Papers by Birger Karlsson
Materials Science and Technology, 1991
... have shown that the thermal mismatch stresses are high enough to cause plastic flow in the ma... more ... have shown that the thermal mismatch stresses are high enough to cause plastic flow in the matrix.l4,lS In one study,16 residual microstresses associated with forma-tion of martensite in steel were seen to increase the effective threshold stress intensity ~Kth,eff' Once present ...
Materials Science and Engineering, 1975
The yield and work hardening of ferritepearlite aggregates with continuous ferrite matrix have be... more The yield and work hardening of ferritepearlite aggregates with continuous ferrite matrix have been studied, special attention being paid to the relative deformation of the individual constituents, which was followed by TEM and measurements of microhardness and X-ray line broadening. FEM calculations of the deformation of inclusions of similar geometry in a softer matrix have been performed for varying hardness ratio between inclusion and matrix. Hard and soft pearlite inclusions plastify at different degrees of overall strain. The flow stress of the aggregate structure can be described in terms of load transfer from the matrix to the inclusions, using a mixture rule which divides both stress and strain among the constituents in the ratio of their volume fractions.
Materials Science and Engineering, 1975
Using the finite difference method the homogenization of two-phase structures with moving interfa... more Using the finite difference method the homogenization of two-phase structures with moving interfaces has been studied. Boundary conditions involving solid/solid and solid/liquid structures representing typical technical situations have been utilized. As a special case the austenitization of normalized steels with different carbon contents has been investigated. The effects of austenitization temperature, concentration dependent diffusion coefficient and size distribution have been analyzed. It is shown that within the geometries and boundary conditions studied, the total homogenization time for solid/solid and solid/liquid structures is controlled by the final one-phase diffusion and that total homogeneity is achieved for Dt/a 2 = 0.3. It is also demonstrated that for austenitization the linearly concentration dependent diffusion coefficient can be approximated by that corresponding to the mean concentration. Increasing the standard deviation of the austenite cell size distribution drastically increases the austenitization time.
Kvvs Arsbok 2012 Pp 119 128, 2012
Det är 1960-tal. Gösta Ottervik är universitetets överbibliotekarie, tillika Kungl. Vetenskaps-oc... more Det är 1960-tal. Gösta Ottervik är universitetets överbibliotekarie, tillika Kungl. Vetenskaps-och Vitterhets-Samhällets bibliotekarie. Han begrundar Kungl. Samhällets emblem, som återkommer på årsbok och andra trycksaker. Han finner att emblemet (föreställande bl.a. en läsande kvinna) härrör från en minnesmedalj som präglades i samband med Kungl. Samhällets 100-årsjubileum år 1878. Men vad hade funnits tidigare? Han formulerar sin undran: Att K. Samhället, som tillkom redan på 1770-talet, först 100 år senare skulle ha vidtagit åtgärder för att anskaffa ett emblem tedde sig a priori föga sannolikt. Gösta Ottervik bedriver omsorgsfulla arkivstudier och finner mycket riktigt ett emblem/sigill från Kungl. Samhällets tillblivelse på 1770-talet. Det återinfördes vid 200-årsjubileet 1978 och är den bild vi är vana att se idag. Dess tillkomst, en rätt komplicerad historia om man skall gå i detalj, är tack vare Otterviks studier dokumenterade. Den återges i en kortversion nedan tillsammans med beskrivningar av emblemets vidare användning. Användning av emblem Numismatik-och främst då den del som avser medaljer av olika slagkan möjligen betraktas som ett uttryck för äldre tiders intresse för hederstecken och symbolik. Det avtagande bruket av ordnar och medaljer återspeglar också de förändringar som har skett i detta avseende. Samtidigt har emblem av olika slag, och då kanske främst i tryckt form, aldrig tillmätts så stor betydelse som i våra dagar. Varje företag, universitet, kulturinstitution och liknande av någon dignitet lägger ned stora resurser
HTM Journal of Heat Treatment and Materials, 2009
The bending fatigue strength of case hardened pulsator test gear wheels has been investigated for... more The bending fatigue strength of case hardened pulsator test gear wheels has been investigated for wheels in V2158 (20MnCrS5) and fatigue isotropic 158Q (≈ 20NiMo10) steels. The gear wheels in V2158 were forged either vertically or horizontally, the wheels in 158Q just vertically. Structural anisotropy levels were investigated in the horizontally forged V2158 gears. There was no noteworthy level of bending fatigue anisotropy to detect in the V2158 gears. However, the horizontally forged gears performed some 4% better than the vertically forged ones which may be explained by a somewhat more beneficial orientation and dispersion of sulfide inclusions in the horizontal gears. The fatigue isotropic 158Q steel is, in case-hardened components, obviously not required for isotropy reasons but highly appreciated for its outstanding fatigue performance. With identical heat treatment and surface condition, gears in 158Q outperform V2158 gears by some 23% in bending fatigue strength. This is exp...
