Articles you may be interested inLithiation-induced tensile stress and surface cracking in silicon thin film anode for rechargeable lithium battery Finite element modeling of indentation-induced superelastic effect using a three-dimensional constitutive model for shape memory materials with plasticity Elastic moduli, strength, and fracture initiation at sharp notches in etched single crystal silicon microstructures Constitutive modeling of silicon materials is currently restricted to the very early stage of deformation. Uniaxial tensile testing of monocrystals oriented for single glide is traditionally simulated by a scalar model relying on the so-called machine equation. The present work uses a crystal plasticity framework to identify the role of secondary slip systems in the yield region. A three-dimensional finite element model of a tensile apparatus is validated by comparison of its outputs to the results yielded by a scalar formulation. Best fits of the constitutive model of Alexander and Haasen to experimental data reveal strong variations in its parameters with temperature. An improved constitutive model for intrinsic silicon monocrystals deformed in single slip is described. Its parameters are identified as analytical functions of temperature. We show its excellent agreement with the observed steady state of deformation in stage I.

AlexanderG.Ulyashin@sintef.no, Phone: þ47 93 00 22 24, Fax: þ47 22 06 73 50The purpose of this work is to check the potential of innovative processes for the Si wafers production toward the solar cell industry. Studies have been focused on a comparative analysis of mechanical properties of such wafers, since: (i) reduced wafer strength leads to a high breakage rate during subsequent handling and solar cell processing steps, (ii) cracking of solar cells has become one of the major sources of solar module failure and rejection. Therefore while developing new types of wafer materials and processing, it is essential to assess the mechanical strength of the wafers. Mechanical properties of several innovative Si based substrates are estimated. The bending strength measurements of the silicon wafer are performed using the ring-on-ring set-up coupled with a numerical model to obtain estimate of the fracture stress and the Weibull parameters of the fracture distribution. Results are presented for five different materials: sintered Si powder, standard multi-crystalline Si, Czochralski monocrystalline Si, and two types of thermal sprayed Si wafers.

A new internal variable constitutive model for the use in finite element (FE) simulation of local hot forming of 6xxx aluminum alloys is presented. The model relates the flow stress to the temperature, total strain rate, and internal variables, which represent the dislocation density and the contributions to the hardening stress from elements in solid solution and precipitates. The time evolutions of the internal variables are modeled by an equation representing the accumulation/annihilation of dislocations and by a precipitate model developed elsewhere, taking into account a size distribution of precipitates. The parameters of the constitutive model have been fitted to tensile tests at different temperatures, strain rates, and precipitate states.

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The article presents a three-dimensional coupled numerical solution of momentum, mass, energy and solute conservation equations, for binary alloy solidification. The interdendritic flow in the mushy zone is assumed to obey the Darcy's law. Microsegregation is governed by the lever rule, assuming local equilibrium at phase interfaces. The resulting energy and solute advection-diffusion equations are solved using the Streamline-Upwind/Petrov-Galerkin (SUPG) finite element method. A SUPG-PSPG velocity-pressure formulation is applied for the momentum equation. The full algorithm was implemented in the 3D code THERCAST, together with an anisotropic remeshing method. Two applications have been considered: a small ingot of Pb-48wt%Sn alloy and a large steel ingot. The numerical results of these two cases are presented with the evolution of temperature, liquid velocity, and solute concentration fields during solidification.