Optimal design of a commercial rubber isolator based on creep and creep-resistance analyses

Creep is a common important physical phenomenon in rubber material, which induces the instability of geometrical dimension and deteriorates the mechanical performances. The present work develops an optimal design approach of a commercial rubber isolator based on creep analysis. First and foremost, a nonlinear creep constitutive model of rubber material is established, which can capture the hyper-elastic and time-dependent creep behaviors. Complete mechanical and creep tests of rubber materials are conducted, and material parameters are identified according to the experimental data. Then, the parametric finite element model of a rubber isolator is established, with which the time-dependent creep analysis based on the proposed creep constitutive model is conducted. The accuracy of the numerical creep analysis is validated at material level and structural component level. For engineering application, a sensitivity analysis and optimization design for creep-resistance of the rubber isolator is developed by combing finite element simulation and optimization method. The results show that creep-resistance characteristics of the optimal rubber isolator is largely improved, which provides a long-term stable behavior in vibration attenuation. The proposed method may provide an efficient tool for predicting the creep performance and optimal analysis of other commercial rubber-base products.

Study of the Lifetime Testing of Spherical Rubber Isolators

This study aims to identify the fatigue lifetime of a thin-walled hollow spherical rubber isolator subjected to harmonic and random vibrations. Firstly, the nonlinear characteristics of the rubber materials are tested and analyzed through vibration experiments. The relationship among the nonlinear stiffness, nonlinear damping, and relative displacement amplitude is established. Secondly, an accelerated lifetime experiment under random excitation is carried out. The correlation between the root-mean-squared acceleration response of the random vibration system and the stiffness attenuation of the rubber isolator is established and modeled. A lifetime prediction method for rubber isolators is proposed based on the model. Finally, the influence of different loads on the lifetime of the rubber isolator is investigated. These methods provide an additional rationale for the further theoretical research and practical engineering application of rubber damping systems.

Design, Optimization and Experimental Verification of a Metal Rubber Isolator for Momentum Wheels

The inertial actuator, such as momentum wheels, is the key mechanical component of spacecraft for attitude stability and accuracy maintenance. However, the inertial actuators are under excessive vibration during the rocket launch phase. In order to prevent the inertial actuators from structural damage and equipment failure, isolating vibration from the base must be considered. Metal rubber (MR) is a kind of porous functional damping material, manufactured through the process of entangling, stretching, weaving and molding of metallic wires. With its excellent mechanical properties of high damping, designable stiffness and environmental adaptability, MR is widely used in the area of aerospace and aviation for vibration isolation. To this end, a method to design and optimize a MR isolator for momentum wheels is developed. The MR isolator consists of a transverse groove spring and MR in parallel. A FEM model coupling the transverse groove spring and the simplified momentum wheel is established to assist in the optimization of the configuration of the spring, and the goal is to minimize the frequency bandwidth of the first six modes. The influence of the parameters on the frequency of the first six modes is also discussed. The MR is then designed to provide damping and additional stiffness. Finally, the performance of the MR isolator is analyzed by simulation and verified through experiments.

Properly designed expansion joint to ensure successful seismically Isolated Structures

<p>Seismic isolation system has become one of the most efficient approaches chosen by design engineers for having better seismic performance and cost-efficiency for structures located in high seismicity area. For bridges, the seismic isolation system is usually done by replacing the conventional bearings (pot or spherical bearings) with seismic isolator bearings (rubber isolator bearings or pendulum bearings). In general, only these isolator bearings that will be the focus of considerations during design phase. It is commonly forgotten that the seismic isolation system shall be also coupled with properly installed seismic expansion joint that can accommodate large movements on the bridge deck due to isolation effect of the seismic system. Improperly designed expansion joint is usually shown by the use of small non-seismic joint that leads to very narrow provided gaps in between the concrete deck and its adjacent structure. These gaps are not able to accommodate large movements on the deck of a seismically isolated bridge. Collisions or poundings during seismic event are inevitable. This leads to dysfunctionality of seismic isolation system, and in the worst case it may generate excessive impact forces that will result to undesired performance level and damages on the structures.</p>