Experimental Analysis of Viscoelastic Properties of Room Temperature Vulcanized Silicone based Magnetorheological Elastomer

Magnetorheological Elastomers (MRE) endure a change in mechanical properties with the application of an externally applied magnetic field. It consists of an elastomeric matrix reinforced with ferromagnetic powdered particles. This paper focuses on the investigation of viscoelastic properties of Room Temperature Vulcanized (RTV) silicone based isotropic MRE in sandwich beam configuration by varying the volume percentage of Carbonyl Iron Powdered (CIP) reinforcement. Viscoelastic properties of the MRE core material were calculated by following the ASTM E756-05 standard. The magnetic field was applied by employing a Halbach array which was numerically analyzed using Finite Element Method Magnetics (FEMM). The magnetic field was varied up to 0.15 T. Loss factor and shear modulus were found to be strongly influenced by the percentage content of CIP. The loss factor and shear modulus of 30% MRE at 0.15 T were higher than other tested samples. The variation of natural frequency with respect to the addition of CIP was validated numerically using Modal analysis conducted in Hyperworks.

Study on dynamic mechanical properties of O-ring with large ring diameter ratio based on metal rubber

The demand for High temperature resistant metal rubber seals (MRS) with large ring-to-diameter ratio is very urgent in the industrial field. In this work, an O-type MRS with a large ring-to-diameter ratio was developed by embedding the spiral network metal rubber into the stainless steel ring with a special preparation process. The effects of frequency, porosity, and amplitude on the dynamic experimental performance of O-type MRS were studied in detail. The mechanical properties of the MRS were characterized by dynamic tests, and the damping sensitivity were analyzed by orthogonal tests. The results show that MRS has better stability under different frequencies of vibration. The energy consumption and loss factor of the sample increase with increases of porosity. With an increase in loading amplitude, the energy consumption and loss factor of the same porosity test sample increases, whereas the dynamic average stiffness of the specimen gradually decreases. Furthermore, the range analysis of the orthogonal experiment shows that the factors affecting the damping performance of the seal are porosity>amplitude>frequency. This study fills in the dynamic mechanical properties of O-shaped MRS, and provides a certain foundation for the engineering application of O-shaped MRS.

Combined Effect of Temperature and Oil and Salt Contents on the Variation of Dielectric Properties of a Tomato-Based Homogenate

Tomato-based processed foods are a key component of modern diets, usually combined with salt and olive oil in different ratios. For the design of radiofrequency (RF) and microwave (MW) heating processes of tomato-based products, it is of importance to know how the content of both ingredients will affect their dielectric properties. Three concentrations of olive oil and salt were studied in a tomato homogenate in triplicate. The dielectric properties were measured from 10 to 3000 MHz and from 10 to 90 °C. Interaction effects were studied using a general linear model. At RF frequencies, the dielectric constant decreased with increasing temperature in samples without added salt, but this tendency was reversed in samples with added salt. The addition of salt and oil increased the frequency at which this reversion occurred. At MW frequencies, the dielectric constant decreased with increasing temperature, salt, and oil content. The loss factor increased with increasing salt content and temperature, except in samples without added salt at 2450 MHz. Penetration depth decreased with increasing frequency and loss factor. Salt and oil contents have a significant effect on the dielectric properties of tomato homogenates and must be considered for the design of dielectric heating processes.

Epoxy Casting Systems with Harmless Hardeners for Outdoor Applications

Presented thesis is focused on studying of electro-insulating casting systems based on epoxy resin. The aim of the article is to acquaint the reader with the development of this systems – epoxy resin with hardeners that comply with REACH authorization. The temperature and frequency dependence of complex permittivity, complex electric modulus, loss factor and inner and surface resistivity of the given samples are investigated.

