Comparison between friction stir and submerged arc welding applied to joining DH36 and E36 shipbuilding steel

With the impending development of FSW tools for steel with useful lifetimes, attention has turned to the mechanical properties of the welds that can be made in a range of industrially significant steels. This work reports on a comparative study undertaken to examine the use of friction stir and submerged arc welding on DH36 and E36 shipbuilding steels. The study made an assessment of the distortion induced in fabricating plates by the two welding techniques, and provides initial comparative data on weld tensile strength, toughness and fatigue life. In each case, friction stir welding was shown to outperform submerged arc welding

A comparison between single sided friction stir welded and submerged arc welded DH36 steel thin plate

The adoption of the friction stir welding (FSW) process into the shipbuilding industry is being considered as a medium term issue. Currently the data on friction stir welded mild steels tends to be fragmented, with critical areas being short on specific data e.g. toughness. The work described has been put in place to directly compare friction stir welded and submerged arc welded thin plate. The plate thicknesses used were 4, 6 and 8mm thick DH36 grade steel, which are commonly used in the construction of vessels such and destroyers, frigates corvettes and offshore patrol vessels. Friction stir welding was carried out using the currently best established parameters for a single sided process and this was compared against Submerged Arc Welding (SAW) over the same thickness range. Distortion was found to be lower in friction stir welded steel, but the 4mm thick was still showing significant distortion. No issues were identified with weld metal strength, and toughness at -20OC was found to be comparable but more uniform across the weld area than with the submerged arc welded material. Microstructural observations have been linked to hardness, toughness and fatigue test data. The fatigue data includes the observation of preferential crack initiation relative to the trailing/leading side of the welding process. An assessment on the feasibility of the process in a shipbuilding environment will be included based on the data presented

A comparison between single sided and double sided friction stir welded 8mm thick DH36 steel plate

As part of an ongoing process to fully evaluate the potential for friction stir welding (FSW) to be used in the shipbuilding industry, a comparison has been made between two variants of the process. 8mm thick DH36 steel plate was friction stir welded using a single sided and a double sided process. An assessment of the processes was made to report on the resultant distortion behaviour, hardness, yield strength, toughness and microstructure. As a further comparison, additional work on 8mm thick submerged arc welded (SAW) DH36 plate has been included as the current shipbuilding benchmark. The overall process feasibility will be assessed including the issue of the requirement to rotate the workpiece through 180° to complete the second side of the double sided process

Friction stir welding of thin DH36 steel plate

A series of 4, 6 and 8 mm DH36 steel welds were produced using optimum conditions for friction stir welding (FSW). Comparator welds in the same thickness from the same plates were produced using a single sided single pass process submerged arc welds (SAW). This work was carried out to evaluate the mechanical properties of FSW material with a view to its possible application in a shipbuilding production process route. Overall, the performance of the FSW material was superior to the SAW comparators. Areas such as distortion and fatigue were particularly positive in the FSW material. An 8 mm thick plate was also produced using two FSW passes, one from either side, and it was found to have superior toughness and fatigue performance when compared to the single sided 8 mm FSW material. Some of these benefits are thought to have originated from the internal overlap zone between the two passes

Advances in friction stir welding of steel : Project HILDA

A microstructure and property evaluation of friction stir welded DH36 6mm plate has been undertaken. The study examined a wide range of process parameters and, from this, a process parameter envelope has been developed and an initial process parameter set established that gives good welding properties. Thermo-mechanical deformation studies were developed to generate flow stress regimes over a range of stain rates and temperatures and these data will support the on-going local numerical modelling development. A preliminary thermo-fluid model has been developed to predict temperature and material flow during the FSW of steel grade DH36. In this model, materials are considered as highly viscous incompressible fluid. The welded material is flowing around the rotating tool thanks to the modelling of the friction at tool/workpiece interface. In parallel, a global numerical model is being developed to predict the inherent residual stresses and distortion of FSW butt welded assemblies often in excess of 6m long plate

A techno-economic evaluation of friction stir welding of DH36 steel

Friction stir welding of steel presents an array of advantages across many industrial sectors such as shipbuilding when compared to conventional fusion welding techniques. However, there seems to be very limited techno-economic assessment studies on its potential introduction in industry, and particularly in shipbuilding. A microstructure and property evaluation of friction stir welded low alloy steel grade DH36 plate, commonly used in ship and marine applications has been undertaken. In this comprehensive study, steel plates were butt welded together at increasing traverse speeds in order to improve the technical competitiveness of the process. Samples were examined microscopically and by traverse tensile testing, Charpy impact testing and micro-hardness testing in various regions of the weld. The study has examined a wide range of traverse speeds; from this, initial process parameter data have been established that are able to produce commercially attractive excellent quality welds through a substantial increase in the conventionally recognised welding traverse speed. In parallel, a comparative economic evaluation between friction stir welding and submerged arc welding has revealed a number of areas where the former is superior. However, the cost of the friction stir welding tool for steel has been exposed as the dominant obstacle for the wider commerical acceptance of the process on steel

The upgraded low-background germanium counting facility Gator for high-sensitivity γ-ray spectrometry

We describe the upgrade and performance of the high-purity germanium counting facility Gator, which is dedicated to low-background γ-ray spectrometry. Gator is operated at the Gran Sasso Underground Laboratory in Italy, at an average depth of 3600 meter water equivalent, and employed for material screening and selection in ultra-low background, rare-event search experiments in astroparticle physics. The detector is equipped with a passive shield made of layers of copper, lead and polyethylene, and the sample cavity is purged with gaseous nitrogen maintained at positive pressure for radon suppression. After upgrading its enclosure, the background rate is (82.0 ± 0.7) counts/(kg·day) in the energy region 100 keV to 2700 keV, a 20% reduction compared to the previously reported rate. We show the stability of various operation parameters as a function of time. We also summarize the sample analysis procedure, and demonstrate Gator's sensitivity by examining one material sample, a candidate photosensor for the DARWIN experiment

Pismenost nakon decentralizacije. Nudi li Mreža novi oblik pismenosti?

