Papers by Author: Jose Zapatero

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Authors: Pablo Lopez-Crespo, Belen Moreno, Jose Zapatero
Abstract: There are a number of theories available to model biaxial fatigue problems. Among these, the critical plane models try to predict not only the fatigue life but also the orientation of the crack or failure plane. This work attempt to analyse the biaxial tension-torsion problem from a strain-based analysis focused on plane failures predictions. Fatigue life and critical plane predictions are carried out applying multiaxial models proposed by Brown-Miller, Fatemi-Socie and Smith-Watson-Topper. The theoretical results are compared with constant amplitude test data, in-phase and out-of-phase (90˚) in a structural steel. The results suggest that Smith-Watson-Topper model predictions of fracture plane do not match the real fracture plane. The critical fracture plane predictions of the Brown-Miller and Fatemi-Socie models do not match in most cases with experimental observations either, but considering the second plane of the maximum shear strain amplitude, the predictions of the fracture plane and fatigue life improve substantially.
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Authors: Belen Moreno, Pablo Lopez-Crespo, Antonio González-Herrera, Jose Zapatero
Abstract: Many mechanical components are subjected to multiaxial fatigue. These conditions are typically coming from external loads, the geometry of the component and/or residual stresses. However the majority of experimental data available in the literature are focused on the simpler uni-axial fatigue problem. The present work describes a series of experimental tests conducted to characterise in a comprehensive way the multiaxial behaviour of a ST52-3N structural steel. First, the monotonic properties of the steel were obtained experimentally. Then cyclic properties were also measured both in the longitudinal and torsional axes. Finally another series of tests were carried out to study the multiaxial response of the material. Both in-phase (proportional) and out-of-phase (non proportional) loadings were employed, thus providing a complete database for improving current models which describe the multiaxial behaviour of materials.
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Authors: Pablo Lopez-Crespo, Daniel Camas, Antonio González-Herrera, J.R. Yates, Eann A Patterson, Jose Zapatero
Abstract: The fatigue life of metallic materials is strongly influenced by crack closure effects. Finite element (FE) methods allow the study of crack closure with great detail and can provide valuable information about phenomena occurring in the bulk of the material. In this work the distribution of stresses through the thickness of a cracked specimen has been studied using 3D FE simulations. It was found that the transition between the interior of the specimen (plane strain) and the surface (plane stress) differs from that predicted by 2D plane stress models. In addition, an attempt is presented to experimentally validate the results at the surface level. For this purpose full-field image correlation technique was utilized. This allowed direct comparison between the displacement field predicted by the numerical simulations and the experimental results measured by digital image correlation.
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Authors: Antonio González-Herrera, J. Garcia-Manrique, A. Cordero, Jose Zapatero
Abstract: This paper focuses on the study of the plastic zone in fatigue crack closure based on the results obtained by means of 3D Finite Element Analysis (FEA). These results show the crack behavior through the thickness. The plastic zone is visualized and quantified. It does not correspond to the classical shape. The plastic zone in the interior surface is similar to those obtained in 2D plane strain conditions and a reduced effect of closure is observed. However, close to the external surface, 2D plane stress results are not reproduced, the plastic zone size is smaller and an important change is observed. This transition is developed in a thin external portion of the specimen and it can only be captured if a fine mesh of the thickness is done.
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Authors: J. Pascual Cosp, Jose Zapatero, A. Ramírez del Valle, J.C. Galiano Serrano
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