Good Damping Research Articles

Preparation and molecular dynamics study of polyurethane damping elastomer containing dynamic disulfide bond and multiple hydrogen bond

Using damping materials is an effective measure to control vibration and noise, which is widely used. However, it is relatively difficult for polymer damping materials to find a balance between damping and mechanical properties. Herein, a polyurethane is designed containing dynamic disulfide bonds and hydrogen bonds of different strength to address the dilemma. The polyurethane is endowed with good damping and mechanical properties (effective damping temperature range of 117 °C and a tensile strength of 14.98 ± 0.50 MPa). The molecular dynamics were studied by combining dynamic mechanical analysis (DMA) and broadband dielectric relaxation spectroscopy (BDRS). The microphase separation morphology and degrees of separation were used to help explain molecular dynamics. The segmental motion of soft phase becomes difficult in the glass-transition temperature (Tg) and faster in a high temperature with increasing 2, 2′-Dithiodibenzoic acid (DTSA) contents. These results explain the mechanism improving damping performance and provide some references for designing damping materials in the future.

Study on the Structure and Performance of an Antagonistic Pneumatic Bidirectional Rotary Joint

An antagonistic pneumatic bidirectional rotary flexible joint was developed to improve both safety and environmental adaptability of service robots and associated human interactions. The joint comprises two semicircular rotary actuators with positive and negative symmetrical distributions and a pneumatic brake. As such, it achieves forward and reverse rotations, and its damping and braking are adjustable in real time, enabling it to maintain its position. According to the force/torque balance at the free end of the rotary actuator, the rotation angle static model was established. The relationship between the actuator rotation angle, driving torque, impedance torque, and air pressure was obtained experimentally. The brake airbag was manufactured using additive manufacturing and silicone gel casting technologies. The mathematical model of the braking torque was established next, and the model was verified through experiments. Furthermore, an experimental system was constructed to carry out the air pressure-angle, air pressure-torque, and speed response experiments without the load on the joint. The results have shown that the joint can achieve any position within ± 68.5° when the driving air pressure varies from 0 to 0.30 MPa; the time required to reach the maximum angle was 0.85 s. The joint has shown good adjustable damping characteristics. Lastly, the braking torque reached 4.21 Nm at 0.32 MPa, effectively maintaining the position.

Cyclic behavior of SMA slip friction damper

This paper proposes a new type of self-centering (SC) damper which exploits the shape memory alloy (SMA) bolts and variable friction mechanism, termed the SMA slip friction damper (SMASFD). The theoretical equations governing the force–displacement relationship, the equivalent stiffness and the equivalent viscous damping are first derived. Then, the application potential of such damper is briefly discussed. In the experimental study, the results of the experimental validations of the SMA bolts and the friction mechanism are presented, followed by the results of proof-of-concept test on the fabricated SMASFDs. According to the testing results, the damper exhibited a symmetric tension–compression flag-shaped hysteresis characterized by excellent SC capacity and good damping capability. The prestrain treatment was applied to the SMA bolts in one test, which was found effectively increased the initial stiffness of the damper. To provide a further understanding on the damper and examine the stress and strain demands of the components, high-fidelity finite element models were established for numerical simulations. Both the analytical method and numerical simulation were validated by the experimental data.

Non-isocyanate poly(acyl-urethane) obtained from urea and castor (Ricinus communis L.) oil

A new material non-isocyanate polyurethane (NIPU), a poly(acyl-urethane) (PUAcyl), was obtained using castor oil (Ricinus communis L.), urea, and BF3⋅OEt2 as a promoter under a solvent-free methodology. The structure of the PUAcyl was confirmed by Fourier-transform infrared spectroscopy (FTIR), showing the carbamate carbonyl stretching vibration and 1H and 13C nuclear magnetic resonance (NMR), which also presented characteristic carbamate chemical shifts. In addition, the appearance of a carbamate peak in the 13C NMR spectrum, in the solid state, corroborates the structure of the PUAcyl. The confirmation that PUAcyl is a polymer was carried out by gel permeation chromatography (GPC) and a reaction mechanism for its formation has been proposed. The PUAcyl showed a satisfactory thermal stability measured by thermogravimetry (TG), furthermore the differential scanning calorimetry (DSC) and dynamic mechanical analyses (DMA) suggest that the material has polymeric chains with varying sizes and exhibit good damping properties in a temperature range compatible with daily applications. Therefore, this work provides an effective way to prepare isocyanate-free PUAcyl with promising applications such as acoustic coating.

