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- André, Alann, et al.
(författare)
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Finite element delamination study of a notched composite plate under flexural loads
- 2009
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Ingår i: ICCM-17, 17th International Conference on Composite Materials, Edinburgh, UK. - London : IOM Communications.
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Konferensbidrag (refereegranskat)abstract
- The delamination process in notched composite plates under flexural loading has been investigated using finite element analysis. Cohesive elements implemented in the commercial finite element package ABAQUS have been used in the region around the drilled-hole, and positioned between layers where delamination was observed during experiments presented in an accompanying paper. The delamination initiation and subsequent propagation was studied between the layers at the tension side separately and simultaneously. For all FE models, the load displacement curve was in good agreement with the one from experiments. However, the amount of damage reported from the fractography study was more extensive than that predicted by the models. Finally, it was shown that the models with only one cohesive layer show significantly different results to that of the model with four cohesive layers in terms of size of the degradation area.
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| 3. |
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| 4. |
- Ringsberg, Jonas, 1971, et al.
(författare)
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Sheet metal fatigue near nuts welded to thin sheet structures
- 2008
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Ingår i: International Journal of Fatigue. - : Elsevier BV. - 0142-1123. ; 30:5, s. 877-887
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Tidskriftsartikel (refereegranskat)abstract
- One of the fatigue design processes of a car body is stress-based sheet metal fatigue near nuts welded to thin sheets (weld nuts). In this investigation, the influence from nut geometry and dimension, as well as sheet material and thickness on sheet metal fatigue life was studied by fatigue experiments and numerical analyses. The fatigue experiments were force-controlled and carried out on a weld nut specimen which, during the reversed loading that was applied, was designed to result in bending fatigue loading conditions of the sheet metal near the weld nut. The results from the experiments were Fa–N curves for various combinations of nut geometry and dimension, sheetmaterial and thickness. Numerical analyses of the experiments were carried out by linear elastic finite element (FE) analyses, in order to transform the Fa–N curves to Wöhler (sig_a–N) curves. A simplified FE model of the weld nut, which is suitable for structural analysis of car body structures, was used. The structural stresses calculated using the FE model showed good agreement with the structural stresses calculated using an analytical model that is based on plate theory. The conclusion was that the simplified representation of the weld nut, and the mesh density used in the FE model, was appropriate for computation of the stress response near a weld nut subjected to bending fatigue loading conditions. Finally, ra–N curves were computed for each weld nut configuration using its experimental data set. A sig_a–N curve fitted to all data sets resulted in the relation sig_a = 9888N^0.312. The sig_a–N curves for the 21 weld nut configurations tested were gathered within a factor of three in fatigue life from this curve.
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| 5. |
- Ryttberg, Kristina, 1977, et al.
(författare)
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Electron microscopy of white-etching band generated by high-velocity parting-off of 100CrMn6 steel
- 2008
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Ingår i: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - : Elsevier BV. - 0921-5093. ; 480:1-2, s. 489-495
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Tidskriftsartikel (refereegranskat)abstract
- High-velocity parting-off has been applied to 80 mm bars of pearlitic 100CrMn6, resulting in shear localisation and white-etching bands in a severely deformed region below the fracture surface. Electron microscopy showed that going from the bulk material towards the fracture surface the grains become elongated and refined. The region below the fracture surface can be divided into three subzones: 50–100 μm below the surface grains are elongated, cementite lamellae are distorted, break up and the lamellar spacing decreases.
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| 6. |
- Ryttberg, Kristina, 1977, et al.
(författare)
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High strain rate deformation induced by high-velocity forming of 100Cr6 steel
- 2008
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Ingår i: proceedings of The 9th International Conference on Technology of Plasticity (ICTP), Gyeongju, Korea, September 7-11, 2008. - 9788957081525 ; , s. On CD or www.ictp2008.org-
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Konferensbidrag (refereegranskat)abstract
- This paper concerns the development of the near-net-shape manufacturing technique of high-velocity forming. The microstructural response to the high strain-rate deformation was evaluated for 100Cr6 steel in two differently heat treated conditions: spheroidise annealed (hardness 250 HV) and quenched and tempered (330 HV). A high-velocity pressing machine was used to conduct the forming tests on cylindrical specimens. By applying different impact velocities on samples with varying sizes deformation mechanisms could be related to strain and strain rate. Extreme localization of deformation resulting in white etching bands was seen in quenched and tempered samples but not in spheroidise annealed samples. Furthermore, the strain and strain rates were shown to affect the tendency for extreme localization. No white etching bands were found in samples strained to less than 1. Appearance of white etching bands could be seen in the macroscopic shape of the samples where the more homogeneously deformed samples showed a typical barrel shape while the strongly localized samples were slightly more bell shaped. It can be concluded that for high-velocity forming to be applicable to 100Cr6 steel a careful choice of the combination strain/strain rate needs to be made.
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| 7. |
- Ryttberg, Kristina, 1977, et al.
