Vibration Damping Characteristics Research Articles

Method for determining automotive brake structure vibration damping and friction material bonding

A method and apparatus for determining the vibration damping characteristics of an automotive brake structure measures the vibration response of a brake structure during application of random-frequency wide spectrum excitation, followed by measuring vibration of the structure at particularly noted modal frequencies, using a confined bandwidth random-frequency vibratory excitation. The method and apparatus may be used also to assess the bonding or attachment characteristics of damping materials.

Apparatus having flexible mounting mechanism

An apparatus having a flexible mounting mechanism according to the present invention includes a storage section, a casing accommodating and holding the storage section, a protective housing accommodating and protecting the casing, a supporting member provided between the casing and the protective housing for supporting the casing, and a maintaining member supporting the protective housing. The supporting member and the maintaining member have different vibration damping characteristics.

308 構造減衰を考慮した FRP 構造材料の振動特性

Fiber-reinforced composite materials, such as boron-epoxy and graphite-epoxy, are used in the field of an aerospace vehicle. Due to the anisotropic material properties, composite structures show various vibration response for different fiber directions. This paper presents the theoretical prediction of effect of fiber direction of on flexural damping characteristics of FRP pipes with considering the material damping. The analysis is applied to angle-ply laminated beams. Vibration damping characteristics are obtained in the case of frequency, impulse and step responses.

Analysis of damping characteristics for viscoelastic laminated beams

Vibration is normally viewed as undesirable, not only owing to the resulting unpleasant motions, noise, and dynamic stresses possibly leading to fatigue and failure of the structure or machine, but also owing to the energy losses and degraded performance. Technological advances have further enhanced the means of controlling vibration in mechanical engineering, aerospace engineering, civil engineering and related applications. The feasibility of developing a viscoelastic damping material of structures for vibration damping has received extensive interest. Surface treatment uses high damping viscoelastic materials firmly attached to the surface of structural elements. Optimal design depends on the ability to accurately predict and effectively control the vibration of a structure with viscoelastic damping treatment. Understanding the damping characteristics of viscoelastically damped structures becomes necessary. This study analyzes the design parameters for constrained layer damping structures by employing the Ross–Kerwin–Ungar (RKU) model. The effects of temperature, frequency and the dimensions of damped structures on vibration damping characteristics are also discussed.

H ∞ Control of Active Constrained Layer Damping

Conventional passive constrained layer damping treatments with viscoelastic cores are provided with built-in sensing and actuation capabilities to actively control and enhance their vibration damping charac teristics. Two configurations of the resulting hybrid treatment are considered in this paper. In the first configuration, the active control and passive operate separately, whereas in the second configuration, the two operate in unison to maximize the energy dissipation characteristics. In this study, three objectives are accomplished. The first objective aims at the design and implementation of robust H ∞) controllers for the separated and unified control strategies. In the second, the performance of the H∞ controllers at different operating frequencies and temperatures is compared with that of a conventional proportional/derivative controller to demonstrate robustness. Finally, a control effort study involving the H ∞ controllers for the separated and unified control strategies is shown to assess the efficiency of the active control scheme in controlling structural vibration. The results obtained emphasize the potential of the optimally design unified control strategy as an effective means for providing broad-band attenuation capabilities over a wide range of operating temperatures.

Tailoring the Performance of Molded Flexible Polyurethane Foams for Car Seats

The automobile seat is a major element of contact between the occupant, the vehicle and ultimately the road surface. Flexible polyurethane foams are the material of choice for this application, not only because of the economies offered by large scale operations, but also because the cushioning characteristics of the foam/seat assembly can be adjusted. Commercially useful foams can be made from a variety of polyurethane molding chemistries. Recent advances in polyol and copolymer polyol technology, together with multiple isocyanate choices and even new foam manufacturing technologies, present the foam producers, seat assemblers and seat designers with a myriad of options. The automotive original equipment manufacturers (OEM's) worldwide are looking for optimization of the balance between foam weight and foam specifications, with more emphasis than ever on comfort and durability. This goes with specific requirements for the various foam pads, i.e., front cushion, rear cushion, front back-rest and rear back-rest. This paper presents new data showing how the choice of molding chemistry impacts not only foam processing and physical properties, but also the comfort and durability that can be expected from the final seat assembly. Results from recent studies carried out by The Dow Chemical Company on a global basis and concentrating on static and dynamic fatigue, resiliency, vibration damping characteristics and humid aging, are presented in an effort to provide foam producers and users worldwide with up-to-date information useful in helping them to meet their present and future performance targets.

