Both experimental and modeling studies of magnetic field induced viscoelastic properties of magnetorheological (MR) elastomers under different loading cases are discussed. Anisotropic MR elastomer (MRE) samples with different concentrations of carbonyl iron powder, natural rubber and additives are fabricated and four MRE vibration mitigation devices are manufactured to investigate the dynamic viscoelastic properties of MREs under varying magnetic fields, displacement amplitudes and frequencies in the shear mode. The characteristics of the dynamic properties of the MRE devices are obtained in terms of the experimentally determined shear storage modulus and loss factor. These results demonstrate that the MREs exhibit variable stiffness and damping properties. Based on the studies of properties of viscoelastic materials and the experimental results of MREs, a parameter model is proposed to describe MRE performances. The four parameters under various working conditions, such as magnetic field, displacement amplitude and frequency, are identified by using the Matlab optimization algorithm. Comparisons between experimental and numerical results are discussed, and the results show that the proposed parameter model can describe the performances of MRE devices very well.

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The objective of this paper was to explore the bond–slip relationship between carbon fiber-reinforced polymer (CFRP) sheets and concrete under cyclic loading through experimental and analytical approaches. Modified beam tests were performed in order to gain insight into the bond–slip relationship under static and cyclic loading. The test variables are the CFRP-to-concrete width ratio, and the bond length of the CFRP sheets. An analysis of the test results in this paper and existing test results indicated that the slope of the ascending segment of the bond–slip curve decreased with an increase in the number of load cycles, but the slip corresponding to the maximum shear stress was almost invariable as the number of load cycles increased. In addition, the rate of reduction in the slope of the ascending range of the bond–slip curve during cyclic loading decreased as the concrete strength increased, and increased as the load level or CFRP-to-concrete width ratio enhanced. However, these were not affected by variations in bond length if the residual bond length was longer than the effective bond length. A bilinear bond–slip model for CFRP sheets that are externally bonded to concrete under cyclic loading, which considered the effects of the cyclic load level, concrete strength, and CFRP-to-concrete ratio, was developed based on the existing static bond–slip model. The accuracy of this proposed model was verified by a comparison between this proposed model and test results.

A new kind of magnetorheological elastomer with the matrix of the bromobutyl rubber is developed. The magnetoviscoelasticity properties of the magnetorheological elastomer specimens are investigated with respect to different magnetic fields, displacement amplitudes, and frequencies under sinusoidal loadings. The experimental results show that the shear storage modulus and the loss factor of magnetorheological elastomers increase with the increasing magnetic field, excitation frequency, and the weight fraction of particles, but decrease with the increasing strain amplitude, and the magnetorheological elastomers have a high loss factor which can reach to 0.682. Then, a microphysical model based on the assumption of the chi-square distribution of the distance between adjacent ferromagnetic particles is proposed, which can eliminate the error generated by the assumption of the uniform distribution and describe the magnetorheological effect more exactly. Based on the proposed microphysical model, the magnetoviscoelasticity parameter model is modified to describe the dynamic properties of magnetorheological elastomers. It can be concluded from comparison between the numerical and experimental results that the modified magnetoviscoelasticity parameter model can describe the magnetorheological elastomer’s performance well.