A fracture-mechanics model for debonding of external fibre reinforced polymer plates on reinforced concrete beams

A Fracture-mechanics model for debonding of external fibre reinforced polymer plates on reinforced concrete beams is presented. The conventional methods of concrete-FRP interface analysis use finite element models, which require details of unknown and unknowable interface characteristics. The present model assumes flaws in the vicinity of the interface and assesses whether sufficient energy can be released to cause these flaws to propagate. Energy released by an extension of an existing flaw depends on the change of recoverable energy stored in the system. This paper concentrates on the moment-curvature model for a cracked reinforced-concrete beam under a prestress caused by the force in a FRP plate. The use of the proposed model to determine the energy released from the system with the extension of an existing flaw is also presented. The energy required to create the associated new surfaces depends on interface fracture energy which is first reviewed and methods to determine is also discussed

Fracture mechanics of plate debonding: experimental validation

Premature 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

Fracture mechanics of plate debonding

The study has shown that the phenomena of plate debonding can be studied by means of a fracture-mechanics approach, which obviates the need for a finite element analysis which would have dubious validity in the presence of infinite stress concentrations.It has been necessary to produce a modified form of Branson’s method to allow the calculation of the beam stiffness when the section is partially cracked and when subjected to an axial load imposed by the FRP plate.Hutchinson’s interface breakdown model has proved to be a very useful tool for the study of the debonding of FRP plates from concrete structures. More work remains to be done to study the importance of the various parameters that influence the result. Comparisons with experimental data in the literature are being undertaken

An CFRP fabrics as internal reinforcement in concrete beams

This paper presents preliminary results of an experimental programme that investigated mechanical properties of a balanced-symmetric CFRP fabric laminate. Although FRP fabrics have potential to be formed into efficient reinforcement systems that can enable the development of innovative low embodied energy concrete structures, very little research on applications of FRP fabrics has been reported in the literature. In accordance with the classical laminate theory, in a balanced-symmetric laminate there is no coupling between in-plane deformation and curvature, nor between in-plane normal loading and shear deformation. As a result of the choice of lay-up arrangement the flexural reinforcement systems in concrete beams can be designed by considering the conventional section equilibrium analysi

Mupirocin resistance of <em>Staphylococcus aureus</em> in clinical isolates and nasal carriage isolates

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Residual stress in geometric features subjected to laser shock peening

This 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

Residual stress distribution in a functionally graded alumina-silicon carbide material

Functionally graded ceramic structures have a range of potential applications as they enable the exploitation of two ceramic materials with very different properties, such as coefficient of thermal expansion. We report the microstructural investigation of a novel functionally graded structure for alumina and silicon carbide with systematically varied composition. Stresses in the structure have been modelled analytically and by finite element modelling, and are consistent with fluorescence microscopy measurements of residual stress in the structure