High frequency vibration of gas turbine fan blades is a high cycle fatigue concern. Friction damping devices are ineffective in suppressing high frequency vibration modes and external damping treatments are plagued by creep concerns. An alternative approach is to apply viscoelastic material internally in the blades. In this paper, an analytical comparison of internal damping treatments for fan blades is presented. The fan blade is modeled as a solid, flat, cantilevered titanium plate. Internal portions are removed producing cavities that are filled with viscoelastic material. Configurations with one, two, and three cavities are modeled using the modal strain energy method in conjunction with finite element analysis to estimate damping. Results show that appreciable damping levels for high frequency modes are possible with stiff viscoelastic material. Other design criteria are also considered. Results indicate that the hydrostatic load from the viscoelastic material on the cavity walls may be a concern.

A preliminary design and analysis procedure for locating an integral damping treatment in composite turbo-propeller blades has been developed. This finite element based approach, which is based upon the modal strain energy method, is used to size and locate the damping material patch so that the damping (loss factor) is maximized in a particular mode while minimizing the overall stiffness loss (minimal reductions in the structural natural frequencies). Numerical results are presented to illustrate the variation in the natural frequencies and damping levels as a result of stacking sequence, integral damping patch size and location, and border materials. Experimental studies were presented using flat and pretwisted (30 degrees) integrally damped composite blade-like structures to show how a small internal damping patch can significantly increase the damping levels without sacrificing structural integrity. Moreover, the use of a soft border material around the patch can greatly increase the structural damping levels.

FORTE is a small satellite being developed by Los Alamos National Laboratory (LANL) and Sandia National Laboratories Albuquerque (SNLA). It will be placed into orbit via a Pegasus launch in 1996. Testing a full-scale engineering model of the structure using the proto- qualification, system-level vibration spectrum indicated that acceleration levels caused by structural resonances exceed component levels to which certain sensitive components had previously been qualified. Viscoelastic struts were designed to reduce response levels associated with these resonances by increasing the level of damping in key structural modes of the spacecraft. Four identical shear-lap struts were fabricated and installed between the two primary equipment decks. The struts were designed using a system finite element model (FEM) of the spacecraft, a component FEM of the strut, and measured viscoelastic properties. Direct complex stiffness testing was performed to characterize the frequency-dependent behavior of the struts, and these measured properties (shear modulus and loss factor) were used to represent the struts in the spacecraft model. System-level tests were repeated with the struts installed and the response power spectral densities at critical component locations were reduced by as much as 10 dB in the frequency range of interest.

This paper illustrates something of a 'potpourri' of activities related to passive damping, some of them incidental to the main thrust of the investigations in question. This paper is not intended to provide a full review of space related European activities in this field. A wider perspective may be gleaned from other works. An issue in current project developments is the impact of in orbit spacecraft equipment induced structural vibrations. Such microvibrations can be of concern for experiments requiring zero gravity conditions or for telescopes where jitter can disturb the pictures. Clearly a similar problem can emerge for very high stability antennas. Many of the ongoing passive and active damping studies are related to suppressing the effects of such unwanted vibrations of which examples of the former are given here. In conducting terrestrial experiments, the presence of air and in particular radiation damping is unrepresentative. Investigations into the importance of air damping are illustrated. Some of the devices under development that can be used to suppress these unwanted vibrations are outlined. They usually involve modifications to the connecting mounts of the vibration inducing equipment or those of the vibration sensitive instrument. Other possible means of passively (or actively) attenuating the levels of vibration in the spacecraft structure are briefly considered. Despite the sensitivity of viscoelastic materials to changes in frequency and temperature, their use in some applications is still foreseen. Some allied work to check prediction tools is presented together with a review of earlier work that can be used to predict the damping provided by pinned and similar connections.

