| 1. |
- Häggblad, Hans-Åke, et al.
(författare)
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A micro mechanical based constitutive model for finite element simulation of hot isostatic pressing of powder
- 1995
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Ingår i: Computer Methods in Applied Mechanics and Engineering. - : Elsevier BV. - 0045-7825 .- 1879-2138. ; 128:1-2, s. 191-198
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Tidskriftsartikel (refereegranskat)abstract
- Hot isostatic pressing (HIP) facilitates new designs and product shaping, for example by direct manufacture of composite products with differing materials in the various parts (compound). The specific material characteristics are thus created at the manufacturing stage (consolidation), and these in themselves often give good possibilities regarding shape, so-called NS (Net Shape)-or NNS (Near Net Shape)-manufacture. The HIP-technique is used economically in the low series production of complex-shaped steel parts. In order to achieve quality products, an integration of material, design and manufacturing technology is necessary, since the function and cost of the final component depends to a large extent on the development of production technology and its integration with design technology. Simulation of the hot isostatic pressing process is required to reduce the need for expensive and time-consuming experimental design. The use of finite element techniques in analyses of the highly non-linear process is preferable, especially for complex-shaped components. In this work, a micro-mechanical based continuum mechanics model for finite element analysis is presented. The model is used in the finite element simulation of hot isostatic pressing of two components. The results from the analyses correspond well with the experimental results.
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| 2. |
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| 3. |
- Li, Wen Bin, et al.
(författare)
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Stresses developed in reaction-bonded ceramics
- 1995
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Ingår i: Ceramic materials and components for engines. - : World Scientific Publishing Co Pte Ltd. - 9810219059 ; , s. 465-468
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Konferensbidrag (refereegranskat)abstract
- For a number of reaction-bonded ceramics, the reaction starts from the surface of the particles, forming a shell of products surrounding a reactant core. The reaction is continued by inward growth of the shell by means of diffusion of the reactant elements from the particle surface to the interface between the shell and core and vice versa. Since there exists a volumetric change due to the reaction, the products forming at the shell/core interface will be severely constrained. Strain and stress fields are then built up within the particles. A physical and mathematic model to calculate the strain and stress during and after the reaction bonding process is constructed. The preliminary results of estimation of stresses within the particles and their possible effect on reaction kinetics are presented and briefly discussed
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| 4. |
- Li, Wen Bin, et al.
(författare)
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Stresses developed in reaction-bonded ceramics
- 1999
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Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 19:3, s. 277-283
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Tidskriftsartikel (refereegranskat)abstract
- A physical model is presented that predicts the stress distribution created in a particle during its reaction with a surrounding reactant to form a uniform layer of reaction product on its surface, when the reaction involves a volume change. The results of the model are applied specifically to the case of silicon reacting with nitrogen to form Si3N4. The model predicts the generation of a high, tensile hydrostatic stress in the Si core as well as high tensile radial stress and compressive tangential stress in the nitride layer. Although the model is restricted to elastic deformation only and therefore predicts unrealistically high stresses in some cases, the results are anyway of relevance in the consideration of possible non-elastic processes such as creep and fracture and also in assessing the possible effect of stress on the reaction equilibrium. It is predicted that the nitride reaction layer would fracture during the nitridation process. A second model is also presented predicting the residual stresses arising during cooling of a partially reacted particle as a result of the difference in thermal expansion of the reactant core and the reaction product layer. In the case of the reaction of silicon to silicon nitride these thermal expansion mismatch stresses are significant but small compared to the stresses due to the chemical reaction.
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| 5. |
- Liu, Wei, et al.
(författare)
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Biosynthesis and function of all-trans- and 9-cis retinoic acid in parathyroid cells
- 1996
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Ingår i: Biochemical and Biophysical Research Communications - BBRC. - : Elsevier BV. - 0006-291X .- 1090-2104. ; 229:3, s. 922-929
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that cultured human and bovine parathyroid cells incubated with all-trans-[11,12-3H]-retinol convert this tracer into all-trans- and 9-cis-retinoic acid. By using RT-PCR, cellular retinol-binding protein type I (CRBP I), cellular retinoic acid binding protein I and II (CRABP I and II), retinoic acid receptors (RARs) alpha, beta and gamma, and 9-cis-retinoic acid receptor (RXR) alpha transcripts were detected in human parathyroid cDNA. CRBP I and CRABP I expression was confirmed by immunohistochemistry. Both 9-cis- and all-trans-RA were found to suppress parathyroid hormone (PTH) secretion from dispersed human adenomatous parathyroid cells, which was augmented by combined treatment with 1mM RA and 100 nM 1,25 (OH)2D3. The present data establish parathyroid gland as a target for retinoids and as a site of synthesis of the hormonal forms of vitamin A (retinol), all-trans- and 9-cis-retinoic acid.
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