Understanding how stress is distributed within a mechanical system is a critical aspect of the design process as it provides grounds to assess how a structure will behave during certain operating conditions. Stress concentrations are a major cause of fatigue failures.
It is well known that stress concentration factors around holes in flat plates can be reduced through the addition of a reinforcement typically consisting of an integral boss or stiffening ring, however, determining weight-optimised reinforcement design dimensions quickly and effectively is a key issue as it requires consideration of a large number of potential reinforcement geometries due to stress concentration factor varying dependent on the thickness and diameter of the designed part.
This problem particularly affects the safety critical aerospace industry where additional compont weight is key, as in this case, but is also applicable to many other industries.
Jesmond Engineering used Finite Element Analysis (FEA) technique to model a large number of reinforcement geometries and to illustrate how the stress concentration varies dependent on the thickness and diameter and fillet radius around the reinforcement of hole in a plate loaded in tension. Due to the geometry having 3 planes of symmetry with only one eighth of the overall geometry, modelling was carried out with symmetry constraints applied which significantly reduced the computational time and therefore the cost efficiency of the analysis for the client.
Since weight optimisation is a critical requirement in the aerospace sector, Jesmond Engineering also created design curves in terms of constant added volume.
The FEA results showed that for a range of geometries the notible conclusion is that the maximum stress at the fillet radius can exceed the stress at the hole bore. This effect can generally be avoided by use of a suitably large radius.
The optimum weight studies mapped the thickness and diameter in increments whilst keeping the volume constant. The resulting curves can be utilised to determine the minimum additional weight required to achieve the required reduction in stress concentration factor.
Safety-critical parts that contain reinforced holes can now be designed, optimised and checked quickly and efficiently without need for further FE analysis, thanks to the stress concentration factors developed by Jesmond Engineering. These factors were not previously avaiable in other sources.
