Testing and modelling of butt-welded connections in thin-walled aluminium structures

The present paper experimentally investigated the mechanical behaviour of butt-welded joints and evaluated suitable numerical approaches for modelling them in thin-walled structures with large shell-based models. Welded connections of both similar and dissimilar materials were first experimentally investigated. Two extruded plates in 6060 and 7003 in temper T6 were used as parent materials for Metal Inert Gas (MIG) welding. Three welded joints were made by combining the two parent materials. Extensive testing was carried out to investigate microstructure, hardness and mechanical stress–strain behaviour of the base materials, heat-affected zones (HAZ) and weld metals. Cross-weld tensile tests with two weld orientations (with respect to the loading direction) were performed to study the load–displacement and fracture behaviour of the welded joints. The experimental results were also used to provide inputs to calibrate and validate shell element-based models simulating the response of welded aluminium structures. Two modelling approaches were investigated. The first approach, which is a conventional “mechanical analysis”, used material model inputs from the experimental testing, assuming uniform HAZ strength. The second modelling approach, which is proposed in this study for engineering applications, relies on inverse modelling of the load–displacement behaviour of similar material cross-weld tension tests to optimize the HAZ and weld properties. The newly proposed modelling approach was further verified based on a set of verification tests of cross-weld tension, using shell-based models with different mesh sizes. A good agreement between numerical and experimental results both in terms of load–displacement and fracture behaviour was obtained, suggesting that the novel modelling approach could be a reliable and efficient method for designing butt-welded aluminium structures.publishedVersio

Numerical simulations of submerged and pressurised X65 steel pipes – COMPLAS XII

While in service, pipelines may from time to time be exposed to impact loads from anchors or trawl gear. A lot of parameters influence the behaviour of the pipeline during impact, e.g. the diameter and thickness of the pipeline, the impactor’s mass and velocity, and of course the material used. Also potentially influencing the deformation pattern is the presence of surrounding water, which can be a difficult parameter to include experimentally. The pressurised contents of the pipeline can also be an influencing factor. To gain some insight into how the water and possible pressure inside the pipeline affect the global impact behaviour, numerical investigations have been carried out using FSI- techniques available in the explicit finite element code Europlexus. One case was set up for validation against available experimental data, and additional cases examined numerically the effect of including pressure and/or surrounding water. The simulations generally captured the deformation and load levels from the experiments well, and may be assumed to represent the events with reasonable accuracy. Adding internal pressure generally led to a higher peak load, and created a more localised deformation. Submerging the pipe in water seemed to be of minor importance with respect to global and local deformation, but this depended heavily on the FSI conditions. Other parameters than the surrounding water, which for design purposes may be omitted, appear to be more significant to the global and local response

A comprehensive profile of circulating RNAs in human serum

Non-coding RNA (ncRNA) molecules have fundamental roles in cells and many are also stable in body fluids as extracellular RNAs. In this study, we used RNA sequencing (RNA-seq) to investigate the profile of small non-coding RNA (sncRNA) in human serum. We analyzed 10 billion Illumina reads from 477 serum samples, included in the Norwegian population-based Janus Serum Bank (JSB). We found that the core serum RNA repertoire includes 258 micro RNAs (miRNA), 441 piwi-interacting RNAs (piRNA), 411 transfer RNAs (tRNA), 24 small nucleolar RNAs (snoRNA), 125 small nuclear RNAs (snRNA) and 123 miscellaneous RNAs (misc-RNA). We also investigated biological and technical variation in expression, and the results suggest that many RNA molecules identified in serum contain signs of biological variation. They are therefore unlikely to be random degradation by-products. In addition, the presence of specific fragments of tRNA, snoRNA, Vault RNA and Y_RNA indicates protection from degradation. Our results suggest that many circulating RNAs in serum can be potential biomarkers

En rocka arena for sosial utvikling. En kvalitativ studie av rockebandet som arena for utvikling av sosial kompetanse hos ungdom med sammensatte lærevansker

