosslinked TGDDM-3,3-DDS system. The input system should be a well-relaxed MD output, as we have provided here. We will run three different cyclic stress strain simulations with maximum strains of 4, 8, and 16% on the crosslinked system to investigate fatigue in the system and compare the results based on differences in the maximum strain.

Figure 3-1. Opening the Stress Strain Panel.

  1. Ensure that disordered_system_TGDDM_33DDS_3 is selected(1) the atoms are chosen in the Workspace. These atoms are referred to as "the selection" or "the atom selection". Workspace operations are performed on the selected atoms. (2) The entry is chosen in the Entry List (and Project Table) and the row for the entry is highlighted. Project operations are performed on all selected entries and includedthe entry is represented in the Workspace, the circle in the In column is blue in the entry lista simplified view of the Project Table that allows you to perform basic operations such as selection and inclusion
  2. Go to Tasks > Materials > Classical Mechanics > Stress Strain > Stress Strain Calculations

Figure 3-2. Enabling cyclic stress strain.

  1. For Strain parameters, check Cyclic stress strain
    • Additional Strain parameters appear

Let’s understand the settings and capabilities of the Stress Strain panel a bit more:

  • With respect to the strain parameters:
    • The Strain parameters section defines the parameters for the application of strain to the system
    • Type defines the type of strain to be applied
    • Main axis is the axis along which the strain is applied
    • The Maximum strain steps along with the Step size determines the maximum strain applied to the system: Maximum strain = Maximum strain steps * Step size
    • The Number of cycles determines the number of times we cycle between the maximum and minimum strain value
    • The Half cycle info defines parameters for the cycling of strain application such as the Number of steps of increasing strain and Step size which is the size of the strain increment. The minimum strain applied to the system during the cycling is defined by these parameters: Minimum strain = Maximum strain - (Number of steps * Step size)
  • With respect to the simulation protocols:
    • The Simulation protocols section defines the conditions for the molecular dynamics simulation at each strain value
    • Be cautious when choosing Save intermediate data or Combined trajectory as these options are extremely disk space intensive.
    • Please note that the number of molecular dynamics jobs can be significant and can result in long simulation times. To estimate the total number of molecular dynamics jobs, use the expression as follows: Total number of jobs = Half cycle Number of steps * Number of cycles * 2 + Maximum strain steps
    • To estimate the total simulation time multiply the number of total jobs by the simulations time, i.e.: Total simulation time = Total number of jobs * Simulation time The total simulation time is automatically updated in the panel for default inputs:  
  • Visit the help documentation for a complete summary of the parameters

Figure 3-3. Setting Stress Strain parameters.

  1. For Type, select Isotropic expansion from the drop-down menu
    • The η (eta) value is automatically updated to -1.00
    • For the different Types of strain supported, please visit the thorough help documentation
  2. For Maximum strain steps, enter 10
  3. For Number of cycles, enter 20
  4. For Half cycle info: Number of steps, enter 10
  5. For Step size, enter 0.004
    • The parameters above along with this step size allow us to calculate that the maximum strain the system will be subjected to is 0.04 (or 4%) and the minimum strain is 0.00 (or 0%)
  6. For Simulation protocols, set Simulation time to 50.0 ps
    • At each value of strain, a 50 ps MD simulation will run
  7. Set Trajectory recording interval to 5.0 ps

 

For a more in depth understanding of the Stress Strain panel and the parameters shown here, please visit the help documentation

MD Simulations have a number of files associated with the job, for a full description of each file type see the help documentation on Desmond Files

Figure 3-4. Running the Stress Strain calculation.

  1. Change the Job name to stress_strain_max_4
  2. Adjust the job settings () as needed This job requires a GPU host. The job can be completed in 10 hours on a GPU host
  3. If you would like to run the job yourself, click Run. Otherwise, go to File > Import Structures, navigate to the provided tutorial files and Open  Section_03 > stress_strain_max_4 > stress_strain_max_4-out.cms
  4. Close the Stress Strain panel

Figure 3-5. Viewing the job output.

  1. When the job is finished or after importing, select(1) the atoms are chosen in the Workspace. These atoms are referred to as "the selection" or "the atom selection". Workspace operations are performed on the selected atoms. (2) The entry is chosen in the Entry List (and Project Table) and the row for the entry is highlighted. Project operations are performed on all selected entries and includethe entry is represented in the Workspace, the circle in the In column is blue the new disordered_system_TGDDM_33DDS_3 entry from the MD: disordered_system_TGDDM_33DDS_3_system entry group
    • Feel free to visualize the output system in the workspacethe 3D display area in the center of the main window, where molecular structures are displayed

Figure 3-6. The entry list after importing or running the three stress strain calculations. The Stress Strain calculation with maximum strain of 16% is shown in the workspace.

