959 resultados para residual effect
Resumo:
A mechanical model of a laser transformation hardening specimen with a crack in the middle of the hardened layer is developed to quantify the effects of the residual stress and hardness gradient on crack driving force in terms of J-integral. It is assumed
Resumo:
A method of determining the micro-cantilever residual stress gradients by studying its deflection and curvature is presented. The stress gradients contribute to both axial load and bending moment, which, in prebuckling regime, cause the structural stiffness change and curving up/down, respectively. As the axial load corresponds to the even polynomial terms of stress gradients and bending moment corresponds to the odd polynomial terms, the deflection itself is not enough to determine the axial load and bending moment. Curvature together with the deflection can uniquely determine these two parameters. Both linear analysis and nonlinear analysis of micro-cantilever deflection under axial load and bending moment are presented. Because of the stiffening effect due to the nonlinearity of (large) deformation, the difference between linear and nonlinear analyses enlarges as the micro-cantilever deflection increases. The model developed in this paper determines the resultant axial load and bending moment due to the stress gradients. Under proper assumptions, the stress gradients profile is obtained through the resultant axial load and bending moment.
Resumo:
A mechanical model of a coating/laser pre-quenched steel substrate specimen with a crack oriented perpendicular to the interface between the coating and the hardened layer is developed to quantify the effects of the residual stress and hardness gradient on the crack driving force in terms of the J-integral. It is assumed that the crack tip is in the middle of the hardened layer of the pre-quenched steel substrate. Using a composite double cantilever beam model, analytical solutions can be derived, and these can be used to quantify the effects of the residual stress and the hardness gradient resulting from the pre-quenched steel substrate surface on the crack driving force. A numerical example is presented to investigate how the residual compressive stress, the coefficient linking microhardness and yield strength and the Young's modulus ratio of the hardened layer to the coating influence the crack driving force for a given crack length. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Resumo:
The technology of laser quenching is widely used to improve the surface properties of steels in surface engineering. Generally, laser quenching of steels can lead to two important results. One is the generation of residual stress in the surface layer. In general, the residual stress varies from the surface to the interior along the quenched track depth direction, and the residual stress variation is termed as residual stress gradient effect in this work. The other is the change of mechanical properties of the surface layer, such as the increases of the micro-hardness, resulting from the changes of the microstructure of the surface layer. In this work, a mechanical model of a laser-quenched specimen with a crack in the middle of the quenched layer is developed to quantify the effect of residual stress gradient and the average micro-hardness over the crack length on crack tip opening displacement (CTOD). It is assumed that the crack in the middle of the quenched layer is created after laser quenching, and the crack can be a pre-crack or a defect due to some reasons, such as a void, cavity or a micro-crack. Based on the elastic-plastic fracture mechanics theory and using the relationship between the micro-hardness and yield strength, a concise analytical solution, which can be used to quantify the effect of residual stress gradient and the average micro-hardness over the crack length resulting from laser quenching on CTOD, is obtained. The concise analytical solution obtained in this work, cannot only be used as a means to predict the crack driving force in terms of the CTOD, but also serve as a baseline for further experimental investigation of the effect after laser-quenching treatment on fracture toughness in terms of the critical CTOD of a specimen, accounting for the laser-quenching effect. A numerical example presented in this work shows that the CTOD of the quenched can be significantly decreased in comparison with that of the unquenched. (C) 2008 Elsevier B.V. All rights reserved.
Resumo:
The effect of group delay ripple of chirped fiber gratings on composite second-order (CSO) performance in optical fiber CATV system is investigated. We analyze the system CSO performances for different ripple amplitudes, periods and residual dispersion amounts in detail. It is found that the large ripple amplitude and small ripple period will deteriorate the system CSO performance seriously. Additionally, the residual dispersion amount has considerable effect on CSO performance in the case of small ripple amplitude and large ripple period. (c) 2004 Elsevier B.V. All rights reserved.
