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The purpose of this paper is to compare two different methods for describing the sedimentation in different MRFs. It was decided to obtain electric resistivity of the MR fluid under magnetic field and to measure inductance of the solenoid, which is around the MR fluid, for diagnostic of the sedimentation. The electrical resistivity of the MR fluids and inductivity of the solenoid was measured daily for 11 days for 5 different MR fluids: (Lord MRF-140CG, Lord MRF-122EG, Liquids Research Company MRHCCS4-A and Liquids Research Company MRHCCS4-B and MUDZH-3 made in A. V. Luykov Heat and Mass Transfer Institute, Minsk, BY). These two methods and according procedures are described below. [ABSTRACT FROM AUTHOR]

In this paper, pool boiling of ethanol at atmospheric pressure was analyzed. The enhanced surfaces were made of copper, on which grooves with a depth ranging from 0.2 to 0.5 mm were milled in parallel. The widths of the microchannels and the distances between them were 0.2 mm, 0.3 mm and 0.4 mm, respectively. The highest heat transfer coefficient, 90.3 kW/m2K, was obtained for the surface with a microchannel depth of 0.5 mm and a width of 0.2 mm. The maximum heat flux was 1035 kW/m2. For the analyzed surfaces, the maximum heat flux increase of two and a half times was obtained, while the heat transfer coefficient increased three-fold in relation to the smooth surface. In the given range of heat flux 21.2–1035 kW/m2, the impact of geometric parameters on the heat transfer process was presented. The diameters of the departing bubbles were determined experimentally with the use of a high-speed camera. A simplified model was proposed to determine the diameter of the departure bubble for the studied surfaces. [ABSTRACT FROM AUTHOR]

The aim is to overcome the issues of high-hardness material welding by different additives used to achieve the desired improvements. The research is focused on Hardox 450 steel welding and factors to be considered in order to maintain the required mechanical properties of the weld. The selection of best suited welding materials or additives, including filler metals and shielding gases, are within the important factors to be taken into account. During the welding of Hardox 450 steel, cobalt, nickel, tungsten and titanium additives and cobalt and tungsten mixture additives were used and their influence on the microstructure and mechanical properties of the fusion and heat-affected zones was investigated. The microstructure of the weld zone is related to certain mechanical properties of the weld and heat-affected zone, such as hardness, tensile and bending strength, yield strength, strain at ultimate tensile strength, the Young's modulus and elongation. Research has shown significant differences in the mentioned parameters depending on specific additives used in the welds. It can be concluded that tungsten, used as an additive, increased the hardness of the heat-affected and fusion zones up to 478 HV; the combined presence of cobalt and tungsten additives improves the strength of the seam up to 744 MPa during tensile; and in the case of bending, nickel, when used as an additive, increased ductility (the bending modulus reached the limit of 94 GPa) and at the same time, decreased the risk of cracking. The obtained results highlight the possibilities for strengthening the welded joint of Hardox 450 steel using different additives or their mixtures. The research conclusions and recommendations aim at improving the quality and mechanical properties of welded Hardox 450 steel joints in various applications. [ABSTRACT FROM AUTHOR]

This paper presents comparison of properties of NiSi and Ni(Pd)Si for possible application as interconnect and electrode materials for film bulk acoustic resonators (FBAR) and microelectromechanical systems (MEMS). A number of silicide phases including monosilicide and disilicide phases are found to be formed at various temperatures depending on the composition of the annealed film. The addition of palladium is proved to delay nickel disilicide phase formation which results in a lower sheet resistance at higher temperatures and the possibility to use this material as low resistance interconnect or electrode material rather than pure nickel silicide. At the same time the surface morphology of nickel palladium silicide is found to be more homogeneous, with smaller grain sizes and more uniform alignment of grains in the film, altogether providing the better options for perspective application in FBARs and MEMS, compatible with silicon microelectronics. [ABSTRACT FROM AUTHOR]

The aim of this research was to examine the resistance force generated by linear hydro-cylinder type magnetorheological fluid (MRF) damper acting in different regimes. MRF damper performance has been investigated experimentally by using universal computerized material properties testing machine. Measurements of resistance force have been carried out for different speeds of the damper piston motion under different strength of the magnetic field. Dependences of the force on these parameters (speed and magnetic field strength) have been obtained. It was defined, that the force increases practically linearly when increasing strength of the magnetic field and when increasing piston speed. [ABSTRACT FROM AUTHOR]

