| 1. |
- Ebrahimzadeh, PR, et al.
(författare)
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EFFECTS OF HUMIDITY CHANGES ON DAMPING AND STRESS-RELAXATION IN WOOD
- 1993
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Ingår i: Journal of Materials Science. - 2-6 BOUNDARY ROW, LONDON, ENGLAND SE1 8HN : CHAPMAN HALL LTD. - 0022-2461 .- 1573-4803. ; 28:20, s. 5668-5674
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Tidskriftsartikel (refereegranskat)abstract
- Mechanical damping (tan delta) and stress relaxation on pine veneer samples under stepwise humidity changes were investigated. The loss factor shows a transient peak every time the relative humidity (RH) of the surrounding atmosphere is changed, The effect appears to be associated with the diffusion of water molecules into or out of the material, the peaks being observed both when the sample is humidified (5%-85% RH) or subjected to drying. The results are supplemented by stress relaxation data obtained on similar specimens. Also in this case a higher relaxation rate is observed when the RH level around the sample is changed, the total stress decrease after several cycles being significantly larger than the corresponding value observed after the same period at the higher RH level.
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| 2. |
- Guo, S.J., et al.
(författare)
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Magnetic field dependence of the critical current density for the bismuth-based bulk high-Tc superconductors
- 1992
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Ingår i: Journal of Materials Science. - 0022-2461 .- 1573-4803. ; 27:11, s. 3043-3049
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Tidskriftsartikel (refereegranskat)abstract
- Three types of bismuth-based bulk samples were prepared through uniaxial pressing at room temperature, hot isostatic pressing (HIP) and drawing and rolling. Transport current properties were characterized in a steady field up to 1.12 T at 77 K (T/T c=0.75). The Josephson weak-link decoupling fields have been found to be 5 mT for the cold-pressed pellet and 30 mT for the HIPed pellet and the rolled tape. At the decoupling field the transport critical current density,J c, drops 80% from 124 (OT) to 29 A cm-2 (5 mT) for the cold-pressed pellet, 80% from 582 (OT) to 126 A cm-2 (30 mT) for the HIPed sample and 50% from6500 (0 T) to 2850 A cm-2 (30 mT) for the rolled tape. In the flux flow regime, whereB is perpendicular to thec-axis a modified Kim's modelJ c=(α/B 0)/[(1+B/B 0)] n can be used to describe the field dependence of the critical current density, Jc, in the field range 0.2-1.12 T. The effective upper critical fields were estimated to be 0.98, 1.54 and 1.94 T for the three types of samples, respectively. An adjustable range ofB c2 for bismuth-based bulk highT c superconductors is given. Flux shear may operate in these materials. The prediction of this pinning mechanism is yielded from fitting the equation qualitatively. WhenB is parallel to thec-axis, the absence of strongly intragranular flux-pinning is emphasized by the poor flux flow regime for the rolled tape sample.
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| 3. |
- Ion, John, et al.
(författare)
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Laser surface modification of a 13.5% Cr, 0.6% C steel
- 1991
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Ingår i: Journal of Materials Science. - 0022-2461 .- 1573-4803. ; 26:1, s. 43-48
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Tidskriftsartikel (refereegranskat)abstract
- A 13.5% Cr, 0.6% C steel, with an initial microstructure of chromium carbides in a ferrite matrix, was heat-treated by scanning a high-power laser beam over the surface. The aim was to compare the physical and chemical properties produced by this type of selective surface treatment with those resulting from a conventional furnace desensitization and quench-hardening heat treatment. Surface heating homogenized the carbon originally bound in the carbides sufficiently to produce martensite, giving hardening to levels comparable with a conventional heat treatment. Chromium-rich zones, carbides and retained austenite were also detected in the heated microstructure. Surface melting produced complete homogenization of both carbon and chromium, which resulted in the retention of large amounts of austenite in the microstructure on cooling to room temperature. Subsequent refrigeration at - 196 °C transformed some of the austenite to martensite. Pitting corrosion and local reductions in hardness were observed adjacent to treated areas under certain conditions, due to precipitation of secondary carbides and elevated tempering, respectively.
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| 4. |
- Larker, Rickard, et al.
(författare)
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AEM investigation of ceramic/incology 909 diffusional reactions after joining by HIP
- 1994
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Ingår i: Journal of Materials Science. - 0022-2461 .- 1573-4803. ; 29:16, s. 4404-4414
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Tidskriftsartikel (refereegranskat)abstract
- Diffusion bonding by hot isostatic pressing (HIP) was performed between Incoloy 909 and five different ceramics. Two of the ceramics were composites made from powder mixtures of Si3N4 and either 60 vol% TiN or 50 vol% TiB2, while three were monolithic materials, namely Si3N4 with 2.5 wt% Y2O3 as a sintering additive, Si3N4 without additives, and Si2 N2O without additives. A diffusion couple geometry was developed to facilitate the preparation of thin-foil specimens for examination by analytical electron microscopy (AEM). Diffusion bonding was performed by HIP at 927°C (1200K) and 200 MPa for 4 h. The formation of reaction layers was very limited, being less than 1 μm in total layer thickness. Two reaction products were found by AEM; a continuous, very thin, (≤100 nm) layer of fine TiN crystals at the initial ceramic/metal interface, and larger grains extending about 100–500 nm into the superalloy and forming a semi-continuous layer of a G-phase suicide containing mainly nickel, silicon and niobium.
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| 5. |
- Lindberg, K. A. H., et al.
(författare)
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Morphology of polyamide 6-polybutadiene multiblock copolymers
- 1991
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Ingår i: Journal of Materials Science. - 0022-2461 .- 1573-4803. ; 26:16, s. 4383-4388
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Tidskriftsartikel (refereegranskat)abstract
- The morphology of polyamide 6-polybutadiene multiblock copolymers, commonly used for reaction injection moulding, have been investigated using transmission electron microscopy, dynamic mechanical techniques, calorimetry and wide angle X-ray diffraction. Phase separation is found to be almost complete and the crystallization of the PA6 blocks is slightly higher than in pure PA6. The morphology shows similarities to what has been reported for segmented polyether-esters. The PA6 lamellar dimensions found in the micrographs agree with dimensions calculated from melting point depression and X-ray data.
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| 6. |
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| 7. |
- Wadsö, Lars
(författare)
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Describing non-Fickian water-vapour sorption in wood
- 1994
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Ingår i: Journal of Materials Science. - 0022-2461. ; 29:9, s. 2367-2372
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Tidskriftsartikel (refereegranskat)abstract
- Moisture transport and sorption in wood may not be accurately described by Fick's law of diffusion. The problem of making a model of non-Fickian behaviour (NFB) for wood is discussed. Some measurements in which NFB in wood is clearly seen are also reviewed. Four criteria, which must be satisfied by a model describing sorption in wood cell walls, are presented: (1) the model should not only describe the response to step changes in vapour pressure; (2) it should be able to predict sorption with more than one time scale; (3) the sorption rate should not depend on the thickness of the cell wall; (4) small rapid changes in vapour pressure should give slower fractional weight change than large rapid changes. A review of models of NFB in synthetic polymers indicates that there is presently no model of NFB which fulfills the above criteria. More measurements of the sorption behaviour of the cell wall are needed to construct such a model for wood. This model can then probably be used, together with a Fickian diffusion model, to model the sorption behaviour of whole wood.
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