Fracture-damage

[IvarStefansson]

Proposed changes

Functionality for computing history-dependent damage for fracture mechanics.
Main functionality

• New variable and equation in models.fracture_damage.
• New constitutive laws for friction and shear dilation.
• Ad function for computing 1/val, where val may contain zeros. This function may need improvements.
• Example with complete classes, also used for testing.

Please consider naming of new files, classes and methods inside during review. Also search for new todos, these should be resolved during the PR.

Note that a skipped test (slow) was added. Thus, we must remember to run the full suite before merging.

Types of changes

What types of changes does this PR introduce to PorePy?
Put an x in the boxes that apply.

• Minor change (e.g., dependency bumps, broken links).
• Bugfix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as expected).
• Testing (contribution related to testing of existing or new functionality).
• Documentation (contribution related to adding, improving, or fixing documentation).
• Maintenance (e.g., improve logic and performance, remove obsolete code).
• Other:

Checklist

Put an x in the boxes that apply or explain briefly why the box is not relevant.

• The documentation is up-to-date.
• Static typing is included in the update.
• This PR does not duplicate existing functionality.
• The update is covered by the test suite (including tests added in the PR).
• If new skipped tests have been introduced in this PR, pytest was run with the --run-skipped flag.