Tomsilav Jarak, Boris Jalušić, Jurica Sorić: Mixed Meshless Local Petrov-Galerkin Methods for Solving Linear Fourth-Order Differential Equations

The paper presents meshless methods based on the mixed Meshless Local Petrov-Galerkin approach used for solving linear fourth-order differential equations. In all the methods presented here, the primary variable and its derivatives up to the third order are approximated separately. Three different mixed meshless methods are derived by different choices of test and trial functions and are verified using available analytical and reference solutions. The numerical performance of the presented algorithms is demonstrated by several representative numerical examples.

Key words: meshless; mixed Meshless Local Petrov-Galerkin methods; fourth-order differential equations; thin beams; strain gradient elasticity

Nataša Soldat, Radivoje Mitrović, Ivana Atanasovska, Radoslav Tomović: A Methodology for Analyzing Radial Ball Bearing Vibrations

This paper presents the development of a methodology for calculating radial ball bearing vibrations. First, analytical and numerical models were developed and then, the obtained results were experimentally verified. In the experiment, a test rig for a dynamic testing of bearings subjected to an external load was used. Special attention was paid to the analysis of the total bearing deformations and stiffness, being the main parameters that define the dynamic behaviour of a bearing. In order to determine total deformations of a ball bearing as an assembly, a finite element model of the bearing was developed. The results obtained from the new methodology for a particular ball bearing type have been verified by experimental results. The obtained correlations of the experimental and the numerical results are about 2.5%. Based on the calculations and the experimental testing of the chosen ball bearing type, under conditions of a variable radial load, the analysis of the influence of the radial load on the dynamic behaviour of a ball bearing was performed. The analysis of the obtained results showed that the vibration amplitude increases with a similar multiple factor as loads increase.

Key words: radial ball bearings; dynamics; vibrations; finite element analysis

Matija Sakoman, Danko Ćorić, Tamara Aleksandrov Fabijanić, Saša Kovačić: Tribological Properties of Coatings Applied on Near-Nano and Nanostructured WC-Co Hardmetals by Using Plasma-Assisted Chemical Vapour Deposition Technique

Samples of nanostructured hardmetals were sintered as a substrate material by applying two different powder metallurgy processes. The starting powders had an average grain size from 95 um to 150 um. The plasma-assisted chemical vapour deposition technique was used for the deposition of coatings and two coating systems, i.e. the 2 um titanium nitride and 3.8 um titanium carbon nitride were produced. Scratch tests were conducted with an increasing load ranging from 5 to 200 N. Critical normal loads of coating delamination during the scratch tests were registered. The sliding wear resistance was investigated with a ball-on-disc test. The ball-on-disc test showed that the porosity of the sintered product had the highest impact on the wear volume loss. Nanostructured hardmetals showed a great potential for application of plasma-assisted chemical Vapour deposition.

Key words: plasma-assisted chemical vapour deposition; titanium nitride; titanium carbon nitride; hardmetals; cemented carbides

Andrzej Piotrowski, Rafał Gołębski, Piotr Boral: Geometrical Analysis of Composite Hobs.

The paper presents the universal mathematical model-based geometric analysis of a composite hob with replaceable sintered carbide cutting inserts. Composite hobs are characterised by lower accuracy compared to monolithic hobs and are generally used in roughing. Based on a computational algorithm developed by the authors of this study a computer program has been created to model the position and the geometry of the cutting insert placed on the rake face. A generalised case of a composite hob with a flat rake face not parallel to the hob axis and with rake angles different from zero has been analysed. Methods for correcting the cutting insert position and geometry to improve the composite hob accuracy are presented.

Key words: composite hobs; geometric analysis; hob accuracy

Ivan Grujic, Nadica Stojanovic, Radivoje Pesic: Numerical Analysis of IC Engine Operation with High-Pressure Hydrogen Injection

The limited quantities of oil reserves and the exhaust emissions from IC engines have become a threat to the existence of IC engines. One of the best solutions to the problem is the use of alternative fuels. Hydrogen is an alternative fuel that is called a fuel of the future. A disadvantage of hydrogen is its high combustion speed. Experimental results were used for the determination of inputs for numerical analysis. The numerical analysis is performed for a 3D model of the engine in order to determine the working parameters of the engine (pressure and temperature). The main goal of this study is to investigate a possibility of modifying the diesel engine so that it can run on hydrogen. It was found that in such an engine the greatest loads occur in the combustion chamber; thus, the vital parts of the engine are protected. Therefore, a mechanical analysis of the combustion chamber was performed (calculation of stresses and deformations). The obtained results are encouraging because they indicate that by applying the presented solution a much cheaper technology than the modern diesel engine systems is made possible.

Key words: hydrogen; experimental results; 3D model; numerical analysis; chamber

Aleksandar Miltenović: Thermal Analysis of a Crossed Helical Gearbox Using FEM

Overheating of gearboxes with crossed axes, such as crossed helical gearboxes, is one of the greatest disadvantages of these gearboxes in comparison with other drives, such as gearboxes with bevel or cylindrical gears. High friction results in the overheating of the transmission and the occurrence of scuffing. The main cause of the overheating is the generation of heat inside the gearbox due to bearing friction, sealing friction and above all, friction between tooth flanks during engagement. By applying the finite element method, thermal stability of a gearbox was predicted, and this procedure was verified on the case of a crossed helical gearbox with an axial distance of 30 mm. Based on the performed numerical investigation, a new procedure for the prediction of heat generation in the crossed helical gear transmission was proposed.

Key words: temperature distribution; gearbox; FEM

Wenwen Lin, Yuejun Zhang: Integrated Production and Maintenance Planning for Flow Line Systems

This study extends the investigation of the capacitated lot-sizing problem to the production and maintenance planning in unreliable flow line systems. An integrated modelling framework is proposed with the aim of seeking a cost-optimal plan for both production and maintenance. In the model, preventive maintenance is scheduled to avoid unplanned failures, and corrective maintenance is carried out in any machine in which an unplanned failure occurs. A regression-based approximation approach was introduced to calculate the production time under random failures. Then, the integrated planning model can be solved by any commercial optimization software. The numerical example demonstrates that the integrated model guarantees the effectiveness of the production and maintenance plan. It also showed that the buffer capacity has significant effects on the capacity utilization.

Key words: production planning; maintenance; flow line system; simulation; polynomial regression

D Loganathan: Grey Relational Analysis-Based Optimisation of Input Parameters of Incremental Forming Process Applied to the AA6061 Alloy

Incremental forming is mainly based on the deformation occurring locally on sheet metal. A hemispherical head tool deforms the sheet metal progressively, and its path is controlled by means of a CNC machine. Even though the process is a time-consuming one, the cost reduction connected with punches and dies makes this process attractive for rapid prototyping. In single point incremental forming, the quality of formability mainly depends on the forming parameters and the tool path generated. In this study, cone-shaped components were formed from AA6061 alloy sheets with a thickness of 1.15 mm. Factors, such as feed rate, spindle speed, and step depth are considered as input parameters to determine the output response in terms of surface roughness and wall thickness. Taguchi’s technique was used for conducting the experiments with the smallest number of repetitions to evaluate the output. Grey relational analysis was introduced to determine the optimal forming parameters with respect to the output response. The experiments conducted with the optimised parameters show a minimal deviation of 0.15% in the grade value compared to the predicted grade which is acceptable.

Key words: Incremental forming; Grey relational analysis; Surface roughness; Wall thickness