MONOTONIC BEHAVIOUR OF NORMALISED AND QUENCHED AND TEMPERED STEEL 42CrMo4

U radu je predstavljeno na eksperimentu zasnovano utvrđivanje ponašanja normaliziranoga i poboljšanoga niskolegiranog čelika 42CrMo4 (AISI4140) izloženog djelovanju monotonoga aksijalnog vlačnog opterećenja te njegova karakterizacija putem odgovarajućih monotonih parametara. Eksperimenti su izvođeni na ispitnim tijelima standardnog oblika i dimenzija uz korištenje servohidrauličkog stroja pri sobnoj temperaturi. Analizirano je i uspoređeno ponašanje materijala različitih tvrdoća. Određene su vrijednosti osnovnih monotonih parametara materijala te je utvrđena i jednostavnim izrazima okarakterizirana veza između vrijednosti granice tečenja i lomne čvrstoće te temperature popuštanja odnosno postignute tvrdoće materijala.The presented work is concerned primarily with experimental determination of the behaviour of normalised and quenched and tempered low-alloy steel 42CrMo4 (AISI4140) subjected to monotonic uniaxial tensile loading and determination of its monotonic parameters. Experiments were performed on standard specimens using a servo-hydraulic testing machine at room temperature. The behaviours of materials with differing hardnesses were analyzed and compared. After determination of principal monotonic parameters values, correlation was confirmed to exist between tempering temperature, i.e. achieved materials’ hardness, and the monotonic yield strength as well as the ultimate strength. Simple expressions are proposed for fast estimation of cited monotonic properties from hardness

Sustainable urban development in a city affected by heavy industry and mining? Case study of brownfields in Karvina, Czech Republic

Due to recent societal changes ‘brownfield’ sites have gradually become a significant element in planning urban development. Brownfields can occur as a barrier and obstacle to the development of the urban organism but simultaneously they also represent unrealised potential. Brownfields, ex-industrial sites, are greater in those cities whose development was based on heavy industry or mining. In the first part of this paper theoretical concepts linked to the regeneration of brownfields are discussed, the second part is devoted to a case study of Karvina, in the Czech Republic, where the driving forces behind the occurrence of brownfields, their spatial distribution, and their prospects for regeneration are analysed. It was found that 28 brownfield sites on 121 ha are located in surveyed city with the majority having industrial and mining origins. Majority of local brownfields are owned by a local mining company. The perception of individual sites by the local population was ascertained via a questionnaire survey (n = 150). This found that awareness about problems connected to brownfields is quite limited and that local population perceive post-mining brownfields, located in more distant locations, as an opportunity for new industries to create job opportunities in city with significant unemployment problems

Circular polarization in a non-magnetic resonant tunneling device

We have investigated the polarization-resolved photoluminescence (PL) in an asymmetric n-type GaAs/AlAs/GaAlAs resonant tunneling diode under magnetic field parallel to the tunnel current. The quantum well (QW) PL presents strong circular polarization (values up to -70% at 19 T). The optical emission from GaAs contact layers shows evidence of highly spin-polarized two-dimensional electron and hole gases which affects the spin polarization of carriers in the QW. However, the circular polarization degree in the QW also depends on various other parameters, including the g-factors of the different layers, the density of carriers along the structure, and the Zeeman and Rashba effects

Fabrication of highly dense isotropic Nd-Fe-B bonded magnets via extrusion-based additive manufacturing

Isotropic bonded magnets with a high loading fraction of 70 vol.% Nd-Fe-B are fabricated via an extrusion-based additive manufacturing, or 3D printing system that enables rapid production of large parts for the first time. The density of the printed magnet is 5.15 g/cm3. The room temperature magnetic properties are: intrinsic coercivity Hci = 8.9 kOe (708.2 kA/m), remanence Br = 5.8 kG (0.58 Tesla), and energy product (BH)max = 7.3 MGOe (58.1 kJ/m3). The as-printed magnets are then coated with two types of polymers, both of which improve the thermal stability at 127 {\deg}C as revealed by flux aging loss measurements. Tensile tests performed at 25 {\deg}C and 100 {\deg}C show that the ultimate tensile stress (UTS) increases with increasing loading fraction of the magnet powder, and decreases with increasing temperature. AC magnetic susceptibility and resistivity measurements show that the 3D printed Nd-Fe-B bonded magnets exhibit extremely low eddy current loss and high resistivity. Finally, we show that through back electromotive force measurements that motors installed with 3D printed Nd-Fe-B magnets exhibit similar performance as compared to those installed with sintered ferrites

Communication in the Third Dimension: Song Perch Height of Rivals Affects Singing Response in Nightingales

