Bergara, A. (Asier)

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    Fatigue crack propagation analysis in offshore mooring chains and the influence of manufacturing residual stresses
    (Elsevier, 2022) Arredondo, A. (Alberto); Bergara, A. (Asier); Altuzarra, J. (Jorge); Martínez-Esnaola, J.M. (José Manuel)
    The main objective of this work has been the validation of a methodology to assess fatigue crack propagation in offshore mooring chains under service conditions. For this purpose, analytical Stress Intensity Factor (SIF) so- lutions with step-by-step application of the Paris law and the Extended Finite Element Method (XFEM) imple- mented in the Abaqus® 2018 software have been studied. The fatigue crack propagation analysis is divided in two stages. First, a static analysis -pre-stretch and subsequent unloading-representative of the manufacturing process is performed. Next, the fatigue crack propagation simulation is performed under simplified loading conditions and taking into account the residual stresses induced in the previous analysis. Finally, analytical solutions, numerical simulations and experimental results have been compared. Results justify the use of the Extended Finite Element Method (XFEM) for fatigue crack propagation analysis in mooring chains.
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    Fabrication and characterization of SiC sandwich material for Flow Channel Inserts in HT-DCLL blanket by gel casting
    (2022) Malo, M. (Marta); Bre, A. (Arturs); Bergara, A. (Asier); Garcia-Rosales, C. (Carmen); Hernández, T. (Teresa); García-Goikoetxea, J. (Javier); Kravalis, K. (Kalvis); Pérez-Polo, B. (Beatriz); Martinez Esnaola, J.M.(José Manuel); Platacis, E. (Ernest); Etxeberria-Uranga, J.J. (Jon Joseba)
    Flow Channel Inserts (FCIs) are key elements in the high temperature DCLL blanket concept since they provide the required thermal insulation between the He-cooled structural steel and the hot PbLi flowing at a maximum temperature of 700 ?, and the necessary electrical insulation to minimize magnetohydrodynamic (MHD) effects. In this paper, the use of SiC-sandwich material for FCIs consisting of a porous SiC core (thermal and electrical insulator) covered by a dense Chemical Vapor Deposition (CVD) SiC layer (protection against PbLi infiltration) has been studied. Lab-scale FCI prototypes were produced by the gel casting method and characterized in terms of thermal and electrical conductivities (the latter before and after exposure to ionizing radiation) and flexural strength. Corrosion tests under flowing PbLi at 500-700 ?& nbsp;in presence of a magnetic field up to 5 T were performed obtaining promising results regarding the reduction of MHD pressure drop and the compatibility of SiC and PbLi under dynamic conditions. Additionally, thermomechanical finite elements simulations were performed in a 3D channel geometry to identify black spots regarding thermal stresses.
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    XFEM rolling contact fatigue crack propagation in railways considering creepages on contact shear stresses
    (2022) Bergara, A. (Asier); Gil-Negrete, N. (Nere); Rodríguez-de-Arana, B. (Borja); Nieto-Fernández, F.J.(Francisco Javier)
    In this work the influence of considering wheel-rail contact creepages on fatigue crack growth rates due to Rolling Contact Fatigue (RCF) is studied. For this purpose, the FASTSIM algorithm, which considers the moving complex pressure distribution with slipping and adhesion zones of the wheel-rail contact patch, has been implemented in Abaqus using FORTRAN code subroutines. The developed methodology has been validated with a 60E1 rail profile model which uses XFEM, by comparing the obtained Stress Intensity Factors (SIFs) and sub-surface shear stresses with numerical results available in the literature. Finally, the RCF crack propagation analysis of a 60E1 rail profile with different contact conditions has been performed using the XFEM. The obtained results justify the necessity of considering contact creepages on contact shear stresses for crack growth analysis.