Srečko Glodež

The relationship between progressive tooth-flank wear and acoustic indicators in polymer–metal gear transmissions remains insufficiently quantified. In the presented study, an experimental procedure was developed to evaluate the influence of tooth flank wear on the noise behaviour of the POM/steel gear pair. The vibroacoustic analysis was evaluated using time–frequency analysis (TFA) and adapted transform analysis (ATA). The normalised spectral entropy (NSE), the normalised window spectral entropy (NWSE) and the normalised adaptive spectral entropy (NASE) were also considered when evaluating the noise behaviour of the analysed gear pair. The experimental results showed that the sound pressure level increases with increasing gear flank wear. After the running-in phase, a strong correlation was observed between the average wear of the tooth flank and sound pressure level (R² = 0.962 for stages II–V), whereas entropy indicators showed close associations with wear. The reported entropy–wear fits yielded R² = 0.994 for NSE, 0.999 for NWSE, and 0.996 for NASE. Frequency and time–frequency analysis of the sound signals showed that the dominant frequency components correspond to the gear meshing frequency (600 Hz) and its higher harmonics, which increase with increasing wear. The results of this study contribute to a better understanding of how wear affects the vibroacoustic response of polymer gears and provide a basis for developing diagnostic methods to detect wear conditions under the investigated conditions. Future research should expand the experimental analysis to different combinations of polymer gear materials and to a wider range of operating conditions, including higher loads and different temperature regimes.

The paper presents the mechanical, fatigue, and metallographic characterisation of friction stir-welded (FSW) AA 6060 aluminium alloy. The FSW process was performed at a constant rotational speed of 950 min⁻¹ and at traverse speeds of 46 and 93 mm/min. Two specimen conditions were investigated: as-welded and post-weld T6 heat-treated. Quasi-static tensile and fatigue tests were performed using a Zwick/Roell Vibrophore 100 testing machine to determine the engineering stress–strain response and fatigue life of the FSW joints. A comprehensive metallographic investigation was conducted to characterise the as-received material and FSW joints and to analyse the fracture surfaces after quasi-static and fatigue loading. The results showed that post-weld T6 heat treatment significantly improved both the mechanical properties and fatigue performance of the FSW joints, whereas the influence of traverse speed was comparatively less pronounced. Fractographic analysis revealed that fracture location and fatigue crack propagation were strongly influenced by material condition and stress amplitude. As-welded specimens fractured predominantly in the softened heat-affected zone (HAZ), whereas T6 heat treatment shifted the fracture location towards the transition zone (TZ) and stir zone (SZ). Fatigue cracks generally initiated at or near the specimen corners and propagated predominantly transcrystallinely in Stage I, followed by characteristic faceted propagation with fatigue striations in Stage II.

In the presented study, an experimental procedure was developed to evaluate the influence of tooth flank wear on the noise behaviour of the POM/steel gear pair. Changes in sound pressure level were monitored as a function of the POM pinion's wear rate by measuring noise and vibration under controlled test conditions. The vibroacoustic analysis was evaluated using time-frequency analysis (TFA) and adapted transform analysis (ATA). Furthermore, the normalised spectral entropy (NSE), the normalised window spectral entropy (NWSE) and the normalised adaptive spectral entropy (NASE) were also considered when evaluating the noise behaviour of the analysed gear pair. The experimental results showed that the sound pressure level increases with increasing gear flank wear. Frequency and time–frequency analysis of the sound signals showed that the dominant frequency components correspond to the gear meshing frequency and its higher harmonics, which increase with increasing wear. Furthermore, the entropy-based indicators can also effectively characterise the dynamic behaviour of the gear system.,The results of this study contribute to a better understanding of the influence of wear on the vibroacoustic response of polymer gears and provide a basis for developing diagnostic methods to detect wear conditions across different engineering applications. Future research should expand the experimental analysis to different combinations of polymer gear materials and to a wider range of operating conditions, including higher loads and different temperature regimes.

