Contents of Journal of Mechanical Engineering 61, 2 (2010)

RENDE, H., ALTA, Z. D.: Stress concentration factors (SCFs) 
in notched shaft under torsion or bending 63

KOMPIŠ, V., VANČO, M., FERENCEY, V.: Shock waves propagation
in composite materials 73

Stability analysis of turning the continuous workpiece model 89

WANG, G., DONG, Z.: Modeling and design optimization of the
elastic foundation for vertical roller mills 105

Stress concentration factors (SCFs) in notched shaft under torsion or bending


The presence of a notch in a structural component is a common occurrence in engineering practice, and such a geometric discontinuity can easily provoke the initiation of a surface crack due to stress concentration. For this reason, strength and fatigue life of structural components should be determined by taking into account the notch effect. In this study, stress concentration factors (SCFs, Kt) of a round bar with more than one notch are considered and overlapped notch effects are examined. A simulation was presented to obtain SCFs for shaft designs with changes in section and a keyway under torsion and bending. According to the results at D/d ³ 2 and the ratio of r/d is between 0.1 and 0.5, it was found that SCFs had not changed significantly when the distance between the keyway and shoulder fillet on the shaft under torsion or bending was 7-10 mm. SCFs for the shaft with shoulder and keyway were found between 16.5 % and 24.5 % and between 4.3 % and 12.5 % more than SCFs for the shaft with only a shoulder around the fillet area under torsion and bending, respectively.

Shock waves propagation in composite materials


Dynamic response of material is important in variety of engineering applications. Careful structural design taking the dynamic response into account has the potential to prevent catastrophic failure and save lives. Shock wave propagation in heterogeneous materials is a complex matter. Phenomenon of material and geometric dispersion is yet poorly understood as complex pattern generated by a continuous interaction of compression and rarefaction waves generated by interface in material inhomogeneities. The aim of this paper is to contribute to better understanding of scattering and dispersion of shock waves by material interfaces between matrix and fibres and the role of material inelasticity in governing elastic precursor decay and late-time wave dispersion. Because of great complexity of such problems and large demands on both the solution time and memory of computer, the research is realized only for some simple problems as they are presented in the paper. In this way, of course, the problem cannot be studied in full complexity and only some effects can be explained.

Stability analysis of turning the continuous workpiece model


This paper proposes a realistic analytical stability model of regenerative chatter in orthogonal turning operation. Tool geometry is initially developed as a solid model and analysed at different tool overhang conditions. In each case, stiffness, fundamental bending mode, and corresponding damping ratios of the tool are evaluated. With these data, cutting tool can be represented with a lumped parameter single-degree of freedom vibration oscillator. Workpiece dynamics, on the other hand, is considered independently using a discrete finite element beam model. At some contact node of the workpiece, tool mass imposes a regenerative cutting force and second-order dynamic delay differential equations are formulated in terms of tool and modal parameters. Stability criterion is formulated from the characteristic equation. Influence of tool overhang and workpiece cross-section on the stability of the proposed model is reported. Results are illustrated with a commonly used HSS cutting tool with tailstock-supported workpiece.

Modeling and design optimization of the elastic foundation for vertical roller mills


Vertical roller mills are widely used for pulverizing cement raw material, cement, coal, and other minerals. During their operation, these machines often produce considerable vibrations in its vicinity, causing disturbance, damage, and interruptions of plant operations. Elastic foundation has been introduced and used for these roller mills to better isolate vibrations with a more compact mill base. In this work, a new method for determining the key design parameters of a roller mill elastic foundation for more effective vibration isolation is introduced. The method minimizes the maximum vertical dynamic force that is transmitted to ground through the mill elastic foundation under the excitation forces introduced in the mill operation. A system dynamics model on the mill elastic foundation is first introduced, and the fifth-order Runge-Kutta-Fehlberg method is used to evaluate the dynamic performance of the elastic foundation using this model. The system dynamics model and simulation method are validated through experiments on a roller mill elastic foundation. Based on the introduced dynamics model and solution method, a foundation design optimization problem is formulated. The stiffness of the springs, the damping coefficient of the dampers, and the mass of the inertia block of the mill elastic foundation are considered as design variables. Two groups of design constraints, the desired limits on the static and dynamic deformations, and the needed safety margins between the natural frequencies of the foundation system and the frequencies of the excitation forces introduced by the roller mill are considered. Due to the complexity of the elastic foundation system dynamics and the multi-modal form of the objective function, the genetic algorithm (GA) is used to solve the formulated optimization problem. The new method is illustrated using elastic foundation design for a typical roller mill as an example. The system dynamics and vibration isolation capabilities of the elastic foundations, designed using conventional design approach, and the newly introduced optimization method are compared to illustrate the advantage of the new design method. The design optimization leads to better vibration isolation and smaller foundation with lower costs. This research contributes to the development of new design methods for the elastic foundations.