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[FAQ]

Erosion controls are defined under Analysis Settings. A material element can be eroded (removed) when its geometric strain limit is reached (default 1.5), or when the material in the element fails (default yes), or when the time step controlled by the element reaches a given minimum value (default no). The attached image “analysis_settings.png” shows the typical settings of the erosion controls. The inertia of the eroded material was retained by default, so elements that were eroded away still had their mass continuing to contribute to the results as opposed to just completely removing all traces of the eroded elements because the fragments should still play a part in the outcome predicted. For a typical impact simulation such as a circular cylinder impacting a flat plate, attached three images in pdf file show how the erosion controls affect the outcome of the impact simulation. The first attached image “no_erosion.png” shows the material location plot when all of the erosion controls are set to “No”. You will find that material elements are distorted and the calculation is stopped before the end time is reached due to error messages such as “time step too small” or “degenerate cell”. The second attached image “erosion_mat_failure_yes.png” shows the material location plot when “On Material Failure” is set to “Yes” under erosion controls, where the material elements in failure are eroded away. The calculation runs successfully to the end time. The third attached image “erosion_geom_strain_yes_mat_failure_yes.png” shows the material location plot when both “On Material Failure” and “On Geometric Strain Limit” are set to “Yes” under erosion controls. The “Geometric Strain Limit” is set to much less than the default value. You will find that both the material elements in failure and the material elements that reach the specified geometric strain limit (may not fail yet) are eroded away. Since some material elements that have not failed are eroded away by geometric strain limit, please be aware that material strength will be under-estimated. Thus it is not advisable to use very small geometric strain limit for erosion.