The forced vibration of a sandwich beam integrating a shear thickening fluid (STF) core and with conductive skins subjected to a periodic excitation was investigated theoretically in this study. The rheological properties of the STF material including viscosity, plasticity, and elasticity may be changed under the periodic vibration, and hence they were considered. The governing equation of motion was derived based on the complex stiffness method and some key parameters were derived based on the Timoshenko beam theory. Effects of the excitation frequency, the excitation amplitude, the excitation location, and the skin/core thickness ratio on the nature frequency of the sandwich beam were investigated. It was found that the STF core has a significant effect on the dynamic property of the sandwich beam. Based on the findings, integrating the STF core in a sandwich beam can reduce the vibration of the beam.

A new model for the free transverse vibration of axially functionally graded (FG) tapered Euler-Bernoulli beams is developed through the spline finite point method (SFPM) by investigating the effects of the variation of cross-sectional and material properties along the longitudinal directions. In the proposed method, the beam is discretized with a set of uniformly scattered spline nodes along the beam axis instead of meshes, and the displacement field is approximated by the particularly constructed cubic B-spline interpolation functions with good adaptability for various boundary conditions. Unlike traditional discretization and modeling methods, the global structural stiffness and mass matrices for beams of the proposed model are directly generated after spline discretization without needing element meshes, generation, and assembling. The proposed method shows the distinguished features of high modeling efficiency, low computational cost, and convenience for boundary condition treatment. The performance of the proposed method is verified through numerical examples available in the published literature. All results demonstrate that the proposed method can analyze the free vibration of axially FG tapered Euler-Bernoulli beams with various boundary conditions. Moreover, high accuracy and efficiency can be achieved.

Summary In this study, a shear thickening fluid (STF) damper was experimented upon under different loading frequencies and amplitudes to investigate its nonlinear hysteretic behavior and energy dissipation capacity. An STF sample with 20% mass fraction and dispersion medium were prepared by nanoparticle silica (SiO2) and polyethylene glycol (PEG200). By using a parallel‐plate rheometer, steady‐state experiments were carried out to characterize the rheological properties of the sample. The results indicate that the STF sample shows an abrupt increase in viscosity/stress beyond a critical shear rate/strain. The results also show that the STF sample has good reversibility, thixotropy, and stability and can be used as a smart damping material in damper devices. Also, a prototype damper was developed and manufactured. Its nonlinear hysteretic behavior and energy dissipation capacity were experimentally investigated through the responses of damping force–displacement and damping force–velocity. The results show that the STF damper has excellent damping force as the loading condition increases and the controllability can be increased up to 3.21 times. The results also show that the energy dissipation capacity formed by damping force–displacement becomes fuller as the loading condition increases. Moreover, the results show that the graphical shapes of hysteretic loops of damping force–velocity can exhibit various styles as the STF's mechanism changes but the shapes are not stable when the velocity exceeds a certain value.

An experimental study on the effects of loading cycles on the performance of STF dampers (STFDs) are presented. The rheological properties of a STF sample are investigated under both ascending and descending loads. A smart damper is then developed and manufactured by employing the STF sample. Two series of cyclic tests were conducted to investigate the behaviour of the STFD under various sinusoidal loading conditions with a constant amplitude of 20 mm. Eight different loading frequencies (0.01, 0.1, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 Hz) were imposed to research on the effect of frequency. Three different loading frequencies (1, 2 and 3 Hz) were applied to the STFD under a constant amplitude (20 mm) with long-term loading (200 cycles). The energy dissipation and dynamic properties of STFD were investigated by analysing the force-displacement and force-velocity curves. The STF damping force is found to decay exponentially as the loading cycles increase. An equation is proposed for the description of STFD force at different loading cycles and frequencies.

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Summary Inerter dampers (IDs) and other inerter‐based vibration absorbers have elicited growing interest for vibration mitigation of stay cables. This study systematically investigates the vibration mitigation mechanism of tuned IDs (TIDs) for stay cables based on a continuous cable model. A TID consists of an ID connected with a spring stiffness in series (TID‐S) or parallel (TID‐P). On the basis of systematical parametric analyses, the impact of stiffness in series or parallel connections is evaluated, and the interrelations among ID, TID‐S, and TID‐P are elaborated. Subsequently, a detailed tuning procedure is summarized. Two optimal tuning formulas are also obtained to facilitate the rapid design of TID‐S and TID‐P. According to the optimized results, the damping ratios contributed by ID, TID‐S, or TID‐P to a stay cable are essentially determined by the inertance value. When the inertance deviates from the optimal value, the performance of ID drops significantly, but this adverse effect can be mitigated by tuning the stiffness in TID‐S or TID‐P.

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