Alternative vibration control systems are of interest to the appliance industry to improve the performance of the automatic washer suspension. Consumer benefits from improved suspension performance include noise and vibration reduction, lighter machines and larger baskets for increased clothes load capacity. Passive dynamic absorbers are investigated because of their ability to control system resonances and absorb energy from vibrating components. Since the suspended mass is variable due to different clothes loads and the amount of water in the clothes, performance limitations exist for the passive vibration absorber. Adaptive passive dynamic absorbers are investigated as an alternative vibration control system. A set of design variables and constraints for a fundamental model of an automatic washer suspension incorporating both passive and adaptive passive dynamic absorbers is presented. Numerical integration is used to obtain each system response. Optimization of the fundamental automatic washer model incorporating a passive dynamic absorber is performed. Design of experiment techniques and general design studies are used to gain information concerning the importance of the design variables on the performance of the adaptive passive dynamic absorber. Both ideal and real absorber stiffness controller schemes are investigated. The results suggest some benefit of applying adaptive passive dynamic absorbers. Design constraints are found to play a major role in the feasibility of application of this technology to the appliance industry. When considering design cost and performance, the optimum passive dynamic absorber is shown to be the better choice. Examples of various methods of implementation of both passive and adaptive passive dynamic absorbers to an automatic washer are presented.

When a tennis ball strikes a racket the impact causes vibrations which are distracting and undesirable to the player. In this work a passive damping system used to reduce vibration is described. The damping system uses a viscoelastic material along with a stiff composite constraining layer which is molded on the inner surface of the tennis racket frame. When a ball strikes a racket with this damping system the vibration causes shearing strain in the viscoelastic material. This strain energy is partially dissipated by the viscoelastic material, thereby increasing the racket damping. An analysis of the design was performed by creating a solid CAD model of the racket using Pro/Engineer. A finite element mesh was created and the mesh was then exported to ANSYS for the finite element modal analysis. The technique used to determine the damping ratio is the modal strain energy method. Experimental testing using accelerometers was conducted to determine the natural frequency and the damping ratio of rackets with and without the damping system. The natural frequency of the finite element model was benchmarked to the experimental data and damping ratios were compared. The modal strain energy method was found to be a very effective means of determining the damping ratio, and the frequencies and damping ratios correlated well with the experimental data. Using this analysis method, the effectiveness of the damping ratio to the change in key variables can be studied, minimizing the need for prototypes. This method can be used to determine an optimum design by maximizing the damping ratio with minimal weight addition.

Damping properties of a viscoelastic material were determined using a standard resonant beam technique. The damping material was then applied to 1 by 2 foot gypsum panels in a constrained layer construction. Damping loss factors in panels with and without the constrained layer were determined based on reverberation times after excitation at third-octave band center frequencies. The constrained damping layer had been designed to increase damping by an order of magnitude above that of a single gypsum panel at 2000 Hz; however, relative to a gypsum panel of the same overall thickness as the panel with the constrained layer, loss factors increased only by a factor of three to five. Next modal damping loss factors in 9 by 14 foot gypsum single and double walls were calculated from the experimentally determined quality factor for each modal resonance. Results showed that below 2500 Hz, modes in 1 by 2 foot gypsum panels had nearly the same damping loss factors as modes in a 9 by 14 foot gypsum wall of the same thickness; however, loss factors for the wall were an order of magnitude lower than those of the 1 by 2 foot panels at frequencies above 2500 Hz, the coincidence frequency for 5/8-inch thick gypsum plates. Thus it was inconclusive whether or not damping loss factors measured using small panels could be used to estimate the effect of a constrained damping layer on transmission loss through a 9 by 14 foot wall unless boundary conditions and modal frequencies were the same for each size.

