Dejan Momčilović

Explicit Parametric Method for Optimal Spur Gear Tooth Profile Definition

The gear tooth profile has an immense effect on the main operating parameters of gear pairs (load capacity, working life, efficiency, vibrations, etc). In current engineering research and practice, there is a strong need to develop methods for tooth profile optimization. In this paper a new method for selecting the optimal tooth profile parameters of spur gears is described. This method has been named the Explicit Parametric Method (EPM). The addendum modification coefficient, radius of root curvature, and pressure angle of the basic rack for cylindrical gears, have been identified as the main tooth profile parameters of spur gears. Therefore, the EPM selects the optimal values for these three tooth profile parameters. Special attention has been paid to develop a method of adjustment for the particular working conditions and explicit optimization requirements. The EPM for optimal tooth profile parameters of gears uses contact nonlinear Finite Element Analysis (FEA) for calculation of deformations and stresses of gear pairs, in addition to explicit comparative diagrams for optimal tooth profile parameter selection.

Assessment of the Effect of Pitting Corrosion on Fatigue Crack Initiation in Hydro Turbine Shaft

Energy efficiency is a key issue worldwide, and not confined solely to the realm of engineers. Past failures of mechanical power system components must be examined carefully in order to minimise future occurrences and increase energy efficiencies. Improved design procedures have been highly sought by engineers and researchers over the past few decades. The latest verified method with strong application potential within the power industry is that of the Theory of Critical Distances (TCD). TCD is not one method, but a group of methods that have a common feature; the use of a characteristic material length parameter, the critical distance L, for calculating the influence of notch-like stress raisers under static and fatigue loading. A case study from a hydro power plant turbine shaft was chosen to illustrate the development of this methodology. The paper illustrates the application of TCD to the fatigue life assessment of a turbine shaft with stress concentrations due to pitting corrosion.

Development of the universal tool for testing of tensile properties of hexagonal steel wire mesh for civil engineering

The developing of the universal tool for testing of tensile properties of hexagonal steel wire mesh for civil engineering is described in this paper. The developed tool allows repeated testing of hexagonal steel wire mesh of different dimensions without tool changes and is generally related with the procedure for the determination of tensile strength properties of different wire meshes. The construction of the tool which is related to the aims of the decreased mass consumption and high operation safety is described in detail. Particular attention is focused on the safety component of the tool which ensuring safety testing by preventing slipping of the wire mesh samples during loading. The paper also presents the Finite Element Analysis performed in order to verify the high safety factor of the developed tool. The contact regions with stress concentration behavior are analyzed by non-linear solvers. The obtained results and conclusion about the possible contributions of the developed universal tool for extensively testing of wire meshes for civil engineering are discussed.

Spur gear model for prediction of fatigue damage initiation in contact zone

The objective of this paper is to give a new viewpoint in contact fatigue assessment in the spur gears. The presented research is based on up-to-date methods and multidisciplinary approach, and enables direct prediction of fatigue damage initiation in contact zones. The special attention is paid to the developing of model for precise simulation of spur gear teeth contact by finite element method (FEM). The contact stress calculation based on true contact involute geometry provides the stress gradients for theory of critical distances (TCD) application in damage initiation prediction. One particular spur gear pair is analysed for presenting the spur gear model developing.

The Influence of Corrosion on Stress Concentration Factor at Shaft to Flange Radius

This paper describes the influence of corrosion on stress concentration factor and crack initiation at shaft-flange transition section. The real turbine shaft failure case study is used for research. This case study and numerical calculations show that the seal box solution led to constant leakage of river water in the zone of critical radius and resulted in corrosion fatigue cracks and turbine shaft failure. Thus, the Finite Element Analysis is performed to calculate the stress concentration factor increase as a result of corrosion occurrence. The corrosion at shaft-flange transition section is modelled in the zone with maximum stresses with a corrosion pit dimensioned to comply with real in situ dimension of pits. The presented research points new trends in stress concentration factor calculation. The obtained numerical results for maximum stress and stress concentration factor in critical zone confirmed failure analysis study outcome.