On the Steinmetz hysteresis law

The behavior of the Steinmetz coefficient has been described for several different materials: steels with 3.2% Si and 6.5% Si, MnZn ferrite and Ni-Fe alloys. It is shown that, for steels, the Steinmetz law achieves R(2)> 0.999 only between 0.3 and 1.2 T, which is the interval where domain wall movement dominates. The anisotropy of Steinmetz coefficient for non-oriented (NO) steel is also discussed. It is shown that for a NO 3.2% Si steel with a strong Goss component in texture, the power law coefficient and remanence decreases monotonically with the direction of measurement going from rolling direction (RD) to transverse direction (TD), although coercive field increased. The remanence behavior can be related to the minimization of demagnetizing field at the surface grains. The data appear to indicate that the Steinmetz coefficient increases as magnetocrystalline anisotropy constant decreases. (c) 2008 Elsevier B.V. All rights reserved.

Tandem-MAG-hitsauksen soveltuvuus isojen levylakanoiden valmistamiseen

Diplomityön tavoitteena oli selvittää tandem-MAG-hitsausmenetelmän soveltuvuus isojen levylakanoiden valmistamiseen. Päätavoitteena oli selvittää suurimmat saavutettavat hitsausnopeudet sekä railonvalmistukselle asetettavat vaatimukset kahdella laivanrakennusteräksellä. Tutkimuksessa käytettiin omia hitsauskokeita ja liitokset testattiin luokitusseurojen vaatimusten mukaisesti. Selvitettiin myös syntyvät hitsausmuodonmuutokset sekä edut ja rajoitukset verrattuna laserhitsaukseen. Lisäksi laadittiin ei-synergiselle pulssihitsauslaitteistolle suuntaa-antava synergiakäyrä tätä sovellusta varten hitsauskokeiden perusteella. Tandem-MAG-hitsaus osoittautui erittäin kilpailukykyiseksi hitsausmenetelmäksi sovelluksessa. Magneettisen puhalluksen havaittiin olevan merkittävä häiriötekijä tällä menetelmällä hitsattaessa.

Desenvolvimento de microcélula eletroquímica para estudos de microrregiões

The construction and optimization of a device that can be applied to electrochemical studies in flat micro regions are described. This was developed as an attempt to study small regions of metallic samples, whose properties may differ completely from its macroscopic behavior and for studies in highly resistive medium. Some results were obtained for individual grains of polycrystalline samples, welded regions, pure copper, platinum, glassy carbon, single crystals of Cu-Zn-Al alloy, and steel in biodiesel without electrolyte intentionally added. The device showed to be useful for the proposed purpose, allowing to be automated and has potential possibilities of other applications.

Raskaita teräsrakenteita valmistavan tilauskonepajan tuotannon kehittäminen

Diplomityössä tarkastellaan raskaita teräsrakenteita valmistavan tilauskonepajan tuotannon kehittämiskohteita. Tuotannon kehittämisellä halutaan nopeuttaa tuotannon läpimenoaikoja, vähentää laatukustannuksia ja parantaa yrityksen tiedonkulkua. Näillä toimenpiteillä pyritään vaikuttamaan yrityksen kilpailukykyyn, jolloin se voi nousta suomalaisessa toimittajaverkostossa korkeammalle portaalle. Työn teoriaosassa paneudutaan tuottavuus- ja laatuajatteluun hitsaavassa konepajassa. Samalla esitellään eräitä konepajoissa tyypillisimmin käytettyjä laatustandardeja, joita ovat: SFS-EN ISO 9001, SFS-EN ISO 3834 ja SFS-EN 1090. Lisäksi teoriaosiossa on kerrottu erilaisista tuotannonohjausjärjestelmistä ja layout-teorioista. Tämän diplomityön kohdeyritys on Karjalan Konepaja Oy. Yrityksen nykytilanteen kartoittamiseksi suoritettiin useita haastatteluita sekä laadittiin koko organisaatiota koskeva kysely. Tilauskonepajan haasteena ovat alati muuttuvat tilaukset. Tilauskonepajan tuotannon kehittäminen tulee aloittaa sopivien tuotannontehokkuutta mittaavien mittareiden määrittämisellä. Usein kapasiteetti ja tuottavuus kuvastavat parhaiten työvaiheiden tehokkuutta. Mittareiden tarkoitus on auttaa konepajaa löytämään ne tuotannon pullonkaulat, joista yrityksen kehittäminen tulisi aloittaa. Lean-filosofian avulla tulee kehittää tuotannosta hitaimmin suoriutuvia työvaiheita. Tarkoituksena on poistaa valmistusketjusta sellaiset työvaiheet, jotka eivät anna tuotteelle lisäarvoa. Lisäksi työpisteiden layout kannattaa kyseenalaistaa aika ajoin, sillä jo pienilläkin muutoksilla voidaan saada parannuksia työpisteiden tuottavuuteen ja kapasiteettiin.