Development of an Aluminum-Based Hybrid Billet Material for the Process-Integrated Foaming of Hollow Co-Extrusions

Metal foams are attractive for lightweight construction in the automotive sector since they provide high-energy absorption and good damping properties, which is crucial, e.g., for crash structures. Currently, however, foams are produced separately and then pasted into the components. Consequently, the overall mechanical properties depend significantly on the quality of the adhesive bond between the foam and the structural component. A new process route for the manufacture of hybrid foamed hollow aluminum profiles is proposed. In this approach, a foamable precursor material is directly integrated into the extrusion process of the hollow structural profile. To this end, special low-melting alloys were developed in this study to enable foaming inside the aluminum profile. The melting intervals of these alloys were examined using differential scanning calorimetry. One of the promising AlZnSi alloys was atomized, mixed with a foaming agent and then compacted into semi-finished products for subsequent co-extrusion. The foaming behavior, which was investigated by means of X-ray microscopy, is shown to depend primarily on the mass fraction of the foaming agent as well as the heat treatment parameters. The results demonstrate that both the melting interval and the foaming behavior of AlZn22Si6 make this particular alloy a suitable candidate for the desired process chain.

Modulating impact resistance of flax epoxy composites with thermoplastic interfacial toughening

The application of natural flax fibre/epoxy composites is growing in the automotive sector due to their good stiffness and damping properties. However, the impact damage resistance of flax/epoxy composites is limited due to the brittle nature of both epoxy and flax fibres and strong fibre/matrix adhesion. Here, biobased thermoplastic cellulose acetate (CA) is deployed as a fibre treatment to alter the damage development of flax/epoxy composites subjected to low-velocity impact. The perforation threshold energy and the perforation energy of unmodified cross-ply composites increased respectively by 66% and 42% with CA-treated flax fibres. The CA-modification modestly decreased the transverse tensile strength and in-plane tensile shear strength of the composites. However, it altered the brittle nature of flax/epoxy laminates in quasi-static tests into ductile failure with clearly increased fibre–matrix debonding.

Prototype Test and Numerical Analysis of a Shallow Cable with Novel Viscous Inertial Damper

As an essential component of offshore bridges, stay cables are prone to vibrations due to their low inherent damping characteristics. Various dampers have been used for cable vibration control; however, the experimental research and theoretical study of inertial dampers on real cables have not been conducted sufficiently. This study aims to investigate the damping performance of a novel viscous inertial damper (VID) and focuses on the frequency-dependent and displacement amplification phenomena of a cable-damper system. Tests were first conducted to verify the energy consumption capacity of a prototype damper. A shallow cable-VID system was established. Theoretically, complex-valued modes were analyzed to determine the influence of the inertial and viscous coefficients on the cable’s frequency and mode damping ratio. The test results and numerical analysis show that the VID has a good damping effect on the shallow cable. Considering multiple adjacent cable modes, the inertial and viscous coefficients can be optimized. After optimizing, the VID can simultaneously maximize both adjacent symmetric and antisymmetric modes’ damping ratios. The two frequencies are almost the same. The displacement amplification of the VID shows that a VID can overcome the shortcomings of displacement loss caused by traditional oil dampers. The implications of these findings of the VID on shallow cable are discussed, which will guide future research and applications of the VID or other inerter dampers.

