Ivo Senjanović,Damjan Čakmak, Neven Alujević, Ivan Ćatipović, Nikola Vladimir: Ring Buckling Analysis Based on the Toroidal Shell Theory

The in-plane and the out-of-plane buckling theory of rings exposed to external pressure is presented. A ring is considered as a segment of a toroidal shell. The governing ring equations are obtained by deducing the toroidal shell energy equations for the linear and the nonlinear strain. The obtained formulae for critical load are compared with those known in relevant literature. The critical load depends on the assumption concerning the load behaviour during buckling. Illustrative examples are solved numerically by means of several commercial FEM computer programs in order to investigate which assumptions are introduced in the ring buckling analysis.

Key words: ring buckling; energy approach; in-plane buckling; out-of-plane buckling; critical load; analytics; FEM

Jasmin Sehovic, Ivan Filipovic, Boran Pikula: Experimental Determination of Non-Linear Characteristics of the Passenger Vehicle Suspension System

The vehicle suspension system is supposed to provide comfort to the driver and to passengers, as well as to ensure the vehicle stability, especially while driving through curves, i.e. while cornering. Simulation is frequently used to analyse the vehicle behaviour under various driving conditions. When defining a physical model of a suspension system, as the initial step in the simulation program development, it is important to determine, as precisely as possible, the following key parameters: mass, mass moments of inertia, stiffness, damping properties of the material, damping of elastic vehicle parts (stabilisers, tyres), damping properties of particular vehicle dampers, damping of joints and links as individual components of the suspension system, as well as other characteristics.
A telescopic damper is an essential part of the suspension system. Its damping properties are highly non-linear. Most publications deal with damping in general terms. Specific data is usually not provided. This paper is, however, focused on determining both the magnitude and the character of damping. A methodology that combines experiment and calculation has been developed for that purpose. As part of the experiment, kinematics (accelerations) at characteristic positions of the suspension system is first determined. By combining a one-dimensional (1D) mathematical model and experimental results, the instantaneous values of damping force and the magnitude of damping coefficient, as a function of the piston velocity and the travel of the telescopic damper, were determined. The suspension system of an in-production passenger vehicle is investigated using a combined analytical and experimental method. The results of real damping and of damping coefficients are presented.
Finally, the results of the simulation, created by using the parameters determined in the previous step, and of the experiment were compared.

Key words: Vehicle oscillations; telescopic damper; damping coefficient

Lucija Č. Lipuš, Marko Katić: Influence of Intracavity Power on Frequency Characteristics of Iodine-Stabilized He-Ne Laser

Following a shift in the industry to solid-state lasers during the past decade, resonator tubes which can be used in iodine-stabilized helium-neon (He-Ne) lasers are being discontinued by most manufacturers. After installing a replacement tube, it was discovered that its intracavity power was not equal to that of the original tube. The influence of this change on the uncertainty of frequency was determined over the course of several months. Mirrors in the optical cavity were adjusted for optimal intracavity power using short heterodyne beat frequency measurements with a reference laser. Data for stability and absolute value of the reference frequency were well-known and provided in advance by calibration with the comb method. The sensitivity coefficient of the output beam power was estimated from beat frequency deviations measured at several values of power inside the range of the stabile operation of the laser. Finally, a long-term measurement of beat frequency provided data about the stability and frequency offset.

Key words: laser; frequency stability; traceability; optical interferometry

Dominik Rybarczyk, Andrzej Milecki: Electrohydraulic Drive with a Flow Valve Controlled by a Permanent Magnet Synchronous Motor

This article presents an electrohydraulic drive with a new electrohydraulic flow valve controlled by a Permanent Magnet Synchronous Motor (PMSM), designed and built by the authors. In comparison to a valve with a proportional electromagnet, the use of a PMSM has enabled significant improvements in the key characteristics of the valve. A theoretical framework and a model of a PMSM are presented; subsequently, a valve with this motor is proposed and tested. Step responses of the real valve and its static and frequency characteristics are measured. The characteristics obtained in the simulation are compared with those obtained in the laboratory investigations, showing their good compliance. The obtained characteristics of the new valve are better than those of a typical proportional valve. The new valve is applied in an electrohydraulic linear actuator. For positioning tasks, two types of controllers are applied and compared: a proportional-derivative controller and a fractional order proportional-derivative controller showing satisfactory parameters.

