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  • Open Access

    ARTICLE

    The Numerical Analysis of Reinforced Concrete Beams Using Embedded Discontinuities

    R. Costa1, J. Alfaiate2

    Structural Durability & Health Monitoring, Vol.2, No.1, pp. 11-18, 2006, DOI:10.3970/sdhm.2006.002.011

    Abstract In this paper a numerical simulation is performed on the behaviour of reinforced concrete beams, submitted to initial damage, subsequently strengthened with external steel plates bonded with epoxy. Modelling these structures requires the characterization of the behaviour of different materials as well as the connection between them. Fracture is modelled within the scope of a discrete crack approach, using a formulation in which strong discontinuities are embedded in the finite elements. In this approach, the displacement field is truly discontinuous and the jumps are non-homogeneous within each parent element [Alfaiate, Wells and Sluys (2000)]. More >

  • Open Access

    ARTICLE

    The Theory of Critical Distances: a History and a New Definition

    D.Taylor1

    Structural Durability & Health Monitoring, Vol.2, No.1, pp. 1-10, 2006, DOI:10.3970/sdhm.2006.002.001

    Abstract Current theories of fracture recognize the importance of material length scales, i.e. parameters having the dimensions of length which are included, either explicitly or implicitly, in many methods of fracture prediction. This paper is a review of the development of one particular approach, which we have called the Theory of Critical Distances (TCD). The history of this approach -- which is presented here for the first time - is a story of parallel developments in the areas of fatigue and brittle fracture and in different material fields: metals, polymers, ceramics and composites. A particular milestone in the development of the… More >

  • Open Access

    ARTICLE

    A Frequency Method for Fatigue Life Estimation of Mechanical Components under Bimodal Random Stress Process

    C. Braccesi1, F. Cianetti1, G. Lori1, D. Pioli1

    Structural Durability & Health Monitoring, Vol.1, No.4, pp. 277-290, 2005, DOI:10.3970/sdhm.2005.001.277

    Abstract This paper describes an original frequency method for fatigue life estimation of mechanical components subjected to random inputs. Currently mechanical components life design under random loads is an important task of the research, due to the increasing importance of virtual simulation in opposition to the experimental tests. The frequency domain approach, in this context, seems to be able to supply reliable estimations with small computational effort. The proposed method belongs to the class of corrective coefficient to narrow-band formula methods and it has been thought for bimodal PSDs. The definition of the generalized bimodal processes and the research of the… More >

  • Open Access

    ARTICLE

    Fatigue Resistance of Thin Hard Coated Spur Gears

    S. Baragetti1, A. Terranova2

    Structural Durability & Health Monitoring, Vol.1, No.4, pp. 267-276, 2005, DOI:10.3970/sdhm.2005.001.267

    Abstract Aim of this work is to investigate into the possibility of enhancing the fatigue resistance of CrN PVD coated components. In particular PVD coated spur gears were tested and numerical simulation of crack propagation was carried out. The coating layer micro-hardness and the residual stresses characterising the surface film were measured and the obtained results were introduced in a numerical modelling predicting fatigue life procedure of coated gears used in gearboxes for automotive applications. The number of cycles necessary to reach specified crack depths of coated and uncoated samples was numerically determined and represents a powerful tool to predict fatigue… More >

  • Open Access

    ARTICLE

    Fatigue Crack Growth Behaviour of Nitrided and Shot Peened Specimens

    C. Colombo1, M. Guagliano1,2, L. Vergani1

    Structural Durability & Health Monitoring, Vol.1, No.4, pp. 253-266, 2005, DOI:10.3970/sdhm.2005.001.253

    Abstract In this paper the fatigue crack growth properties of a nitrided and shot-peened steel is dealt with: different peening intensities were considered and the resulting residual stresses measured by means of an X-ray diffractometer. Rotating bending fatigue tests were executed on specimens including a blind micro hole, acting as a pre-existent crack. The fracture surface of broken specimens was observed with a SEM to detect the crack growth initiation point. The run-out specimens were broken after the test and the presence of non-propagating cracks detected. The results allowed to determine the propagation threshold of the nitrided and shot peened material. More >

  • Open Access

    ARTICLE

    Fatigue Resistance of AA2024-T4 Friction Stir welding Joints: Influence of Process Parameters

