Magnetorheological elastomers (MREs) are a class of smart materials composed of an elastomer and micron-sized magnetic particles. Besides the loading amplitude and frequency, the elastic and rheological properties of MREs are also dependent on the external magnetic field and temperature. Previous studies focused on the influences of external magnetic field, strain amplitude and frequency on the dynamic properties, however, the temperature effect was rarely reported. In this paper, the dynamic mechanical analysis (DMA) tests were carried out to investigate the viscoelastic properties of the anisotropic MRE samples under various temperatures and magnetic fields. A transition behavior of the anisotropic MRE samples was observed at about 50°C for dynamic modulus. The storage modulus initially decreased with the increasing of temperature up to 50°C and then increased or maintained a stable value when temperature increased until to 60°C. The time-temperature superposition (TTS) principle was extended to construct the dynamic modulus master curve of the MREs by using the horizontal shift factor and the vertical shift factor. The good correlations between the measured and predicted data were confirmed by performing statistical analysis for the goodness of fit. The constructed master curve and shift factors can be used to predict the viscoelastic properties of the MREs beyond the DMA experiment range of temperatures and frequencies.

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Temperature effect on viscoelastic properties of anisotropic magnetorheological elastomers under compression

Thermorheologically simple materials: A bayesian framework for model calibration and validation

The aim of this paper is to propose a methodology for the modelling, testing, and the parameter identification of viscoelastic supports for rotating machines at the component and system level. Although the use of this type of dampers is common in rotordynamic applications, the strict dependence on the working frequency of the material parameters makes their behavior hard to predict and recommends grounding the design on experimental data of the characteristics. A dedicated test rig is adopted to characterize the supports and validate the modelling approach at component level. A parameter identification procedure is carried out from the experimental results to extract the mechanical properties of the supports. To this end, a Genetic Algorithm (GA) is adopted to search the most fitting values of damping and stiffness of the reference model. The choice of GA is motivated by the need of adopting a technique that can be easily implemented on industrial control units, being that the dedicated machine is supposed to be used in production lines for testing procedures. The results are obtained in terms of complex stiffness as a function of the frequency and are then translated in classical stiffness and damping components that are commonly used in rotordynamics. Afterwards, they are introduced in the model of a turbo-molecular pump adopted as a case study to evaluate the correctness of the proposed methodology at system level at stand-still and with the pump in rotation. The proposed approach is effective, showing a good match between the numerical model and the experimental results even with a relatively low order model of the viscoelastic supports and on a complex rotordynamic system.

Viscoelastic Dampers for Rotors: Modeling and Validation at Component and System Level

A method for analyzing the influence of temperature on the dynamic characteristics of structures with viscoelastic dampers is proposed in this paper. Dampers which are described by so-called fractional rheological models are considered. The temperature–frequency superposition principle is used to describe the influence of temperature on the dynamic characteristics. The concept of continuous dependence of damping on an artificially introduced parameter is adopted for solving, in an approximate way, the nonlinear eigenvalue problem from which dynamic characteristics are determined. The correctness and effectiveness of the method was verified by means of two examples.

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Approximate method for temperature-dependent characteristics of structures with viscoelastic dampers

Previous studies have shown that fractional derivative models present a plausible level of accuracy when it comes to capturing the behavior of viscoelastic dampers due to being capable of expressing the effects of excitation frequency and ambient temperature in viscoelastic damper parameters. Considering the possibility of earthquake occurrence during a structure lifetime, minimizing the life-cycle cost of a building is a practical way of optimizing the seismic design or retrofit plan and performance of the structure. In this paper, the total life-cycle cost of a structure with fractional viscoelastic dampers is chosen as the objective of an optimization problem while considering the effects of the changes in the ambient temperature and uncertainty related to the ground motion excitation which are the decisive parameters in the life-cycle cost analysis. The results for a 5-story steel frame show lower total life-cycle cost, initial cost, and story drift for the optimized structure compared to one with uniform distribution of dampers. Also, more use of dampers in optimized structure with life-cycle cost minimization objective, compared to a structure designed to minimize the cost of the dampers, has led to a significant reduction in the expected life-cycle damage costs.

Optimal seismic retrofit of fractional viscoelastic dampers for minimum life-cycle cost of retrofitted steel frames

The design of passive damping treatments using viscoelastic materials requires both an accurate numerical analysis approach, usually making use of the finite element method, and a realistic means of material description. While the former has been widely studied and several and valuable approaches have become available during the last years, the latter is still an issue requiring additional efforts. The experimental characterization, the data modeling and finally the constitutive models able to be directly used along analytic and numerical analysis, are still important research areas. Several viscoelastic models, able to be directly applied into a finite element analysis either in a time or in a frequency domain analysis, are available and have been widely used during the last years in most of the published work. Despite the general description and straightforward use that such modeling approaches may provide, temperature effect is usually disregarded and isothermal analysis are usually performed. Moreover, this temperature effect is naturally not directly considered as an input parameter for most of the viscoelastic material models and isothermal conditions are also considered in the experimental characterization data analysis. This work presents an extended viscoelastic model, based on well known isothermal models, where the temperature-frequency superposition effect is directly considered. The extended model is applied to the analysis of the experimental data using a data fitting procedure to identify a set of global parameters able to represent the effect of the frequency and the temperature.

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J. Dias Rodrigues

Papers

A Gneralized Frequency-Temperature Viscoelastic Model