This paper focuses on the investigation of the diagnostic system for health monitoring and defects, detecting in composite structures using a piezoelectric sensor. A major overview of structural defects in composite materials that have an influence on product performance as well as material strength is presented. Particularly, the proposed diagnostic (health monitoring) system enables to monitor the composite material plate defects during the exploitation in real-time. The investigated health monitoring system can indicate the material structure defects when the periodic test input signal is provided to excite the plate. Especially, the diagnostic system is useful when the defect placement is hard to be identified. In this work, several various numerical and experimental studies were carried out. Particularly, during the first study, the piezoelectric transducer was used to produce mechanical excitation to the composite plate when the impact response is measured with another piezoelectric sensor. The second study focuses on the defect identification algorithms of the raw hologram data consisting of the recorded oscillation modes of the affected composite plate. The main paper results obtained in both studies enable us to determine whether the composite material is characterized by mechanical defects occurring during the response to the periodic excitation. In case of damage, the observed response amplitude was decreased by 70%. Finally, using the time-domain experimental results, the frequency response functions (FRFs) are applied to damage detection assessment and to obtain extra damage information. [ABSTRACT FROM AUTHOR]

Multi-layer fabrics are commonly used in ballistics shields with a lower bulletproof class to protect against pistol and revolver bullets. In order to additionally limit the dynamic deflection of the samples, layers reinforced with additional materials, including non-Newtonian fluids compacted by shear, are additionally used. Performing a wide range of tests in each case can be very problematic; therefore, there are many calculation methods that allow, with better or worse results, mapping of the behavior of the material in the case of impact loads. The search for simplified methods is very important in order to simplify the complexity of numerical fabric models while maintaining the accuracy of the results obtained. In this article, multi-layer composites were tested. Two samples were included in the elements subjected to shelling. In the first sample, the outer layers consisted of aramid fabrics in a laminate with a thermoplastic polymer matrix. The middle layer contained a non-Newtonian shear-thickening fluid enclosed in hexagonal (honeycomb) cells. The fluid was produced using polypropylene glycol and colloidal silica powder with a diameter of 14 µm in the proportions of 60/40. The backing plate was made using a 12-layer composite made of Twaron® para-aramid fabrics with a DCPD matrix—not yet used in a wide range of ballistics. Then, numerical simulations were carried out in the Abaqus/Explicit dynamic analysis. The Johnson–Cook constitutive strength model was used to describe the behavior of elastic–plastic materials constituting the elements of the projectiles. For the non-Newtonian fluid, a Up-Us EOS was used. The inner layers of the fabric were treated as an orthotropic material. Complete homogenization of the sample layers was carried out, thanks to which each layer was treated as a homogeneous continuum. As a parameter of fracture mechanics for shield components, the strain criterion was used with the smooth particles hydrodynamics method (SPH). Then, the results of simulations were compared with the results of the ballistic test for both samples placed next to each other, which resulted in the formation of a multi-layer composite in one ballistic test subjected to impact loads during firing with a 9 × 19 mm Parabellum FMJ projectile with an initial velocity of 370 ± 10 m/s. The results of numerical tests are very similar to the ballistic tests, which indicates the correct mapping of the process and the correct conduct of layer homogenization. The applied proportions of the components in the non-Newtonian fluid allowed a reduction in the deflection compared to previous studies. Additionally, the proposal to use a DCPD matrix allowed to obtain a much lower deflection value compared to other materials, which is a novelty in the field of production of ballistic shields. [ABSTRACT FROM AUTHOR]

This paper presents a robust nonlinear control law that combines a parametric uncertainty of the single one-degree-of-freedom active magnetic bearing (AMB) system with disturbance. The robust nonlinear feedback tool such as control Lyapunov function (CLF) and robust stability techniques are developed. The control objective is to globally stabilise the mass position of an AMB with flux feedback. The flux-based control model for an AMB system is derived due to voltage switching strategy with voltage saturation. This strategy enables the flux control under a zero-bias or low-bias flux operation. In the zero-bias control, only one electromagnet in each axis of the AMB is active at any given time, depending on the rotor displacement. The proposed robust nonlinear CLF with a zero-bias for an uncertain AMB system can achieve a dynamic performance superior to that of a linear controller with the zero-bias or with the classical bias operations. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of measuring the electromagnetic flux in the air gap of the active magnetic bearing (AMB) without mechanical structure modifications. The designed and fabricated flux measurement and conditioning system based on the ultra-thin flexible Kapton-foil Hall sensors (developed by IFW Dresden Institute for Integrative Nanosciences) and signal amplifiers are presented. The flexible sensors are directly mounted on the curved surfaces of stator poles of the AMB and measure flux density in the AMB air gap. Then, the measurement itself and the conditioning system are verified in different measuring conditions of the heteropolar radial AMB with the air gap width of 0.4 mm. The measurement results were used in identifying crucial rotor flux-AMB system parameters. The proposed direct flux measurement system is successfully verified in the designed test rig in the presence of rotor position disturbances or coil current oscillation. The advantages and drawbacks of the presented measurement setup are discussed. [ABSTRACT FROM AUTHOR]