Nucleon propagation induced by electroweak excitation of atomic nuclei

nrpages: 184status: publishe

Experimentally induced errors in digital image correlation measurement of small strains with large gradients

Digital Image Correlation or DIC is an already widespread and commonly used technique to perform full field strain measurements. Usually, a so called 'speckle pattern' is put on the specimen and then, pictures are taken first in the undeformed stage, which is the reference and then in various deformed states. The technique itself consists of comparing the image of a deformed pattern with a reference image and determining the displacements of the so called 'subsets'. The mathematical algorithm eliminates rigid rotations of the subset and is able to determine the strain field. This technique was originally designed for large-strain measurements and as such, it works very well when large strains are present, but when determining (very) small strain fields, especially in combination with large (rigid body) deformations or large strain gradients, this technique becomes a lot more sensitive to the boundary conditions of the experimental setup. This manuscript will illustrate the errors induced by experimental factors such as in-plane rotation, in-plane rigid body translation, out-of-plane rigid body rotation, which are in fact all related to how the specimen is gripped in the tensile machine, on the eventual derived strain field. Furthermore, processing parameters such as subset and step size and the used strain window on numerically and experimentally induced transformations will be assessed

IDENTIFICATION OF LÜDERS BANDS USING DIGITAL IMAGE CORRELATION

This paper presents the characterization of Lüders bands by digital image correlation on niobium microalloyed steel during a static tensile testing.Digital image correlation with the qualitative and quantitative analysis of the Lüders bands on the microalloyed steel was proved asa very precise and suitable method for determining the strain amountin the deformation zone.In this research was determined that the strain amount is the highest in the area behind the Lüders band front and the lowest in the area in front of the Lüders band

Validation of welding simulations using thermal strains measured with DIC

Residual stresses can affect the performance of steel tubes in many ways and as a result their magnitude and distribution is of particular interest to many applications. Residual stresses in cold-rolled steel tubes mainly originate from the rolling of a flat plate into a circular cross section (involving plastic deformations) and the weld bead that closes the cross section (involving non-uniform heating and cooling). Focus in this contribution is on the longitudinal weld bead that closes the cross section. To reveal the residual stresses in the tubes under consideration, a finite element analysis (FEA) of the welding step in the production process is made. The FEA of the welding process is validated with the temperature evolution of the thermal simulation and the strain evolution for the mechanical part of the analysis. Several methods for measuring the strain evolution are available and in this contribution it is investigated if the Digital Image Correlation (DIC) technique can record the strain evolution during welding. It is shown that the strain evolution obtained with DIC is in agreement with that found by electrical resistance strain gauges. The results of these experimental measuring methods are compared with numerical results from a FEA of the welding process

Consequences of gestational diabetes mellitus on neonatal cardiovascular health: MySweetHeart Cohort study

Hyperglycaemic disorders of pregnancy are associated with offspring cardiovascular alterations. MySweetHeart cohort study aimed to assess the effect of maternal gestational diabetes (GDM) on offsprings' cardiovascular health. Newborns underwent clinical and echocardiographic examinations between 2016 and 2020. Compared to mothers without GDM (n = 141), mothers with GDM (n = 123) were more likely to have had GDM in previous pregnancies and had higher weight, BMI, blood glucose, and HbA1c. Newborns of both groups showed similar clinical characteristics. Echocardiography was performed on the 3rd (interquartile range, IQR, 2nd-4th) day of life in 101 offsprings of mothers without and 116 offsprings of mothers with GDM. Left ventricular (LV) mass was similar. Children born to mothers with GDM had a thicker posterior LV wall (z-score +0.15, IQR -0.38/0.62, versus +0.47, IQR -0.11/+1.1, p = 0.004), a smaller end-systolic (1.3 mL, IQR 1.0-1.5 mL, versus 1.4 mL, IQR 1.2-1.8 mL, p = 0.044) but a similar end-diastolic LV volume. They also had shorter tricuspid valve flow duration and aortic valve ejection time, lower tricuspid E-wave and pulmonary valve velocities. Newborns of mothers with or without GDM had similar clinical characteristics and LV mass. However, some echocardiographic differences were detected, suggesting an altered myocardial physiology among infants of mothers with GDM. ClinicalTrials.gov (NCT02872974). Hyperglycaemic disorders of pregnancy are known to be associated with offspring cardiovascular alterations. Clinical characteristics and estimated left ventricular (LV) mass were similar in children issued from mothers with and without gestational diabetes (GDM). Children born to mothers with GDM had a thicker posterior LV wall and a smaller end-systolic LV volume. Although LV mass is not different, myocardial physiology may be altered in these infants. Further studies should investigate the endothelial function of this population and the cardiovascular evolution of these children over time

Nucleon propagation induced by electroweak excitation of atomic nuclei

nrpages: 184status: publishe

Study of systematic errors in strain fields obtained via DIC using heterogeneous deformation generated by plastic FEA

In this article, systematic errors that arise in the derivation of strain fields based on displacement fields obtained by digital image correlation (DIC) are analyzed. Attention is paid to errors that arise from different implementations of the DIC technique. In particular, we investigate the influence of the shape function, the interpolation order and the subset size on the derived strains. In addition, we focus on errors that can be directly attributed to the derivation of the strain fields, e.g. the strain-window size and the strain-window interpolation order. The errors are estimated using numerically deformed images that were obtained by imposing finite element (FE) displacement fields on an undeformed image yielding plastic deformation of the specimen. This FE procedure simulates realistic experimental heterogeneous deformations at various load steps. It is shown that the errors on the strain fields can be substantially reduced if conscious choices in the abovementioned implementations are made.status: publishe

An FE-based image deformation tool to quantify the metrological performance of stereo-DIC

Stereo-Digital Image correlation (stereo-DIC) is being used increasingly when it comes to mea- suring shape, motion and deformation since the cost of computational power has dropped the last few years and since more commercial solutions are becoming available. The stereo-DIC process chain is how- ever largely non-linear, making the quantication of the metrological performance very cumbersome. As a consequence, usually empirical rules of thumb are being used together with user expertise. Since the uncer- tainty on a measurement is not known, the transition from valuable research tool to industrial measurement tool is being stalled. An FE-based image deformation tool is proposed to generate images as if they were made during a real experiment, giving ground truth simulated data and thus oering the possibility to evaluate and validate existing DIC-codes. It also oers the users an understanding on how the dierent parameters are in uencing the result of a DIC-measurement, giving the possibility to improve their results by introducing new rules of thumb. Since the image generator uses an FE-mesh and a real speckle pattern a best-case set up for each experiment can be determined.status: accepte