The ensuring the structural integrity of ageing aircraft is one of RUAG’s core businesses and is one of the focus points of the structural engineering group. To be able to accurately predict the life of a part the precise calculation of the stress concentrations at potential damage locations is very important. One of the more difficult locations to calculate a stress concentration is around a loaded fastener hole as it depends not only on the through stresses in the part but also on the fastener bearing loads and other factors such as the elastic modulus of the fastener, the thickness of the part or the distance to other fasteners.

The original method to calculate stress concentrations around loaded fastener holes consisted of a number of manual calculations and using the resulting values in different diagrams to come up with the resulting stress concentration at different locations around the hole. This method is very time consuming and error prone even when partially automated using Excel spreadsheets.

The automated solution developed by RUAG makes use of HyperMesh to automatically extract the forces around the hole and transferring them to a local model of the hole surroundings in StressCheck to calculate the stress distribution around the hole.