Contents of the Journal of Mechanical Engineering 50, 6 (1999)

J. SLADEK, V. SLADEK: Stress intensity factors for corner 
quarter-elliptical crack in a finite thickness plate                     365

C. T. FERNANDES, V. A. LEITAO: On a least-squares Trefftz 
collocation method for plate bending                                     387

A. TONDL, R. NABERGOJ: A nonlinearly coupled system with parametric 
excitation                                                               398

A. S. KRAVCHUK: Roughness creep in contact of elastic cylinders          412

CZ. KUNDERA: Non-contacting face seals with control system               420

Approximate weight function for a corner quarter-elliptical crack in a finite thickness plate is presented. The stress intensity factors at both surface crack points are analysed. The weight function is found in a polynomial form with three unknown parameters. They are determined directly from expressions for reference stress intensity factors. Once a weight function for a particular cracked body has been determined, the stress intensity factor for any loading applied to that body can be obtained by integrating the product of the loading and the weight function. The weight functions are used to calculate stress intensity factors for a corner quarter-elliptical crack at a hole in a finite plate. The plate is subjected to a uniform tension. A cracked plate under a thermal load is analysed too.

This paper, which was developed in the context of a multi-region indirect Trefftz collocation method for the analysis of bending of thin homogeneous plates, presents an algorithm for the determination of the optimal set of scaling factors representing the relative strength of the different boundary conditions. The algorithm is based on the use of nonlinear optimization techniques. Numerical examples are presented.

A single-mass plane system having two degrees of freedom, where the motion in both directions is coupled only by pure nonlinear coupling and is parametrically excited in one direction, is investigated. This system is governed by two differential equations, which are mutually coupled by cubic terms. The effect of these terms on the parametric resonance is investigated.

A method for estimation of roughness-creep effect in the contact problem of an elastic disk and plate with cylindric hole is developed. It is based on roughness-creep behaviour obtained by Demkin for plain joints. The contact problem is reduced to an integral-differential equation for normal contact stress. The dependence of the contact half-angle on time for some combinations of materials of the cylinders, parameters of the bearing area curves and hardness is found.

A conception of active non-contacting face seals with a control system is presented. Two methods of control of displacements of the flexible ring were applied. A mathematical model of an active non-contacting seal taking into account hydrodynamic forces present in the seal gap was formulated. Assumptions concerning the algorithm of the solution of the model were described. Results of numerical simulations including displacements of the flexible ring and variation of the height of the sealing gap in an active seal were compared with results obtained for a traditional seal without a control system.