399 research outputs found

    Multiple crack propagation by DBEM in a riveted butt-joint: a simplified bidimensional approach

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    A Multi-Site Damage (MSD) crack growth simulation is presented, carried out by means of Dual Boundary Element Method (DBEM), in a two-dimensional analysis of a cracked butt-joint made of aluminium 2024 T3. An equivalent crack length is proposed for an approximated 2D analysis of a 3D problem where the crack front assumes a part elliptical shape due to secondary bending effects. The assumptions made to perform such simplified bidimensional analyses are validated by comparing numerical results with experimental data, the latter obtained from a fatigue tested riveted butt-joint

    Residual strength evaluation by DBEM for a cracked lap joint

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    The present work summarizes a numerical procedure aimed at the evaluation of the residual strength of a cracked lap joint, based on the competing failure mechanisms regulated by the R-curve analysis and plastic collapse. The model adopted for Stress Intensity Factors (SIFs) evaluation is based on the use of the Dual Boundary Element Method (DBEM) within the theoretical frame of Linear Elastic Fracture Mechanics (LEFM). The value of failure load was available from experiments, allowing a comparison with numerical results and consequent validation of the described procedure

    Multiaxial Fatigue Crack Propagation of an Edge Crack in a Cylindrical Specimen Undergoing Combined Tension-Torsion Loading

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    A three-dimensional crack propagation simulation of a hollow cylinder undergoing coupled traction and torsion loading conditions is performed by the Dual Boundary Element Method (DBEM). The maximum tension load and torque are equal to 40 kN and 250 Nm respectively. Specimens, made of Al alloys B95AT and D16T, have been experimentally tested with in-phase constant amplitude loads. The Stress Intensity Factors (SIFs) along the front of an initial part through crack, initiated from the external surface of the hollow cylinder, are calculated by the J-integral approach. The crack path is evaluated by using the Minimum Strain Energy Density (MSED) criterion whereas the Parisâ law, calibrated for the material under analysis, is used to calculate crack growth rates. A cross comparison between DBEM and experimental results is presented, showing a good agreement in terms of crack growth rates and paths

    Multiple crack propagation in friction stir welded aluminium joints

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    This paper is concerned with the simulation of crack propagation in friction stir welded butt joints, in order to assess the influence of process induced microstructural alterations and residual stresses on the fatigue behaviour of the assembly. The approach employed is based on the coupled use of the finite element method and the dual boundary element method in order to take advantage of the main capabilities of the two methods. The distribution of the process induced residual stresses has been mapped by means of the contour method. Then, the computed residual stresses field has been superimposed, in a dual boundary element environment, to the stress field as a result of a remote fatigue traction load and the crack growth is simulated. A two-parameter crack growth law, based on the evaluation of two thresholds, for the material being analysed, is used for the crack propagation rate assessment. The stress intensity factors are evaluated using the J-integral technique. Computational results have been compared with experimental data, provided from constant amplitude crack propagation tests on welded samples, showing the subdivision of the overall fatigue life in the two periods of crack initiation and crack propagation

    LCF assessment on heat shield components of nuclear fusion experiment "Wendelstein 7-X" by critical plane criteria

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    Abstract The Wendelstein 7-X modular advanced stellarator has started operations at the Max Planck Institute for Plasma Physics in Greifswald, Germany, in 2016. In the first phase, the machine operated restricting the plasma pulses to low power and short lengths. Plans to achieve actively cooled components are scheduled to start in 2020 when the machine will operate in steady-state at full power. FEM simulations for steady-state operations revealed high plastic strains at several locations, for most of all the rigidly supported Plasma Facing Components; therefore, there is the risk of a premature fatigue failure before the end of the scheduled operations of the machine. The aim of this study is to analyse, by means of the commercial code ABAQUS, the behavior of such critical components estimating, eventually, their fatigue life by means of the commercial code fe-safe

    Multiple crack propagation by DBEM in a riveted butt-joint: a simplified bidimensional approach

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    A Multi-Site Damage (MSD) crack growth simulation is presented, carried out by means of Dual Boundary Element Method (DBEM), in a two-dimensional analysis of a cracked butt-joint made of aluminium 2024 T3. An equivalent crack length is proposed for an approximated 2D analysis of a 3D problem where the crack front assumes a part elliptical shape due to secondary bending effects. The assumptions made to perform such simplified bidimensional analyses are validated by comparing numerical results with experimental data, the latter obtained from a fatigue tested riveted butt-joint

    Thermal–Mechanical FEM Analyses of a Liquid Rocket Engines Thrust Chamber

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    The Italian Ministry of University and Research (MIUR) funded the HYPROB Program to develop regeneratively cooled liquid rocket engines. In this type of engine, liquid propellant oxygen–methane is used, allowing us to reach very good performances in terms of high vacuum specific impulse and high thrust-to-weight ratio. The present study focused on the HYPROB final ground demonstrator, which will be able to produce a 30 kN thrust in flight conditions. In order to achieve such a thrust level, very high chamber pressures (up to 50 bar) and consequently high thermal fluxes and gradients are expected inside the thrust chamber. Very complex and high-fidelity numerical FEM models were adopted here to accurately simulate the thermal–mechanical behavior of the thrust chamber cooling channels, accounting for plasticity, creep, and low-cycle fatigue (LCF) phenomena. The aim of the current work was to investigate the main failure phenomena that could occur during the thrust chamber’s service life. Results demonstrated that LCF is the main cause of failure. The corresponding number of loading cycles to failure were calculated accordingly

    Coupled FEM-DBEM Simulation of 3D Crack Growth under Fatigue Load Spectrum

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    Abstract Numerical predictions of fatigue crack growth under load spectrum are obtained by coupled FEM-DBEM approach. An initial part-through corner crack, in a pre-notched specimen undergoing a traction fatigue load, propagates becoming through the thickness. A two parameter crack growth law ("Unified Approach") is calibrated by in house made constant amplitude experimental tests and the crack growth retardation after an overload application is reproduced. The residual stresses responsible for such retardation are calculated by a sequence of elastic-plastic static FEM analysis; such stresses are then applied to the crack faces for the propagation simulation in a DBEM environment. A satisfactory agreement between numerical and experimental crack growth rates are displayed, for both part-through crack and through the thickness crack. This approach provide general modeling capabilities, with allowance for general crack front shape and fully automatic propagation

    Robust design of a polygonal shaft-hub coupling

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    In this work, the Taguchi method is applied for the optimal choice of design parameter values for a polygonal shaft-hub coupling. The objective is to maximize a performance function, minimizing, at the same time, its sensitivity to noises factors (robust design). The Design of Experiments (DoE) is adopted to set up a plan of numerical experiments, whose different configurations are simulated using the Boundary Element Method (BEM)
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