Influence of surface hardening by laser irradiation on the loss factor of cast iron

Surface hardening by laser irradiation was examined regarding the loss factor, which is the parameter of the vibration-damping characteristics, for flake graphite cast irons and spherical graphite cast irons. The surface of the samples was quenched by changing speed of beam, gas pressure, and beam frequency. It was found that the depth of the hardening region was from 0.12 mm to 1.11 mm, and the hardness of the boundary between the hardening and the nonhardening regions changed suddenly. It was confirmed that the loss factor of the laser hardened specimens increased considerably as compared with that of the as-cast specimens. The internal friction at the vicinity of the boundary between the hardening and the nonhardening regions may be responsible for this result.

ROBUST CONTROL OF ACTIVE CONSTRAINED LAYER DAMPING

ConventionalPassiveConstrainedLayerDamping (PCLD) treatments with visco-elastic cores are provided with built-in sensing and actuation capabilities to actively control and enhance their vibration damping characteristics. The control gains of the resultingActiveConstrainedLayerDamping (ACLD) treatments are selected, in this paper, for fully treated beams using the theory of robust controls. In this regard, an optimal controller is designed to accommodate the uncertainties of the ACLD parameters, particularly those of the visco-elastic cores which arise from the variation of the operating temperature and frequency. The controller is also designed to reject the effects of the noise and external disturbances. The theoretical performance of beams treated with the optimally controlled ACLD treatment is determined at different excitation frequencies and operating temperatures. Comparisons are made with the performance of beams treated with PCLD treatments. The results obtained emphasize the potential of the optimally designed ACLD as an effective means for providing broadband attenuation capabilities over a wide range of operating temperatures as compared to PCLD treatments.

Backstepping boundary control of flexible-link electrically driven gantry robots

Gantry robots are used for precision manufacturing and material handling in the electronics, nuclear, and automotive industries. Light, flexible links require less power, but may vibrate excessively. An implementable boundary controller is developed to damp out undesirable vibrations in a flexible-link gantry robot driven by a brushed DC motor. Hamilton's principle produces the governing equations of motion and boundary conditions for the flexible link. The electrical subsystem dynamics for a permanent magnet brushed DC motor couple with the link dynamics to form a hybrid system of partial and ordinary differential equations. A boundary voltage control law is developed based on Lyapunov theory for distributed parameter systems. Through an embedded desired-current control law, the integrator backstepping controller generates the desired control force on the mechanical subsystem. A velocity observer estimates the gantry velocity, eliminating one feedback sensor. Modal analysis and Galerkin's method generate the closed-loop modal dynamics. Numerical simulations demonstrate the improved vibration damping characteristics provided by the backstepping boundary control law. Experimental results confirm the theoretical predictions, showing the high performance of backstepping boundary control.

DYNAMIC BOUNDARY CONTROL OF BEAMS USING ACTIVE CONSTRAINED LAYER DAMPING

A globally stable boundary control strategy is developed to damp the vibration of beams fully treated with active constrained layer damping (ACLD) treatments. The devised boundary controller is compatible with the operating nature of the ACLD treatments where the strain induced generates a control force and moment acting at the boundary of the treated beam. The development of the boundary control strategy is based on a distributed-parameter model of the beam/ACLD system in order to avoid the classical spillover problems resulting from using ‘truncated’ finite element models. Such an approach makes the boundary controller capable of controlling all the modes of vibration of the ACLD-treated beams and guarantees that the total energy norm of the system is decreasing continuously with time. The control strategy is provided also with a dynamic compensator to shape the vibration damping characteristics of the ACLD in the frequency domain. The effectiveness of the ACLD in damping out the vibration of cantilevered beams is determined for different control gains and compared with the performance of conventional passive constrained layer damping (PCLD). The results obtained demonstrate the high damping characteristics of the boundary controller particularly over broad frequency bands.