This paper discusses the results of a project aimed at developing an effective constrained layer damping system for a large steel box beam. The primary box beam evaluated was a 4.0-inch by 8.0-inch by 0.375-inch section box which was 96.0 inches long. The goal of the project was to obtain the most damping possible in the bending, twisting, and axial modes while meeting cost, weight, and installation requirements. The project started with the evaluation of the box beam as an appropriate solid beam with a continuous constrained layer damping system applied using a 6th order theory analysis program. The next analysis step was to advance to finite elements. During the FEA, bending modes in both planes, twisting modes, and axial modes were examined. The design iterations considered damping on the 8.0-inch surfaces only, damping on all surfaces, the effects of a standoff, and multiple segmentation in the constraining layer. After the analysis had developed the best damping configuration which met all the nondamping requirements, the damping system was fabricated and installed on the box beam for testing. This paper presents the results of the project from concept development through the test results.

The use of viscoelastic spheres for damping the vibrations of square-section and rectangular- section hollow steel beams is presented. The transfer inertance frequency response functions of the beams in their vertical and horizontal orientations were measured under free-free boundary conditions. These frequency response characteristics were also measured when the beams were empty and when they were filled with low density viscoelastic spheres of 9 mm, 15 mm and 18 mm diameters. Using a nonlinear least squares curve fitting approach in conjunction with the modal analysis technique, the modal frequencies and the modal loss factors of the composite viscoelastic sphere-filled beams were determined from the measured transfer inertance frequency response functions. It is shown that the modal loss factors of the hollow steel beams when empty were in the range of 0.2% to 1.0%, whereas the modal loss factors of the hollow steel beams when filled with the viscoelastic spheres were in the range 2% to 31%. Thus, it is concluded that the modal loss factors of the hollow beams could be increased up to 40 times by filling them with the viscoelastic spheres.

An innovative method for transient response analysis of controlled structures with viscoelastic damping layers is developed. The method yields closed-form transient response by an accurate inverse Laplace transform procedure. Unlike existing techniques, the method does not depend on any orthogonal relations for the system eigensolutions. Another advantage of the method is that the contributions of specific modes in the transient response can be independently evaluated without involving the computation related to other modes. These features render the proposed method efficient in modeling and control of viscoelastically damped flexible structures.

A methodology is presented for detecting damage of highly damped structural systems. Direct frequency response functions along with a correlated analytical model of the undamaged structure are used to detect and assess damage using residual force vectors. A sensitivity analysis using a least-squares approximation is used to assess the extent of damage in the face of changes in the system mass distribution, damping mechanism, and structure stiffness. Both VEM and fluid strut (one-dimensional) dampers are applied to an analytical model of a space truss. Numerical results are presented to validate and assess the proposed approach. The advantages and limitations of this method are examined. This methodology can also be used to perform system identification.

Viscoelastic dampers to reduce building structural vibration were first utilized in the Twin World Trade Center Towers in New York in 1969 for wind induced vibrations. In the 1980s, the Columbia SeaFirst and Two Union Square Buildings in Seattle utilized dampers for wind. In 1994 the Chien-Tan railroad station roof in Taipei, Taiwan utilized viscoelastic dampers to reduce wind induced vibrations. Recent seismic studies at several universities have demonstrated the benefits of viscoelastic dampers for steel and concrete structures. A 13 story steel moment frame building in Santa Clara County was retrofitted with viscoelastic dampers in 1994 to reduce seismic vibrations. A non-ductile concrete building in San Diego will be retrofitted with viscoelastic dampers in 1996. The results of university testing and building application installations are reviewed in this paper.

Passive base isolation systems used for the seismic response control of structures appear to be effective for small to medium strength earthquakes. Hybrid base isolation systems, which use an active system together with the passive base isolation system, may be used to control the response of structures subjected to larger ground motions created by larger magnitude earthquakes. A hybrid base isolation system which uses passive base isolation pads together with deflection inserting actuators is proposed. The system, placed between the foundation of the building and its superstructure, is used to minimize the forces imposed on the superstructure by the earthquake induced ground motion. A three dimensional structural model is developed to study the effectiveness of the adaptive base isolation system. The effect of the base isolation system on the flexible modes of the structure, including the torsional modes, is studied.

