| 1. |
- Akshantala, Nagendra V., et al.
(författare)
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A micromechanics based model for predicting fatigue life of composite laminates
- 2001
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Ingår i: Materials Science & Engineering. - 0921-5093 .- 1873-4936. ; 285:1-2, s. 303-313
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Tidskriftsartikel (refereegranskat)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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| 2. |
- Asnafi, Nader, 1960-, et al.
(författare)
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Theoretical and experimental analysis of stroke-controlled tube hydroforming
- 2000
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 279:1-2, s. 95-110
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Bergquist, Bjarne
(författare)
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The importance of experimental design
- 2002
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Ingår i: Materials Science & Engineering. - 0921-5093 .- 1873-4936. ; 328:1-2, s. 348-349
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 4. |
- Eriksson, C. L., et al.
(författare)
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Strain-hardening and residual stress effects in plastic zones around indentations
- 2003
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Ingår i: Materials Science & Engineering. - 0921-5093 .- 1873-4936. ; 340:02-jan, s. 193-203
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Gunnars, Jens, et al.
(författare)
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Determination of growth-induced strain and thermo-elastic properties of coatings by curvature measurements
- 2002
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Ingår i: Materials Science & Engineering. - 0921-5093 .- 1873-4936. ; 336:1-2, s. 7-21
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Johansson, Sten, 1948-, et al.
(författare)
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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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Ingår i: Materials Science & Engineering. - 0921-5093 .- 1873-4936. ; 315:1-2, s. 129-135
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Moverare, Johan, 1973-, et al.
(författare)
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Deformation behaviour of a prestrained duplex stainless steel
- 2002
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Ingår i: Materials Science & Engineering. - 0921-5093 .- 1873-4936. ; 337:1-2, s. 25-38
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Tidskriftsartikel (refereegranskat)abstract
- The anisotropic flow behaviour due to a change in strain path during uniaxial deformation of a duplex stainless steel has been investigated. The anisotropic flow behaviour of the as-received material could be predicted from the crystallographic texture. However, it was found that prestraining introduces a transient work hardening behaviour during the second stage deformation, which causes an anisotropic flow behaviour immediately after yielding that cannot be described by the crystallographic texture. Samples subjected to a coaxial second stage deformation show a small increase in flow stress and similar work hardening rate as in the monotonic loading. Samples subjected to noncoaxial second stage deformation show a pronounced transient stage characterised by early yielding and a high work hardening rate in the first part of the transient stage. Beyond the earliest stage of deformation a higher flow stress and a lower work hardening rate compared to monotonic loading is observed for the noncoaxial samples. The transient phenomena are discussed based on the measured internal stresses and the differences in dislocation structures in the two different phases.
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| 8. |
- Nygårds, Mikael, et al.
(författare)
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Micromechanical modeling of ferritic/pearlitic steels
- 2002
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Ingår i: Materials Science & Engineering. - 0921-5093 .- 1873-4936. ; 325:1-2, s. 435-443
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Tidskriftsartikel (refereegranskat)abstract
- A two-dimensional micromechanical model based on the Voronoi algorithm is presented to model two-phase ferritic/pearlitic steels. Special care is taken to generate periodic grain structures as well as periodic finite element meshes. The model is evaluated by generalized plane strain finite element calculations, periodic representative cells are generated with the desired volume fraction pearlite. Loading by an arbitrary combination of average stresses or strains is possible by application of periodic boundary conditions. Uniaxial tension tests are performed on pure ferrite and pearlite specimens, as well as on materials containing 25 and 58% pearlite. Modeling of the two-phase materials was performed by using the stress-strain curves of the pure phases, in the description of the plastic properties. Comparisons between generated data and experiments at a loading strain of 2% show good agreement. Moreover, local stresses and strains are studied within the different unit cells. In addition, the model is used to investigate the plastic behavior under biaxial loading. It is shown that Hill's yield criterion gives a good fit to the numerical data.
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| 9. |
- Papachristos, V.D., et al.
(författare)
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Effect of annealing on the structure and hardness of Ni-P-W multilayered alloy coatings produced by pulse plating
- 2000
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Ingår i: Materials Science & Engineering. - 0921-5093 .- 1873-4936. ; 279:1-2, s. 217-230
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Tidskriftsartikel (refereegranskat)abstract
- Ni-P-W multilayered alloy coatings were deposited on copper foils by pulse plating, using a rotating cylinder electrode. They consisted of layers of high (Ni-5 wt.% P-45 wt.% W) and low (Ni-8 wt.% P-15 wt.% W) W content. The wavelengths studied were 8, 40 and 400 nm and the total thickness of the coatings was approximately 25 µm. The multilayered coatings were annealed in the temperature range between 200 and 800°C and the effect of annealing on their structure was studied by using X-ray diffraction, cross-sectional transmission electron microscopy equipped with selected area electron diffraction facility, and differential thermal analysis. The initially amorphous multilayered coatings crystallise in steps as the annealing temperature increases (first the low-W crystallise layers and then the high-W layers), and the layered structure is lost around 600°C. The main crystalline phases formed during annealing are Ni-W solid solution and Ni3P. The wavelength of the coatings seems to affect the onset temperature of the crystallisation processes. The hardness of the coatings initially increases reaching a maximum in the 500-600°C range, and then decreases as the annealing temperature increases. (C) 2000 Elsevier Science S.A. All rights reserved.Ni-P-W multilayered alloy coatings were deposited on copper foils by pulse plating, using a rotating cylinder electrode. They consisted of layers of high (Ni-5 wt.% P-45 wt.% W) and low (Ni-8 wt.% P-15 wt.% W) W content. The wavelengths studied were 8, 40 and 400 nm and the total thickness of the coatings was approximately 25 µm. The multilayered coatings were annealed in the temperature range between 200 and 800°C and the effect of annealing on their structure was studied by using X-ray diffraction, cross-sectional transmission electron microscopy equipped with selected area electron diffraction facility, and differential thermal analysis. The initially amorphous multilayered coatings crystallise in steps as the annealing temperature increases (first the low-W crystallise layers and then the high-W layers), and the layered structure is lost around 600°C. The main crystalline phases formed during annealing are Ni-W solid solution and Ni3P. The wavelength of the coatings seems to affect the onset temperature of the crystallisation processes. The hardness of the coatings initially increases reaching a maximum in the 500-600°C range, and then decreases as the annealing temperature increases.
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| 10. |
- Peng, Ru, 1960-, et al.
(författare)
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Intergranular strains and plastic deformation of an austenitic stainless steel
- 2002
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Ingår i: Materials Science & Engineering. - 0921-5093 .- 1873-4936. ; 334:1-2, s. 215-222
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Tidskriftsartikel (refereegranskat)abstract
- Intergranular strains due to tensile plastic deformation were investigated in a sheet material of austenitic stainless steel. The objective was to study the development of residual intergranular strains in samples unloaded from the intermediate and large plastic deformation regimes for which few theoretical and experimental studies were available. By using neutron diffraction, residual lattice strain distribution as a function of sample direction was mapped for a number of crystallographic planes. Deformation microstructures were examined by both transmission electron microscopy and the electron back scattering pattern technique. Residual intergranular strains were observed in samples deformed significantly beyond the elastic limit and the strains varied with sample directions as well as the amount of applied plastic strain. In addition, a different tendency of intergranular strain evolution was observed after large plastic deformation, which could be attributed to the change of dominant plastic deformation mode from slip to mechanical twinning. The results are discussed based on the observed deformation microstructure studies. ⌐ 2002 Elsevier Science B.V. All rights reserved.
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