Search results

An algorithm is described for the incremental solution of elastic—plastic finite element analysis using a piecewise holonomic constitutive law based on a von Mises yield condition. The holonomic assumption effectively converts each incremental problem into a non‐linear elastic—plastic problem. The algorithm is iterative, substituting the non‐linear strain potential by a quadratic potential at each iteration, and convergence is proved. The algorithm has been implemented into a finite element program as a series of secant modulus approximations, and results for a variety of problems are given. The rate of convergence is fairly slow, but the algorithm can be very easily programmed as an extension of an elastic program, and may have value as an independent method of determining incremental elastic—plastic solutions.

This paper considers the classical problem of the deformation of an elastic‐plastic body subjected to a prescribed history of loading. Attention is focused on the basis for the time discretization of the problem for numerical solution. It is suggested that this discretization can be achieved consistently by conceiving of the problem as a sequence of holonomic, or non‐linear elastic, problems. Complementary work bounds can be given, in special circumstances, for increasing numbers of time steps. The holonomic problem for a single time step is a non‐linear mathematical programming problem: it is shown that the conventional Newton‐Raphson algorithm used in elastic‐plastic finite element analysis can be interpreted as an iterative procedure for finding the least value of the holonomic potential work functional.

Aims to analyse the labour market outcome when there are two unions in the industry, representing heterogeneous workers – imperfect substitutes in production.

Competition between union policies are viewed in terms of both employment and wage strategies. Results for substitutes and complements are inspected. Attention is given to the strategic behaviour of the unions, towards one another and/or the employer side. Cooperation is modelled using the Nash‐maximand approach.

Gathers some notes and enlargements to the standard collective bargaining problem in which unions maximise utility. Extends the framework to model union competition behaviour for jobs and/or employment that reproduces the standard market product analysis of imperfect competition. Focuses on heterogeneous labour.

The analysis concentrates on the case of union duopoly, but can easily be enlarged to the n‐union setting – which is left for further investigation.

A simple analytical example with Stone‐Geary union utility functions and a linear labour demand system is forwarded.

Wonders whether companies actually have employees best interests at heart across physical, mental and spiritual spheres. Posits that most organizations ignore their workforce – not even, in many cases, describing workers as assets! Describes many studies to back up this claim in theis work based on the 2002 Employment Research Unit Annual Conference, in Cardiff, Wales.

The finite element quasi‐static analysis of elastoplastic systems is studied by making use of a generalized variable approach for the spatial discretization and a generalized mid‐point rule for the time integration. Both the classical form of the constitutive law and the convex analysis formulation are presented. The relation between the mid‐point time integration and the extremal path theory is discussed. Extremal properties for the finite‐step solution are formulated.

The paper considers a plane joint or interface element suitable for implementation into a standard non‐linear finite element code. Sliding of the joint is assumed to be governed by Coulomb friction, with a non‐associated flow rule and no cohesion. The constitutive equations are formulated in a manner appropriate for a backward difference discretization in time along the path of loading. It is shown that the backward difference assumption can lead to an explicit formulation in which no essential distinction need be drawn between opening and closing of the joint and sliding when the joint is closed. However, an inherent limitation of the dilatant Coulomb model becomes evident; the final formulation is internally consistent but does not describe reversed shear displacement in a physically reasonable way. Explicit equations for the consistent tangent stiffness and for the corrector step (or return algorithm) of the standard Newton—Raphson iterative algorithm are given. The equations have been implemented as a user element in the finite element code ABAQUS, and illustrative examples are given.

A solution algorithm for the transient analysis of bodies undergoing creep under constant or time varying loads is presented. The constitutive equation adopted is of the form: έc=γσm. The finite element formulation is carried out in terms of displacements and creep strains as internal variables. The time discretization is achieved with a trapezoidal time integration scheme. The creep strains are condensed out to give an equation for displacement increments involving a modified stiffness matrix and force vector. A Newton—Raphson iterative scheme is used for the non‐linear creep strain rate‐stress relation, and creep strains are updated at the end of the time step. The algorithm has been implemented in NOSTRUM for two‐dimensional structural and plane continuum problems, with a von Mises type potential function governing the multiaxial creep constitutive relationship. Numerical results are presented.

FINANCIAL fears are only less cruel than those of war, and lead men into extravagances which they would repudiate indignantly in their cooler moments. If the doings of the Economy Committee at Manchester in relation to children's libraries, as described in the article by Mr. Lamb in our last issue, are true, we have in them an example of a kind of retrenchment at the expense of the young which we hope is without parallel and will have no imitators. Some reduc‐tion of estimates we hear of from this or that place, but in few has the stupid policy which urges that if we spend nothing we shall all become rich been carried into full effect. Libraries always have suffered in times of crisis, whatever they are; we accept that, though doubtfully; but we do know that the people need libraries.

This paper examines the impact of technological alliance announcements in a nonfavorable environment, using event study methodology that includes robust tests to allow heteroskedasticity across firms and over time. The study is based on Spanish data, and focuses on the fact that Spanish market conditions do not favor firms that are deciding whether to enter a technological alliance. The paper is extended to analyze different features of alliances. Results suggest no stock market reaction on the day of the announcement, and a negative reaction on the days that follow. Our results also show that the stock market exacts no penalty on joint venture alliances, alliances involving public entities, alliances between Spanish firms, or alliances between competitors. The common feature revealed in these subgroups is the pursuit of security, a phenomenon that is consistent with the study environment.

The objective, sustenance and reward of research is information. But information does not yet grow on trees nor through the agency of monoclonal antibodies. It requires careful harvesting, winnowing and dissemination, albeit with electronic tools.