Element Deletion

In the steps that follow, we'll use the HIN file to define our criterion for deleting elements. There are two element deletion criteria available for unidirectional materials: TYPE=MATRIX and TYPE=FIBER. Let's take a closer look at each option.

TYPE=MATRIX

For MATRIX element deletion, the only criterion available to use is RELOAD. The RELOAD criterion will delete the element if the stress levels in the element reach a certain magnitude after the matrix has failed. Once matrix failure occurs, σ_vm^t, the von mises stress contribution from the σ₂₂, σ₃₃, σ₁₂, σ₁₃, and σ₂₃ terms is compared to σ_vm, the full von mises stress (including σ₁₁). If the ratio of σ_vm^t to σ_vm exceeds a user specified value, the element is flagged for deletion.

The RELOAD criterion is evaluating the level of the stress tensor in the non-fiber dominated directions. After matrix failure, we want the stiffness in these directions to remain as low as possible (because the matrix is cracked). However, in some cases the stresses can reload due to large strains. The RELOAD criterion can eliminate elements with this behavior so they don't offer significant energetic contributions to the analysis where it is not reasonable.

When using CRIT=RELOAD, you must specify the maximum ratio of σ_vm^t to σ_vm allowable. This is specified on the first data line following the *ELEMENT DELETION keyword. For example:

*ELEMENT DELETION, TYPE=MATRIX, CRIT=RELOAD
0.1

In this case, if σ_vm^t meets or exceeds 10% of the full von mises stress, σ_vm, the element will be deleted.

TYPE=FIBER

For FIBER element deletion, the only criterion available to use is ANY. The ANY criterion indicates that any fiber failure will automatically trigger deletion of the element. For example:

*ELEMENT DELETION, TYPE=FIBER, CRIT=ANY

Back to the Tutorial

For our tutorial, we will control element deletion using the TYPE=FIBER.

Open the HIN file created in the previous step
After the job termination keyword and data lines, add the following:
```
*MATERIAL, NAME=IM7_8552
*ELEMENT DELETION, TYPE=FIBER, CRIT=ANY
```
Save the file

The complete HIN file should now look like:

*JOB TERMINATION, MONITOR=LOAD
0.2, 3

*MATERIAL, NAME=IM7_8552
*ELEMENT DELETION, TYPE=FIBER, CRIT=ANY

Practice

For some additional practice with the element deletion criteria, try using the following settings:

*ELEMENT DELETION, TYPE=MATRIX, CRIT=RELOAD
0.10

*ELEMENT DELETION, TYPE=MATRIX, CRIT=RELOAD
0.05

Tip: Copy the existing input file and HIN file and rename them. Modify the HIN file for each case above and run the analysis. We will explore all of the results later.