Numerical studies of welding residual stresses in tubular joints and experimental validations by means of x-ray and neutron diffraction analysis

The influence of residual stresses on the structural behavior of the material is of high importance for accurate integrity assessment of welded components and structures. In the absence of reliable information on magnitude and distribution of residual stresses, it is generally assumed that residual stresses are as high as the yield strength of the material which could lead to over-conservatism in the failure assessment and consequently economic problems. Accordingly, a growing need to the more realistic and reliable determination of welding residual stresses has been raised. In this paper finite element approach is applied in order to calculate the welding residual stresses in a tube out of S355J2H steel using the commercial software package SYSWELD. For comparison with the numerical investigations x-ray and neutron diffraction measurements (XRD and ND) are carried out to determine the distribution of residual stresses in three orthogonal directions, on the surface and in the bulk of the material respectively. The numerical results are compared directly with the measured data. The overall aim is to evaluate the use of finite element approach in the accurate calculation of residual stress states for use in the integrity assessments

Numerical investigation of welding residual stress field and its behaviour under multiaxial loading in tubular joints

The lack of clarities in estimating the residual stress threat to the structural integrity has led to conservative assumptions in the current design of welds. The complexities become more in the case of multiaxial loading of welded structure, considering fracture or fatigue. To what extent the residual stresses influence the performance of a welded structure, depends on how stable they are under service loads. Finite element analyses are used here to describe the development of welding residual stresses in tubular joints and their relaxation under multiaxial loading. It is observed that the effect of the torsion load is more significant than the effect of tension load in releasing of the residual stresses. For pure tensile loading, the relaxation of the residual stresses are negligible as long as the applied load is lower than 50% of the yield strength of the material. For a combined tension-torsion loading of 75% of the yield strength, the residual stresses are almost completely released, and in the weld zone they become compressive

Fatigue assessment of the welded joints containing process relevant imperfections

Internal weld imperfections and defects affect the fatigue behavior of the welded joints significantly. Their effects become more important when the weld seam does not have a sharp weld toe transition. These imperfections and defects in the welded area are classified by different instructions such as the DVS-guideline or the IIW recommendation. These instructions and guidelines introduce different FAT classes for the same weld imperfection type. FAT is the magnitude of the stress to failure in two million cycles. Furthermore, they do not take into account the importance of the position and the size of weld imperfections. This introduces uncertainty for the user due to differences between guidelines and the lack of information. As a result, in order to eliminate the inconsistency in the available weld recommendations and guidelines, it is necessary to perform a new investigation on different weld imperfections. This study considers the effects of imperfections on the weld quality both experimentally and numerically. The experimental study considered the effect of weld imperfections on weld quality with respect to the post weld treatment procedure on the weld seam. Then, a numerical method was introduced and validated by experimental results to predict the fatigue life in crack initiation and propagation steps. Fatemi-Socie approach as a fatigue damage model and fracture mechanics estimated the fatigue life in the crack initiation and propagation steps, respectively. The experimental and numerical results were plotted in S-N diagrams, and based on this work, new FAT classes w ere recommended. It was seen that if the type of weld defect is a single pore, the suggested value by IIW recommendation is more realistic than the other guidelines

MiRNAs in early brain development and pediatric cancer

The size and organization of the brain are determined by the activity of progenitor cells early in development. Key mechanisms regulating progenitor cell biology involve miRNAs. These small noncoding RNA molecules bind mRNAs with high specificity, controlling their abundance and expression. The role of miRNAs in brain development has been studied extensively, but their involvement at early stages remained unknown until recently. Here, recent findings showing the important role of miRNAs in the earliest phases of brain development are reviewed, and it is discussed how loss of specific miRNAs leads to pathological conditions, particularly adult and pediatric brain tumors. Let-7 miRNA downregulation and the initiation of embryonal tumors with multilayered rosettes (ETMR), a novel link recently discovered by the laboratory, are focused upon. Finally, it is discussed how miRNAs may be used for the diagnosis and therapeutic treatment of pediatric brain tumors, with the hope of improving the prognosis of these devastating diseases.A.P. was funded by a predoctoral fellowship from Fundación Tatiana Pérez de Guzmán el Bueno. Work in the lab was supported by grants from the European Research Council (309633) and the Spanish State Research Agency (PGC2018-102172-B-I00, as well as through the “Severo Ochoa” Programme for Centers of Excellence in R&D, ref. SEV-2017-0723).Peer reviewe