Base isolated structures can be sensitive to the frequency content and magnitude of the input earthquake (EQ) ground motions. One effective method of addressing the sensitivity of base isolated structures is to add passive damping devices in the superstructure, resulting in implementing hybrid passive control techniques. In this paper, a simple comparison of various hybrid passive control techniques is performed. This paper demonstrates the comparative merits of various hybrid control techniques and assess the effectiveness of hybrid passive control technology in mitigating seismic hazard for base isolated structures.

Wind induced structural vibration of mast and tower structures on top of tall buildings can generate structural fatigue of the masts ad transmit vibration into the building. A method of reducing these vibrations is by installing a vibration absorber into the top of the mast. An experimental investigation into the use of cylinder-cup vibration absorbers for reducing motions of two model masts is reported in this paper. Test data include coefficients of friction, damping ratios and several dimensionless groups associated with vibration. These absorbers can be used successfully to reduce mast vibrations when properly scaled.

The loss and storage moduli, and tan (delta) , of cement pastes were measured at 25 to 150 degrees Celsius and 0.2 to 2.0 Hz. The addition of latex or methylcellulose increases all three quantities, though latex is more effective in increasing tan (delta) , while methylcellulose is more effective in increasing the storage modulus. The addition of silica fume also increases all three quantities. The addition of short fibers increases all three quantities if the mix contains no other additive; it increases only tan (delta) and loss modulus if the mix contains methylcellulose; it decreases all three quantities if the mix contains either latex or (methylcellulose plus silica fume). For energy dissipation applications, a mix with latex is recommended at greater than 1.5 Hz, whereas a mix with methylcellulose plus silica fume is recommended at less than 1.5 Hz; the use of fibers is not recommended.

The optimum design of structures is obtained for three different types of damping treatments and the resulting designs are compared. The three types of damping treatments considered are constrained layer damping, active constrained layer damping and active damping. Piezoelectric material is used for actuators and sensors in the active damping and active constrained layer damping cases. The constraining layer of the active constrained layer damping case is the piezoelectric actuator. The structure is designed for minimum weight with constraints on the frequency and damping ratio. The problem is modeled using a two dimensional finite element based on the QUAD4 element. The QUAD4 element is modified to include viscoelastic and piezoelectric layers in the composite layup. The damping treatment is also allowed to move on the structure and to distort its shape so as to improve the damping characteristics of the initial design. Both beam and plate structures are considered to illustrate this concept. A proportional-derivative controller is used for the active control of the beam and the linear quadratic regulator (LQR) is used to design the active controller for the plates.

A variational formulation of active constrained layer (ACL) damping treatments has indicated that the power dissipated through the active damping is the product of the electric field and the axial velocity of the piezoelectric constraining layer at the boundaries. This feature, unique to this formulation, suggests that a self-sensing and actuating piezoelectric constraining layer using rate of strain feedback may be an appropriate method of dissipating vibration energy with less instability, since the sensor and actuator are truly collocated. A partial ACL damping treatment design for an Euler-Bernoulli beam using a self-sensing actuator (SSA) as the active layer has been developed. The open loop transfer functions of the treated beam given by the SSA rate of strain circuit show great similarity to transfer functions taken from a reference sensor laminated directly to the beam. It has been shown experimentally that this beam treatment significantly increased the damping coefficient of the first mode in closed loop.

This paper is concerned with the investigations of viscoelastic material (VEM) effects on active constrained layer (ACL) based structures. Specific interests are on how the VEM parameters will influence the passive damping ability and the active action transmissibility in an ACL configuration. The study has identified the VEM parameter regions that will provide the best active-passive hybrid actions. This research also developed guidelines to synthesize ACL structures that will outperform both the purely passive and active systems.

Conventional passive constrained layer damping (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 resulting active constrained layer damping (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 broad-band attenuation capabilities over a wide range of operating temperatures as compared to PCLD treatments.