Resumo:
The effect of sodium lactate is compared with sucrose + sorbitol + sodium tri-poly phosphate as cryoprotectant on gel forming ability & protein denaturation of croaker surimi during frozen storage at -20±2°C for 90 days was evaluated. The quality of Croaker surimi with 6% (w/v) sodium lactate was examined in terms of biochemical parameters of muscle protein, thaw drip, gel strength and calcium ATPase activity :.omparing with those of surimi added with sucrose/sorbitol & without additive as control. Both the cryoprotectants minimized the negative effects of frozen storage on physico-chemical traits of myofibrillar proteins which was evident from the biochemical and sensory parameters. The residual Ca2+ ATPase activity and gel strength of surimi with sodium lactate were higher than those of control throughout 90 days of storage. Ca2+ A TPase activity and gel strength found a high positive correlation. From the results, it was found that sodium lactate was equally effective in preservation of croaker muscle protein native structure during frozen storage as the sucrose/ sorbitol and also less sweet without any risk of maillard browning.
Resumo:
High-dose ion implantation of phosphorus into 4H-SiC (0001) has been investigated with three different ion fluxes ranging from 1.0 to 4.0 x 10(12) P(+)cm(-2.)s(-1) and keeping the implantation dose constant at 2.0 x 10(15) P(+)cm(-2). The implantations are performed at room temperature and subsequently annealed at 1500 degrees C. Photoluminescence and Raman scattering are employed to investigate the implantation-induced damages and the residual defects after annealing. The electrical properties of the implanted layer are evaluated by Hall effect measurements on the sample with a van der Pauw configuration. Based on these results, it is revealed that the damages and defects in implanted layers can be greatly reduced by decreasing the ion flux. Considering room temperature implantation and a relatively low annealing temperature of 1500 degrees C, a reasonably low sheet resistance of 106 Omega/square is obtained at ion flux of 1.0 x 10(12) P(+)cm(-2.)s(-1) with a donor concentration of 4.4 x 10(19)cm(-3).
Resumo:
The stress states in unintentionally doped GaN epilayers grown on Si(111), 6H-SiC(0001), and c-plane sapphire, and their effects on optical properties of GaN films were investigated by means of room-temperature confocal micro-Raman scattering and photoluminescence techniques. Relatively large tensile stress exists in GaN epilayers grown on Si and 6H-SiC while a small compressive stress appears in the film grown on sapphire. The latter indicates effective strain relaxation in the GaN buffer layer inserted in the GaN/sapphire sample, while the 50-nm-thick AlN buffer adopted in the GaN/Si sample remains highly strained. The analysis shows that the thermal mismatch between the epilayers and the substrates plays a major role in determining the residual strain in the films. Finally, a linear coefficient of 21.1+/-3.2 meV/GPa characterizing the relationship between the luminescent bandgap and the biaxial stress of the GaN films is obtained. (C) 2003 American Institute of Physics.
Resumo:
The reduction of residual strain in cubic GaN growth by inserting a thermoannealing process is investigated. It is found that the epilayer with smaller tensile strain is subject to a wider optimal "growth window." Based on this process, we obtain the high-quality GaN film of pure cubic phase with the thickness of 4 mum by metalorganic chemical vapor deposition. The photoluminescence spectrum at room temperature shows the thick GaN layer has a near-band emission peak with a full width at half maximum of 42 meV which confirms its high crystal quality, further supported by the x-ray (002) diffraction measurement. A simplified model is demonstrated to interpret this strain effect on the growth process. (C) 2003 American Institute of Physics.
Resumo:
The free electron concentration of as-grown liquid encapsulated Czochralski (LEC) InP measured by Hall effect is much higher than the concentration of net donor impurity determined by glow discharge mass spectroscopy. Evidence of the existence of a native donor hydrogen-indium vacancy complex in LEC undoped and Fe-doped InP materials can be observed with infrared absorption spectra. The concentration increase of the donor complex correlates with the increase of ionized deep acceptor iron impurity Fe~(2+) concentration in Fe-doped semi-insulating (SI) InP. These results indicate that the hydrogen-indium vacancy complex is an important donor defect in as-grown LEC InP, and that it has significant influence on the compensation in Fe-doped SI InP.