    L. Fratini1, S. Pasta2

    Structural Durability & Health Monitoring, Vol.1, No.4, pp. 245-252, 2005, DOI:10.3970/sdhm.2005.001.245

    Abstract In the last years friction stir welding (FSW) has reached a quite large diffusion in the welding of aluminium alloys, difficult to be welded with traditional technologies. The objective of this investigation was to investigate the influence of FSW process parameters on the fatigue strength of the developed joints. Moreover, in order to improvement the strength of joint, the effect of a post-welding treatment has been highlighted; what is more a surface finish treatment has been developed with the aim to eliminate the stress concentration caused by welding process on the surface of the joints. Finally, the fracture locations have… More >

  • Open Access

    ARTICLE

    Cohesive Strength and Separation Energy as Characteristic Parameters of Fracture Toughness and Their Relation to Micromechanics

    W. Brocks1

    Structural Durability & Health Monitoring, Vol.1, No.4, pp. 233-244, 2005, DOI:10.3970/sdhm.2005.001.233

    Abstract A review on phenomenological fracture criteria is given, based on the energy balance for cracked bodies, and the respective toughness parameters are related to micromechanical processes. Griffith's idea of introducing a "surface energy" and Barenblatt's concept of a "process zone" ahead of the crack tip build the foundation of modern cohesive models, which have become versatile tools for numerical simulations of crack extension. The cohesive strength and the separation energy used as phenomenological material parameters in these models appear to represent a physically significant characterisation of "fracture toughness". Micromechanical interpretations of these parameters can be derived, depending on the specific… More >

  • Open Access

    ARTICLE

    Structural Integrity Analysis Using the Numerical Green's Function and the Local Boundary Integral Equation Method

    L.S. Miers1, J.C.F. Telles2

    Structural Durability & Health Monitoring, Vol.1, No.3, pp. 225-232, 2005, DOI:10.3970/sdhm.2005.001.225

    Abstract The present paper aims at introducing the concept of Green's function type fundamental solutions (i.e., unit source fundamental solutions satisfying particular boundary conditions) into the context of meshless approaches, particularly dealing with the local boundary integral equation method (LBIE) derived from the classic boundary integral equation procedure. The Green's functions discussed here are mainly the so-called half-plane solution, corresponding to a unit source within a semi-plane bounded by a flux-free straight line and an infinite plane containing internal lines of potential discontinuity. The latter is here introduced in numerical fashion, as an extension of the authors' previous numerical Green's function… More >

  • Open Access

    ARTICLE

    Computational Analysis of Surface and Subsurface Initiated Fatigue Crack Growth due to Contact Loading

    S. Glodež1, B. Aberšek1, G. Fajdiga2, J. Flašker2

    Structural Durability & Health Monitoring, Vol.1, No.3, pp. 215-224, 2005, DOI:10.3970/sdhm.2005.001.215

    Abstract A computational model for simulation of surface and subsurface initiated fatigue crack growth due to contact loading is presented. The model is based on fracture mechanics theory where the required materials properties are obtained from common fatigue tests. For computational simulations an equivalent model of two contacting cylinders is used instead of simulating the actual contact of mechanical elements. The discretised model with the initial crack on or under the surface is then subjected to normal contact pressure, which takes into account the elasto-hydro-dynamic (EHD) lubrication conditions, and tangential loading due to friction between contacting surfaces. The model considers also… More >

  • Open Access

    ARTICLE

    An Improved Wheeler Model for Remaining Life Prediction of Cracked Plate Panels Under Tensile-Compressive Overloading

    A. Rama Ch,ra Murthy1, G.S. Palani1, Nagesh R. Iyer1

    Structural Durability & Health Monitoring, Vol.1, No.3, pp. 203-214, 2005, DOI:10.3970/sdhm.2005.001.203

    Abstract This paper presents an improved Wheeler residual stress model for remaining life prediction of the cracked structural components under variable amplitude loading. The improvement to the Wheeler residual stress model is in two folds. One is expressions for the shaping exponent, which are generally obtained through experiments. Another is calculation of effective plastic zone size to incorporate the sequent effects under tensile-compressive overloading. The remaining life prediction has been carried out by employing the linear elastic fracture mechanics (LEFM) principles. Studies on remaining life prediction of cracked plate panels subjected to tensile-compressive overloading have been carried out for validating the… More >

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