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  • Open Access


    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


    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


    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


    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


    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


    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 >

  • Open Access


    Cyclic plasticity and damage of a metal matrix composite by a gradient-enhanced CDM model

    G. Minak1, F. E. G. Chimisso2, H. S. Costa Mattos3

    Structural Durability & Health Monitoring, Vol.1, No.3, pp. 193-202, 2005, DOI:10.3970/sdhm.2005.001.193

    Abstract Cyclic plasticity and damage of a metal matrix composite have been studied in the framework of continuum damage mechanics. The material was considered as macroscopically homogeneous and a model incorporating damage gradient was applied. Strain-controlled fully reversed low-cycle fatigue uniaxial tests were performed to identify material parameters related to yield stress, isotropic and kinematic hardening, fatigue life and damage diffusion. From previous studies it has been found that in the most general case the parameters of the model are constant or depend exponentially on total strain so that only two or three tests are needed for the characterisation. The results… More >

  • Open Access


    Effect of correct statistical description of fatigue crackpropagation data on the time to first inspection

    G. Bertrand1

    Structural Durability & Health Monitoring, Vol.1, No.3, pp. 185-192, 2005, DOI:10.3970/sdhm.2005.001.185

    Abstract Each maintenance strategy demands for the definition of an inspection threshold and further inspection intervals. A general criterion for the calculation of the time to first inspection is high probability of detection of a certain crack size and low failure probability in case a predicted crack size was not detected. The proposed method demonstrates that a top down analysis of crack development from critical sizes to detectable sizes reveals an economic benefit with respect to the frequency of inspections. The dispersion of fatigue stress cycles at rupture obtained from component tests at riveted lap joints is transformed to the distribution… More >

  • Open Access


    Finite Element Modeling of Fatigue Crack Growth in Curved-Welded Joints Using Interface Elements

    M. S. Alam1, M.A. Wahab1,2

    Structural Durability & Health Monitoring, Vol.1, No.3, pp. 171-184, 2005, DOI:10.3970/sdhm.2005.001.171

    Abstract Fatigue life of curved structural joints in ship structures under constant amplitude cyclic loading has been studied in this research. A new approach for the simulation of fatigue crack growth in welded joints has been developed and the concept has been applied to welded curved butt-joints. The phenomena of crack propagation and interface debonding can be regarded as the formation of new surfaces. Thus, it is possible to model these problems by introducing the mechanism of surface formation. In the proposed method, the formation of new surface is represented by interface element based on the interface surface potential energy. The… More >

  • Open Access


    The Theory of Critical Distances Applied to the Prediction of Brittle Fracture in Metallic Materials


    Structural Durability & Health Monitoring, Vol.1, No.2, pp. 145-154, 2005, DOI:10.3970/sdhm.2005.001.145

    Abstract The Theory of Critical Distances (TCD) is a general term for any of those methods of analysis which use continuum mechanics in conjunction with a characteristic material length constant, L. This paper discusses the use of two simple versions of the TCD: a point-stress approach which we call the Point Method (PM) and a line-average approach: the Line Method (LM). It is shown that they are able to predict the onset of unstable, brittle fracture in specimens of metallic materials containing notches of varying root radii. The approach was successful whatever the micromechanism of crack growth (cleavage or ductile tearing);… More >

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