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# Residual Strength Analysis

## Residual Strength Analysis

(OP)
Hi,

I have to perform a residual strength analysis using Nastran and Femap to represent a crack propagation by the energy method.

By a global model of a fuselage, I´m trying to do a submodel.
To do this submodel, I´ve seen that the boundary conditions for this model are forces and moments applied to the interface nodes. These loads represent the load coming from the neighbor structure. To calculate the loads of the boundary, the global FEM, which include the detailed model, is run requesting the grid point forces (GPF) for the interfaces nodes.

Only one node have to be constrained, in order to correlate the external work with the Strain Energy. But, my results are not good, because the displacement of the submodel is not following the Global FEM (stress and displacement) and the stress is concentrating near the contraint.

I´m combinaning pressure, forces and moment to the load case.

Anyone have an idea?

Tks

### RE: Residual Strength Analysis

1) use Abaqus; it can done very easily and automatically
2) its a PITA to do with Nastran

### RE: Residual Strength Analysis

Extract displacements from global FEM and apply in local model

### RE: Residual Strength Analysis

If you also have pressure applied inside the boundary nodes of this model, also apply this pressure in addition to displacements.

Then your stress & displacement plot should be very similar. If it is not, then you need to think about where to spply the GFEM forces and where to apply GFEM displacements. And where to apply pressure..

Spaceship!!
Aerospace Engineer, M.Sc. / Aircraft Stress Engineer

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