The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
G. Toselli - One of the best experts on this subject based on the ideXlab platform.
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Transient finite element analysis of deep penetration laser welding process in a singlepass butt-welded thick steel plate
Computer Methods in Applied Mechanics and Engineering, 1999Co-Authors: Costantino Carmignani, Rafael Mares, G. ToselliAbstract:The laser welding residual Stresses and strains in a rectangular thick steel plate are investigated by means of a fully three dimensional finite element analysis. Temperature field and Stress–strain field decoupling is assumed to be essential in order to perform an efficient finite element analysis. Moreover, ad hoc constitutive elastoviscoplastic equations have been adapted in order to overcome the unreliable behaviour of rate independent (plastic) constitutive models. Evolution of temperature and Stress during the welding process has been numerically simulated as a function of the motion of the travelling laser beam. The results obtained showed also the three dimensional character of Stress field due to the typical keyhole form of the molten material under the laser beam, and the relative sound contribution of the Stress Component along the thickness to the triaxial state of Stress, often neglected in previous calculations.
Joe Coventry - One of the best experts on this subject based on the ideXlab platform.
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thermoelastic Stress in concentrating solar receiver tubes a retrospect on Stress analysis methodology and comparison of salt and sodium
Solar Energy, 2018Co-Authors: William Logie, John Pye, Joe CoventryAbstract:Abstract Temperature distribution in nonaxisymmetrically concentrating solar thermal receivers tubes is calculated for the steady-state solution with a Gauss-Seidel iteration in cylindrical coordinates. The classical plane-biharmonic thermoelastic approach to nonaxisymmetrically heated tube Stress is applied. Calculation of the dominant axial thermal Stress Component is included. Validation is obtained with the linear-elastic thermal Stress OpenFOAM® solver. Thermoelastic Stress in stainless steel 316 Schedule 5S DN25 (1″) tubes containing liquid sodium is found to be 35% lower than in tubes containing molten salt. The difference is due to the higher conductivity of liquid sodium which maintains a smaller temperature difference between the front and back tube sides. A simplified thermal Stress formula is shown to be erroneous if not implemented as originally documented. The sensitivity of tube thermoelastic Stress to tube material and flow properties is illustrated with parameter variation, and the impact of solar concentrated heat flux is explored with some typical and ideal tube circumference flux profiles.
Robert Street - One of the best experts on this subject based on the ideXlab platform.
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reversible and irreversible trapping at room temperature in poly thiophene thin film transistors
Applied Physics Letters, 2005Co-Authors: Alberto Salleo, F Endicott, Robert StreetAbstract:We measured the bias Stress characteristics of poly(thiophene) semicrystalline thin-film transistors (TFTs) as a function Stress times, gate voltages, and duty cycles. At room temperature, the bias Stress has two Components: a fast reversible Component and a slow long-lived Component. We hypothesize that the irreversible Component is due to charge trapping in the disordered areas of the semiconductor film. At low duty cycle (<2%), the fast bias Stress Component is reversed during the off-part of the cycle therefore the observed threshold voltage (VT) shift is only caused by long-lived trapping. Long-lived trapping follows power-law kinetics with a time exponent approximately equal to 0.37. We use these findings to estimate the lifetime of TFTs used as switches in display backplanes.
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reversible and irreversible trapping at room temperature in poly thiophene thin film transistors
arXiv: Materials Science, 2005Co-Authors: Alberto Salleo, F Endicott, Robert StreetAbstract:We measured the bias Stress characteristics of poly(thiophene) semi-crystalline thin-film transistors (TFTs) as a function Stress times, gate voltages and duty-cycles. At room temperature, the bias Stress has two Components: a fast reversible Component and a slow irreversible Component. We hypothesize that the irreversible Component is due to charge trapping in the disordered areas of the semiconductor film. At low duty-cycle (<2%), the fast bias Stress Component is reversed during the off-part of the cycle therefore the observed VT shift in only caused by irreversible trapping. Irreversible trapping follows power-law kinetics with a time exponent approximately equal to 0.37. We use these findings to estimate the lifetime of TFTs used as switches in display backplanes.
Costantino Carmignani - One of the best experts on this subject based on the ideXlab platform.
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Transient finite element analysis of deep penetration laser welding process in a singlepass butt-welded thick steel plate
Computer Methods in Applied Mechanics and Engineering, 1999Co-Authors: Costantino Carmignani, Rafael Mares, G. ToselliAbstract:The laser welding residual Stresses and strains in a rectangular thick steel plate are investigated by means of a fully three dimensional finite element analysis. Temperature field and Stress–strain field decoupling is assumed to be essential in order to perform an efficient finite element analysis. Moreover, ad hoc constitutive elastoviscoplastic equations have been adapted in order to overcome the unreliable behaviour of rate independent (plastic) constitutive models. Evolution of temperature and Stress during the welding process has been numerically simulated as a function of the motion of the travelling laser beam. The results obtained showed also the three dimensional character of Stress field due to the typical keyhole form of the molten material under the laser beam, and the relative sound contribution of the Stress Component along the thickness to the triaxial state of Stress, often neglected in previous calculations.
Yo Tomota - One of the best experts on this subject based on the ideXlab platform.
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Effect of ferrite grain size on tensile deformation behavior of a ferrite-cementite low carbon steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Noriyuki Tsuchida, Yo Tomota, Yasunori Harada, Kenzo Fukaura, H. Masuda, Kotobu NagaiAbstract:Abstract Stress–strain curves for ferrite-cementite (FC) steels with ferrite grain sizes between 0.47 and 13.6 μm were studied by tensile tests with strain rates of 103, 100, and 3.3 × 10−4 s−1 at 296 K. The Stress–strain curves for the FC steels are categorized into two different types. In one type, the Luders deformation is interrupted due to the onset of necking, and in the other type, the Luders band propagates throughout the gage section of a tensile specimen followed by work-hardening. The lower yield and flow Stresses increase while uniform and total elongations decrease with a decrease in ferrite grain size. The effect of ferrite grain size on flow Stress is hardly dependent on strain rate. These experimental results reveal that the grain refinement strengthening contributes mainly to an increase in the athermal Stress Component.
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in situ neutron diffraction during tensile deformation of a ferrite cementite steel
Acta Materialia, 2003Co-Authors: Yo Tomota, P Lukas, D Neov, Stefanus Harjo, Y R AbeAbstract:A fully pearlitic steel (specimen P1) was subjected to cold-drawing (P2) followed by aging at 423 K (P3) or 673 K (P4). Some drawn samples were annealed to make cementite particles spherical (P5). By using neutron diffraction, high compressive residual Stress Component parallel to the drawing direction was detected in the ferrite matrix of specimen P2, whereas this Stress level was partly relaxed in P3 and mostly in P4. In situ neutron diffraction experiments performed during tensile tests have revealed different work hardening behaviors in these specimens. Based on the data provided by a profile analysis of diffraction spectra, i.e. microstrain related to dislocation density and block size, strength and work-hardening of these specimens are discussed. In particular, it is documented that the treatment of the specimen P4 which is equivalent to commercially Zn-plated steel wires produces the largest internal Stress by tensile deformation leading to a good balance of strength and uniform elongation.
