A modified magneto-rheological rubber (MRR) which resistance can be reduced to 1KΩ was fabricated by dispersed multi-walled carbon nanotubes (MWNTs) and carbonyl iron particles (CIPs) into polydimethylsiloxane (PDMS) matrix. Based on the excellent piezo-resistive properties of this modified MRR, a MR bearing with self-sensing characteristics was proposed and systematic researched. In order to study the self-sensing characteristics of the MR bearing based on modified MRR under load and magnetic fields, the structure and working conditions of the bearing were simulated and compared. The optimal structure size of the bearing was selected and used for the build-up of experiment test system. The results showed that, under the action of preload condition by bearing, due to piezo-resistance and magnetoresistance behavior of the modified MRR, the electrical resistance of it also can be changed over 28%. It suggests that, in the MR semi-active vibration isolation system, the modified MRBs are potentially capable of being used as an actuator and sensor in the same time.
In this article, we propose a 3D FEM model to analyze the anisotropic thermal behavior of oriented GNPs/polymer composites. The model considers the effect of microstructural characteristics such as the shape and aspect ratio of filler, interfacial thermal resistance, volume fraction, dispersion state and orientation of GNPs dispersion to simulate a steady state heat flow in the composite. In the simulation model, the composite is treated as a cubic unit cell and GNPs are modeled as oblate spheroid with a long axis diameter of 1μm and the aspect ratio is in the range of 0.01 to 0.05. The oblate spheroids align in the cubic to represent the microstructure of the oriented GNPs/polymer composites. By varying the number of the GNPs in the representative unit cell, the volume fractions of fillers are determined. The simulation results show that the parallel thermal conductivity (//) increase in a nonlinear trend and the perpendicular thermal conductivity (⊥) is slightly linear increasing. Compared with experimental results, the trends predicted by the finite element models are consistent.
We perform a theoretical simulation to investigate how the magnetic field induces the interaction of ferromagnetic particles inside MRE, and consequently how the surface microstructures of MRE are changed. Firstly, we propose a mesoscopic model of the MRE by assuming that particles have the same radius, and they are randomly distributed in the matrix. Both particles and matrix are considered as linear elastic materials. We apply Monte-Carlo method to produce the initial surface microstructure of the MRE before considering the magnetic field effect. Further, we use sequential decoupling FEM method to solve the magneto-mechanical coupling problem. The relationships of surface roughness of MREs with the volume fraction of ferromagnetic particles, the magnetic field strength, the initial surface microstructure, and the matrix modulus have been numerically investigated.
This paper proposes an extended Preisach model in which the combination of magnetic field and mechanical stress are treated as an effective field and Preisach diagram is used to qualitatively analyze magnetomechanical behaviors for any kinds of magnetization history. Magnetomechanical behaviors under a certain kind of magnetization history are discussed. The corresponding experiments are carried out. The results show that it is helpful in forecasting the trend of magnetomechanical behavior which gives a reasonable understanding of the various magnetomechanical behaviors that appeared to be contradictory. Moreover, it is useful in improving the stress measurement accuracy by determining the magnetic condition.
A magneto-rheological bearing (MRB) is proposed to improve the vibration isolation performance of a floating slab track
system. However, it’s difficult to carry out the test for the full-scale track vibration isolation system in the laboratory. In
this paper, the research is based on scale analysis of the floating slab track system, from the point view of the
dimensionless of the dynamic characteristics of physical quantity, to establish a small scale test bench system for the
MRBs. A small scale MRB with squeeze mode using magneto-rheological grease is designed and its performance is
tested. The major parameters of a small scale test bench are obtained according to the similarity theory. The force
transmissibility ratio and the relative acceleration transmissibility ratio are selected as evaluation index of system
similarity. Dynamics of these two similarity systems are calculated by MATLAB experiment. Simulation results show
that the dynamics of the prototype and scale models have good similarity. Further, a test bench is built according to the
small-scale model parameter analysis. The experiment shows that the bench testing results are consistency with that of
theoretical model in evaluating the vibration force and acceleration. Therefore, the small-scale study of
magneto-rheological track vibration isolation system based on similarity theory reveals the isolation performance of a
real slab track prototype system.
