Home About us Contact
|
Home About us Contact | ||
|
|
||
Constitutive Parameters (constitutive + parameter)
Selected AbstractsEffect of Rigid Inclusions on the Densification and Constitutive Parameters of Liquid-Phase-Sintered YBa2Cu3O6+x Powder CompactsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2003Samuel M. Salamone The presence of rigid inclusions in a powder compact leads to a reduction in the densification rate of the compact and may also lead to processing defects. In this paper, the densification rate and the constitutive parameters of both homogeneous YBa2Cu3O6+x and composite powder compacts (YBa2Cu3O6+x powder with 10 vol% dense inclusions of YBa2Cu3O6+x) are reported. A small amount of liquid phase, which formed during sintering, was present in the samples. However, even with the presence of a liquid phase, the addition of inclusions still reduces the densification rate of the composite and increases its viscosity. The results have been compared with a published analysis of the problem using measured values of the constitutive parameters. Both the viscosity and viscous Poisson's ratio of the porous body have been measured. [source] Experimental evaluation of creep and fatigue behaviour for microscale solder interconnectFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 2 2007H. LU ABSTRACT This paper presents a novel experimental study for creep and fatigue of solder-interconnects in microstructures. The strains are directly measured in the fillet area of solder-joints with a typical linear dimension of 50 ,m. An analytical approach is developed for calculating shear stress based on the shear strain measurement and the established solder constitutive relations. Also obtained is the strain-rate as well as the separated elastic, plastic and creep components from the measured total strain. The data enables the determination of the strain energy density per temperature cycle for the characterization of the solder joint creep fatigue behaviour. Case studies provide evidence for the shear dominance and the creep fatigue mechanism in thermally induced solder joint deformation in surface-mounted electronic assemblies. Though a similar trend of variation in stress,strain is found in the joints of different solders, the substantial differences in the hysteresis loop area and shape as well as in the creep rate suggest that the solder constitutive parameters should have a profound impact on the creep fatigue endurance of the joints. [source] Numerical simulation of bolt-supported tunnels by means of a multiphase model conceived as an improved homogenization procedureINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 13 2008Patrick de Buhan Abstract This paper examines the possibility of applying a homogenization procedure to analyze the convergence of a tunnel reinforced by bolts, regarded as periodically distributed linear inclusions. Owing to the fact that a classical homogenization method fails to account for the interactions prevailing between the bolts and the surrounding ground and thus tends to significantly overestimate the reinforcement effect in terms of convergence reduction, a so-called multiphase model is presented and developed, aimed at improving the classical homogenization method. Indeed, according to this model, the bolt-reinforced ground is represented at the macroscopic scale as the superposition of two mutually interacting continuous phases, describing the ground and the reinforcement network, respectively. It is shown that such a multiphase approach can be interpreted as an extension of the homogenization procedure, thus making it possible to capture the ground,reinforcement interaction in a proper way, provided the constitutive parameters of the model and notably those relating to the interaction law can be identified from the reinforced ground characteristics. The numerical implementation of this model in a finite element method-based computer code is then carried out, and a first illustrative application is finally presented. Copyright © 2008 John Wiley & Sons, Ltd. [source] A hypoplastic constitutive model for claysINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 4 2005D. Ma Abstract This paper presents a new constitutive model for clays. The model is developed on the basis of generalized hypoplasticity principles, which are combined with traditional critical state soil mechanics. The positions of the isotropic normal compression line and the critical state line correspond to the Modified Cam clay model, the Matsuoka,Nakai failure surface is taken as the limit stress criterion and the non-linear behaviour of soils with different overconsolidation ratios is governed by the generalized hypoplastic formulation. The model requires five constitutive parameters, which correspond to the parameters of the Modified Cam clay model and are simple to calibrate on the basis of standard laboratory experiments. This makes the model particularly suitable for practical applications. The basic model may be simply enhanced by the intergranular strain concept, which allows reproducing the behaviour at very small strains. The model is evaluated on the basis of high quality laboratory experiments