Radivoje Mitrovic

Design for reliability of a vehicle transmission system

Robust vehicle design for improved reliability and quality has been one of the key areas of interest in the automotive industry for a number of years. Based on this approach, reliability is designed into the vehicle following a rigorous vehicle design and development process coupled with appropriate design methods, such as failure mode and effects analysis (FMEA), quality function deployment (QFD), design of experiments (DoE), the Taguchi method, and others. While significant progress has been achieved to date in improving the reliability and quality of vehicles, there is still some need to incorporate parts and subsystems with specific reliability functions within the vehicle system reliability model early in the design concept stage and throughout the vehicle design process so that the reliability of systems and subsystems can be designed-in with more confidence. A comprehensive design for reliability model for critical vehicle systems and subsystems coupled with the failure mode and effects analysis (FMEA) method could help identify and alleviate potential failure modes, and hence maximize vehicle reliability. This article proposes a design for reliability process that aims to achieve this particular outcome in the case of a mechanical vehicle transmission system. A detailed case study involving design for reliability of a vehicle transmission system is presented.

Analysis of the Nominal Load Effects on Gear Load Capacity Using the Finite-Element Method:

This research investigates the effects of the nominal load value on load distribution of simultaneously meshing gear teeth pairs, and on the involute gear load capacity. The research results presented in this article confirm that the nominal load value has a significant influence on the gear load capacity calculations. However, this influence is generally neglected in standard gear calculations, which can result in oversized gear dimensions. This can lead to inadequate gear designs in practice due to increased demand for reduced gear size and weight in modern machinery. The article provides a detailed description of the iterative numerical method developed in this research to support the modelling and analysis of load distribution in meshed gears using the finite-element method.

Reliability of Transportation Belt Rollers Used in Surface Coal Digging

Transport of ground and coal at the surface coal dig in Kostolac, Serbia, is done using transportation belts (3 - 5 kilometres in length) using the systems of BTR (Bagger-Transporter-Remover) and BTM (Bagger-Transporter-Mill). The transporter belt during circular movement is suspended on carry-rollers (during transport of weight) and on support-rollers (without weight). Two or three carry-rollers, or three support-rollers make a garland. Garlands (5 carry and 3 supporting) are built into a section and they enable the movement of belt over them. The number of sections depends on the transportation system length. Reliability of these systems is governed by the reliability of the carry and support rollers. In order to determine the reliability of the BTR and BTM systems, reliability analysis of both carry and support rollers was performed using the method of Fault Tree Analysis (FTA) and Reliability Block Diagrams (RBD). In this paper the assessment of roller reliability is described using the FTA method with failure elements. The reliability function was determined on the basis of the RBD in the case where all of the constructive elements of the rollers are in operation the complex relationship, and when some of the elements are in failure mode the quasi-complex relationship.

Surface characterisation of Pb1−xMnxTe alloy by atomic force microscopy and magnetic force mode

Abstract In this paper the authors present the results of surface characterisation of a lead telluride alloy conducted by atomic force microscopy and magnetic force microscopy. Relationship between surface morphology, in the range of several nanometres, and the magnetic properties allows precise determination of nanomagnetic particles size with their distribution within a scanned area. This method allows the characterisation of nanoparticles in dimensional and magnetic sense since the paramagnetic and diamagnetic range can be examined.

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.

Magnetic Force Microscopy Application in Steel Structure and Milling Process Parameters Evaluation

Application of scanning probe microscopy techniques in evaluating process quality is presented. We conducted a surface characterization and comparison of topographical and magnetic features for three steel plate samples that were processed with the same milling parameters. The topographical features have presented an interesting discourse with magnetic features leading us to propose the magnetic fingerprint of matter on the nanometer level as a possible guideline in early crack detection and process parameter optimization.

Analysis and prediction of vibrations of ball bearings contaminated by open pit coal mine debris particles

Preliminary communication Analysis of the relevant literature has shown that only few researches are dealing with the bearings dynamic behaviour in real environmental conditions where high concentration of solid contaminant particles is evident. There is still no established mathematical correlation between bearings vibration characteristics, working time and concentration level of contaminant particles in their grease. Solving this problem was the main goal of research described in this paper. First step was thorough analysis of the chemical composition and structure of contamination particles directly causing the sample bearings failure on open pit coal mines. After that, specific experimental methodology was developed and implemented. Finally, by processing of the experimental results, new mathematical correlation between listed bearings characteristics was determined.

Data Acquisition and Automatisation of a Conveyor Idler Test Stand

Precise determination of the time-to-failure for conveyor idlers allows the planning of regular conveyor system maintenance and well-timed replacement of worn conveyor garlands. Incidental delays in power plant coal supply leads to a significant reduction in overall thermal power plant efficiency. This paper describes a test stand for the laboratory testing of conveyor idlers, under the influence of different radial loads, which was developed by the Faculty of Mechanical Engineering at the University of Belgrade. Data acquisition and processing are also considered, which includes control, monitoring and automatisation of the test stand. Machine protective systems, which ensure a high level of machine safety, were specifically redesigned due to the importance of operator safety and health.

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.

Determination of the Wing Conveyor Idlers’ Axial Loads Using the Finite Element Method

The impact of the axial load is often completely neglected in the design of the conveyor idlers (rollers) testing machines. The subject of the present research is focused primarily on the conveyor idlers load determination by numerical simulation of the contact between the conveyor belt and idlers. A nonlinear theory of the finite element method is applied, taking into account the effects of large displacements and the contact problems. The basic information required for the presented calculation was the modulus of elasticity of the conveyor belt in the lateral direction. An experimental apparatus in accordance with the DIN 22102 standard was developed and used to determine the load representative value. The adopted approach to the numerical modelling was initially checked by the simulation of the designed experimental testing. A significant match of the results confirmed the applicability of the presented approach to the modelling of the considered problem. The axial load on the wing (side) idlers is generated only during the partial loading of the conveyor. It has considerably high intensity only until the conveyor belt touches the horizontal idler. Applying the gradually increasing load on the conveyor belt in the numerical model and monitoring the vertical distance between the belt and the horizontal conveyor idler, the exact moment of contact was determined. The reaction forces registered in the contact of the belt and the wing idlers are used as the experimental loads in the custom designed conveyor idlers testing machine – where conveyor idlers are tested under the simultaneous action of the radial and axial load.