Many animals use long-range signals to compete over mates and resources. Optimal transmission can be achieved by choosing efficient signals, or by choosing adequate signalling perches and song posts. High signalling perches benefit sound transmission and reception, but may be more risky due to exposure to airborne predators. Perch height could thus reflect male quality, with individuals signalling at higher perches appearing as more threatening to rivals. Using playbacks on nightingales (Luscinia megarhynchos), we simulated rivals singing at the same height as residents, or singing three metres higher. Surprisingly, residents increased song output stronger, and, varying with future pairing success, overlapped more songs of the playback when rivals were singing at the same height than when they were singing higher. Other than expected, rivals singing at the same height may thus be experienced as more threatening than rivals singing at higher perches. Our study provides new evidence that territorial animals integrate information on signalling height and thus on vertical cues in their assessment of rivals

The importance of friction coefficient between vehicle tyres and concrete safety barrier to vehicle rollover

The most important mechanical factors in an impact scenario of a vehicle into a concrete safety barrier are vehicle speed, the impact angle, the static stability factor of the vehicle as well as the concrete safety barrier design and conditions. Concrete safety barriers (CSB) are primarily designed to minimize vehicle damage by allowing the vehicle to be lifted when riding up on the lower slope and then redirected back on to the road. In some cases, though, the vehicle-CSB contact might end up with a rollover often with fatal consequences. To reduce the rollover risk, different concrete barrier shapes were designed in the past while omitting the importance of the friction coefficient between the tyre and barrier. Therefore, the aim of this paper is to research and emphasize the importance of the friction coefficient between the vehicle tyres and the CSB in rollover accidents. For that purpose, a series of Finite Element analyses were performed using different values of the friction coefficient between the vehicle tyres and the CSB. Experimental measurements of the coefficient of friction between the rubber and CSB blocks of different surface were additionally performed in dry and wet conditions in order to examine the real onsite friction characteristics. The results show that the coefficient of friction can have a crucial impact in vehicle rollover scenarios and should therefore be kept as low as possible by the concrete safety barriers manufacturers and maintainers

Decelerations of passenger vehicles on gravel arrester beds

Gravel-filled arrester beds, also called safety-escape ramps or vehicle run-out areas, have long been a road-safety feature for safely stopping heavy road vehicles from running off the road. In the recent past, there has been consideration given to installing these features on highway access ramps to provide safe areas to stop passenger cars driving at highway speeds. The work presented in this article was performed to investigate the behaviour of standard-size passenger cars on gravelfilled arrester beds, with a particular focus on the achievable vehicle decelerations and the ability of the arrester beds to safely stop a passenger car coasting in an uncontrolled manner. The findings show that the achievable average decelerations are in the range of 0.3 g for coasting vehicles and up to 0.9 g when the vehicles are braking. The results prove that more research is required to quantify the influence of the gravel parameters on the achievable decelerations

Krmilni sistem naprave za natezne preizkuse z uporabo cenovno ugodne strojne opreme in odprtokodnega programja

The aim of this study is to verify whether a Raspberry Pi 3 B+ can be utilized as a low-cost device for controlling a tensile-testing device used for material research purposes. A list of requirements based on already-available hardware was drawn up, which the new control system had to fulfil. To connect all the necessary equipment, a connection board was constructed, and some additional hardware was acquired for the system to be able to perform all the necessary tasks. The whole controlling system was also put in a small enclosure to make it portable. The control-system software was written in C++ using the Pigpio library. The developed system was then tested, and the results were compared to a commercially available Instron 8802 device. A comparison of the results shows that the upgraded equipment can produce comparable results to commercially available devices and is sufficiently accurate to be applied for research purposes for the characterization of soft tissues and other materials

The bearing stiffness effect on in-wheel motors

In-wheel motors offer a promising solution for novel drivetrain architectures of future electric vehicles that could penetrate into the automotive industry by transferring the drive directly inside the wheels. The available literature mainly deals with the optimization of electromagnetically active partshowever, the mechanical design of electromagnetically passive parts that indirectly influence motor performance also require detailed analysis and extensive validation. To meet the optimal performance of an in-wheel motor, the mechanical design requires optimization of housing elements, thermal management, mechanical tolerancing and hub bearing selection. All of the mentioned factors have an indirect influence on the electromagnetic performance of the IWM and sustainabilitytherefore, the following paper identifies the hub bearing as a critical component for the in-wheel motor application. Acting loads are reviewed and their effect on component deformation is studied via analytically and numerically determined stiffness as well as later validated by measurements on the component and assembly level to ensure deformation envelope and functionality within a wide range of operations