(författare)
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Microstructural evolution during fracture induced by high strain rate deformation of 100Cr6 steel
- 2009
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Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136. ; 209:7, s. 3325-3334
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the influence on parting-off mechanisms of a significantly higher impact velocity compared to commercial methods. A specially developed method, allowing for parting-off velocities ranging from 38 to 285 m/s has been applied to 100Cr6 steel bars. Two different heat treatments; spheroidise annealing (SA) and quench and tempering (QT) were employed to produce two different microstructures of a hardness of 255 and 310HV, respectively. It appears that the failure mechanisms active in the current process are virtually identical to failure occurring during high-velocity parting-off using commercially available machines, which displays shear fracture and adiabatic shear banding. It was also concluded that the estimated energy consumed during parting-off is not dependent on microstructure. Prior to parting-off, impact results in shear localisation, which is somewhat increased with increased impact speed. Furthermore, shear strains at fracture also increaseswith impact speed, from a value of about 2.2 at the lowest impact velocity to almost 3.5 at an impact velocity of 285 m/s. The heavy deformation causes a grain refinement. Right below the fracture surface three subzones can be found in the microstructure; a white etching band (WEB) (only present on some locations), equiaxed grains and then elongated subgrains. The grain size within these zones varies between 50 and 150 nm. The findings of elongated subgrains of a mutual orientation, adjacent subgrains having {110} type of planes in parallel, support the theory of formation of white etching bands being a mechanically rate controlled process.
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| 8. |
- Ryttberg, Kristina, 1977, et al.
(författare)
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Microstructure and texture development during ring rolling of 100Cr6
- 2008
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Ingår i: Ceramic Transactions. - 1042-1122. - 9781574982961 ; 200, s. 301-309
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Konferensbidrag (refereegranskat)abstract
- Pre-turned 100Cr6 steel rings with spheroidised annealed microstructure have been cold ring rolled to two levels: expanding the outer diameter by 10 and 20%. The final microstructure was shown to be varying throughout the cross-section of the ring, where the largest deformation was found close to the surface of the inner diameter. This was reflected in the hardness profile showing the highest hardness values close to the inner surface. Scanning electron microscopy showed that the microstructure below the surface of the outer diameter consisted of a greatly refined ferrite. Close to the surface of the inner diameter the structure was even more refined. Electron back scatter diffraction together with X-ray diffractometry showed that cold ring rolling changed the existing texture of the ring blanks, where {110}-planes were parallel to the axial direction of the rings, towards {110}-planes becoming parallel to the rolling direction. This resulted in a weak {110}-texture. Close to the surface of the outer diameter the greatly refined ferrite had decomposed into a more random orientation distribution.
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| 10. |
- Ahmed, Istaq, 1972
(författare)
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Acceptor-Doped BaZrO3 Perovskite: Synthesis, Structure and Proton Conductivity.
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Acceptor-doped perovskite oxides exhibit significant proton conductivity in hydrogen containing atmospheres. Therefore, they have potential for use as separator materials for various electrochemical devices including gas sensors, electrolysers and fuel cells. For example, yttrium doped BaZrO3 perovskites have shown high bulk proton conductivity and high chemical stability. However, significant grain boundary resistance has subdued the technological applications.The work constituting this thesis has mainly been focused on synthesis, structural characterisation and electrochemical investigations of acceptor-doped BaZr1-xMxO3-d (M = Ga3+, Sc3+, In3+, Yb3+ and Y3+: x = 0-0.75) perovskite oxides in bulk form. The polycrystalline samples were prepared via a traditional solid-state sintering route and by wet chemical routes. A combination of techniques such as x-ray and neutron powder diffraction, thermogravimetry, scanning electron microscopy (SEM) and impedance spectroscopy (IS) have been used to characterize the samples. Rietveld analysis of high resolution low temperature neutron powder diffraction data revealed that the deuteron site was localised at, or close to, the 12h crystallographic position of BaZr0.5In0.5O2.5(OD)0.5. It was also confirmed that the hydration/deuteration reaction caused an expansion of the cell parameter, while keeping the lattice symmetry, and thus the basic structure intact. Moreover, from Rietveld analysis of the neutron data the oxygen vacancy concentration was determined and they were found to be statistically distributed in the structure. Heavily doped samples showed higher proton conductivity compared to lightly doped samples, indeed this is an option to improve the conductivity in the material for certain dopants, e.g., In, Sc and Yb. Interestingly, at the same level of doping the proton conductivity differs significantly for different acceptors dopants. The effects of co-doping at the B-site, e.g. BaZr0.9In0.05M0.05O3-d (M = Ga and Yb) were investigated. Surprisingly, lower proton conductivity was obtained for these co-doped samples compared to the sample containing a single dopant ion e.g. BaZr0.9M0.1O3-d (M = Ga, In and Yb).It was also confirmed that samples with smaller grain size show lower total proton conductivity due to high grain-boundary resistance.Through the present work an increased understanding of the factors influencing the proton conductivity in acceptor doped BaZrO3 has been obtained. In particular, the highly doped materials were found to be of considerable interest in the effort of producing materials with high proton conductivity.
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