We will now import the cyclic stress strain calculation with maximum strain of 8 and 16%. If you wish to learn more about how these simulations were run, or run them on your own, see the Optional step below

  1. Go to File > Import Structures, navigate to the provided tutorial files and Open  Section_03 > stress_strain_max_n > stress_strain_max_n-out.cms where n = 8 and 16

 

Optionally: Repeat steps 1 through 13 to run cyclic stress strain simulations with a maximum strain of 8% and 16% respectively. Use the same parameters above with slight modifications:

  • For a maximum strain of 8%: Maximum strain steps = 20, Number of steps = 20, Job name = stress_strain_max_8
  • For a maximum strain of 16%: Maximum strain steps = 40, Number of steps = 40, Job name = stress_strain_max_16

Note that these calculations take a couple of days. Feel free to visualize the output systems in the workspacethe 3D display area in the center of the main window, where molecular structures are displayed

4. Analyzing Cyclic Stress Strain Calculations

In this section, we will analyze the results of the three stress strain calculations run in Section 3. We will first visually investigate the output and then use the Stress Strain Results panel for a more quantitative analysis.

Figure 4-1. Viewing the output for a Stress Strain calculation with maximum strain of 4%.

Let’s visually compare the results of the stress strain simulations at different maximum strains. If you ran the calculations instead of importing, it may be useful to group the entries, as shown in the Figure, to differentiate the three outputs

 

  1. Select(1) the atoms are chosen in the Workspace. These atoms are referred to as "the selection" or "the atom selection". Workspace operations are performed on the selected atoms. (2) The entry is chosen in the Entry List (and Project Table) and the row for the entry is highlighted. Project operations are performed on all selected entries and includethe entry is represented in the Workspace, the circle in the In column is blue the output of the 4% maximum strain simulation

 

Visualize the output in the workspacethe 3D display area in the center of the main window, where molecular structures are displayed. It is difficult to tell if 4% maximum strain induced any serious defects or cracks in the material through visualization only. We will look at more quantitative analyses in just a few steps. First, let’s see the impact of increasing the maximum strain on the crosslinked polymer by viewing all three outputs simultaneously

Figure 4-2. Tiling all the outputs.

  1. Includethe entry is represented in the Workspace, the circle in the In column is blue the output of all three stress strain calculations (Cmd + Click or Ctrl + Click) in the workspacethe 3D display area in the center of the main window, where molecular structures are displayed
  2. Open the Workspace Configuration Panel 
  3. Click on Tile ()
    • The three strained crosslinked systems are tiled in the workspacethe 3D display area in the center of the main window, where molecular structures are displayed

Let’s take a closer look:

 

Maximum Strain: 4%

Maximum Strain: 8%

Maximum Strain: 16%

 

As maximum strain increases, we can see the structure of the crosslinked polymer system begin to separate. There are much larger voids in the simulation run with a maximum strain of 16% compared to that of the 4%. Additionally, the lattice constants (specifically the a, b, and c values displayed on the unit cell) increase with an increase in the maximum strain. Indeed, the cell expands as expected in all directions as the maximum strain is increased.

Figure 4-3. Undoing the workspace tiling all the outputs. The Stress Strain calculation with maximum strain of 4% is shown in the workspace.

Now we will turn to the Stress Strain results panel to extract some quantitative metrics from our simulation:

First, undo the workspace tiling:

  1. Open the Workspace Configuration Panel 
  2. Click on Tile ()
    • The three strained crosslinked systems are no longer tiled in the workspacethe 3D display area in the center of the main window, where molecular structures are displayed
  3. Select(1) the atoms are chosen in the Workspace. These atoms are referred to as "the selection" or "the atom selection". Workspace operations are performed on the selected atoms. (2) The entry is chosen in the Entry List (and Project Table) and the row for the entry is highlighted. Project operations are performed on all selected entries and includethe entry is represented in the Workspace, the circle in the In column is blue the output of the 4% maximum strain simulation

Figure 4-4. Opening the Stress Strain Results panel.

  1. Use the WAM button () to open the Stress Strain Result panel
    • Alternatively, access the panel via Tasks > Materials > Classical Mechanics > Stress Strain > Stress Strain Results
    • The Stress Strain Results panel opens

The Stress Strain Results panel opens with a plot of the effective stress against the effective strain from the 4% maximum strain calculation.

 

Effective strain is estimated according to the expression as follows:

Since the isotropic expansion strain type was selected for this tutorial, strains in all directions are the same resulting in zero effective strain.

Effective stress is calculated based on a similar equation:

The effective stress is relatively small and does not result in any significant damage to the system.

Figure 4-5. Viewing the normal stress and strain.

