Contents of Journal of Mechanical Engineering 53, 4 (2002) 


 

R. JANCO: Solution of thermo-elastic-plastic problems with consistent 
integration of constitutive equations                                       197

P. LIU, Ch. LU: Indentation of cubic single-crystals with anisotropic 
elastic properties                                                          215

J. STEIN: Wind induced vibration of cables of simple overhead 
transmission lines (in Slovak)                                              228

B. BELIK: Differential and difference based changes of position 
of the last segment of an open kinematic chain of a robot (in Slovak)       249

Abstracts



Solution of thermo-elastic-plastic problems with consistent integration of constitutive equations

ROLAND JANCO

In the paper the algorithmically consistent integration of constitutive equations over the time step (tn, tn+1) is presented by using the one-step backward Euler scheme for solution of thermo-elastic-plastic problems. Basic equations are derived in the theoretical part. In that part we can also find the description of the solution procedure. The solution procedure was implemented in the FE code. The thermoplastic part of the model utilises the von Mises yield function with the option of isotropic hardening. Finally, numerical examples for mechanical and thermal loading condition are presented.

Indentation of cubic single-crystals with anisotropic elastic properties

PING LIU, CHUN LU

We have carried out finite element calculations to study the indentation on the {100}, {110} and {111} surfaces of cubic single-crystals with anisotropic elastic properties. It is shown that the indentation orientations significantly affect the stress distributions and the onset of plastic deformation. The indentation moduli obtained by the present finite element method through the unloading curves are consistent with those obtained by a semi-analytical method. In addition, empirical formulae are proposed to relate indentation moduli with elastic properties. These formulae allow the estimation of elastic properties with reasonable accuracy.

Wind induced vibrations of cables of simple overhead transmission lines

JURAJ STEIN

Wind induced vibrations (Aeolian vibrations) of simple overhead transmission lines and resulting conductors fatigue breakages constitute a problem for utility companies in maintaining uninterrupted supply of electrical energy. Therefore, there is a need for better understanding of this phenomenon, not hitherto well described in domestic literature.

The contribution describes briefly the aim of study of Aeolian vibrations of simple conductors of overhead transmission lines; it explains the excitation mechanism and vibration synchronization at the so called Strouhal's frequency. Further, a simplified analysis of the partial differential equation describing these vibrations is presented using the unifying concept of characteristic length as a single quantity describing the mechanical properties of the given conductor. An example is used to illustrate the minute differences between the approach to the conductor as a taut spring and a taut fixed-fixed beam leading to the conclusion that in the "free field" the taut string approach is sufficient. However, the "local effects" in calculating the theoretical value of bending strain at the clamped end have primary importance.

Differential and difference based changes of position of the last segment of an open kinematic chain of a robot

BARTOLOMEJ BELIK

This paper presents a difference method that allows to control a robot activity in order to move the gripper point along a given planar or space trajectory. It is particularly suitable to control gripper position changes of the open and closed robot mechanism for the compensation of misplacements caused by various external influences.

The control of a robot with the number of degrees of freedom i > 6 cannot be performed exactly. In such cases various numerical and variation methods are employed. The most frequently used methods in the control theory are numerical solutions of difference equations and the use of Z-Transformation Method which is presented in this paper.