Reduced numerical integration in thermal transient finite element analysis

The stability and accuracy of the so-called “ga-family”, two level time integration algorithms for thermal transient problems are considered. In particular, the influence on the solution characteristics of the order of numerical integration rule employed in the evaluation of the element matrices is examined. Consideration is restricted to the four node bilinear and eight node biquadratic isoparametric elements. The time integration schemes considered in detail are the Crank Nicolson, Galerkin, Modified Galerkin and Euler Backward algorithms. The stability of each process is related to both the eigenproperties of the conductivity and heat capacity matrices and to the eigenvalue spectrum of the thermal equation system. It is shown that inaccuracies and instabilities can arise in solution which are associated with the poor prediction of the element properties by reduced numerical integration rules. For eight node biquadratic elements, the source of error is the inadequate modelling of the eigenvalue spectrum of the heat capacity matrix by reduced quadrature; with both full and reduced integration rules providing very similar values for the conductivity (or stiffness matrix). However, for four node bilinear elements, reduced quadrature can result in an inadequate representation of both the conductivity and heat capacity matrices. It is shown that these inaccuracies are confined to the higher thermal frequencies which can be dominant in the initial stages of a transient response and cause deterioration of the numerical solution. Therefore an “adaptive” scheme is proposed in which a full integration order is used for the first few timesteps, after which a reduced integration rule is employed. Recommendations are made for the selection of time integration algorithms, quadrature rules and element dimensioning which are substantiated by the solution of several numerical examples.     

Computer-oriented method for linearization of dynamic models of active spatial mechanisms

A new computer oriented method for linearized dynamic model construction of open-chain active mechanisms is developed. The method is an extension of an existing algorithm for automatic setting of nonlinear dynamic models [1,2], based on general theorems of mechanics. The developed procedure involves vectorial algebraic recursive relations, but not numerical differentiation and other numerical operations which cause cumulative computing errors. Such a method is of essential importance in manipulation robot control synthesis when small perturbations are present. The results of application of the algorithm to three joints of a 6 degrees-of-freedom manipulator system are given.     

Structural changes during pressing of fine nickel powders

Structural changes that take place during pressing of carbonyl powder of nickel are discussed. Particular attention has been paid both to the formation and state of the oxide powder surface during this process.     

Investigation of anodic alumina by a photoluminescence method: II

Photoluminescence emission spectra of anodic oxide films on aluminium were measured under the conditions where an interference of the Lummer-Gehrke type takes place (the emission angle was approximately equal to the total reflection angle). Both barrier (obtained in 0.1 M ammonium tartrate) and porous (obtained in 0.1 M oxalic acid) oxide films were investigated. From the positions of sharp interference maxima and minima in the emission spectra, a very precise determination of film thickness d and anodization rate ? is possible. The ? values obtained (?₁ = 1.33 nm V^-1 in ammonium tartrate; ?₂ = 0.317 nm min^-1 in oxalic acid) are in excellent agreement with the results of other workers and with our previous results obtained by other luminescence methods. This procedure is more precise than the photoluminescence method described previously and it does not need any assumption about the spatial distribution of photoluminescence centres.     

Failure physics of integrated circuits — A review

This paper is a review of the most important results on failure physics of integrated circuits, as a synthesis of what has been recently encountered in the literature concerned with these problems.In the first part of the paper systematization of failure modes in integrated circuits is accomplished so that all failure modes are divided into four groups according to their origin: (i) failure modes associated with chip; (ii) failure modes resulting from leads and bonds; (iii) failure modes associated with encapsulation; and (iv) failure modes due to external effects and overstress. Also, some typical failure mode distributions of different types of integrated circuits are given and the effects of the changeover from LSI to VLSI on failure mode distributions are discussed.In the second part of the paper the most important tests for enhancing of the failure modes are enumerated and relationship between the failure modes and the tests for their detection is given. Also, the role of electrical testing by the curve tracer and the accompanying analytical techniques (scanning electron microscopy, transmission electron microscopy, electron beam microprobe, Auger electron spectroscopy and X-ray radiograph) are discussed. Finally, the diagnostic technique is described which, using simple electrical testing by the curve tracer and some tests for enhancing of the failure modes (high temperature bake and high temperature burn-in), enables simple detection of integrated circuit failure modes.In the third part of the paper a survey of test structures for failure analysis of integrated circuits is made. Test structures are divided into three groups according to the kind of the failure mode tested by them. First, the test structures for the analysis of the failures due to the process induced defects are described. Then, the test structures for the analysis of the failures due to traps at the interface silicon-oxide and mobile alcali ions in oxide are discussed. Finally, the test structures for the analysis of the metallization failures are considered.     

Die Betriebsphasenimpedanzen eines dreiphasigen Leitersystems als Folge des Leistungsaustausches zwischen den Phasen

Übersicht Dies ist die erste von zwei Abhandlungen, welche sich mit der Ermittlung der elektromagnetischen Eigenschaften von Dreiphasenleitersystemen mit hohen Strömen befassen. Die Verfasser zeigen analytisch an einem einfachen Beispiel, bei welchem jede Phase nur einen Leiter hat, wie die Phasenströme und-Spannungen, die Phasenimpedanzen, die Verlustleistungen und die Unsymmetrien des Leitersystems ohne Nulleiter bestimmt werden. Besonderer Wert wird auf die Abhängigkeit der Phasenimpedanzen von der Last und auf die Erklärung der phyksialischen Verhältnisse in einem solchen Leitersystem gelegt.

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Contents This is the first of two articles which deal with the determination of the electromagnetic properties of three-phase conducting systems with high currents. The authors show analytically trough a simple example, each phase having only one conductor, the determination of the phase currents and tensions, the phase impedances, the loss energy and the asymmetrics of a conducting system without zero conductor. There is especially emphasized the dependency of the phase impedances from the load and the explanation of the physical conditions in such a conducting system.

     

The effect of the overpotential of deposition on the porosity of metal deposits

The porosity of copper deposits on steel obtained by constant and pulsating overpotential electrolysis has been investigated and determined as a function of the overpotential of deposition. Optimal conditions for copper plating on steel from pyrophosphate baths have been established.