  1. For a more detailed analysis of the results for Stress type, choose Normal from the drop down menu
    • The Strain component automatically updates to Normal
    • Normal stress is the raw stress value from the simulation. For more on stress and strain types, visit the thorough help documentation

 

In this exercise we focus on the XX normal direction of the stress as the YY and ZZ directions are similar for isotropic expansion. Similarly it is possible to select normal or transverse strain directions which are the same in this example.

The blue and red curves are the normal stress and normal strain as a function of time, respectively. We can gain the most insight into the fatigue of the system by visualizing all three cyclic stress plots simultaneously. We can use the steps above to generate a similar plot for 8 and 16% maximum strain

Let’s take a closer look:

 

 

Maximum Strain: 4%

Maximum Strain: 8%

Maximum Strain: 16%

 

First, let us verify that the calculations proceeded as we expected based on the initial settings. In all three cases the cyclic strain changes from its maximum 4, 8, 16% to its minimum 0 value in cycles. The cycles repeat 20 times as the settings dictate. The total simulation time can be estimated based on the expression introduced in Section 3:

4%: (10*20*2+10)*50 ps = 20,500 ps = 20.5 ns

8%: (20*20*2+20)*50 ps = 41,000 ps = 41 ns

16%: (40*20*2+40)*50 ps = 82,000 ps = 82 ns

The estimated total simulation times correspond well with the plots shown above. 

As the maximum strain is increased, we see a decrease in the stress as the simulation time increases.

Figure 4-6. The Summary tab.

The Summary tab is more telling of the fatigue in the material. Let’s take a look at that now:

  1. Ensure the output of the 4% maximum strain simulation is selected(1) the atoms are chosen in the Workspace. These atoms are referred to as "the selection" or "the atom selection". Workspace operations are performed on the selected atoms. (2) The entry is chosen in the Entry List (and Project Table) and the row for the entry is highlighted. Project operations are performed on all selected entries and includedthe entry is represented in the Workspace, the circle in the In column is blue
  2. Return to the Stress Strain Result panel and click Load Data from Workspace
  3. For Stress type, choose Normal from the drop down menu
  4. Go to the Summary tab

 

Once again, we will view the contents of the summary tab for all three stress strain simulations

The red and yellow curves are the stress at maximum strain and average stress as a function of cycle, respectively.

 

 

Maximum Strain: 4%

Maximum Strain: 8%

Maximum Strain: 16%

 

From these plots, we can say that the system likely did not reach the fatigue point at the 4% and 8% maximum strain simulations because the range of stress values for the yellow and red curves between the two simulations are consistent. At a maximum strain of 16%, the system is fatigued within the first cycle. We can determine this because the stress values for both curves are much lesser than those in the 4 and 8% plots. The material fatigues at some point between the application of 8% and 16% maximum strain.

Based on these results, we could imagine further studies. For example, we could fine-tune our simulations to further explore at what maximum strain the material first fatigues. Additionally, increasing the number of cycles of the 4 and 8% maximum strain simulations could provide more information. It would be interesting to see how many more cycles of straining and relaxing the material can undergo at a lower max strain until it fatigues.

Figure 4-7. The Modulus tab.

Feel free to explore the Viewer panel further. In addition to the Cyclic Stress and Summary tabs, you can also analyze the Modulus of the system as a function of the cycles that represents the derivative of the stress over the strain i.e.:

By viewing the modulus plots of all three simulations, it is clear that the modulus decreases as the maximum strain increases, as expected. 

In the following section, we will perform additional analyses to quantify the impact of the different max strains on the crosslinked system.

  1. Go to the Modulus tab
  2. Close the Stress Strain Viewer

5. Performing Free Volume Analyses

For additional insights, in this section, we will perform Free Volume analyses of the initial system and the outputs of the three stress strain simulations. Free Volume calculations can be performed on the output of our Stress Strain calculations to determine the size and location of the voids in the new strained system. The location and sizes of the voids in the structures are determined by a grid-based method. Analyzing void nucleation between the systems can be helpful in understanding the physical impact of the strain simulations. Here, we will run a free volume calculation on the initial configuration imported in Section 2 as well as the outputs of the three stress strain simulations. For more information on the Free Volume tool visit the Free Volume and Polymer Property Prediction tutorials and the help documentation.

Figure 5-1. Opening the Free Volume Analysis panel.

  1. Select(1) the atoms are chosen in the Workspace. These atoms are referred to as "the selection" or "the atom selection". Workspace operations are performed on the selected atoms. (2) The entry is chosen in the Entry List (and Project Table) and the row for the entry is highlighted. Project operations are performed on all selected entries and includethe entry is represented in the Workspace, the circle in the In column is blue the initial configuration, disordered_system_TGDDM_33DDS_3, imported in Section 2
  2. Go to Tasks > Materials > Tools > Free Volume Calculations

Figure 5-2. Running the Free Volume Analysis.