Desenvolvimento de microcélula eletroquímica para estudos de microrregiões

DEVELOPMENT of AN ELECTROCHEMICAL MICROCELL FOR STUDIES of MICRO REGIONS. The construction and optimization of a device that can be applied to electrochemical studies in flat micro regions are described. This was developed as an attempt to study small regions of metallic samples, whose properties may differ completely from its macroscopic behavior and for studies in highly resistive medium. Some results were obtained for individual grains of polycrystalline samples, welded regions, pure copper, platinum, glassy carbon, single crystals of Cu-Zn-Al alloy, and steel in biodiesel without electrolyte intentionally added. The device showed to be useful for the proposed purpose, allowing to be automated and has potential possibilities of other applications.

An Investigation of a Particular Weldment Failure

Two sets of weld-test coupons, supposedly made under identical conditions, were submitted to this institution last year for approval and certification under the A.S.M.E. Welder's Qualification Code. The first set of coupons was unsatisfactory. The second set, made by the same operators one month later, was satisfactory.

Magnetic drive system for a new centrifugal rotary blood pump

The purpose of this investigation was to design a novel magnetic drive and bearing system for a new centrifugal rotary blood pump (CRBP). The drive system consists of two components: (i) permanent magnets within the impeller of the CRBP; and (ii) the driving electromagnets. Orientation of the magnets varies from axial through to 60° included out-lean (conical configuration). Permanent magnets replace the electromagnet drive to allow easier characterization. The performance characteristics tested were the axial force of attraction between the stator and rotor at angles of rotational alignment, Ø, and the corresponding torque at those angles. The drive components were tested for various magnetic cone angles, ?. The test was repeated for three backing conditions: (i) non-backed; (ii) steel-cupped; and (iii) steel plate back-iron, performed on an Instron tensile testing machine. Experimental results were expanded upon through finite element and boundary element analysis (BEM). The force/torque characteristics were maximal for a 12-magnet configuration at 0° cone angle with steel-back iron (axial force = 60 N, torque = 0.375 Nm). BEM showed how introducing a cone angle increases the radial restoring force threefold while not compromising axial bearing force. Magnets in the drive system may be orientated not only to provide adequate coupling to drive the CRBP, but to provide significant axial and radial bearing forces capable of withstanding over 100 m/s2 shock excitation on the impeller. Although the 12 magnet 0° (?) configuration yielded the greatest force/torque characteristic, this was seen as potentially unattractive as this magnetic cone angle yielded poor radial restoring force characteristics.

Temperature effects on the mechanism of time independent hydrogen assisted fatigue crack propagation in steels

The effects of temperature on hydrogen assisted fatigue crack propagation are investigated in three steels in the low-to-medium strength range; a low alloy structural steel, a super duplex stainless steel, and a super ferritic stainless steel. Significant enhancement of crack growth rates is observed in hydrogen gas at atmospheric pressure in all three materials. Failure occurs via a mechanism of time independent, transgranular, cyclic cleavage over a frequency range of 0.1-5 Hz. Increasing the temperature in hydrogen up to 80°C markedly reduces the degree of embrittlement in the structural and super ferritic steels. No such effect is observed in the duplex stainless steel until the temperature exceeds 120°C. The temperature response may be understood by considering the interaction between absorbed hydrogen and micro-structural traps, which are generated in the zone of intense plastic deformation ahead of the fatigue crack tip. © 1992.

Electrochemical study of modified non-functional bis-silane layers on Al alloy 2024-T3

In the last few years great efforts have been made in order to find and to develop environmentally friendly substitutes for Cr6+ pre-treatments applied on aluminium alloys used in the aircraft industry. Among the potential substitutes, silane layers have attracted considerable interest from researchers and from the industry. The present work investigates the anti-corrosion behaviour of (bis-1, 2-(triethoxysilyl) ethane (BTSE)) silane layers modified with Ce ions and/or silica nanoparticles applied on Al alloy 2024-T3 substrates. The corrosion behaviour was investigated in 0.1 M NaCl solution via d.c. polarization and electrochemical impedance spectroscopy (EIS). Contact angle measurements and XPS were used to assess information on the chemistry of the silane pre-treated surfaces. The results have shown that the introduction of additives improves the corrosion protection properties of the silane layer. (c) 2008 Elsevier Ltd. All rights reserved.

Fracture modes and acoustic emission characteristics of hydrogen-assisted cracking in high-strength low-alloy steel weldment

The aim of the present paper is to study the relationship between the fracture modes in hydrogen-assisted cracking (HAC) in microalloied steel and the emission of acoustic signals during the fracturing process. For this reason, a flux-cored arc weld (FCAW) was used in a high-strength low-alloy steel. The consumable used were the commercially available AWS E120T5-K4 and had a diameter of 1.6 mm. Two different shielding gases were used (CO2 and CO2+5% H2) to obtain complete phenomenon characterization. The implant test was applied with three levels of restriction stresses. An acoustic emission measurement system (AEMS) was coupled to the implant test apparatus. The output signal from the acoustic emission sensor was passed through an electronic amplifier and processed by a root mean square (RMS) voltage converter. Fracture surfaces were examined by scanning electron microscopy (SEM) and image analysis. Fracture modes were related with the intensity, the energy and the number of the peaks of the acoustic emission signal. The shielding gas CO2+5% H2 proved to be very useful in the experiments. Basically, three different fracture modes were identified in terms of fracture appearance: microvoid coalescence (MVC), intergranular (IG) and quasi-cleavage (QC). The results show that each mode of fracture presents a characteristic acoustic signal.