Resumo:
Undoped liquid encapsulated Czochralski (LEC) InP samples have been studied by Hall effect, glow discharge mass spectroscopy (GDMS) and infrared absorption spectroscopy. A systematic discrepancy has been found between the Han electron concentration and net donor concentration measured by GDMS. The electron concentration is always higher than the net shallow donor concentration by about (3-6)x10(15)cm(-3). A hydrogen indium vacancy complex donor defect VInH4 was detected regularly by infrared absorption spectroscopy in all undoped LEC InP samples. The fact can be explained by taking into account the existence of the donor defect in as-grown undoped LEC-InP.
Resumo:
The effect of thermal annealing on the Raman spectrum of Si0.33Ge0.67 alloy grown on Si (100) by molecular beam epitaxy is investigated in the temperature range of 550-800 degrees C. For annealing below 700 degrees C, interdiffusion at the interface is negligible and the residual strain plays the dominant role in the Raman shift. The strain-shift coefficients for Si-Ge and Ge-Ge phonon modes are determined to be 915 +/- 215 cm(-1) and 732 +/- 117 cm(-1), respectively. For higher temperature annealing, interdiffusion is significant and strongly affects the Raman shift and the spectral shape.
Resumo:
Immersion in various media has different effect on the properties of dental composites, such as sorption, solubility, elution of unreacted monomers, flexural strength, and flexural elastic modulus. In the present work, the effect of immersion in various media and the relationship between the variation of these properties and the components of dental composite were investigated.
Resumo:
BACKGROUND: Interleukin-10 (IL-10) is currently being extensively studied in clinical trials for the treatment of Crohn's disease (CD). Only marginal effects have, however, been reported, and the dose-response curve was bell-shaped contrasting with the reported data from in vitro experiments. AIM: To use another in vitro model to analyze the effect of rhIL-10 and rhIL-4 on the spontaneous mucosal TNF-alpha secretion in patients with CD, and to characterize the phenotype of the cells targeted by rhIL-10. METHODS: Non-inflamed colon biopsies from CD patients were cultured for 16 hours in presence of different concentrations of rhIL-10 or rhIL-4. The numbers of TNF-alpha-secreting cells among isolated lamina propria mononuclear cells (LPMNC) were estimated by Elispot. RESULTS: Both rhIL-10 and rhIL-4 down-regulate TNF-alpha secretion by LPMNC from CD patients, with a more pronounced effect with rhIL-10. These effects were closely linked to the cytokine concentrations used, with a bell-shaped dose-response curve. Residual TNF-alpha secretion, in the presence of optimal rhIL-10 concentration was mainly attributable to CD3+ T cells. In contrast, at higher rhIL-10 concentrations, CD3- cells contributed significantly to the TNF-alpha secretion. CONCLUSIONS: The in vitro model we used, demonstrates that IL-4, but mostly IL-10, efficiently suppresses TNF-alpha secretion in LPMNC from CD patients, with a dose-response curve similar to results obtained in vivo. Resistance at high rhIL-10 concentrations was associated with a change in the phenotype of TNF-alpha-secreting cells.
Resumo:
In this paper, thermal cycling reliability along with ANSYS analysis of the residual stress generated in heavy-gauge Al bond wires at different bonding temperatures is reported. 99.999% pure Al wires of 375 mum in diameter, were ultrasonically bonded to silicon dies coated with a 5mum thick Al metallisation at 25degC (room temperature), 100degC and 200degC, respectively (with the same bonding parameters). The wire bonded samples were then subjected to thermal cycling in air from -60degC to +150degC. The degradation rate of the wire bonds was assessed by means of bond shear test and via microstructural characterisation. Prior to thermal cycling, the shear strength of all of the wire bonds was approximately equal to the shear strength of pure aluminum and independent of bonding temperature. During thermal cycling, however, the shear strength of room temperature bonded samples was observed to decrease more rapidly (as compared to bonds formed at 100degC and 200degC) as a result of a high crack propagation rate across the bonding area. In addition, modification of the grain structure at the bonding interface was also observed with bonding temperature, leading to changes in the mechanical properties of the wire. The heat and pressure induced by the high temperature bonding is believed to promote grain recovery and recrystallisation, softening the wires through removal of the dislocations and plastic strain energy. Coarse grains formed at the bonding interface after bonding at elevated temperatures may also contribute to greater resistance for crack propagation, thus lowering the wire bond degradation rate