on reconstituted London clay. Contrary to a reference hypoplastic relation, the proposed model may be applied to highly overconsolidated clays. Improvement of predictions in the small strain range at different stress levels is also demonstrated. Copyright © 2005 John Wiley & Sons, Ltd. [source] Parameter identification for lined tunnels in a viscoplastic mediumINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 12 2002B. Lecampion Abstract This paper is dedicated to the identification of constitutive parameters of elasto-viscoplastic constitutive law from measurements performed on deep underground cavities (typically tunnels). This inverse problem is solved by the minimization of a cost functional of least-squares type. The exact gradient is computed by the direct differentiation method and the descent is done using the Levenberg,Marquardt algorithm. The method is presented for lined or unlined structures and is applied for an elastoviscoplastic constitutive law of the Perzyna class. Several identification problems are presented in one and two dimensions for different tunnel geometries. The used measurements have been obtained by a preliminary numerical simulation and perturbed with a white noise. The identified responses match the measurements. We also discuss the usage of the sensitivity analysis of the system, provided by the direct differentiation method, for the optimization of in situ monitoring. The sensitivity distribution in space and time assess the location of the measurements points as well as the time of observation needed for reliable identification. Copyright © 2002 John Wiley & Sons, Ltd. [source] Multi-Scale Study of Sintering: A ReviewJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2006Eugene A. Olevsky An integrated approach, combining the continuum theory of sintering with a kinetic Monte-Carlo (KMC) model-based mesostructure evolution simulation is reviewed. The effective sintering stress and the normalized bulk viscosity are derived from mesoscale simulations. A KMC model is presented to simulate microstructural evolution during sintering of complex microstructures taking into consideration grain growth, pore migration, and densification. The results of these simulations are used to generate sintering stress and normalized bulk viscosity for use in continuum level simulation of sintering. The advantage of these simulations is that they can be employed to generate more accurate constitutive parameters based on most general assumptions regarding mesostructure geometry and transport mechanisms of sintering. These constitutive parameters are used as input data for the continuum simulation of the sintering of powder bilayers. Two types of bilayered structures are considered: layers of the same particle material but with different initial porosity, and layers of two different materials. The simulation results are verified by comparing them with shrinkage and warping during the sintering of bilayer ZnO powder compacts. [source] Effect of Rigid Inclusions on the Densification and Constitutive Parameters of Liquid-Phase-Sintered YBa2Cu3O6+x Powder CompactsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2003Samuel M. Salamone The presence of rigid inclusions in a powder compact leads to a reduction in the densification rate of the compact and may also lead to processing defects. In this paper, the densification rate and the constitutive parameters of both homogeneous YBa2Cu3O6+x and composite powder compacts (YBa2Cu3O6+x powder with 10 vol% dense inclusions of YBa2Cu3O6+x) are reported. A small amount of liquid phase, which formed during sintering, was present in the samples. However, even with the presence of a liquid phase, the addition of inclusions still reduces the densification rate of the composite and increases its viscosity. The results have been compared with a published analysis of the problem using measured values of the constitutive parameters. Both the viscosity and viscous Poisson's ratio of the porous body have been measured. [source] Effective constitutive parameters of structured chiral metamaterialsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 9 2006O. Ouchetto Abstract In this paper we present a novel procedure for predicting the effective constitutive parameters of three-dimensional periodic materials with chiral component phases. The method combines the mathematical homogenization technique and the finite element method. The homogenization is accomplished by solving a local problem in the unit cell. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1884,1886, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21795 [source] Beltrami field phasors are eigenvectors of 6×6 linear constitutive dyadicsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2001Akhlesh Lakhtakia Abstract When the constitutive parameters of a linear, homogeneous, bianisotropic medium are arranged in a certain way as a 6×6 dyadic, it is shown that the eigenvectors of that dyadic may yield admissible Beltrami field phasors whose wavenumbers are directly proportional to the corresponding eigenvalues. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 127,128, 2001. [source] | |||||||||||||