Experimental research on suppressing unbalanced vibration of rotor by integral squeeze film damper

Abstract As a novel structural damper, the unique structural characteristics of the integral squeeze film damper (ISFD) solve the nonlinear problem of the traditional squeeze film damper (SFD), and it has good linear damping characteristics. In this research, the experimental studies of ISFD vibration reduction performance are carried out for various working conditions of unbalanced rotors. Two ball bearing-rotor system test rigs are built based on ISFD: a rigid rotor test rig and a flexible rotor test rig. When the rotational speed of rigid rotor is 1500 rpm, ISFD can reduce the amplitude of the rotor by 41.79%. Under different unbalance conditions, ISFD can effectively improve the different degrees of unbalanced faults in the rotor system, reduce the amplitude by 43.21%, and reduce the sensitivity of the rotor to unbalance. Under different rotational speed conditions, ISFD can effectively suppress the unbalanced vibration of rigid rotor, and the amplitude can be reduced by 53.51%. In the experiment of the unbalanced response of the flexible rotor, it is found that ISFD can improve the damping of the rotor system, effectively suppress the resonance of the rotor at the critical speed, and the amplitude at the first-order critical speed can be reduced by 31.72%.

Experimental research on suppressing unbalanced vibration of rotor by integral squeeze film damper

Abstract As a novel structural damper, the unique structural characteristics of the integral squeeze film damper (ISFD) solve the nonlinear problem of the traditional squeeze film damper (SFD), and it has good linear damping characteristics. In this research, the experimental studies of ISFD vibration reduction performance are carried out for various working conditions of unbalanced rotors. Two ball bearing-rotor system test rigs are built based on ISFD: a rigid rotor test rig and a flexible rotor test rig. When the rotational speed of rigid rotor is 1500 rpm, ISFD can reduce the amplitude of the rotor by 41.79%. Under different unbalance conditions, ISFD can effectively improve the different degrees of unbalanced faults in the rotor system, reduce the amplitude by 43.21%, and reduce the sensitivity of the rotor to unbalance. Under different rotational speed conditions, ISFD can effectively suppress the unbalanced vibration of rigid rotor, and the amplitude can be reduced by 53.51%. In the experiment of the unbalanced response of the flexible rotor, it is found that ISFD can improve the damping of the rotor system, effectively suppress the resonance of the rotor at the critical speed, and the amplitude at the first-order critical speed can be reduced by 31.72%.

Modeling and static characteristics study of the double-layer bump gas foil bearing

This paper presents a frictional structural model for the double-layer bump gas foil bearing (DGFB) based on contact mechanics. Using this model, the load carrying mechanism and the static characteristics of the DGFBs are analyzed. The investigations on the foil layouts and structural parameters yield valuable observations. Loading-unloading simulations show that the adjustment of the bump foil layout can enhance the structural stiffness of the DGFB whilst still maintaining relatively good damping. The static analyses indicate that an excessively stiffer lower bump foil hinders the improvement in the maximum load capacity of DGFBs.

Preparation process and new progress in carbon fiber reinforced magnesium matrix composites

The carbon fiber reinforced magnesium matrix (Cf/Mg) composites are considered as the most promising structural materials with great potential in both aerospace and automotive applications, which have high specific strength, high specific stiffness, excellent thermal conductivity, great electrical conductivity and good damping properties, as well as close to zero thermal expansion coefficient and good dimensional stability. In the present review, the craft principles and characteristics, as well as the current development status and the key technical problems of powder metallurgy, diffusion bonding, squeeze casting, etc that can be used to prepare Cf/Mg composites are discussed deeply. Then the new progresses made in the preparation of Cf/Mg composites in recent years are hackled. Furthermore, engineering application cases of Cf/Mg composite that have a significant promotion effect and potential application prospects in the fields of national defense and national economy are introduced. Additionally, the facing challenges of Cf/Mg composite are analyzed, and the future development directions are prospected.