Denne oppgaven handler om utvikling av sosial kompetanse og på hvilke arenaer man kan se en slik utvikling. Sosial kompetanse er noe man opparbeider seg gjennom oppveksten ved blant annet å samhandle og samarbeide med andre mennesker i ulike situasjoner og på ulike arenaer. Musikk er en slik arena hvor man for eksempel i et band samarbeider om begrepet samspill for å sammen formidle et felles budskap gjennom musikken. Det jeg ønsker å se på i denne oppgaven er nettopp dette og har dermed kommet frem til problemstillingen: ”Bandet som arena for utvikling av sosial kompetanse for ungdommer med sammensatte lærevansker”. Formålet med prosjektet er å finne ut om musikk og bandmiljøet som dannes ved samspill i læringssituasjon har positiv effekt for utvikling av sosial kompetanse for ungdommer med sammensatte lærevansker. Dette er en casestudie hvor jeg har studert en bandgruppe med ungdommer i målgruppen. Jeg har sett mine observasjoner i lys av blant annet Gundersens og Moynahans tanker om sosial kompetanse og presenterer resultatene fra undersøkelsen i lys av denne teorien. Det fins ikke mye litteratur innenfor spesialpedagogikk som dreier seg om musikk utenfor musikkterapien, og derfor kan en studie som denne være et viktig bidrag. Som musikkpedagog som arbeider med utviklingshemmede eller mennesker med sammensatte lærevansker, er det viktig å ha en åpen holdning til egen pedagogikk og fremme inkludering og tilpasset opplæring

Strain localization and ductile fracture in advanced high-strength steel sheets

An experimental-numerical approach is applied to determine the strain localization and ductile fracture of high-strength dual-phase and martensitic steel sheet materials. To this end, four different quasi-static material tests were performed for each material, introducing stress states ranging from simple shear to equi-biaxial tension. The tests were analysed numerically with the nonlinear finite element method to estimate the failure strain as a function of stress state. The effect of spatial discretization on the estimated failure strain was investigated. While the global response is hardly affected by the spatial discretization, the effect on the failure strain is large for tests experiencing necking instability. The result is that the estimated failure strain in the different tests scales differently with spatial discretization. Localization analysis was performed using the imperfection band approach, and applied to estimate onset of failure of the two steel sheet materials under tensile loading. The results indicate that a conservative failure criterion for ductile materials may be established from localization analysis, provided strain localization occurs prior to ductile fracture.acceptedVersio

Combined three-point bending and axial tension of pressurised and unpressurised X65 offshore steel pipes – Experiments and simulations

Subsea pipelines are occasionally struck and hooked by objects such as anchors or trawl gear. The initial denting, followed by potential hooking and displacement of the pipeline, give rise to a complex load and deformation history. Transverse displacements cause a simultaneous increase in tensile axial forces, further complicating the load sequence. This study examines the effect of applying one of three different axial loads (zero, constant, and linearly increasing) to a pipe while simultaneously deforming it transversely. The three tests were repeated with an internal pressure of 10 MPa (100 bar), and all tests were recreated numerically in finite element simulations using both iterative (implicit) and non-iterative (explicit) approaches. As expected, adding an axial load increased the pipe's resistance to bending in terms of force-displacement, and the same can be said of including internal pressure. However, a more localised dent was observed in the pressurised pipes, which in turn could affect the onset of failure. The experimental results were well captured by the finite element simulations

Behaviour of plated structures subjected to blast loading

An experimental investigation using a new shock tube facility to study blast-load effects on thin aluminium plates is presented. The shock tube is designed to expose materials and structures to extreme loading conditions, such as accidental explosions or terrorist attacks. The intensity of the loading in the present study was determined by the initial conditions of the compressed gas, i.e. volume and pressure, and the resulting loading on the target plate was compared to experimental data from explosive detonations found in the literature. The square plates were manufactured from a low-strength aluminium alloy and had an exposed area of 0.3 × 0.3 m2. Piezoelectric pressure sensors were used for pressure recordings and synchronized with two high-speed cameras operating at a frame rate of 21,000 fps in a stereoscopic setup to capture the dynamic response using a three-dimensional digital image correlation (3D-DIC) technique. The experiment showed that the shock tube is capable of recreating a loading similar to that of an unconfined far-field airblast, and worked as an easily controllable alternative to explosive detonations when studying the dynamic response of structures subjected to blast loading

Mechanical modeling of the polymeric coating on a subsea pipeline

Offshore pipelines may be exposed to a range of extreme loading situations during operation on the seabed such as impact by trawl gear or anchors. While not primarily being designed for it, thermal insulating polymeric coatings are experienced to provide beneficial contributions to the structural integrity of subsea pipeline designs. In recent editions, the prevailing standards and design guidelines are allowing for the inclusion of external coating products in the mechanical design evaluation. This secondary functionality of insulating coatings presents a great potential in terms of more optimized pipeline designs. However, due to the lack of reliable and versatile mechanical models, any beneficial effects from these complex polymeric insulating coatings are often omitted in simulations. This work presents a finite element based approach for assessing the mechanical response of polymeric coatings on offshore pipelines with different porous structures imaged using X-ray micro computed tomography. The modeling approach is also compared with experimental results