HTM Journal of Heat Treatment and Materials, 2011
The bending fatigue strength of case-hardened pulsator test gear wheels has been investigated for... more The bending fatigue strength of case-hardened pulsator test gear wheels has been investigated for wheels in fatigue isotropic 20NiMo10 (Ovako 158Q) steel. The pulsator gears where either in un-peened (but shot-cleaned), single shotpeened or double shot-peened condition. Single shot peening increased the bending fatigue strength of the gears by some 11 per cent as compared with the un-peened. Double shotpeening was not successful and did not result in any further increase of bending fatigue strength. That was explained with wrongly chosen parameters of the second shot peening moment and therewith over-peening of the component. That second moment was a trial and had never been tested before. 20NiMo10 can be used on current production lines and can be case-hardened in current production furnaces. If availability of the steel is guaranteed, 20NiMo10 has the potential to replace current production material.
HTM Härtereitechnische Mitteilungen, 2007
Quench crack propensity has been investigated for two identical medium carbon steels (50CrMo4) wh... more Quench crack propensity has been investigated for two identical medium carbon steels (50CrMo4) which only differed in sulfur content. The standard variant of the material was affected by manganese sulfide inclusions whereas the low sulfur material was essentially free of sulfides. 80 mm, cylindrical test specimens were used. The test specimens had been cut out of cross rolled steel plates in which the manganese sulfide were flattened to discoid shape. The specimen orientation was in direction of principal deformation where the flattened sulfides were aligned with the test specimen axis. The largest sulfides reached lengths of 150 μm. Both materials were austenitized at 850 °C for 60 minutes, quenched in a salt-bath at 180 °C and immediately annealed at 425 °C for one hour. It turned out that the standard material developed quench cracks which initiated at manganese sulfide. No cracks could be found in the low sulfur material. Thermal and transformational stresses, which develop during quenching, aggravate the stress situation around the manganese sulfide and cause the cracking. The results are interpreted in fracture mechanical terms.
Materials Science and Engineering, 1973
Summao'* Grain refinement of plain, hypoeutectoid steels by means of repetitive short time austen... more Summao'* Grain refinement of plain, hypoeutectoid steels by means of repetitive short time austenitization is' studied. For carbon levels of 0.38, 0.I8 and O.05 wt. '% this' technique allows a reduction of grain size of up to 1 : I0 in Jerritic-pearlitic condition for original grain sizes of 50-100 t~m, The rapid nucleation of ferrite during controlled high speed cooling from the austenite temperature is important for the mechanism of yrain refinement.
Materials Science and Technology, 1997
ABSTRACT
Materials Science and Technology, 2006
An AA7030 alloy (Al-5. 4Zn-1. 2Mg) was tested for evidence of dynamic strain aging in naturally a... more An AA7030 alloy (Al-5. 4Zn-1. 2Mg) was tested for evidence of dynamic strain aging in naturally aged and peak aged condition and under varying conditions in terms of strain rate and temperature. Clear evidence in terms of strain rate sensitivity, serrated yielding (Portevin-Le Chatelier effect) and propagative plastic instabilities was observed in the naturally aged temper while the peak aged temper only showed serrated yielding. Further evidence of dynamic strain aging was the temperature and strain dependence of the strain rate sensitivity, which can be explained by the additional dislocation activation energy resulting from solute pinning. Investigation of the specimen surfaces was carried out to reveal an orange peel structure with pronounced glide bands. Small cracks within individual grains rather than grain boundary cracking could be observed.
Materials Science Forum, 2006
Abstract. In the present study the influence of strain rate and temperature on the behaviour of t... more Abstract. In the present study the influence of strain rate and temperature on the behaviour of two commercial aluminium alloys, 6063-T6 and 7030-T6, was investigated. Both alloys are high strength precipitation hardened alloys that are expected to have low strain rate and ...
Materials Science Forum, 2006
The effects of temperature and strain rate on the mechanical properties of aluminium alloy AA7030... more The effects of temperature and strain rate on the mechanical properties of aluminium alloy AA7030 (Al-5.4Zn-1.2Mg) in naturally aged and peak aged condition are investigated, with emphasis on the relation to dynamic strain ageing. It is found that the naturally aged material shows more severe signs of dynamic strain ageing, including inverse strain rate and temperature dependence of flow stress, inverse temperature dependence of the ductility and serrated yielding. The peak aged material also shows signs of dynamic strain ageing, but to a lesser extent, most pronounced through serrated yielding. The observed effects can be qualitatively explained in terms of a thermal activation based model for dislocation glide. Furthermore, inhomogeneous deformation is observed on several size scales ranging from localized glide bands to surface deformation effects (orange peel surface) and macroscopic flow localization in shear bands.
Metal cutting …, 2007
Vecka 30-32 kommer CPL-supporten inte att ha telefonservice på 3744 men tar hand om frågor per ma... more Vecka 30-32 kommer CPL-supporten inte att ha telefonservice på 3744 men tar hand om frågor per mail. Vid ev. akuta problem ber vi er kontakta bibliotekets låneexpedition på tfn 031-7723737 under bibliotekets öppettid. Service som vanligt fr. om 13 augusti.
Proceedings of the …, 2009
Abstract. The fatigue properties of two series of truck forged components in as forged and surfac... more Abstract. The fatigue properties of two series of truck forged components in as forged and surface shot blasted condition were studied. The tests were performed in full components in a specially designed rig for such purpose. Both series of components were tested in ...
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Papers by Birger Karlsson