Search results for "Boundary"

A Cohesive-frictional Grain-boundary Technique for Microstructural Analysis of Polycrystalline Materials

2018

The development of a 3D microstructural model for the analysis of degradation and failure in polycrystalline materials is reviewed in the present chapter. The material is explicitly modelled at the grain level, using integral equations in conjunction with a phenomenological crystal plasticity framework for the bulk grains, and with cohesive-frictional laws to represent inter-granular micro-cracking processes. The method allows to capture the initiation, development and coalescence of damage or plasticity at the aggregate scale. The formulation’s key feature is the representation of the mechanical problem in terms of inter-granular variables only, which allows to reduce the computational cos…

On the Porosity of Free Boundaries in Degenerate Variational Inequalities

2000

Abstract In this note we consider a certain degenerate variational problem with constraint identically zero. The exact growth of the solution near the free boundary is established. A consequence of this is that the free boundary is porous and therefore its Hausdorff dimension is less than N and hence it is of Lebesgue measure zero.

COMPUTATIONAL HOMOGENIZATION OF POLYCRYSTALLINE MATERIALS WITH PORES: A THREE-DIMENSIONAL GRAIN BOUNDARY FORMULATION

2012

In this study, the influence of porosity on the elastic effective properties of polycrystalline materials is investigated using a 3D grain boundary micro mechanical model. The volume fraction of pores, their size and distribution can be varied to better simulate the response of real porous materials. The formulation is built on a boundary integral representation of the elastic problem for the grains, which are modeled as 3D linearly elastic orthotropic domains with arbitrary spatial orientation. The artificial polycrystalline morphology is represented using 3D Voronoi Tessellations. The formulation is expressed in terms of intergranular fields, namely displacements and tractions that play …

Estimates of the modeling error generated by homogenization of an elliptic boundary value problem

2016

Erworben im Rahmen der Schweizer Nationallizenzen (http://www.nationallizenzen.ch)

Effect of Hot Dip Galvanized Steel Surface Chemistry and Morphology on Titanium Hexafluoride Pretreatment

2017

Titanium hexafluoride pretreatments are known to improve paint adhesion and function as a barrier between the coating and the hot dip galvanized (HDG) steel surface. Interactions at the zinc/pretreatment interface are of utmost importance for the formation of pretreatment layers and the corrosion resistance of color coated hot dip galvanized steels. Removal rate of inert aluminum oxide from HDG steel samples by chemical dissolution was studied. XPS measurements showed that the surface Al2O3 layer thickness decreased rapidly already at mild alkaline cleaning, while complete removal of Al required severe etching. Low reactivity of an Al2O3-rich surface was confirmed by impaired formation of a…

BIE-based aeroacoustic design procedure

2009

A propeller low noise design procedure based on boundary integral equation is presented. The aerodynamic field is computed via a potential-based boundary element method for lifting body while the aeroacoustic emitted field is calculated on the basis of the Ffowcs Williams-Hawkings equation. Families of airfoils sections are aerodynamically processed to select the ones that meet the requested performance. Successively, the airfoil sections characterized by the lowest noise emission, among the previously selected ones, are chosen to built the propeller blade. Eventually the whole propeller aeroacoustic performances are analyzed. A propeller low noise design procedure based on boundary integra…

Generalized wave propagation problems and discrete exterior calculus

2018

We introduce a general class of second-order boundary value problems unifying application areas such as acoustics, electromagnetism, elastodynamics, quantum mechanics, and so on, into a single framework. This also enables us to solve wave propagation problems very efficiently with a single software system. The solution method precisely follows the conservation laws in finite-dimensional systems, whereas the constitutive relations are imposed approximately. We employ discrete exterior calculus for the spatial discretization, use natural crystal structures for three-dimensional meshing, and derive a “discrete Hodge” adapted to harmonic wave. The numerical experiments indicate that the cumulat…

Il distacco e la separazione emotiva nel rapporto tra genitori e figli adolescenti

2012

Boundary Shear Stress Distribution and Convective Accelerations: a forecast methodology of planimetric evolution of meandering channels

1999

Singular (p, q)-equations with superlinear reaction and concave boundary condition

2020

We consider a parametric nonlinear elliptic problem driven by the sum of a p-Laplacian and of a q-Laplacian (a (Formula presented.) -equation) with a singular and (Formula presented.) -superlinear reaction and a Robin boundary condition with (Formula presented.) -sublinear boundary term (Formula presented.). So, the problem has the combined effects of singular, concave and convex terms. We look for positive solutions and prove a bifurcation-type theorem describing the changes in the set of positive solutions as the parameter varies.