Adaptive Meshing

Coping with Large Strain and Large Deformation in FEA

One of the challenges of analysing the performance of large strain materials like rubbers and synthetic elastomers is how the finite element mesh distorts as the part deforms. 

You may well start out with a lovely mesh where all your elements meet your quality standards, but as the part distorts the element quality gets worse and worse until it can actually prematurely end the analysis because of excessive distortion, let alone give you poor results.

This is not an uncommon problem. 

You can try re-meshing the part so that the effects of distortion are not so pronounced, but this is incredibly time-consuming as a manually iterative process.  You can try using many smaller elements, but this has a negative impact on the solution time and the computing resources needed to solve the problem.  Some FEA codes use a ‘shuffling’ algorithm where nodes are nudged around to improve the quality at each load increment, but there are limits on what this can achieve.

The best solution would be to start with a new mesh each time it becomes distorted, mapping the strain state from the old mesh to the new mesh and resuming the analysis.  This is exactly what MSC Marc can do. 

There are several ways in which this ‘rezoning’ can be triggered.  You can simply tell Marc to re-mesh every nth increment, or set a criterion which when exceeded triggers a re-mesh.  This could be on strain, distortion or a contact event occurring. 

The example above shows an axi-symmetric model of a bushing being forced into a nominally rigid enclosure.  As the mesh is forced into place Marc is detecting distortion in the elements and re-meshing itself automatically.  This ensures that the results are for a mesh of good quality at all stages of the analysis, increasing the confidence the analyst has in decisions taken as a consequence of the analysis. 

MSC Marc is available within the MSC One Start Edition token license scheme.  This makes available top-flight tools as used by global OEM’s but at a price more suited to the SME user. 

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