To ensure the viability of polymer materials, given the properties and limitations of polymers, hybrid materials have been developed that blend the features of all included components. Researchers have not explored the impacts of the length aspect ratio of nanofillers on the mechanical properties of hybrids in great detail previously. Multi-walled carbon nanotubes are a valuable option because they exhibit improved mechanical properties. Using numerical simulation, the impacts of nanofiller content and the size aspect ratio on two base materials—polyamide 6, polyoxymethylene—and their blends, were determined as a function of the volume ratio, the MWCNTs aspect ratio and the base material blend composition. Numerical analysis employed the ANSYS Material Designer. Random samples of chopped-fibre representative volume elements were generated, meshed and analysed by finite element analysis to obtain the Young’s modulus and Poisson’s ratio for each sample. The results showed a generally linear dependence. Rises in both aspect ratio and volume fraction of MWCNTs increased the Young’s modulus up to 46% and decreased the Poisson’s ratio up to 1.6%. The findings suggest that although the impact of the aspect ratio is not as large as that of the volume ratio, longer MWCNTs are preferable.

This study investigates the quasi-static and fatigue strength of copper-brazed 316L stainless steel. Quasi-static and fatigue tests were conducted at room temperature (20 °C) using a Zwick/Roell Vibrophore 100 testing machine and specially designed copper-brazed specimens. Two types of specimens were prepared—tensile and shear specimens—to obtain the stress–strain relationships (σ–ε and τ–ε) and the fatigue life (S–N) curves. Based on the experimental results, the quasi-static and fatigue strengths of the copper-brazed joints under external tensile and shear loading were evaluated. The fatigue tests reveal that the shear fatigue strength is significantly lower than the tensile fatigue strength. Furthermore, a comprehensive investigation was conducted, focusing on the metallographic characterisation of the brazed joint and fractographic analyses of fracture surfaces obtained under quasi-static and fatigue loading, with particular emphasis on the shear strength of the investigated brazed joint. The experimental results obtained may be crucial for designing engineering structures (e.g., plate heat exchangers), where copper-brazed joints are the weakest members of the structure.

Parameters of EPFM are used as relevant parameters in structural integrity assessments. In this research, the fracture toughness of armoured steel was determined. The resulting resistance curves and K_JIC obtained according to the ASTM E1820 standard with normalization, compliance and multi-specimen methods were compared. Also, the K_IC was verified according to the ASTM E399 standard as the most precise method for obtaining the K_IC, which also requires a lot of knowledge. For the experiment, the multi-specimen method was used, which is the most expensive and most accurate method, where the least assumption and crack size is measured on the specimen. A fractographic analysis was also presented, and this heat-treated high-strength steel, which is used for anti-ballistic protection, was fully characterized.

A comprehensive experimental investigation to understand the mechanical properties and fatigue behaviour of glass-reinforced polyamide (PA66 GF30) at different temperatures is presented in this paper. The specimens for quasi-static and fatigue testing were machined from previously extruded plates, where two orientations were considered: (i) the extrusion direction (ED) and (ii) the direction perpendicular to extrusion (PED). Both the quasi-static and fatigue tests were performed under different temperatures (22 °C and 100 °C). The fatigue tests were performed in a load control regime under pulsating loading (R = 0.1) to create S–N curves for all the temperatures and loading directions. The experimental results of the quasi-static tests showed that the test specimens manufactured in the extrusion direction have better mechanical properties when compared to those of the specimens manufactured perpendicular to the extrusion direction. Furthermore, the analysis of the quasi-static tensile test results showed that tensile strength, yield strength, and the modulus of elasticity are significantly dependent on the temperature and deteriorate when the temperature is increased from 22 °C to 100 °C. The results of the fatigue tests showed that at both the temperatures (22 °C and 100 °C), the samples produced in the direction of extrusion exhibited higher fatigue strength than those produced perpendicular to the direction of extrusion. For all the sample orientations, the fatigue strength decreased significantly with increasing temperature. The obtained experimental results could be very useful when designing and dimensioning different dynamically loaded engineering components made of PA66 GF30 subjected to high temperatures.