Acoustic attenuation and vibration damping materials

A means of enhancing the acoustic attenuation and vibration damping of a material by embedding high characteristic acoustic impedance particles, low characteristic acoustic impedance particles, or both high and low characteristic acoustic impedance particles within the matrix of the material is disclosed. The mass of the resultant material may be very low while retaining excellent acoustic attenuation, vibration damping, and structural characteristics. When particles with mismatched characteristic acoustic impedances are embedded within the matrix of a material that can support shearing loads, propagating acoustic energy that encounters the particles of the instant invention is partially reflected in random directions. That is, the propagating energy is diffused. As the propagation vectors and modes of acoustic energy are effectively randomized, the probability of localized energy absorption and damping is increased. We present acoustic attenuation and vibration damping data for some representative examples of the instant invention and other commercially available materials.

Optimum Design and Control of Active Constrained Layer Damping

Conventional Passive Constrained Layer Damping (PCLD) treatments with viscoelastic cores are provided with built-in sensing and actuation capabilities to actively control and enhance their vibration damping characteristics. The design parameters and control gains of the resulting Active Constrained Layer Damping (ACLD) treatments are optimally selected, in this paper, for fully-treated beams using rational design procedures. The optimal thickness and shear modulus of the passive visco-elastic core are determined first to maximize the modal damping ratios and minimize the total weight of the damping treatment. The control gains of the ACLD are then selected using optimal control theory to minimize a weighted sum of the vibrational and control energies. The theoretical performance of beams treated with the optimally selected ACLD treatment is determined at different excitation frequencies and operating temperatures. Comparisons are made with the performance of beams treated with optimal PCLD treatments and untreated beams which are controlled only by conventional Active Controllers (AC). The results obtained emphasize the potential of the optimally designed ACLD as an effective means for providing broad-band attenuation capabilities over wide range or operating temperatures as compared to PCLD treatments.

Optimum Design and Control of Active Constrained Layer Damping

Conventional Passive Constrained Layer Damping (PCLD) treatments with viscoelastic cores are provided with built-in sensing and actuation capabilities to actively control and enhance their vibration damping characteristics. The design parameters and control gains of the resulting Active Constrained Layer Damping (ACLD) treatments are optimally selected, in this paper, for fully-treated beams using rational design procedures. The optimal thickness and shear modulus of the passive visco-elastic core are determined first to maximize the modal damping ratios and minimize the total weight of the damping treatment. The control gains of the ACLD are then selected using optimal control theory to minimize a weighted sum of the vibrational and control energies. The theoretical performance of beams treated with the optimally selected ACLD treatment is determined at different excitation frequencies and operating temperatures. Comparisons are made with the performance of beams treated with optimal PCLD treatments and untreated beams which are controlled only by conventional Active Controllers (AC). The results obtained emphasize the potential of the optimally designed ACLD as an effective means for providing broad-band attenuation capabilities over wide range or operating temperatures as compared to PCLD treatments.

Performance Characteristics of Active Constrained Layer Damping

Theoretical and experimental performance characteristics of the new class of actively controlled constrained layer damping (ACLD) are presented. The ACLD consists of a viscoelastic damping layer sandwiched between two layers of piezoelectric sensor and actuator. The composite ACLD when bonded to a vibrating structure acts as a “smart” treatment whose shear deformation can be controlled and tuned to the structural response in order to enhance the energy dissipation mechanism and improve the vibration damping characteristics. Particular emphasis is placed on studying the performance of ACLD treatments that are provided with sensing layers of different spatial distributions. The effect of the modal weighting characteristics of these sensing layers on the broad band attenuation of the vibration of beams fully treated with the ACLD is presented theoretically and experimentally. The effect of varying the gains of a proportional and derivative controller and the operating temperature on the ACLD performance is determined for uniform and linearly varying sensors. Comparisons with the performance of conventional passive constrained layer damping are presented also. The results obtained emphasize the importance of modally shaping the sensor and demonstrate the excellent capabilities of the ACLD.