The default parameters in the panel are sufficient for our examples

 

  1. Change the Job name to free_volume_initial_configuration
  2. Adjust the job settings () as needed
    • This job requires a CPU host. The job can be completed in 5 minutes on a single CPU host
  3. If you would like to run the job yourself, click Run. Otherwise, go to File > Import Structures, navigate to the provided tutorial files and Open Section 05 > free_volume_initial_configuration > free_volume_initial_configuration-freevolume.maegz
  4. Close the Free Volume panel

Figure 5-3. Viewing the output.

  1. When the job is finished or after importing, select(1) the atoms are chosen in the Workspace. These atoms are referred to as "the selection" or "the atom selection". Workspace operations are performed on the selected atoms. (2) The entry is chosen in the Entry List (and Project Table) and the row for the entry is highlighted. Project operations are performed on all selected entries and includethe entry is represented in the Workspace, the circle in the In column is blue the new disordered_system_TGDDM_33DDS_3 entry from the free_volume_initial_configuration-freevolume1 entry group
    • Feel free to visualize the output system in the workspacethe 3D display area in the center of the main window, where molecular structures are displayed
    • Using the Free Volume Results panel, we can display voids in our structure
  2. Repeat the steps above for the 4, 8 and 16% maximum strain simulations

Figure 5-4. Viewing the Free Volume Results panel.

We can visualize the results of the Free Volume calculation using the Free Volume Results panel:

 

  1. Select(1) the atoms are chosen in the Workspace. These atoms are referred to as "the selection" or "the atom selection". Workspace operations are performed on the selected atoms. (2) The entry is chosen in the Entry List (and Project Table) and the row for the entry is highlighted. Project operations are performed on all selected entries and includethe entry is represented in the Workspace, the circle in the In column is blue the output of the free volume calculation on the initial configuration, disordered_system_TGDDM_33DDS_3
  2. Use the WAM button () to open the Free Volume Results panel
    • Alternatively, access the panel via Tasks > Materials > Tools > Free Volume Results
    • The Free Volume Results panel opens

 

For our brief analysis, we are interested in comparing the Free volume percentage across our four Free Volume calculations. For the initial configuration, the Free volume is reported as 0.03%.

We can repeat these steps to obtain the Free Volume for the remaining calculations. We do so and tabulate them below.

Note: If you ran the stress strain simulations yourself then your values here may differ slightly.

The Free Volume Viewer panel has many more features which are explored in the Free Volume and Polymer Property Prediction tutorials.

 

System

Initial Configuration

Maximum Strain: 4%

Maximum Strain: 8%

Maximum Strain: 16%

Free Volume (%)

0.03

0.54

8.24

23.00

 

The percentage of Free volume in the cell increases as the maximum strain applied to the system increases. This correlates well with our visual inspection of the strained cells in Section 4 where there are more and larger cracks as the max strain was increased.

 

Feel free to further explore the capabilities of the Free Volume Viewer panel. A similar brief analysis can be done using the Density Profile Viewer to confirm that as the cell is expanding with more free volume, the density is decreasing with the increase in maximum strain. The functionality of the Density Profile tool is shown in the Building a Polymer-Polymer Interface Model tutorial.

6. Conclusion and References

In this tutorial, we learned how to use the cyclic stress strain feature of the stress strain calculations panel to investigate the fatigue of a crosslinked polymer.

For further learning:

For introductory content, focused on navigating the Schrödinger Materials Science interface, an Introduction to Materials Science Maestro tutorial is available. Please visit the materials science training website for access to 100+ tutorials.

For self-paced, asynchronous, online courses in Materials Science modeling, including access to Schrödinger software, please visit the Schrödinger Online Learning portal on our website.

For some related practice, proceed to explore other relevant tutorials:

For further reading:

7. Glossary of Terms

Entry List - a simplified view of the Project Table that allows you to perform basic operations such as selection and inclusion

Included - the entry is represented in the Workspace, the circle in the In column is blue

Project Table - displays the contents of a project and is also an interface for performing operations on selected entries, viewing properties, and organizing structures and data

Recent actions - This is a list of your recent actions, which you can use to reopen a panel, displayed below the Browse row. (Right-click to delete.)

Scratch Project - a temporary project in which work is not saved, closing a scratch project removes all current work and begins a new scratch project

Selected - (1) the atoms are chosen in the Workspace. These atoms are referred to as "the selection" or "the atom selection". Workspace operations are performed on the selected atoms. (2) The entry is chosen in the Entry List (and Project Table) and the row for the entry is highlighted. Project operations are performed on all selected entries

Thermosetting composite polymeric materials - synthetic materials that strengthen while being heated and cannot be remolded after their initial heat-forming

Working Directory - the location where files are saved

Workspace - the 3D display area in the center of the main window, where molecular structures are displayed