Digital image correlation in analysis of stiffness in local zones of welded joints

Ponašanje zavarenih spojeva u lokalnim zonama, kao i njihov uzajamni utjecaj, jedan je od glavnih problema u projektu zavarene konstrukcije. Naime, osnovni je problem u određivanju mehaničkih svojstava materijala u zavarenom spoju. Ta su svojstva neophodna za točan proračun zavarenih konstrukcija. Mogućnost dobivanja vrijednosti lokalne deformacije/pomaka čini tehniku "Digital Image Correlation" (DIC) pogodnom za ispitivanje zavarenog spoja i određivanje mehaničkih svojstava. Tijekom ovih ispitivanja za opterećenje je korišten uređaj za vlačnu provjeru, a dvije kamere su korištene za 3D analizu deformacije. Upotrijebljen je uzorak s paralelnim stranama dobiven zavarivanjem V spoja. Prije ispitivanja izvršeno je kalibriranje kako bi se dobili što točniji rezultati. U radu je predstavljena primjena DIC tehnike korištenjem Aramis softvera za mjerenje lokalnog pomaka/deformacije u zavarenom spoju. Dobiveni rezultati pokazuju da je zavareni spoj bio nejednako deformiran s prednje i zadnje strane korijena, u području elastične deformacije, tijekom vlačnog opterećenja. Zbog vlaka u uzorku s V-zavarom (osnovni materijal S235JRG2, žica elektrode - VAC 60), postoji uzajamni utjecaj mehaničkih svojstava lokalnih zona, gdje je krutost korijena zavara najviša.The behaviour of welded joints in local zones, as well as their mutual influence, represents one of the main challenges in welded structure design. Namely, the main issue lies in determining the mechanical properties of materials in a welded joint. These properties are necessary for an accurate calculation of welded structure integrity. The possibility of obtaining local strain/displacement values makes the "Digital Image Correlation" (DIC) technique suitable for welded joint testing and determining of mechanical properties. In this paper a tensile testing machine was used for loading and a two camera system was used for 3D strain analysis. A specimen with parallel sides, obtained by welding of a V joint was used. Calibration was performed prior to testing, in order to ensure dimensional consistency of the system. Application of DIC technique using Aramis software for measuring local displacement/strain in a welded joint is presented in this paper. Due to tension in the V-weld specimen (Base material - S235JRG2, electrode wire - VAC 60), mutual influence of mechanical properties of local zones is present, wherein the root weld had the highest stiffness

Trauma of the frontal region is influenced by the volume of frontal sinuses. A finite element study

Anatomy of frontal sinuses varies individually, from differences in volume and shape to a rare case when the sinuses are absent. However, there are scarce data related to influence of these variations on impact generated fracture pattern. Therefore, the aim of this study was to analyse the influence of frontal sinus volume on the stress distribution and fracture pattern in the frontal region. The study included four representative Finite Element models of the skull. Reference model was built on the basis of computed tomography scans of a human head with normally developed frontal sinuses. By modifying the reference model, three additional models were generated: a model without sinuses, with hypoplasic, and with hyperplasic sinuses. A 7.7 kN force was applied perpendicularly to the forehead of each model, in order to simulate a frontal impact. The results demonstrated that the distribution of impact stress in frontal region depends on the frontal sinus volume. The anterior sinus wall showed the highest fragility in case with hyperplasic sinuses, whereas posterior wall/inner plate showed more fragility in cases with hypoplasic and undeveloped sinuses. Well-developed frontal sinuses might, through absorption of the impact energy by anterior wall, protect the posterior wall and intracranial contents.This work was supported in part by grants from the Serbian Ministry of Education, Science and Technological Development III45005, III41007, ON174028 and EU project FP7 ICT SIFEM 600933

Kinematics of gait:new method for angle estimation based on accelerometers

A new method for estimation of angles of leg segments and joints, which uses accelerometer arrays attached to body segments, is described. An array consists of two accelerometers mounted on a rigid rod. The absolute angle of each body segment was determined by band pass filtering of the differences between signals from parallel axes from two accelerometers mounted on the same rod. Joint angles were evaluated by subtracting absolute angles of the neighboring segments. This method eliminates the need for double integration as well as the drift typical for double integration. The efficiency of the algorithm is illustrated by experimental results involving healthy subjects who walked on a treadmill at various speeds, ranging between 0.15 m/s and 2.0 m/s. The validation was performed by comparing the estimated joint angles with the joint angles measured with flexible goniometers. The discrepancies were assessed by the differences between the two sets of data (obtained to be below 6 degrees) and by the Pearson correlation coefficient (greater than 0.97 for the knee angle and greater than 0.85 for the ankle angle)

Microsecond nonlinear model predictive control for DC-DC converters

status: publishe

The influence of ruptured anterior cruciate ligament on the biomechanical weakening of knee joint and posterior cruciate ligament

The aim of the present study was to estimate biomechanical weakening of human knee joint assuming the conditions that occur when a person is standing on one leg. A patient-specific three-dimensional model of the human knee joint was developed from medical scans, while loads and material characteristics were adopted from the literature. The considered model included the following materials: bones, menisci, articular cartilage and relevant ligaments (posterior cruciate ligament, lateral collateral ligament and medial collateral ligament). The finite element analysis was used for numerical calculation of the stress distribution and failure index of posterior cruciate ligament. The obtained failure index showed that there was no possibility for posterior cruciate ligament failure under the considered conditions. It was concluded that application of the finite element analysis can provide a better insight into the biomechanical condition of the injured knee joint

Three-dimensional reconstruction and NURBS-based structured meshing of coronary arteries from the conventional X-ray angiography projection images

© 2018 The Author(s). Despite its two-dimensional nature, X-ray angiography (XRA) has served as the gold standard imaging technique in the interventional cardiology for over five decades. Accordingly, demands for tools that could increase efficiency of the XRA procedure for the quantitative analysis of coronary arteries (CA) are constantly increasing. The aim of this study was to propose a novel procedure for three-dimensional modeling of CA from uncalibrated XRA projections. A comprehensive mathematical model of the image formation was developed and used with a robust genetic algorithm optimizer to determine the calibration parameters across XRA views. The frames correspondences between XRA acquisitions were found using a partial-matching approach. Using the same matching method, an efficient procedure for vessel centerline reconstruction was developed. Finally, the problem of meshing complex CA trees was simplified to independent reconstruction and meshing of connected branches using the proposed nonuniform rational B-spline (NURBS)-based method. Because it enables structured quadrilateral and hexahedral meshing, our method is suitable for the subsequent computational modelling of CA physiology (i.e. coronary blood flow, fractional flow reverse, virtual stenting and plaque progression). Extensive validations using digital, physical, and clinical datasets showed competitive performances and potential for further application on a wider scale

Generalized lymphadenopathy in patient with fever of unknown origin as a differential diagnostic challenge - case report

Published in May - 202