An analytical procedure is presented for modeling the behavior of rotating blades with integrated piezoelectric devices. The equation of motion and associated boundary conditions are derived for the vibrations of piezoelectrically actuated rotating beams/blades. The effects, so-called 'centrifugal-softening and centrifugal-stiffing,' of the displacement-dependent centrifugal forces are investigated in the present study.

The effect of quadratic nonlinear electrical shunts on the performance of piezoelectric vibration absorbers is presented. The equations of motion are derived in a format suitable for perturbation analysis. An electrical shunt containing cubic and quadratic elements is coupled to the structure via the piezoelectric effect. Nonlinearities are introduced as a combination of the square and/or cube of the charge flowing in the linear inductive-resistive (LR) shunt. Tuning the shunt near a structural mode causes mechanical energy to be transformed to electrical energy and dissipated by the resistive element in the shunt in a manner analogous to a damped vibration absorber. Analysis is carried out using the method of multiple scales. Simulation results are also presented.

A study has been made of piezoelectric shunts using a piezoelectric element shunted with a parallel resistor and inductor circuit for passive structural damping and vibration control. It is found that under the optimum tuning condition, the peak amplitude of the displacement versus frequency curve of a structural mode decreases with the increase of the shunt resistance. It becomes a plateau at the optimum resistance. When the resistance increases further, the middle of the plateau continues to decrease, but two humps appear around the plateau shoulders. They increase with further increase of the shunt resistance. Changes in structural parameters, mass or stiffness, and incorrect shunt inductance also affect the displacement versus frequency curve. Both will distort it from a plateau shape under the optimum condition to that showing a hump on one shoulder of the plateau. If the mass increases (or decreases), the hump appears on the left (or right) shoulder. It becomes larger and moves away from the plateau for larger mass change. For the case of incorrect inductance, when the inductance is larger (or smaller) than the optimum value, the hump appears on the right (or left) shoulder. It moves towards the center of the plateau with further deviation of the inductance.

A new vibration isolation system for a Space Shuttle payload is described. Designed for a large optical instrument to be launched aboard the next Hubble Telescope servicing mission, the system uses a set of eight telescoping struts to mount the payload to a shuttle pallet. Each strut is a combination of a titanium coil spring and a passive damper. The latter dissipates energy through eddy currents induced in a conductor moving in a dc magnetic field. The result is a simple, robust, all-metal isolation mount that is linear over a long stroke, relatively insensitive to temperature, and contains no fluids. Design of the system is described and strut- level test results are given along with predictions for system-level isolation under flight loads.

A high performance passive isolator has been developed for a multiaxis isolation system for vibration isolation of an optical payload. This passive isolator will be used along with an active element to provide improved vibration isolation performance over previous isolators. The isolator has been designed using ideas developed previously for 'tuned' three parameter passive isolators. The isolator has also been developed offering the lowest system passive break frequencies structurally feasible for the lightweight optical payload. The implementations of these passive isolator design considerations complement the active portion of the system, and also provide the best passive isolation at the higher frequencies long after the active system has 'rolled off.' The mathematics used to design the isolator as well as the isolator's physical attributes are discussed. The unique design challenges of incorporating the passive element with the active, forming one 'hybrid' D-strut^$TM, also are discussed. Finally, actual test data from isolator testing are compared to predicted performance, verifying the isolator's exceptional performance and predictability.

The simplest model for vibration isolation design is the single-degree-of-freedom (SDOF) mass-spring-damper system. This system has been widely analyzed, however, it has been argued that the SDOF model is not a good design model and a two-degree-of-freedom (2DOF) model should be used instead. This paper delves into the limitations of the SDOF model and the advantages of the 2DOF model to design vibration isolation systems. The reduction in system transmissibility by using active damping versus passive damping is also discussed for both models.