Key words: electrohydraulic valve; modelling, permanent magnet synchronous motor; control

Yusuf Arslan: The Effect of Cryogenic Treatment on the Punch Wear and the Hole Edge Geometry

The ball joint parts made of forged steel are quite important in the suspension system. The quality of production of ball joint parts is very important because of their role. Some basic defects can be found in the hole edge form. These defects affect the hole quality of ball joint parts. In this study, the effects of cryogenic processing on the wear of AISI D2 punches and the effects of punch wear on the hole edge geometry of hot forged AISI 1040 steel ball joint parts were investigated. The hole geometry changes are generally associated with punch wear and process parameters. For the purpose of investigation, piercing was carried out using an eccentric press with AISI D2 tool steel punches on 6.0 mm-thick ball joint pieces. The punches were traditionally heat treated. Some of the punches were cryogenic-treated at -145 °C in addition to the conventional heat treatment. Weight loss values were measured to assess the punch wear, and SEM and OM images were analysed. At the end of the industrial piercing process, it was found that the D2 tool steel punch wear decreased with cryogenic process applied and the size changes in the hole edge geometry of the punched 1040 hot forged steel parts turned out to be less marked.

Key words: Cryogenic treatment; ball joint; punch wear; edge geometry; AISI D2; AISI 1040

Bashir Salah, Sajjad Khan, Nikola Gjeldum: An Automatic Yogurt Filling System Built from Scratch Based on Industry 4.0 Concept

The movement to digitally transform Saudi Arabia in all sectors has already begun under the focused “Vision 2030” programme. Consequently, the task of renovating and standardizing manufacturing and other production industries to compete with global challenges is essential. The fourth industrial revolution (Industry 4.0), triggered by the development of information and communications technologies (ICTs), provides a basis for smart automation using decentralized control and advanced connectivity (e.g., Internet of Things). In the areas where the spirit of Industry 4.0 has been embraced, some industries have already implemented these ideas and yielded gains. Learning the principles of Industry 4.0 and having knowledge of this digital industrial revolution is essential for future engineering graduates. In this paper, a case study on building a learning factory from scratch based on the concept of Industry 4.0 is introduced. The initial achievement of a fully automated production line is presented. In doing so, a system with a smart design having smart control and smart monitoring is developed.

Key words: learning factories; engineering education; smart control; smart monitoring; industry 4.0

Dušan Arsić, Vukić Lazić, Aleksandar Sedmak, Srbislav Aleksandrović, Jelena Živković, Milan Djordjević, Goran Mladenović: Effect of Elevated Temperatures on Mechanical Properties of Ultra High Strength Hot Work Tool Steel H11

This paper presents an experimental and numerical study into the influence of elevated temperatures on mechanical properties of the heat treated high quality hot work tool steel H11. This steel belongs to a group of alloyed steels with extraordinary mechanical properties. The aim of this study was to determine the highest temperature at which these properties are still maintained. The experimental investigation focused on the tensile testing of specimens at seven different temperatures, including the room temperature. The highest testing temperature was 700 °C. The heat treatment of plates (specimens) consisted of quenching and tempering. Although the strain hardening of this type of materials is small, the strain hardening curves were calculated to show if there was a possibility for the material to increase its strength due to exploitation loads. Also, a numerical analysis of the tensile test by using the finite element method was done in order to define an appropriate model for numerical testing. The obtained results are then compared with the experimental results.

Key words: H11 steel; elevated temperatures; tensile test; strain hardening; FEM

R Ashok Raj, R Pavendhan, B Kumaragurubaran: Investigation Into Tribological Behaviour of AL7075 and AL7075 Hybrid Composites

The aluminium metal matrix composite (AMMC) is widely used in aerospace and automotive applications. The AMMC reinforced with titanium diboride (TiB2), exhibits excellent tribological properties. In this study, molybdenum disulfide (MoS2) was used as a reinforcement to improve the tribological properties of the Al7075-TiB2 composite. The Al7075 hybrid composites were produced with 12 wt% of TiB2 with varied mass loading of MoS2 (x = 0, 1.5, 3, 4.5) by using the powder metallurgy method. The energy dispersive X-ray spectroscopy (EDX) test confirmed the presence of reinforcements. The Al7075 composites were examined for the study of microstructure, microhardness and tribological behaviour by using a scanning electron microscope (SEM), Vickers microhardness tester and pin-on-disc equipment, respectively. The tribological properties of Al7075 hybrid composites are superior to those of aluminium alloy Al7075. The low wear loss (10 mg) and coefficient of friction (0.109) were produced at the sliding velocity of 2 m/s, the sliding distance of 1000 m and the applied load of 5 N in the Al7075-12%TiB2-4.5%MoS2 composite.

Key words: microstructure; microhardness; wear loss; coefficient of friction; reinforcements

In memoriam, Nekrolog: In memoriam Academician Božidar Liščić