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In this study, the residual stress relaxation behaviour occurring during low-cycle fatigue in shot-peened specimens with either a flat or a notched geometry has been studied. A representative low-pressure steam turbine material, FV448, was used. The residual stress and strain hardening profiles caused by shot peening were measured experimentally and were then incorporated into a finite element model. By allowing for both effects of shot peening, the residual stress relaxation behaviour was successfully simulated using this model and correlated well with the experimental data. Although more modelling work may be required to simulate the interaction between shot peening effects and external loads in a range of notched geometries, the model predictions are consistent with the specimens tested in the current study. The novelty of this study lies in the development of such a modelling approach which can be used to effectively simulate the complex interaction between shot peening effects and external loads in notched regions. Compared with the un-notched geometry, the notched geometry was found to be more effective in retaining the improvement in fatigue life resulting from shot peening, by restricting the compressive residual stress relaxation during fatigue loading.

This paper presents a hybrid explicit finite element (FE) /eigenstrain model for predicting the residual stress generated by arrays of adjacent/overlapping laser shock peening (LSP) shots where the use of a completely explicit FE analysis may be impractical. It shows that for a given material, the underlying eigenstrain distribution (in contrast to the resulting stress field) representing a laser shock peen is primarily dependent on the parameters of the laser pulse and the number of overlays rather than the precise component geometry. Consequently the residual stress introduced by complex laser peening treatments can be built up by using static FE models and superposition of individual eigenstrain distributions without recourse to further computationally demanding explicit FE analyses. It is found that beneath a small patch of LSP array the magnitude of the compressive residual stress is higher than for a wider array of LSP shots and that with increasing numbers of layers the compressive stress increases as does the depth of the compressive zone. The model predictions for the eigenstrain distributions are compared well with experimental measurements of plastic strain (full-widthat-half-maximum) obtained by neutron diffraction. The eigenstrain method is also extendedto construct the full residual stress field using measured residual elastic strains at a finite number of measurement locations in a component.

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Exploration of deeper oceans for oil and gas requires increasingly lightweight solutions. A key enabler in this aspect is the use of fiber-reinforced composite materials to replace metals in risers. However, design synthesis and analyses of composite risers are more challenging than for conventional metals due to the complex behavior and damage mechanisms which composite materials exhibit. Composite risers are predicted to be a high-impact technology that will be mainstream in the medium term but there is still relatively little literature pertaining directly to the behavior of these materials under the complex loading scenarios arising from their use in deep water structures. Therefore there is a need to perform a review and assessment of the available technologies and methodologies in the literature to gain a good understanding of their predictive capabilities, efficiency and drawbacks. This article provides a comprehensive review of published research on manufacture, experimental investigations and numerical analyses of composite risers in deepwater conditions determining the gaps and key challenges for the future to increase their application.