Photoelastic evaluation of metallic inserts of optimised shape

A modification of a heuristic method known as ESO (evolutionary structural optimisation method) is introduced for the optimisation of composite pin-loaded joints. The original ESO method is based on finite-element analysis and consists of discarding the lower stressed material of a loaded structure in an incremental stepwise fashion. The modified approach proposed here, consists of changing the properties of highly stressed finite elements around a loaded hole in a stepwise evolutionary fashion, allowing the formation of an insert. This insert provides a localised plastic zone, which reduces the stress concentration on the composite material providing stress relief. The application of this new method to the optimisation of pin-loaded joints has resulted in a large reduction in stress concentration around loaded holes. The prediction of stress-concentration reductions around loaded holes was correlated with mechanical testing, employing photoelastic analysis to determine full strain fields in the vicinity of the loaded hole. The correlation was very successful both in terms of magnitude and patterns of full strain field, proving the potential of this new method.