Shock measurement accelerometers require protection from the high frequency components of input shock spectra which often cause irreversible damage to these transducers. The resonance frequencies of shock accelerometers are usually designed to be much greater than the highest frequency of their operating range. It is not unusual, however, for input shock waveforms to contain spectral components whose frequencies are much greater than the resonance frequencies of shock accelerometers. This is particularly true for shock waveforms of very short duration whose shape approach that of the classical Dirac delta function. Consequently, there is a need for mechanical filters which will isolate the accelerometers from the highest frequency components of shock loadings applied to structures. In this paper, the design of a mechanical filter comprised of metal discs, metal housing and viscoelastic elements is examined using the finite element method. The transformation of the frequency domain complex Young's modulus data to the time domain extensional relaxation function using collocation method is described. The procedures for the derivation of the Prony series coefficients from the time data for input into the finite element analysis code are presented. It is shown that effective mechanical filters can be designed using viscoelastic materials of optimal properties.

Substructure synthesis is an efficient modeling tool for complex vibration isolation systems. The advantages that are demonstrated include the ability to adapt to design changes, and include additional kinematic constraints into the model formulation. In general the advantages of substructure synthesis are that only admissible functions are needed to model the structure and a reduced number of degrees-of-freedom can be used in comparison with other methods such as the more standard finite element method. The problem formulation has a composition similar to the physical construction of actual systems. This enhances the practical understanding of the system modeled. The contribution here is to demonstrate a substructure synthesis method and its application to model complex kinematic constraints for a vibration isolation system.

Composite sandwich panels are increasingly attractive structural components for modern space structures. Their light weight, high stiffness, and 'manufacturability' make them ideal for primary structure. One disadvantage of sandwich panels is the low damping, typically on the order of 0.5 percent. This problem has been addressed during the course of designing an all composite spacecraft bus. A visco-elastic treatment and a constraining layer have been applied to a composite sandwich panel. Analysis and tests were performed on the panel in both the damped, and the un-damped configuration. A five-fold increase in the panel damping was achieved, and some valuable lessons learned. These lessons, the modeling methods, test and analysis results are presented.

A test system designed specifically to acquire the complex moduli of viscoelastic materials in shear is described. Unique and innovative approaches in the mechanical design, temperature control system, and data acquisition methods provide a standard of accuracy that is rarely seen in dynamic mechanical properties of viscoelastic materials. The system operates on the principle of direct complex stiffness measurements. Unique sensors, hardware layout, and data acquisition and reduction methods maximize the frequency bandwidth and the dynamic range of stiffness, data acquisition speed, and temperature uniformity. Forced liquid convection temperature control also provides unparalleled speed and uniformity in specimen temperatures. Results are demonstrated and scrutinized using characterization software. Characterized data are stored in a database that provides the designer with the capability of searching based on the mechanical parameters commonly needed for damping designs. The end product is an end-to- end system capable of superior data accuracy and acquisition rates, and software that enables the most critical evaluation of results and ready storage in a manner that is efficient for damping design applications.

A mathematical model is used to describe the effect of fiber alignment on viscoelastic composite dynamic Young's Moduli and loss factors. The model, supported by experimental validation, requires the dynamic physical properties of the matrix resin for the range of operational temperatures and frequencies of interest. The model predicts that the resulting loss factor of a fiber reinforced viscoelastic resin composite behaves in an anisotropic fashion, however, damping optimization may be achieved in two different ways dependent on the angle of fiber alignment. The model predicts that the loss factors of a viscoelastic composite employing a woven roving with low modulus fibers, aligned in equal proportions at 0 degrees and 90 degrees are highest along a direction where fiber alignment angles are between 30 degrees and 60 degrees. The loss factor is a maximum when matrix resin loss factor is highest. Along a direction of 0 degrees and 90 degrees loss factors are generally lower, they no longer peak as a result of high loss factors in the matrix resin but are highest when the matrix loss modulus is a maximum. Furthermore, it is shown that increase in fiber modulus results in a decrease of composite loss factors at angles around 0 degrees and 90 degrees, but higher loss factors are obtained over a much wider range of angles that are typically between 5 degrees to 85 degrees.

