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Fracture Mechanics

Posted by Andy Woodward on 30-May-2017 11:30:00
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Modelling Cracks the Easy Way

In my previous blog I talked about the advantages of automatic re-meshing in the analysis of rubbers in improving accuracy and stability of a simulation.  One advanced application of this capability that was not touched upon was in the field of crack propagation.

In many industries it is sufficient to use your analysis to predict that a crack could initiate and redesign the part to avoid this occurrence.  In others though it is possible that a crack may be identified from an in-service inspection whereupon it becomes necessary to understand if it will propagate under the loads applied and how quickly so that a replacement can be introduced in a timely manner.

Predicting crack growth in materials with finite elements can seem more art than science.  As an example, in some codes you may need to construct a very precise ‘rosette’ mesh at the crack tip.

Predicting crack growth in materials with finite elements can seem more art than science. 

As an example, in some codes you may need to construct a very precise ‘rosette’ mesh at the crack tip.

A series of angular perturbations to the crack tip node are then simulated to look at the energy release resulting from extending the tip with the assumption being it moves in the direction of the greatest energy release.

In a manual world the crack would then be extended some distance in that direction, the rosette mesh moved and the body meshed around it.  Having done this for an aircraft panel once I know how laborious this can be. 

MSC Marc developers however have automated this, making use of the automatic re-meshing technology in Marc.  Marc detects the direction of growth, moves the crack tip and re-meshes around it iteratively, propagating the crack through the part without human intervention.

Some examples are shown below.

Modelling cracks the easy way - using MSC Marc

 

Modelling Cracks the easy way - MSC Marc gif2

MSC Marc fracture mechanics - Modelling Cracks the Easy Way

This technology is available within the MSC One token system which enables small companies to use the same technology as industry leaders but at an affordable annual cost.

 

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Topics: Various - MSC, MSC Software, FEA, Analysis