Effects Of The Flash Welding Process On Mechanical And Microstructural Properties Of Structural Steel Joints Assessed Using Dest

ASTM A529 carbon¿manganese steel angle specimens were joined by flash butt welding and the effects of varying process parameter settings on the resulting welds were investigated. The weld metal and heat affected zones were examined and tested using tensile testing, ultrasonic scanning, Rockwell hardness testing, optical microscopy, and scanning electron microscopy with energy dispersive spectroscopy in order to quantify the effect of process variables on weld quality. Statistical analysis of experimental tensile and ultrasonic scanning data highlighted the sensitivity of weld strength and the presence of weld zone inclusions and interfacial defects to the process factors of upset current, flashing time duration, and upset dimension. Subsequent microstructural analysis revealed various phases within the weld and heat affected zone, including acicular ferrite, Widmanstätten or side-plate ferrite, and grain boundary ferrite. Inspection of the fracture surfaces of multiple tensile specimens, with scanning electron microscopy, displayed evidence of brittle cleavage fracture within the weld zone for certain factor combinations. Test results also indicated that hardness was increased in the weld zone for all specimens, which can be attributed to the extensive deformation of the upset operation. The significance of weld process factor levels on microstructure, fracture characteristics, and weld zone strength was analyzed. The relationships between significant flash welding process variables and weld quality metrics as applied to ASTM A529-Grade 50 steel angle were formalized in empirical process models.

Effect of cooling rate on intercritically reheated microstructure and toughness in high strength low alloy steel

High strength low alloy steels have been shown to be adversely affected by the existence of regions of poor impact toughness within the heat affected zone (HAZ) produced during multipass welding. One of these regions is the intercritically reheated coarse grained HAZ or intercritical zone. Since this region is generally narrow and discontinuous, of the order of 0.5 mm in width, weld simulators are often employed to produce a larger volume of uniform microstructure suitable for toughness assessment. The steel usedfor this study was a commercial quenched and tempered steel of 450 MN m -2 yield strength. Specimen blanks were subjected to a simulated welding cycle to produce a coarse grained structure of upper bainite during the first thermal cycle, followed by a second thermal cycle where the peak temperature T p2 was controlled. Charpy tests carried out for T p2 values in the range 650-850°C showed low toughness for T p2 values between 760 and 790°C, in the intercritical regime. Microstructural investigation of the development of grain boundary martensite-retained austenite (MA) phase has been coupled with image analysis to measure the volume fraction of MAformed. Most of the MA constituent appears at the prior austenite grain boundaries during intercritical heating, resulting in a 'necklace' appearance. For values of T p2 greater than 790°C the necklace appearance is lost and the second phase areas are observed throughout the structure. Concurrent with this is the development of the fine grained, predominantly ferritic structure that is associated with the improvement in toughness. At this stage the microstructure is transforming from the intercritical regime structure to the supercritically reheated coarse grained HAZ structure. The toughness improvement occurs even though the MA phase is still present, suggesting that the embrittlement is associated with the presence of a connected grain boundary network of the MA phase. The nature of the second phase particles can be controlled by the cooling rate during the second cycle and variesfrom MA phase at high cooling rates to a pearlitic structure at low cooling rates. The lowest toughness of the intercritical zone is observed only when MA phase is present. The reason suggested for this is that only the MA particles debond readily, a number of debonded particles in close proximity providing sufficient stress concentration to initiate local cleavage. © 1993 The Institute of Materials.

A simple method for non-linear analysis of steel fiber reinforced concrete

This paper proposes a physical non-linear formulation to deal with steel fiber reinforced concrete by the finite element method. The proposed formulation allows the consideration of short or long fibers placed arbitrarily inside a continuum domain (matrix). The most important feature of the formulation is that no additional degree of freedom is introduced in the pre-existent finite element numerical system to consider any distribution or quantity of fiber inclusions. In other words, the size of the system of equations used to solve a non-reinforced medium is the same as the one used to solve the reinforced counterpart. Another important characteristic of the formulation is the reduced work required by the user to introduce reinforcements, avoiding ""rebar"" elements, node by node geometrical definitions or even complex mesh generation. Bounded connection between long fibers and continuum is considered, for short fibers a simplified approach is proposed to consider splitting. Non-associative plasticity is adopted for the continuum and one dimensional plasticity is adopted to model fibers. Examples are presented in order to show the capabilities of the formulation.