Comparison of damping parameters based on the half-power bandwidth methods of viscous and hysteretic damping models

The half-power bandwidth method is usually used to calculate structural damping parameters by frequency response function (FRF). In this note, the half-power bandwidth methods for the displacement FRF, the velocity FRF, and the acceleration FRF are proposed based on viscous and hysteretic damping models, respectively. Comparison results show that the application conditions of half-power bandwidth methods for the displacement and acceleration FRFs are limited. They can only be used to calculate the small damping ratio/loss factor. The application condition of half-power bandwidth method for the velocity FRF is not limited. It can be used to calculate the large or small damping ratio/loss factor, which should be the first choice for calculating damping parameters. Besides, when the damping ratio is less than 0.2546 or the loss factor is less than 0.5658, the relative difference between the loss factor and twice the damping ratio is less than 10%. With the increase of the damping ratio or loss factor, the relative difference will increase rapidly, and the approximate relationship is no longer applicable.

Wake Expansion and the Finite Blade Functions for Horizontal-Axis Wind Turbines

This paper considers the effect of wake expansion on the finite blade functions in blade element/momentum theory for horizontal-axis wind turbines. For any velocity component, the function is the ratio of the streamtube average to that at the blade elements. In most cases, the functions are set by the trailing vorticity only and Prandtl’s tip loss factor can be a reasonable approximation to the axial and circumferential functions at sufficiently high tip speed ratio. Nevertheless, important cases like coned or swept rotors or shrouded turbines involve more complex blade functions than provided by the tip loss factor or its recent modifications. Even in the presence of significant wake expansion, the functions derived from the exact solution for the flow due to constant pitch and radius helical vortices provide accurate estimates for the axial and circumferential blade functions. Modifying the vortex pitch in response to the expansion improves the accuracy of the latter. The modified functions are more accurate than the tip loss factor for the test cases at high tip speed ratio that are studied here. The radial velocity is important for expanding flow as it has the magnitude of the induced axial velocity near the edge of the rotor. It is shown that the resulting angle of the flow to the axial direction is small even with significant expansion, as long is the tip speed ratio is high. This means that blade element theory does not have account for the effective blade sweep due to the radial velocity. Further, the circumferential variation of the radial velocity is lower than of the other components.

Study on FE-SEA Modeling and Acoustic Performance of Heavy Duty Commercial Vehicle Based on Experimental Statistical Energy Parameters

Due to the difficulty of obtaining statistical energy parameters of complex structures and the complexity of modeling connection and model verification, the hybrid FE-SEA model has many problems in modeling complex structures. Therefore, in order to solve the above problems, this paper provides a reference for the application of the hybrid FE-SEA model in complex structures. In this paper, the hybrid FE-SEA commercial vehicle model is established by an experimental statistical energy parameter modeling method and a modification method. The model division and subsystem connection modeling of a complex substructure of a heavy vehicle cab are studied. In the hybrid model, the hybrid line connection and the hybrid point connection are established. On this basis, the parameters of the cab model were studied, and the statistical energy parameters such as modal density, internal loss factor, and coupling loss factor were obtained by the experimental method. The statistical energy parameters of the cab acoustic model are modified. Finally, the accuracy of the model is verified by vehicle test. In addition, the acoustic performance of the cab was optimized, and airtightness and acoustic packaging were verified. The full parameter modeling and correction method is adopted in this paper, which is an effective supplement to the traditional statistical energy parameter modeling method.

Variation in the Polarization Loss Factor in an Unmanned Aerial Vehicle Jamming Link Due to the Attitude Change

A method to analyze the variation of the jamming power received by an unmanned aerial vehicle (UAV) receiver according to the change in the attitude of the small UAV is presented. The main interest of the study is in the variation of the polarization loss factor (PLF) in the UAV jamming link due to attitude change, which may be caused by the wind or intended movement. The attitude change is modeled by a combination of three successive rotations using roll, pitch, and yaw, which are defined as UAV rotations. The proposed method is applied to a jamming link, where a small UAV with an omnidirectional antenna is jammed by a jammer antenna on the ground. The method is applied to a plane ground and over a simulated terrain. The variation of the PLF according to the change of UAV attitude may be higher than the generally expected PLF at locations where the height difference between the UAV and the jammer is large, and near the locations where the jammer is located close to the vertical plane containing the rotation axis when the attitude change is represented by one rotation.