Performance Characteristics of Active Constrained Layer Damping

Theoretical and experimental performance characteristics of the new class of actively controlled constrained layer damping (ACLD) are presented. The ACLD consists of a viscoelastic damping layer sandwiched between two layers of piezoelectric sensor and actuator. The composite ACLD when bonded to a vibrating structure acts as a “smart” treatment whose shear deformation can be controlled and tuned to the structural response in order to enhance the energy dissipation mechanism and improve the vibration damping characteristics. Particular emphasis is placed on studying the performance of ACLD treatments that are provided with sensing layers of different spatial distributions. The effect of the modal weighting characteristics of these sensing layers on the broad band attenuation of the vibration of beams fully treated with the ACLD is presented theoretically and experimentally. The effect of varying the gains of a proportional and derivative controller and the operating temperature on the ACLD performance is determined for uniform and linearly varying sensors. Comparisons with the performance of conventional passive constrained layer damping are presented also. The results obtained emphasize the importance of modally shaping the sensor and demonstrate the excellent capabilities of the ACLD.

Studies on interpenetrating polymer networks based on nitrile rubber‐poly(vinyl chloride) blends and poly(alkyl methacrylates)

AbstractSeveral interpenetrating polymer networks (IPNs) based on nitrile rubber‐poly(vinyl chloride) blends and various alkyl methacrylates have been synthesized. The rubber blends were swollen in methacrylate monomers containing required amounts of initiator and crosslinker for specific time periods and then polymerized at higher temperature. The composition of the IPNs could be varied by changing the swelling time. The IPNs were characterized for their glass‐transition temperature, dynamic mechanical properties, and tensile properties. The effect of structure and composition on the vibration damping characteristics of these IPNs are discussed. © 1994 John Wiley & Sons, Inc.

Electrorheological fluids applied to an automotive engine mount

This paper is concerned with the mathematical modelling of electrorheological fluids when used in oscillating squeeze-flow mode; in a prototype automotive engine mount. A solution of the problem is found for the situation in which the non-Newtonian behaviour of the fluid is represented by a Bi-Viscous characteristic. This permits the prediction of the vibration damping characteristics of the device. Finally these results are compared with recently published experimental values.

Effects of fibre orientation on the vibration damping characteristics of virall laminates

acad sinica,inst met res,shenyang 110015,peoples r china.;sui, gx (reprint author), acad sinica,int ctr mat phys,shenyang 110015,peoples r china

Vibration damping characteristics of laminated steel sheet

The use of laminated steel sheets as vibration damping materials was studied. The laminate consisted of a viscoelastic layer which was sandwiched between two steel sheets. The study sought to identify parameters affecting the damping efficiency of the laminate. Two viscoelastic materials, a copolymer based on ethylene and acrylic acid (PEAA) and polyvinyl butyral (PVB), were used. A frequency analyzer was used to measure the loss factor of the laminates. A theoretical analysis of damping efficiency based on a model described by Ungar[2] was also carried out. The results showed that the loss factor of the PEAA-based laminates increased monotonically with increasing thickness of the viscoelastic layer and leveled off at 25.9 pct of total thickness. Ungar’s theory predicted a higher loss factor than the experimental data. This might have resulted from interfacial adhesive bonding, a nonuniform viscoelastic layer thickness, and the extrapolation of the rheological data from low to high frequencies. The loss factor of the laminate increased with increasing temperature, reached a maximum value, and then decreased. An optimum temperature for maximum damping was found for each laminate configuration. The PEAA-based laminates possessed higher damping efficiency than the PVB-based laminates at room temperature. The symmetric laminate (with the same steel sheet thickness) possessed a better damping efficiency than asymmetric laminates. The maximum damping peak of the laminates using a polymer blend, when compared to the laminates using unblended resin, exhibited a lower loss factor value, became broader, and occurred at a temperature between theT g’s of the individual components of the polymer blend.

Computerized automated system for measuring the vibration-damping characteristics of mechanical systems

The apparatus and operating principle of an automated system for measuring vibration-damping characteristics are described. The system makes it possible to record up to 4000 amplitudes of a damping oscillatory process and to obtain the amplitude dependence of the logarithmic vibration decrement fora single test cycle.