Personalized Anti-Vibration Protection for Telematics Devices in Urban Freight Transport Vehicles

Vibrations are a major cause of human health disorders, circuit boards and machinery damage. Vibration dampers are considered to be the best option to counter these issues. Three-dimensional printing techniques play an increasingly important role in manufacturing small polymer parts with tailored properties. Thermoplastic elastomers (TPE) constitute a perfect material for manufacturing small-scale series absorber prototypes due to their thermoplastic nature, good elasticity and damping properties. This paper proposes a novel multi-level approach to the design and manufacturing process, e.g., the first level—selection of material; second level—decision about the geometry of a damper; third—selection of technological printing parameters; fourth—post-printing treatment. This work primarily aims to overview the design and manufacturing process levels. The impact of each step on the damping capacity of small absorbers is assessed. It was found that thermoplastic elastomers and fused deposition modeling (FDM) have huge potential in shaping the physical properties of small, elastomeric absorbers. It was assessed that at every step of the multilevel design and manufacturing process (MDMP), the designer could tailor the damping to meet the desired criteria of a final product: a cylinder-shaped hollow damper that can be made from TPE polymer without post-printing treatment and is characterized by good damping.

DURA-BAR GX

Abstract Dura-Bar GX is a heat-treatable, pearlitic gray cast iron that is used for the production of continuous cast products. It is ideal for applications that require a combination of moderate strength, good wear resistance, and good vibration damping capacity. This datasheet provides information on composition, physical properties, microstructure, hardness, and tensile properties. It also includes information on heat treating and machining. Filing Code: CI-83. Producer or source: Charter Dura-Bar, Inc.

Multiscale Analysis of High Damping Composites Using the Finite Cell and the Mortar Method

Metal lattice structures filled with a damping material such as polymer can exhibit high stiffness and good damping properties. Mechanical simulations of parts made from these composites can however require a large modeling and computational effort because relevant features such as complex geometries need to be represented on multiple scales. The finite cell method (FCM) and numerical homogenization are potential remedies for this problem. Moreover, if the microstructures are placed in between the components of assemblies for vibration reduction, a modified mortar technique can further increase the efficiency of the complete simulation process. With this method, it is possible to discretize the components separately and to integrate the viscoelastic behavior of the composite damping layer into their weak coupling. This paper provides a multiscale computational material design framework for such layers, based on FCM and the modified mortar technique. Its efficiency even in the case of complex microstructures is demonstrated in numerical studies. Therein, computational homogenization is first performed on various microstructures before the resulting effective material parameters are used in larger-scale simulation models to investigate their effect and to verify the employed methods.

Shock absorption analysis based on the tunnel-soil-surface building interaction system

In order to apply damping technology to complex interaction system, a two-dimensional finite element-infinite element coupling model of tunnel-soil-surface building interaction system was established by ABAQUS. By analyzing the acceleration, displacement and stress response of key points of tunnel and surface buildings, the influence of the thickness and buried depth of the shock absorption layer on the damping effect of the system is studied when tunnel shock absorption layer (or foundation shock absorption layer) is set separately. And a combined shock absorption system is proposed for the complex interaction system, and the primary and secondary relationship of different factors on the damping effect is studied by orthogonal experiment. The results showed that: (1) Setting up a tunnel shock absorption layer can significantly reduce the maximum principal stress of the tunnel and the acceleration of the surface building;(2) When the buried depth of the foundation shock absorption layer was 0m, the damping effect was the best, which can significantly reduce the acceleration and relative displacement of the surface building; (3) The combined shock absorption system can achieve good damping effect under different seismic waves excitation and its damping effect was better than single shock absorption layer system.

Efficient Self-Tuned Fuzzy Logic Based Power System Stabilizer

A mechanism for efficient self-tuning of a fuzzy logic-based PSS in real-time is presented. The proposed controller with a self-tuning mechanism can reduce low-frequency oscillations regardless of magnitude or type of disturbance, whether sudden or gradual. It is not necessary to set the initialization or learning factor for each disturbance and its implementation is simple. Speed deviation and its derivative are used as fuzzy controller inputs. The main idea, based on the properties of the conventional PID controller, is to use a fuzzy controller similar to a PID controller but for the nonlinear power system. Since the objective is implementation on a physical system, nonlinearity without any simplification of the system is very important. Therefore, in this mechanism, the full order machine model is considered. The optimal performance is obtained by determining in real-time the appropriate gains for each input. Tests for a wide range of disturbances show the robustness of the controller. The proposed approach has fewer fuzzy rules than similar methods. Therefore, its hardware implementation can be simpler and will require less computation time. Very good damping of all types of disturbances is a prominent feature of this method.