The incorporation of 0.1 - 0.2 micrometer diameter carbon filaments (0.6 vol.%) between continuous carbon fiber (7 micrometer diameter, 56.5 vol.%) layers in an epoxy-matrix composite during composite fabrication was found, under flexure to greatly increase transverse and longitudinal tan (delta) values, increase the storage modulus in the transverse direction, slightly decrease the storage modulus in the longitudinal direction, and increase both longitudinal and transverse loss moduli to values as high as 2 GPa.

Conventional composite materials have high stiffness-to-weight ratios but exhibit little damping; many viscoelastic materials provide high levels of energy dissipation with minimal structural stiffness. The objective of this work was to combine these two material types to produce highly damped structural elements with favorable stiffness and weight characteristics. Cocuring refers to the inclusion of one or more layers of viscoelastic damping material sandwiched between composite plies prior to curing of the composite. Cocured viscoelastic/composite layups were studied experimentally at the material level, modeled analytically, and used to build optimized damped structural components. Measured cocured material properties were used in finite element models to design damped components which were built and tested individually and as part of a truss test structure. Load-carrying and highly damped struts and panels were fabricated. The curing process modified the viscoelastic behavior to some degree, but the materials retained significant, and predictable, damping capability.

Several high-damping materials have been developed in recent years to decrease vibration and noise levels of machines and structures. The most important damping steels have been Fe- 12Cr-based alloys. These steels exhibit high damping capacity combined with rather good mechanical and corrosion properties. A new vibration damping Fe-2.5Al-0.5Si steel has been developed by NKK-Corporation in Japan, and it is produced under a trade name of NKK- SERENA. This steel is a potential multi-purpose damping steel, because it is more economical than the previous steels. Damping capacity of NKK-SERENA is very high in wide temperature and frequency ranges, and its mechanical properties are similar to those of common structural steels. In this study, mechanical, welding and corrosion properties, and the results of the microstructural characterization are presented.

A strategy is presented to develop computationally efficient models for a class of structures containing nonlinearities. Those structures are ones for which the predominant nonlinearity is in the interfaces of linear subsystems. In those cases, one hopes to achieve low order models for the linear subsystems coupled with simplistic models for the interfaces. The theme of this paper is that of deducing the properties of the nonlinear interfaces by examining the properties of the full nonlinear structure in light of the known properties of the linear subsystems. Situations where such problems arise include those where the nonlinearity derives from sliding friction or stick-slip friction. Those conditions can seriously compromise system performance if not addressed adequately, occasionally leading to either sloppy control or complete loss of stability. It is the problem of identifying those nonlinear subsystems that is addressed here.

Linear transfer function models based on frequency response identification techniques are developed to describe the flexural vibration of a cantilever beam when excited using piezoceramic patches bonded to a constrained layer damping treatment. Predictions of dynamic behavior, obtained using the models, are validated by comparison with results from laboratory experiments. The models are then used in open loop and closed loop velocity feedback control simulations to demonstrate the improvements in stability and performance.

We developed a new vibration-isolated platform used for nanometer measurements. This platform is based on the variable pendulum principle in the X-Y direction, and the spring principle in the Z direction. Its vibration-isolated system is made up of four layers of ring elastic material and five groups of rods and springs. Viscous silicon oil is used as damping between each ring layer. Each group of rods and springs includes six rods and twelve springs, which are evenly distributed on the circumference of the circular elastic material and sustain the whole platform. Ultra-low resonant frequency characteristic is provided for the platform, with the horizontal fundamental frequency less than 0.25 Hz, and the vertical 0.47 Hz. It means that the vibration-isolating efficiency of the platform is 3.4 times higher in the vertical direction and 28 times in the horizontal, than that of normal vibration-isolated systems, whose intrinsic frequency is about 1.3 Hz high on the same vibration condition.