Papers by Keyword: Damping

Abstract: This article delineates the characterization of the 3D printed MR elastomer through a forced vibration technique in the squeeze mode of operation. An anisotropic hybrid magnetorheological (MR) elastomer is developed via 3D printing. The 3D printed MR elastomer consists of three different materials; magnetic particles, magnetic particles carrier fluid, and an elastomer. MR fluid filaments are encapsulated layer-by-layer within the elastomer matrix using a 3D printer. When a moderately strong magnetic field is applied, the 3D printed MR elastomer changes its elastic and damping properties. The hybrid 3D printed MR elastomer also shows an anisotropic behavior when the direction of the magnetic field is changed with respect to the orientation of the printed filaments. The relative MR effect is higher when the applied magnetic field is parallel to the orientation of the printed filaments. The maximum change in the stiffness is observed to be 65.2% when a magnetic field of 500 mT is applied to the MR elastomer system. This result shows that the new method, 3D printing could produce anisotropic hybrid MR elastomers or possibly other types.

Abstract: To work out effective damping materials it is necessary to perfect analytical dependences linking dynamic properties of a composite with its structure-forming parameters. The analytical model of the particulate-filled polymers, based on the method of strain energy, convenient for engineering use and allowing to predict damping properties of a composite more reliable is given in this article. The detailed leading-out of formulas for scaling of a bulk modulus and loss factor of both two-phase and three-phase model of a composite is presented. Comparison of numerical values of damping characteristics under the derived formulas with experimental researches show that the offered model allows not only to show a qualitative pattern of dependence of dynamic behavior of a composite from degree of admission, but also to receive comprehensible quantitative results.

Abstract: This paper aims to investigate the damping properties of plate-like carbonyl iron particle (CIP) magnetorheological elastomer (MRE). The damping properties of MRE is mainly dependent on the strength of magnetic field. Anisotropic MRE was fabricated under various magnetic fields strength (70, 210, 345, and 482 mT) and its damping property prior to frequency-dependent was measured using a rheometer. Firstly, the plate-like CIP was first synthesized from spherical CIP using a ball-milling method. The microstructure of plate-like CIP was observed using low vacuum scanning electron microscope. Subsequently, two types of MREs which are isotropic and anisotropic were fabricated using 70 weight percent (wt.%) of plate-like CIP. The experimental results showed that the anisotropic MRE has lower damping factor than isotropic MRE. Meanwhile, the damping factor increases with the increase of frequency.

Abstract: Damping is one of the several important parameters in the dynamic system. It reduces amplitude response of a structure, especially around the resonance. The higher the damping, the better the performance (more comfort, lower stress, less fatigue), and the longer the life cycle of the structure will be. There are many types of damper amongst other is the tuned mass damper (TMD), where mass and spring are designed in such that the TMD frequency is close to the natural frequency of the structure in question where the phase angle is about 180 degree out of phase. Applying steel-rubber composite beam as a damper in the TMD system is expected to increase the damping of the structure of interest. The objective of this study is to test experimentally and numerically the dynamic parameters of the rubber-steel composite beam upon a cantilever support system under static load-displacement test and flexural dynamic excitation. The addition of steel (in the form of wire mesh) embedded in the rubber beam significantly increases the stiffness, but the damping ratio, at a small range of displacement. The effectiveness of rubber material in the steel-rubber composite beam is expected when large displacement occurs, meaning that more energy dissipation and larger damping ratio. The established numerical model is able to generate dynamic parameters close to results of the experimental model, but the damping ratios.

Abstract: Higher seismic performance can be achieved by localizing the inelastic deformation in the connections (fuses) and minimizing the residual drift that are often a determining factor in whether a structure can be repaired or re-occupied after an earthquake. This paper introduces the self-centering damage avoidance steel Moment Resisting Frames (MRFs) using innovative Resilient Slip Friction Joints (RSFJs). The RSFJ provides self-centering and energy dissipation in one compact package requiring no post-event maintenance. In this concept, the beam is connected to the column through a pinned joint at the top, an RSFJ at the bottom and a slotted web plate for transferring the shear forces, when required. The RSFJ allows for gap opening in the connection upon loading and then re-centers the system when unloading. Furthermore, a secondary fuse within the RSFJ is considered to keep maintaining a ductile behavior in the system in case of an earthquake larger than the design earthquake. The conducted experimental tests confirmed the outcomes of this study.