Rad će postaviti pitanje nudi li danas Mreža alat za “osnaživanje čitatelja”, kako je najavljivala hipertekstualna teorija devedesetih. Interaktivnost kao “prirodan” oblik pismenosti postala je ideologem razumijevanja elektroničke pismenosti. No je li danas uistinu riječ o demokratizaciji čitanja-pisanja putem odabira smjera, “kretanja” virtualnim prostorom teksta? Rad će naglasiti razliku između Web 2.0 žanrova i koncepcije hiperteksta te razliku tekstualne i vizualne pismenosti. Ono što ćemo ovdje nazvati “topografskom proizvodnošću” bitno se razlikuje od “distributivne proizvodnosti” kakvu danas susrećemo na Mreži. Mreža nije orijentirana isključivo na proizvodnju virtualnog dérivea, trodimenzionalnog prostora kretanja, već je riječ prvenstveno o komunikacijskom kanalu. Umjesto topografije, za Mrežu će biti ključno povezivanje bilo kojih dviju točaka i uspostavljanje kanala “distribucije”. Temelj distributivne strukture jesu mrežni protokoli, prvenstveno TCP/IP protokol koji omogućava peer-to-peer, izravnu komunikaciju dvaju računala. Kanali neovisne distribucije postojali su i ranije, prvenstveno u polju alternativnih ili opozicijskih kultura u obliku DIY praksi, no domet njihove distributivne mreže bio je slab. Mreža je kanal do sada nezamislive fleksibilne distribucije, nehijerarhijski kanal koji (digitalnoj) proizvodnji pripaja dodatnu vrijednost. Politička, ekonomska i kulturalna pitanja redefinirana su arhitekturom te protokolima koji tu arhitekturu definiraju. Protokoli su pravila koja su podređena socijalnom konsenzusu. U tom smislu politička teorija novih medija mora napustiti mit “osnaživanja čitatelja” i krenuti prema složenom tipu materijalne analize ili analize arhitekture te socijalnih pravila koja tu arhitekturu definiraju. Proizvodno-distribucijski subjekti i tekstovi naseljavaju sve mrežne komunikacijske kanale. Bloganje, Twitteranje, Facebookanje, Flickeranje, YouTubanje naših života dio je procesa lifestreama. Dio je ontologije elektroničkog identiteta ultimativni zahtjev za menadžeriranjem života koji se provodi translacijom identitetskih varijabli na Mrežu

Thermalisation of self-interacting solar flare fast electrons

Most theoretical descriptions of the production of solar flare bremsstrahlung radiation assume the collision of dilute accelerated particles with a cold, dense target plasma, neglecting interactions of the fast particles with each other. This is inadequate for situations where collisions with this background plasma are not completely dominant, as may be the case in, for example, low-density coronal sources. We aim to formulate a model of a self-interacting, entirely fast electron population in the absence of a dense background plasma, to investigate its implications for observed bremsstrahlung spectra and the flare energy budget. We derive approximate expressions for the time-dependent distribution function of the fast electrons using a Fokker-Planck approach. We use these expressions to generate synthetic bremsstrahlung X-ray spectra as would be seen from a corresponding coronal source. We find that our model qualitatively reproduces the observed behaviour of some flares. As the flare progresses, the model's initial power-law spectrum is joined by a lower energy, thermal component. The power-law component diminishes, and the growing thermal component proceeds to dominate the total emission over timescales consistent with flare observations. The power-law exhibits progressive spectral hardening, as is seen in some flare coronal sources. We also find that our model requires a factor of 7 - 10 fewer accelerated electrons than the cold, thick target model to generate an equivalent hard X-ray flux. This model forms the basis of a treatment of self-interactions among flare fast electrons, a process which affords a more efficient means to produce bremsstrahlung photons and so may reduce the efficiency requirements placed on the particle acceleration mechanism. It also provides a useful description of the thermalisation of fast electrons in coronal sources.Comment: 9 pages, 7 figures, accepted for Astronomy & Astrophysics; this version clarifies arguments around Eqs. (11) and (20

Taking Blockchain Seriously

In the present techno-political moment it is clear that ignoring or dismissing the hype surrounding blockchain is unwise, and certainly for regulatory authorities and governments who must keep a grip on the technology and those promoting it, in order to ensure democratic accountability and regulatory legitimacy within the blockchain ecosystem and beyond. Blockchain is telling (and showing) us something very important about the evolution of capital and neoliberal economic reason, and the likely impact in the near future on forms and patterns of work, social organization, and, crucially, on communities and individuals who lack influence over the technologies and data that increasingly shape and control their lives. In this short essay I introduce some of the problems in the regulation of blockchain and offer counter-narratives aimed at cutting through the hype fuelling the ascendency of this most contemporary of technologies