| 1. |
- Haas, Sylvio, et al.
(author)
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Correlation of precipitate evolution with Vickers hardness in Haynes® 282® superalloy : In-situ high-energy SAXS/WAXS investigation
- 2018
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In: Materials Science & Engineering. - : Elsevier BV. - 0921-5107 .- 1873-4944 .- 0921-5093 .- 1873-4936. ; 11, s. 250-258
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Journal article (peer-reviewed)abstract
- The aim of this work is to characterize the precipitation kinetics in Haynes® 282® superalloys using in-situ high-energy Small Angle X-ray Scattering (SAXS) together with Wide Angle X-ray Scattering (WAXS). The phases identified by WAXS include γ (matrix), γ′ (hardening precipitates), MC (metallic carbides), and M23C6/M6C (secondary metallic carbides). The γ'-precipitates are spheroids with a diameter of several nanometres, depending on the temperature and ageing time. From the SAXS data, quantitative parameters such as volume fraction, number density and inter-particle distance were determined and correlated with ex-situ Vickers microhardness measurements. The strengthening components associated with precipitates and solid solutions are differentiated using the measured Vickers microhardness and SAXS model parameters. A square root dependence between strengthening attributable to the precipitates and the product of volume fraction and mean precipitate radius is found. The solid solution strengthening component correlates with the total volume fraction of precipitates.
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| 2. |
- Semchuk, O. Yu., et al.
(author)
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Features of transport phenomenas in magnetic semiconductors with laser-induced periodic nanostructures
- 2007
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In: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936 .- 0928-4931 .- 1873-0191. ; 27:5-8, s. 1360-1363
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Journal article (peer-reviewed)abstract
- The mechanisms of formation of the laser-induced periodic surface and bulk nanostructures in magnetic semiconductors are considered. Their influence on transport phenomena in ferromagnetic semiconductors (FMSC) is investigated. It is shown that under action of laser beams (LB) a laser-induced periodic nanostructures — gratings of the electron and magnon temperatures, electron concentration and electric fields arises in FMSC. It is determined, that the illuminating of an external surface of the FMSC by several LB results in an emerging new effect — appearance of a dropping site on the voltage-current characteristic (VCC) of the FMSC with the static laser-induced periodic nanostructures. This effect can only be observed for the carrier concentration n ≥ 1018 cm−3, since for smaller concentration the contribution of an additional current caused by the presence of the laser-induced periodic nanostructures will be insignificant.
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| 3. |
- Akshantala, Nagendra V., et al.
(author)
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A micromechanics based model for predicting fatigue life of composite laminates
- 2001
-
In: Materials Science & Engineering. - 0921-5093 .- 1873-4936. ; 285:1-2, s. 303-313
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Journal article (peer-reviewed)abstract
- The current practice, as well as the hitherto proposed models, for assessment of fatigue life of composite laminates rely largely on experimental fatigue life data. In this paper, we propose a methodology for fatigue life prediction that utilizes a micromechanics based evaluation of damage evolution in conjunction with a semi-empirical fatigue failure criterion. The specific case treated is that of cross ply laminates under cyclic tension. The predicted results are compared with experimental data for several glass/epoxy and carbon/epoxy laminates, and good agreement is found. Published by Elsevier Science S.A. The current practice, as well as the hitherto proposed models, for assessment of fatigue life of composite laminates rely largely on experimental fatigue life data. In this paper, we propose a methodology for fatigue life prediction that utilizes a micromechanics based evaluation of damage evolution in conjunction with a semi-empirical fatigue failure criterion. The specific case treated is that of cross ply laminates under cyclic tension. The predicted results are compared with experimental data for several glass/epoxy and carbon/epoxy laminates, and good agreement is found.
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| 4. |
- Almqvist, Nils, et al.
(author)
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Surface characterization of SiC composites exposed to deuterium ions, using atomic force microscopy
- 1995
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In: Materials Science & Engineering. - 0921-5093 .- 1873-4936. ; 201:1-2, s. 277-285
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Journal article (peer-reviewed)abstract
- We study the influence of deuterium plasma on the surface structure of SiC based composites. The substrates are silicon carbides doped with titanium diboride, aluminium nitride or graphite. A number of surface sensitive techniques are used to characterize the substrates, before and after exposure to low-energy deuterium ions, the main method being atomic force microscopy. The microscope reveals distinct morphological changes on the irradiated samples. The density and surface area of the samples probably influence the content of deuterium in the surfaces. However, this study shows that the amount of graphite aggregated on the surfaces is of crucial importance for the uptake of deuterium.
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| 5. |
- Asnafi, Nader, 1960-, et al.