Abstract: According to level I and level II stability analysis of the API617 (7^th edition), the stability of a natural gas pipeline compressor system is studied. It is found that the rotor bearing system is unstable. Therefore, adding swirl brake on the system is to improve the damping characteristics. The stability of the unit can meet the requirement of API617 dynamic design. The research demonstrates that the stability of compressor system is not solely determined by the rotor system, but the stator system is also an important factor. In particular, the swirl brake on the diaphragm can reduce the cross coupling stiffness generated by the seal, and it is significant to improve the stability of the compressor system.

Abstract: High damping capacity materials present an increased interest in many applications were vibration and noise reduction is absolutely necessary. Metallic materials with a high internal friction (IF) are becoming valuable because of them usual mechanical properties that fulfill the damping capacity in applications. Some of the shape memory alloys present a huge damping capacity during the solid state transformation (M↔A) based on the re-orientation and accommodation of the material structure. Iron based shape memory alloy present the best advantages for industrial application as dumpers in different areas. Beside civil construction domain these materials can cover also applications in automotive industry as shock impact absorbers for low velocities as protection for engine parts and also for noise reduction. By these means in this article we analyze FeMnSi+Al alloy with a new chemical composition obtained through classical melting method in Ar controlled atmosphere.

Abstract: This paper presents flexural properties related to vibration behavior of jute reinforced polyester composite. The goal of the research is to seek green composite material that exhibits good strength and flexural properties along with good damping property designed for wind turbine blades. The material for reinforcement in the present study is jute fiber. The material for matrix is polyester resin. Glass and carbon fiber are used for hybridization. Specimens were fabricated by vacuum infusion technique. Laminates were constructed by stacking jute fiber clothes. Hybrid laminates were fabricated by stacking jute clothes covered by one ply glass cloth and jute clothes covered by one ply carbon cloth. Static flexural and free vibration tests were carried out to obtain the elastic modulus and vibration behavior of specimens, respectively. The result shows that the configuration of jute fiber cloth and glass fiber hybridized laminates possesses compromised properties between flexural properties and damping ratio.

Abstract: . In technical applications components are often exposed to vibrations with a broad range of frequencies. To ensure structural integrity and a convenient usage for the customer, materials with good damping characteristics are desirable. Especially stiff and lightweight structures tend to be prone to vibrations. Fibre metal laminates (FML) offer great potential for lightweight design applications due to their good fatigue behavior. By using carbon fiber reinforced plastics (CFRP) as part of the laminates very good strength and stiffness to weight ratios can be obtained. To improve the damping characteristics of this hybrid material an additional layer of elastomer can be added between the CFRP and the metal, generating a fiber-metal-elastomer laminate (FMEL). In this present study the damping behavior of different layups of FMEL was examined. Two different metal sheets and two types of elastomer were used, also the layup of the constituents was variated. Vibrations were induced with a frequency range from 100 Hz to 20 kHz by mounting the laminates onto a speaker. The vibration response was measured with a piezoelectric accelerometer. Eventually the different laminate layups were compared with each other to determine the influence of the individual constituents regarding the damping characteristics. The different elastomer types and prepreg layups affected the damping of vibrations, whereas the use of different metal sheet materials showed only little influence.

Abstract: This article focuses on the estimation of a proper logarithmic damping decrement in industrial boilers when flue gases travel in the vertical direction. The structure for this type of facility is quite unified worldwide. The structural conception is rather simple, and the response to any static loading is predictable. Nevertheless, with regard to dynamics and damping, some specifics in the detailed solution make this system unique. For the purpose of this analysis, a Plexiglas scale model was prepared at a geometric scale of 1:20. A set of experimental modal analyses was performed on the model. Each test focused on the damping effect of specific details and compared it with the common structure without a damping effect. Finally, a site modal analysis was conducted on an actual boiler located in the CHP Torun Plant in Poland. The upper part of the structure was reinforced to have a horizontal deflection of 8 mm and was suddenly released. The resulting movement was recorded with an HD camera linked to a theodolite. Experimental results on the scale model of the actual structure confirmed that damping of this type of structure is significantly higher than that considered for common steel structures.