Papers by Keyword: Damping

Abstract: The dynamic characteristics of fiber reinforced polymer skins with the alternate arrangement of continuous and chopped fibers on the polypropylene honeycomb core are investigated. It is envisaged that the damping could be improved by splitting the length of fiber into different short lengths so that more energy can be dissipated. The dynamic characteristics of FRP specimens with different forms of fibers were studied. The fibers were considered in the following five groups:, all continuous fibers, alternate arrangement of continuous and two chopped fibers, the same with three chopped fibers, four chopped fibers, and the five chopped fibers in. The natural frequencies and damping loss factors were evaluated by using the impulse technique with the half power band width method. The results revealed that for a given fiber volume fraction the damping could be improved by reducing the length of fibers.

Abstract: The development of materials with high damping and energy absorption properties in the form of bulk materials or coatings is today a target for designing components and structures with improved durability and survivability to serve in fields such as aeronautical, mechanical, civil and environmental engineering. This paper presents the results of the dynamic mechanical characterization conducted on reinforced polyurea composites. The mechanical properties of two types of composite materials utilizing the polyurea elastomer as a matrix are compared with those of the pure polymer. The composite materials show a substantial increase of the damping ability. Such materials can be produced in the form of coatings and successfully applied for maximizing the damping of mechanical and structural vibrations or for limiting the damage effects of impact events on structures and components.

Abstract: The ecological structures of some organisms that could resist environmental vibration naturally (such as dragonfly, woodpecker and legs of cursorial animals) uncovered by biologists inspire people a new approach to overcome the above problem. In this paper, a new shock isolation system consisting of a pedestal, a rubber layer, an air spring and a shearing viscoelastic damper is designed, fabricated, and characterized to avoid the performance deterioration and physical damage of mechanical manufacturing devices from external mechanical excitations. The nonlinear dynamics model of the platform is developed and the dynamic characteristics are analyzed using numerical analysis. The displacement and velocity response are obtained. The results demonstrate that the stiffness and damping characteristic of the platform change with excitation frequency. The vibration isolation effectiveness will be greatly enhanced.

Abstract: The equivalent linearization method to calculate the stiffness parameters of the elastic element and damping parameters of the vehicle suspension is presented in this paper. With the virtual work principle, the nonlinear characteristics of the suspension are analyzed. The stiffness and damping of the suspension element based on the vibration response of the vehicle ride comfort are calculated. The numerical computation results of a double wishbone suspension with torsion bar show the presented method is feasible and effective.

Abstract: Abstract. The paper presents test stand designed for testing magnetorheological composites (MRC) under dynamic loading, together with the method for obtaining damping characteristics of the tested material. The test stand is based on Single-Degree-Of-Freedom system excited with use of modal hammer. The MRC is stimulated with use of double circular dipolar Halbach array based on neodymium magnets. The analysis of the experimental results is performed with use of the half-power method and the circle-fit method. results presented in the paper show usefulness of the test stand and of the method for obtaining damping parameters of the MRC. The results present change in the damping character of the material under variable magnetic field.

Abstract: This paper describes investigations of magnetorheological elastomers subjected to cyclic loading. The procedure comprised over 1 million of loading cycles per specimen. Mechanical properties of the manufactured composites have a tendency to stabilize in time. This leads to the conclusion that these MRE have a high application potential in the areas which are connected with energy dissipation, such as damping of vibrations.

Abstract: Considering the damping and stiffness for mechanical system of laser heat assisted variable cross-section roll forming machine, in order to obtain the angular acceleration and angular velocity of servo motor and ball screw, the kinetic equation of the system is established using the Lagrange's equations. The results are great significance in depth study and optimization of dynamics of mechanical systems.

Abstract: In order to guide the construction of immersed tube tunnel of Hongkong-Zhuhai-Macao bridge project, the model tests of immersed tunnel tube were done in static water. Movements in six degrees of freedom, including three translational movements (sway, surge and heave) and three rolling movements (roll, pitch and yaw), were conducted. Four groups of environment conditions with different water depths were compared, and the added water mass and damping of tunnel tube changed with water depth were obtained. There test results can offer references for reasonable predictions of motion response of tube tunnel, and provide service to construction of immersed tube tunnel of Hongkong-Zhuhai-Macao bridge project .

Abstract: Modal parameter estimation is the estimation of frequency, damping ratio, and modal coefficients from experimental data. Modal analysis techniques are a common method used to determine these properties. The Least-Squares Complex Exponential (LSCE) and the Eigensystem Realization Algorithm (ERA) are one of the popular methods of modal analysis techniques. This paper presents an experimental verification of the LSCE and ERA methods. The investigation focuses on the estimation of natural frequencies, damping ratio and modal coefficients. To investigate this, artificial analytical data were processed in MATLAB environment to estimate the modal parameters. The identified vibration parameters from the LSCE and ERA were compared with the values based on classical dynamic theory, and the natural frequency and damping ratios percent of error were calculated.

Abstract: As commonly supporting parts of the spindle and the feed systems on the high-end grade CNC machine tool, the dynamic characteristics of angular contact ball bearings had been a research hot spot in the current. Aiming at solving the problem that obtained dynamic stiffness and damping of angular contact ball bearings, an approach to investigate dynamic parameters of bearings joint surfaces was proposed based on the single degree of freedom (SDOF) system, and several groups of modal testing were carried out. The dynamic characteristics of bearings joint surfaces were viewed as several viscoelastic units of spring and damper. Then, models of bearings dynamic parameters in the axial and radial directions were established, and several groups of modal simulation were carried out. The comparison of experiment and simulation results showed that the proposed approach could accurately identify dynamic stiffness and damping of bearings under different load conditions, and the errors were controlled within 7.6%.