Small damages frequently occur on the metallic skin of an aircraft, e.g. due to run-way debris impact during take-off or aircraft handling. Scratches, nicks and other small damages have a negative effect on structural strength, because of the stress concentrations they introduce. To reduce stress concentrations and obtain a smoother distribution of stress, the skin is reworked, resulting in smooth blends.

ALE has developed a user-friendly tool to quickly assess the stress concentrations caused by blends. The tool consists of a parametric Finite Element (FE) model. Starting from a set of parameters describing blend dimensions (size, depth, smoothness, etc.) and location, the FE model is automatically created, analysed and post-processed. In addition, the effect of multiple blends interacting with each other can be taken into account. Also the presence of a blend at a fastener hole can be included.

The complexity of parametric models rapidly increases with increasing number of parameters. Obviously, the parametric model has to be robust in the sense that it should work for all possible combinations of parameters.

The tool has been validated by comparison to theoretical stress concentration values for circular holes. More than 150 different configurations have been analysed automatically without malfunctioning.