1,721,023 research outputs found
Residual stress in geometric features subjected to laser shock peening
No full textThis paper reports selected findings from a collaborative research study into the fundamental understanding of laser shock peening (LSP), when applied to key airframe and aero-engine alloys. The analyses developed include explicit simulations of the peening process together with a simpler eigenstrain approach, which may be used to provide an approximation to the residual stress field in a number of geometries. These are chosen to represent parts of structural components under conditions relevant to service applications. The paper shows that the eigenstrain approach can provide good approximations to the stress field in most circumstances and may provide a computationally efficient tool for exploring different peening strategies. Both explicit and eigenstrain results demonstrate that the interaction between the LSP process and geometric features is important for understanding the subsequent performance of components. Particularly relevant for engineering applications is that not all instances of LSP application may provide an improvement in structural integrity
Prediction of FRP debonding using the global-energy-balance approach
Full text linkA major research programme was carried out to analyse the mechanism of FRP debonding from concrete beams using global-energy-balance approach (GEBA). The analyses developed in the study provide an essential tool that will enable fracture mechanics to be used to determine the load at which FRP plates will debond from concrete beams. This obviates the need for finite element (FE) analyses in situations where reliable details of the interface properties and crack-tip stress fields are not attainable for an accurate analysis. This paper presents an overview of the GEBA analyses that is described in detail elsewhere, and explains the slightly unconventional assumptions made in the analyses
An experimentally validated contour method/eigenstrains hybrid model to incorporate residual stresses in glass structural designs
No full textContour method-based finite element (FE) models together with knowledge of the surface deformation resulted from the stress relaxation along a newly cut plane were used to construct the residual stresses in commercially available float glass. The results show that the residual stress depth profile of float glass is parabolic. The constructed residual stress profiles, validated to some extent against results of scattered-light-polariscope (SCALP) experiments, were then used to establish the misfit strains (i.e. eigenstrains) existed in the original glass specimens. It is shown that, despite the modelling uncertainty of the contour method and the limitations associated with the SCALP measurements, the eigenstrain depth profile in a given float glass specimen can be determined to an acceptable accuracy. The paper shows that once the underlying eigenstrain distribution in a given thickness of glass has been determined, the complete residual stress distribution can simply be determined by incorporating the eigenstrain profile as a misfit strain in an appropriate FE model. It is also shown that the hybrid contour/eigenstrain model enables modelling the residual stress around stress concentration features such as holes and/or stress evolution during subsequent applied loadings, by simply using the knowledge of eigenstrains
Moment-curvature and strain energy of beams with external fiber-reinforced polymer reinforcement
No full textTo calculate the load at which fiber-reinforced polymer (FRP) plates will debond from a reinforced concrete (RC) beam using fracture mechanics principles based on energy release rates, it is necessary to accurately determine the strain energy in the beam. This study presents a moment-curvature model for an RC beam with the presence of a net axial force that is due to the force in the FRP plate. The classical Branson analysis only covers the case of a cracked-elastic concrete beam with no axial force. The paper shows how the model can be extended into the inelastic regime and can be used to determine the moment-curvature relations on loading. Comparisons with the available test data have shown good correlation. The model is then extended into an unloading regime for the strain energy determinations of RC beams with external reinforcement, which may be bonded or partially debonded
Fracture mechanics of plate debonding: experimental validation
No full textPremature plate debonding hampers the efficient use of externally bonded FRP plates for flexural strengthening of concrete beams. Existing research mostly concentrates on finite element (FE) modelling of the concrete–FRP interface but such analyses are of dubious validity because they require far more details than will ever be available for the interface. A fracture-mechanics-based plate debonding model has been developed by the authors; since detailed stress analysis of concrete is unattainable the model is based on the global energy balance of the system. Flaws will inevitability be present in the vicinity of the interface; the model investigates the energy balance when such a flaw propagates. The energy released when the crack extends (GR) is compared with the interface fracture energy required to create the new surfaces GF: If GR > GF the crack will extend causing debonding.Determination of both GR and GF associated with crack extension is not trivial because of the unknowable microstructure of concrete. The early work of the present study developed methods to find both parameters to accuracies sufficient for practical purposes. A modified version of Branson’s model, which takes account of the effects caused by the axial force in the FRP, has been developed for the moment–curvature and subsequent GR analyses, while GF has been determined according to the actual fracture mechanism that takes place in the interface.This paper presents comparisons with a variety of plate debonding test data (including steel plate bonded beams) reported in the literature and shows that the present model can correctly determine both the failure load and the debonding mode. Only simply-supported beams, without additional plate end anchors, under short-term monotonic loads are considered here, but the model could be extendedto analyse more complex practical problems
Assessment of stresses in float and tempered glass using Eigenstrains
No full textResidual stress data determined using the contour method has been used to determine the misfit-strains (i.e., eigenstrains) existent in float glass. Although the uncertainty associated with the results of the contour method analysis may be high the results agree with the residual stress profiles measured using scattered-light-polariscope experiments. The relationship between the eigenstrains and the thickness of glass has been investigated and the results have been validated using scattered-light-polariscopic experiments. The paper shows that the eigenstrain distribution depends on the differential cooling takes place during the manufacturing process. Once the underlying eigenstrain distribution in a given float glass product has been determined this can be used to devise the eigenstrain distribution in tempered glass. It is also shown that eigenstrain analysis can be implemented in finite element models to predict structural response of glass structures thereby to ensure efficient, safe and reliable designs
GFRP reinforced high performance glass–bolted joints: Concept and experimental characterisation
No full textThis paper presents the results of an experimental investigation into the use of externally-bonded Glass Fibre Reinforced Polymer (GFRP) strips as a means of improving the load capacity and delayed failure characteristics of glass-bolted joints. The peak load and the failure behaviour of GFRP reinforced bolted joints in annealed, heat-strengthened and tempered glass were investigated using the experiments of double-lap tension joint configurations. The results were compared with that of reference unreinforced joints, and bolted joints in commercially available laminated-annealed glass. The paper shows that GFRP reinforcement ensured significantly enhanced structural performances of the joints in annealed and heat-strengthened glass. Although the bolted joints in tempered glass showed the highest load capacity, the joints failed with no ductility where tempered glass shattered into small dices
A combined experimental and numerical approach to the investigation of the influence of geometry on residual stresses in structural glass
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