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CONTENTS
Volume 4, Number 6, November 1996
 

Abstract
An explicit 4th order time integration scheme for solving the convection-diffusion equation is discussed in this paper. A system of ordinary differential equations are derived first by discretizing the spatial derivatives of the relevant PDE using the finite difference method The integration of the ODEs is then carried out using a 4th order scheme and a self-adaptive technique based on the spatial grid spacing. For a non-uniform spatial grid, different time step sizes are used for the integration of the ODEs defined at different spatial points, which improves the computational efficiency significantly. A numerical example is also discussed in the paper to demonstrate the implementation and effectiveness of the method.

Key Words
time integration, differential equations, self-adaptive method, numerical analysis

Address
Zhong WX, DALIAN UNIV TECHNOL,RES INST ENGN MECH,DALIAN,PEOPLES R CHINA
MISSISSIPPI STATE UNIV,DEPT MATH & STAT,MISSISSIPPI STATE,MS 39762

Abstract
To simulate the large-scale failure evolution with current computational facilities, a simple approach, that catches the essential feature of failure mechanisms, must be available so that the routine use of failure analysis is feasible. Based on the previous research results, a simple analysis procedure is described in this paper for failure simulation. In this procedure, the evolution of localization is represented by a moving surface of discontinuity, and the transition between continuous and discontinuous failure modes are described via the moving jump forms of conservation laws. As a result, local plasticity and damage models, that are formulated based on thermodynamic restrictions, are still valid without invoking higher order terms, and simple integration schemes can be designed for the rate forms of constitutive models. To resolve localized large deformations and subsequent cracking, an efficient structural solution scheme is given for Static and dynamic problems.

Key Words
localization, jump and moving surfaces, failure analysis

Address
Chen Z, UNIV MISSOURI,DEPT CIVIL ENGN,COLUMBIA,MO 65211

Abstract
The homogenization method is used to develop a beam element in space for thermo-mechanical analysis of unidirectional composites. Local stress and temperature held In the microscale are described using the function of homogenization. The global (macroscopic) behaviour of the structure is supposed to be that of a beam. Beam-type kinematical hypotheses (including independent shear rotations) are hence applied and superposed on the microdescription. A macroscopic stiffness matrix for such a beam element is then developed which contains the microscale properties of the single cell of periodicity. The presented model enables us to analyse without too much computational effort complicated composite structures such as e.g toroidal coils of a fusion reactor. We need only a FE mesh sufficiently fine for a correct description of the local geometry of a single cell and a few of the newly developed elements for the description of the global behaviour. An unsmearing procedure gives the stress and temperature held in the different materials of a single cell.

Key Words
composite materials, beams, homogenization, finite element method, superconducting magnets

Address
Schrefler BA, UNIV PADUA,INST SCI & TECN COSTRUZ,VIA MARZOLO 9,I-35131 PADUA,ITALY
TECH UNIV LODZ,DEPT MECH MAT,PL-93590 LODZ,POLAND

Abstract
Geomaterials such as soil and rock are composed of discrete elements of microstructures with different grains and microcracks. The studies of these microstructures are of increasing interest in geophysics and geotechnical engineering relating to underground space development We first show experimental results undertaken for direct observation of microcrack initiation and propagation by using a newly developed experimental system, and next a homogenization method for treating a viscoelastic behavior of a polycrystalline rock.

Key Words
granite, microscope observation, homogenization method, visco-elastic problem

Address
Ichikawa Y, NAGOYA UNIV,DEPT GEOTECH & ENVIRONM ENGN,NAGOYA,AICHI 46401,JAPAN
ANDONG NATL UNIV,DEPT GEOL,ANDONG 760749,SOUTH KOREA

Abstract
In order to avoid pathological mesh dependency in finite element modelling of strain localization, an isotropic elasto-plastic model with a yield function depending on the Laplacian of the equivalent plastic strain is implemented in a 4-node quadrilateral finite element with one integration point based on a mixed formulation derived from Hu-Washizu principle. The evaluation of the Laplacian is based on a least square polynomial approximation of the equivalent plastic strain around each integration point. This non local approach allows to satisfy exactly the consistency condition at each integration point. Some examples are treated to illustrate the effectiveness of the method.