As the weakest part in the bridge system, traditional bridge bearing is incapable of isolating the impact load such as earthquake. A magneto-rheological elastomeric bearing (MRB) with adjustable stiffness and damping parameters is designed, tested and modeled. The developed Bouc-Wen model is adopted to represent the constitutive relation and force-displacement behavior of an MRB. Then, the lead rubber bearing (LRB), passive MRB and controllable MRB are modeled by finite element method (FEM). Furthermore, two typical seismic waves are adopted as inputs for the isolation system of bridge seismic response. The experiments are carried out to investigate the different response along the bridge with on-off controlled MRBs. The results show that the isolating performance of MRB is similar to that of traditional LRB, which ensures the fail-safe capability of bridge with MRBs under seismic excitation. In addition, the controllable bridge with MRBs demonstrated the advantage of isolating capacity and energy dissipation, because it restrains the acceleration peak of bridge beam by 33.3%, and the displacement of bearing decrease by 34.1%. The shear force of the pier top is also alleviated.
The urgent train braking could bring structural response menace to the bridge under passive control. Based on the analysis of breaking dynamics of a train-bridge vibration system, a magnetorheological elastomeric bearing (MRB) whose mechanical parameters are adjustable is designed, tested and modeled. A finite element method (FEM) is carried out to model and optimize a full scale vibration isolation system for railway bridge based on MRB. According to the model above, we also consider the effect of different braking stop positions on the vibration isolation system and classify the bridge longitudinal vibration characteristics into several cases. Because the train-bridge vibration isolation system has multiple vibration states and strongly coupling with nonlinear characteristics, a human-simulated intelligent control (HSIC) algorithm for isolating the bridge vibration under the impact of train braking is proposed, in which the peak shear force of pier top, the displacement of beam and the acceleration of beam are chosen as control goals. The simulation of longitudinal vibration control system under the condition of train braking is achieved by MATLAB. The results indicate that different braking stop positions significantly affect the vibration isolation system and the structural response is the most drastic when the train stops at the third cross-span. With the proposed HSIC smart isolation system, the displacement of bridge beam and peak shear force of pier top is reduced by 53.8% and 34.4%, respectively. Moreover, the acceleration of bridge beam is effectively controlled within limited range.
We propose a method to analyze and design a laminated MRE bearing, in which the optimal parameters of materials and mechanical structure of the MRE bearing are determined. Based on the multi-scale and magneto-mechanical coupling theories, we establish a comprehensive model for the MRE bearing considering the influence of particle volume fraction, particle distribution, and thickness of MRE laminated layers on its mechanical performance. Within the micro-scale analysis, the representative volume unit (RVU) is used to address the effect of particle volume fraction and distribution on mechanical and magnetic properties of MRE itself. Within the macro-scale analysis, we build both mechanical and magnetic models for the laminated MRE bearing. Based on the theoretical analysis, a laminated MRE bearing with four-layer MRE is designed and fabricated. The performance of the MRE bearing has been tested by using MTS test bench. The results are compared with that of model analysis. It demonstrates that the proposed method can be a useful tool in the development of laminated-MRE bearings for practical applications.
The goal of this study is to investigate dynamic properties and the total energy change of a bio-inspired spider web. To better understand performance, the effects of preload, radial and spiral string stiffness and damping ratio on the natural frequency and total energy of the web are theoretically examined. Different types of web materials and configurations, such as damaged webs are investigated. It is demonstrated that the pretension, stiffness and damping ratio of the web’s strings can significantly affect the natural frequency and total energy of the full and damaged webs. In addition, it is shown that by increasing the pretension in the radial strings one can compensate for the damaged strings and increase the capability of the damaged web to reach that of the full web.