Static and dynamic performances of ferrofluid lubricated long journal bearing

Abstract Due to the advantageous property of reduction of load friction, low wear and good damping characteristics, journal bearings are widely used in industry. They are equipping various rotating machineries like small electrical motors to large generators, internal combustion engines, centrifugal pumps, turbine shaft of most jet engines, crankshaft of an automobile engines, etc. In this paper, static and dynamic performances of ferrofluid (FF) lubricated long journal bearing are studied using rotational and translational approach of the journal. Here, FF is controlled by the transverse uniform magnetic field. The modified Reynolds equation is derived by considering FF flow behaviour given by Shliomis and continuity equation in the film region. The dimensionless expressions for load-carrying capacity, frictional force and coefficient of friction are studied for static case, while the dimensionless expressions for stiffness coefficients and damping coefficients are studied for dynamic case. It is observed that comparing with conventional lubricant the bearing performance is significantly modified in the present analysis.

Damping Behaviour of Multi-Walled Carbon Nanotubes Grafting on Carbon Fiber Reinforced Friction Material


 
 
 An automobile's braking system plays an important role to control the vehicle at various operating speeds. At present, the brake friction industry is mainly focused on effectiveness of braking in addition to aesthetic considerations of an automobile. In this research, carbon fiber reinforced friction material is developed by grafting multi-walled carbon nanotubes functionalized (MWCNTS-F) on CF surface. The surface of CF is basically chemically inert and hydrophobic in nature and needs to be modified by grafting MWCNTS-F on its surface to increase hydroxyl or carboxyl groups. An attempt is made to improve the bonding strength between CF, polymer matrix and the remaining ingredients. Carbon fiber content after surface modification is varied in weight percentor wt% (2%, 3%, 4% and 5%) and mixed with the remaining ingredients of friction material. Composite sheets are prepared using hand lay-up method and characterized for damping, SEM, TGA and FTIR analysis. It is observed that MWCNTS-F grafted on CF 3 wt% possess good damping results. The results also reveal that, optimum selection of ingredients and surface treatment method on CF is the main reason for improvement of the composite’s interfacial adhesion and damping behavior.
 
 

Application of lightweight magnesium alloy in satellite antenna products

Combined with the actual work, the new metal matrix composite has the characteristics of light weight, low thermal expansion (CTE), ultra-high thermal conductivity, high specific strength, specific stiffness, good damping, etc. which is the key to realize the requirements of miniaturization, lightweight, long life and high reliability of aerospace products. This paper introduces the selection analysis and practical application of magnesium alloy in satellite antenna products. Antenna products based on magnesium alloy will be more and more widely used in aerospace field.

Compressive properties of 3-D printed Mg–NiTi interpenetrating-phase composite: Effects of strain rate and temperature

For composite materials applied for energy absorption and vibration/noise reduction, it is of particular significance to clarify the role of strain rate and temperature on their mechanical properties. Here we present a study on the effects of strain rate (from 10−3 s−1 to 1 s−1) and temperature (from room temperature to 350 °C) on the compressive properties of a 3-D printed Mg–NiTi interpenetrating-phase composite, which features high energy absorption efficiency and good damping capacity. Within the regimes of strain rate and temperature, the composite constantly exhibits a stable stress plateau on the stress-strain curves, yet displays markedly different damage mechanisms depending on the specific strain rate and temperature. The 3-D interpenetrating-phase architecture promotes an effective stress transfer in the composite and resists the propagation of local damages, thereby conferring a high strengthening efficiency and outstanding damage tolerance. The unique combination of mechanical properties makes the composite appealing for applications under various conditions, especially for absorbing mechanical energy and reducing vibrations and noise.