Key Words
localization, large strains, gradient plasticity

Address
Cescotto S, UNIV LIEGE,DEPT MSM,QUAI BANNING 6,B-4000 LIEGE,BELGIUM
DALIAN UNIV TECHNOL,NATL LAB STRUCT ANAL IND EQUIPMENTS,DALIAN 116204,PEOPLES R CHINA

Abstract
The paper reports on alternative hybrid/mixed formulations being developed by the Structural Analysis Research Group of Institute Superior Tecnico. These formulations open the scope and increase the power of the finite element method by allowing different fields to be independently approximated, within certain consistency criteria, and by enhancing the use of a wide range of approximation functions. They have been applied to the analysis of 2-D problems, laminar structures and solids, using different constitutive relations, both in quasi-static and dynamic regimes. The fundamental properties of the formulations are identified and assessed and their performance is illustrated using simple, linear applications.

Key Words
hybrid, mixed, equilibrium and Trefftz finite elements

Address
deFreitas JAT, INST SUPER TECN,DEPT CIVIL ENGN,AV ROVISCO PAIS,P-1096 LISBON,PORTUGAL

Abstract
The finite element method is employed in conjunction with micromechanical modelling in order to assess the performance of ceramic thermal barrier coatings applied to structural components. The study comprises the conditions of the deposition of the coating by plasma spraying as well as the thermal cycling of the coated component, and it addresses particularly turbine blades. They are exposed to high temperature changes strongly influencing the behaviour of the core material and inducing damage in the ceramic material by intense straining. A concept of failure analysis is discussed starting from distributed microcracking in the ceramic material, progressing to the formation of macroscopic crack patterns sind examining their potential for propagation across the coating. The theory is in good agreement with experimental observations, and may therefore be utilized in proposing improvements for a delayed initiation of failure, thus increasing the lifetime of components with ceramic thermal barrier coatings.

Key Words
ceramic thermal barrier coatings, finite element analysis, brittle microcracking model, fracture mechanics

Address
StDoltsinis I, UNIV STUTTGART,INST COMP APPLICAT,D-7000 STUTTGART,GERMANY

Abstract
In stochastic analysis, the randomness of the structural parameters is taken into consideration and the response variability is obtained in addition to the conventional (mean) response. In the present paper the structural response variability of plate structure is calculated using the weighted integral method and is compared with the results obtained by different methods. The stochastic field is assumed to be normally distributed and to have the homogeneity. The decomposition of strain-displacement matrix enabled us to extend the formulation to the stochastic analysis with the quadratic elements in the weighted integral method A new auto-correlation function is derived considering the uncertainty of plate thickness. The results obtained in the numerical examples by two different methods, i.e., weighted integral method and Monte Carlo simulation, are in a close agreement. In the case of the variable plate thickness, the obtained results are in good agreement with those of Lawrence and Monte Carlo simulation.

Key Words
stochastic finite element analysis, weighted integral method, auto-correlation function, material and geometrical randomness, Monte Carlo simulation

Address
Choi CK, KOREA ADV INST SCI & TECHNOL,DEPT CIVIL ENGN,TAEJON 305701,SOUTH KOREA

Abstract
This paper presents the concepts of Process Innovation and Concurrent Engineering in view of their use within Integrated CAD Systems. It follows by proposing process models that support an effective implementation. The work is practically founded on the authors\' experience in performing the initial steps of implementation of some of such integrated systems for the construction industry.

Key Words
integrated CAD systems, process innovation, concurrent engineering

Address
PUC RIO,ICAD,DEPT COMP SCI,RIO JANEIRO,BRAZIL
INST SUPER TECN,DEPT CIVIL ENGN,LISBON,PORTUGAL
UFPR,CTR ESTUDOS ENGN CIVIL,CURITIBA,PARANA,BRAZIL


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