Wire drawing parameters such as area reduction and die angle have an important effect on damage generation. One of the most common defects appearing under certain critical configurations are the so-called ¿chevron cracks¿. These defects are difficult to identify since they are typically located at the wire core. To address this, great efforts have been made in the last two decades to develop numerical models capable of predicting damage evolution and failure. Continuum Damage Mechanics (CDM) models present the advantage of being coupled with the constitutive behaviour of the material. Among these models, Lemaitre¿s approach is one of the most widely used. In its original formulation, the model did not distinguish between tension and compression stresses in terms of damage accumulation. An additional parameter was then included to consider the crack closure effect under compressive stresses. However, this formulation is not valid for wire drawing, since it overestimates damage under these conditions. For this reason, a new damage model following Lemaitre¿s approach has been derived by redefining the crack closure effect under compressive stresses. In this way, under high hydrostatic compressive stresses, such as in the case of wire drawing, the model yields more realistic results in terms of damage accumulation. The model has been implemented in ABAQUS through user subroutines UMAT (for implicit cases) and VUMAT (for explicit cases). Single-pass wire drawing simulations have been performed to compare the original model with the new formulation.

In many practical situations, the distribution of residual stresses can have a paramount influence on the fatigue and fracture response of materials. In this paper, we describe a method for the local measurement of residual stresses. It consists of Digital Image Correlation (DIC) of Scanning Electron Microscope (SEM) images of a surface, before and after milling a slit using a Focused Ion Beam (FIB). The DIC algorithm used in this work is based on Fourier analysis, which can reach sub-pixel resolution. In order to calculate the internal stresses released during the milling process, the displacements detected with the DIC algorithm are fitted to Finite Element Method (FEM) simulations. Residual stresses measured by this method on a hard metal sample subjected to different laser surface treatments are successfully compared with X-ray diffraction measurements.

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.

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) solutions with step-by-step application of the Paris law and the Extended Finite Element Method (XFEM) implemented in the Abaqus (R) 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.

This work presents the numerical modeling and validation of two different fatigue propagation tests that attempt to simulate the crack growth situation that takes place at aeronautic engine vane guides. These vanes, which are cylindrical skins of very thin thickness (few millimeters), are responsible for holding the static blades of both the compressor and the turbine. The union of discs and blades is a very conflictive zone due to high stresses and possible manufacturing defects. The first test designed for this work tries to reproduce crack growth at geometric discontinuities and sharp edges, such as the union between the disc and the blades. The second test tries to reproduce the crack growth situation that takes place in skins of very thin thickness, such as vane guides. First, the experimental set-ups as well as the experimental results are presented. Then, the numerical FE models and simulations -corresponding to the experimental tests that have been performed- are explained. Finally, the comparison between the experimental and numerical results is presented. Crack growth was controlled by optical microscopy and by progressive crack surface heat-tinting. For the numerical simulations, the Extended Finite Element Method (XFEM) implemented in Abaqus (R) 2017 software has been used. The comparison between the experimental and numerical results shows very good correlation regarding crack shape and number of cycles until failure. The capabilities of the XFEM-based LEFM approach to simulate fatigue crack growth in complex crack fronts are validated.

In this article, multiaxial fatigue space, fatigue basic unit and fatigue damage map are proposed, as well as out-of phase failure angle and out-of-phase level coefficient. The comprehensive discussion of out-of-phase failure is conducted, it is found that the relative distortion deformation is a proper reflection for out-of-phase failure and it has a limit effect. The validation with 394 samples of 13 materials under 37 loading conditions indicates that the proposed theory has an excellent universal capability with minimum prediction error and favorable error distribution, the prediction ability is improved by 21.1% compared with original Lu criterion.

Rolling contact fatigue (RCF) is a common cause of rail failure due to repeated stresses at the wheel-rail contact. This phenomenon is a real problem that greatly affects the safety of train operation. Preventive and corrective maintenance tasks have a big impact on the Life Cycle Cost (LCC) of railway assets, and therefore cutting-edge strategies based on predictive functionalities are needed to reduce it. A methodology based on physical models is proposed to predict the degradation of railway tracks due to RCF. This work merges a crack initiation and a crack growth model along with a fully nonlinear multibody model. From a multibody assessment of the vehicle-track interaction, an energy dissipation method is used to identify points where cracks are expected to appear. At these points, crack propagation is calculated considering the contact conditions as a function of crack depth. The proposed methodology has been validated with field measurements, conducted using Eddy Currents provided by the infrastructure manager Network Rail. Validation results show that RCF behavior can be predicted for track sections with different characteristics without the necessity of previous on-track measurements.

The results of existing constitutive models describing the behaviour of metal powder during compaction processes are very different. This reveals the high sensitivity of the mechanical behaviour of porous materials to the shape, arrangement and distribution of particles and pores. In order to clarify these discrepancies, the compaction behaviour under hydrostatic loads and high temperatures for a Nickel-based superalloy has been characterized. For this characterization, a numerical optimization procedure has been defined. In parallel, finite element models at a mesoscopic level have been built with the aim of estimating the parameters that define the mechanical behaviour of metallic powder under hydrostatic loads. Then a homogenization procedure has been used to compute the macroscopic behaviour of the powder. The results of both the experimental characterization and the mesoscopic models emphasize the limits of the analysed literature constitutive models to reproduce the compaction behaviour of the considered Astroloy powder.

A full explicit FEM simulation of wheelset passing through switch panel is presented. The real 3D geometry of the switch panel is used, both vertical and lateral response are taken into consideration. The dynamic interaction is analysed and it is found that the damage mechanism on the switch blade and stock rail is a complex interaction of wear, fatigue and impact, which can be well described by explicit FEM simulation. Parametric analysis of running speed, traction coefficient and the friction coefficient between switch blade gauge surface and wheel flange indicate that decreasing running speed can help to reduce the damage on switch panel. The traction coefficient has little influence on the maximum impact response, but a higher traction coefficient is beneficial for eliminating the dynamic response after the maximum impact response point. The influence of the friction coefficient on the dynamic impact response is not significant, but a lower friction coefficient is favourable for decreasing the wear damage on the switch blade and increasing running safety. This work can provide a good understanding of the interaction on switch panel and give theoretical support for maintenance and improving the design.

The main objective of this work has been the validation of a methodology to calculate the Stress Intensity Factors (SIFs) in prospective cracks of offshore mooring chains under service conditions. For this purpose, the analytic methods described in the B57910 have been compared with those calculated by the conventional Finite Element Method (FEM) by means of contour integrals and by the Extended Finite Element Method (XFEM) implemented in the Abaqus 2018 software. First, an axially loaded cylinder has been studied in order to determine the correlation between different methods for a simple case, as well as to establish the most suited finite element methodology. Then, the real case of a mooring chain has been studied, including the residual stresses induced in the manufacturing process. Finally, numerical simulations and experimental results have been compared. Results justify the use of numerical methods, specifically the use of contour integrals, for the calculation of Stress Intensity Factors (SIFs) in offshore mooring chains.

In order to meet the increasing needs from economic and social developments in future, the research on new generation steels with higher strength and longer duration, has become a worldwide issue. It is well known that various mechanisms to strengthen the steels exist, but grain refinement is the only method to improve both strength and toughness simultaneously. A ferrite grain size in the range of 1÷4 um and a steel microstructure characterised by a mixture of ferrite-pearlite and/or martensite, bainite microstructure, could give a very good combination of mechanical (strength, ductility, toughness, fatigue) and technological properties (machinability, cold/warm metal forming, etc.) for final application to automotive components.