(author)
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Theoretical and experimental analysis of stroke-controlled tube hydroforming
- 2000
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In: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 279:1-2, s. 95-110
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Journal article (peer-reviewed)abstract
- To select tube hydroforming instead of conventional fabrication, one has to know the tube material behaviour and tribological effects during hydroforming and how the hydroforming operation itself should be controlled. The hydroforming operation is either force- or stroke-controlled. This paper deals with stroke-controlled hydroforming. Hydroforming consists of free forming and calibration. In this paper, only the so-called free forming is treated. Stroke-controlled free forming is studied theoretically and experimentally. The theoretical part consists of analytical modeling and finite-element simulations. The conducted experiments are used to show the types of errors that might occur, when the theoretically obtained loading paths are transferred to the hydroforming equipment. The forming limit curve (FLC) is normally used as an aid/instrument in component and process design (which include finite-element simulations). The present study shows that the FLC of the tube material must be determined by hydroforming, if component and process design are to rely on this instrument.
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| 6. |
- Bergquist, Bjarne
(author)
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The importance of experimental design
- 2002
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In: Materials Science & Engineering. - 0921-5093 .- 1873-4936. ; 328:1-2, s. 348-349
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Journal article (other academic/artistic)
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| 7. |
- Eriksson, C. L., et al.
(author)
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Strain-hardening and residual stress effects in plastic zones around indentations
- 2003
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In: Materials Science & Engineering. - 0921-5093 .- 1873-4936. ; 340:02-jan, s. 193-203
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Journal article (peer-reviewed)abstract
- Plastic zones were revealed by polishing away Vickers indentations made in soda-lime glass, WC-11% Co, W and 7075 Al. Micro and nanohardness traces were used to explore the local mechanical response. The hardness value within the deformed zone increased up to 21% depending on the material. Soda-lime glass was the only material not to show a hardening effect, in fact it showed a small decrease in hardness. Finite element calculations were used to qualitatively determine the influence from residual stresses at indentation of soda-lime glass. The results are discussed in the context of the influence from work-hardening and residual stresses on indentation quantities.
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| 8. |
- Gunnars, Jens, et al.
(author)
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Determination of growth-induced strain and thermo-elastic properties of coatings by curvature measurements
- 2002
-
In: Materials Science & Engineering. - 0921-5093 .- 1873-4936. ; 336:1-2, s. 7-21
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Journal article (peer-reviewed)abstract
- Curvature measurements on bimaterial specimens are examined for determination of residual strain/stress and thermo-elastic properties of coatings and layered materials. By using specimens with material layers of comparable thickness, large deflections and thereby high measurement accuracy are obtained. Strain-curvature relations are given for beam and plate specimens at different deformation modes. A robust fitting method for simultaneous determination of the mismatch strain and the modulus of elasticity is described. Experiments are performed on a titanium nitride (TiN) coating deposited on a thick high-speed steel substrate by PVD. The modulus of elasticity and the thermal expansion coefficient for the TiN coating are determined to 500 GPa and 7.4 x 10 exp -6 K exp -1 , respectively. The characteristic residual stress, i.e. the thin-film stress at room temperature, is -3.8 GPa, for this material combination and deposition conditions. The temperature independent growth-induced strain is determined to -0.0045, which is 75% of the mismatch strain at room temperature.
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| 9. |
- Hansson, T., et al.
(author)
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Elevated temperature fracture behavior of monolithic and SiCW- reinforced silicon nitride under quasi-static loads
- 1996
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In: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 209:1-2, s. 137-148
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Journal article (peer-reviewed)abstract
- Fracture behavior of a monolithic and SiCw-reinforced Si3N4 over the 1000-1550 °C temperature range with monotonically increasing loads was investigated. Peaks in the fracture initiation toughness, Kc, were found to occur owing to the brittle-to-ductile transition in the fracture behavior. This transition is associated with the onset of viscous deformation of the secondary intergranular amorphous phase present in the microstructure and the concomitant relaxation of the crack-tip stresses. The brittle-to-ductile transition temperature (BDTT) depends on the loading rate. Damage accumulation in terms of nucleation and growth of cavities ahead of the crack-tip promote stable crack growth at temperatures higher than the BDTT. The length of the subcritical crack increases with increasing temperature. Experiments involving the introduction of stable cracks at elevated temperatures followed by room-temperature fracture toughness testing reveal that shielding owing to the crack-wake bridging increases the apparent fracture resistance above the BDTT. Micromechanisms of the brittle-to-ductile transition and subcritical crack growth at elevated temperatures in the Si3N4 ceramics were discussed.
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| 10. |
- Johansson, Sten, 1948-, et al.
(author)
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Measurement of average texture of cold-rolled aluminium sheet by electron back-scattering diffraction : a comparison with neutron diffraction
- 2001
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In: Materials Science & Engineering. - 0921-5093 .- 1873-4936. ; 315:1-2, s. 129-135
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Journal article (peer-reviewed)abstract
- Measurements of the average texture on sheet of commercial pure aluminium have been performed using neutron diffraction and electron back-scattering diffraction (EBSD). Orientation distribution function maps have been calculated and compared. The results show a good correspondence provided that the data from the EBSD measurements are corrected according to a texture index versus inverted number of measurement procedure. Most errors are probably related to differences in investigated volume and calculation technique and to the fact that the microstructure was difficult for EBSD measurements.
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