Contents of the Journal of Mechanical Engineering 50, 4 (1999)

J. DOBIAS: Contact mechanics: engineering view - continuum formulation   217

V. CARVELLI, G. MAIER, A. TALIERCIO: Shakedown analysis of periodic 
heterogeneous materials by a kinematic approach                          229

L. J. MARTIKAINEN, F. G. RAMMERSTORFER: Modelling the local failure 
modes in thin-faced sandwich panels                                      241

E. A. W. MAUNDER, R. T. TENTCHEV: Hybrid equilibrium models 
for plate bending based on Reissner-Mindlin theory                       253

P. MUCKA: Response of a heavy vehicle model with active suspension 
to a solitary bump (in Slovak)                                           265

J. PETRUSKA,  L. JANICEK: Evaluation of ductile fracture criteria 
by numerical simulation of compression test                              278  

The paper covers the fundamental principles behind the continuum formulation of contact between deformable/rigid bodies problems. It introduces basic concepts of the contact mechanics, governing equations, and contact boundary conditions. The penalization of the contact boundary conditions in terms of the penalty method and the augmented Lagrangian method is presented.

A kinematic approach to shakedown analysis of periodic heterogeneous media is presented in the framework of the homogenization theory. The evaluation of the "macroscopic" shakedown limit for a given domain of variable repeated average stresses is computed by an iterative procedure which solves a mathematical programming problem formulated on a Representative Volume (RV) with periodic boundary conditions.

Thin-faced sandwich panels with a soft core are sensitive to failure under localized loads. Support reactions of continuous panels can easily cause local failures, such as buckling of the faces or crushing of the core, at intermediate supports. These failures result in inelastic deformations in the core and, further, in the reduced stiffness and load-carrying capacity of the sandwich panel. This paper studies the Finite Element modelling of local failures. The core of the panel is modelled by continuum elements and the faces by beam elements. The continuum model for the core enables the use of an elastic-plastic material model, called the crushable foam model, to take the hydrostatic pressure dependent yield of the core material into account. Three-point bending tests on panels with steel faces and a core made of polystyrene foam or structural rock wool could be satisfactorily simulated by FE-calculations.

A new hybrid equilibrium element for finite element modelling of plates governed by Reissner-Mindlin theory is reviewed, and its performance is studied in the analyses of a square and a skew plate. A flexibility method of analysis is presented for use with the hybrid model as a more natural method which is also better suited to interactive design based on elastoplastic concepts. Comparisons are made for linear elastic behaviour with conforming elements in the context of dual analyses as regards convergence, error estimation, and distributions of stress-resultants. A Trefftz patch recovery technique is proposed for smoothing local distributions of stress-resultants.

In this paper various concepts of active suspensions for use in the heavy vehicle suspension are analysed. Concepts of real or fictitious dampers placed between parts of the vehicle model are considered. For simulation a two-mass quarter car model is used. The model is kinematically excited by a bump. The aim is to find the most suitable concept from the viewpoint of reduction of the maximum dynamic tyre force. The criteria for estimation are the maximum value and the area of time response of dynamic tyre force. Influence of the cost function weighting coefficient, that emphasizes the road damage reduction, is taken into consideration. The results are compared with those corresponding to passive suspension.

Experimental evaluation of fracture of compressed cylindrical specimens with longitudinal surface notch was combined with a numerical simulation of the experiment. Both the geometry of the specimens (height to diameter ratio, notch depth) and frictional conditions (grooved, dry smooth, and lubricated smooth platens) were changed to obtain a broad spectrum of stress states at fracture. Local stress-strain history at the notch tip, obtained from the numerical analysis, was used for evaluation of the ability of various ductile fracture criteria to predict correctly the fracture initiation. Results of individual criteria for the selected highly ductile steel are presented and discussed in the paper.