Bolted joints are widely used in the auto industry, energy field and Construction, and so on. Due to the wide use of the bolted joints, the degradation of bolts has significant effect on the performance of a whole machine. Under transversal vibration, the self-loosening of bolted joints, which is the biggest form of failure ranked only second to fatigue failure [1], will happen, due to the cyclic shear load. This paper is to study the mechanism of bolted joints’ self-loosening. Aiming at analyzing the self-loosening mechanism of bolted joints under vibration, a three dimensional FEA model of bolted joints, which had taken thread into consideration, was built with the application of APDL, and the preload was applied on the bolted joints by dropping temperature, then FEA transient analysis of the bolted joints under transverse cyclic excitation was conducted. Effect of transverse cyclic excitation’s amplitude, initial preload, thread and bearing friction coefficients, the joints’ surface friction coefficient, the thread pitch and the hole clearance on self-loosening was investigated. The results show that the complete thread slip occurs prior to the complete bearing surface slip under transverse vibration; the smaller amplitude, the smaller thread pitch and the smaller hole clearance is, and the greater initial preload, thread and bearing friction coefficients are, the more difficult self-loosening is to happen; the joints’ surface friction coefficient has little relationship with self-loosening, however, the larger joints’ surface friction coefficient makes the needed shearing force, which induces the transversal vibration, larger. These are of great significance for understanding of fasteners’ self-loosening and designing of bolted joints’ anti-loosening.

In this study, a rail dynamic vibration absorber with negative stiffness is developed to reduce the vibration transmission and radiated noise from the rail components of a ballasted track. The compound models of the ballasted track system with and without the proposed dynamic vibration absorber and a traditional dynamic vibration absorber are constructed. A parametric study is performed to evaluate the effects of the design parameters of the proposed dynamic vibration absorber on the vibration and noise reduction of the track system in terms of the point receptance, the decay rate of rail vibration along the track, and the vibration energy level of the rail. Compared with the traditional dynamic vibration absorber, the proposed counterpart can work effectively over a broad frequency range around resonance. The efficiency of the dynamic vibration absorber can be improved by adjusting the design values of the active mass and damping coefficient. A comparison with the traditional dynamic vibration absorber shows that the vibration and noise suppression capability of the proposed one can be enhanced by increasing the value of the stiffness ratio. However, different from the traditional dynamic vibration absorber, the design parameters of the proposed one can also affect the decay rate and vibration energy at low-frequency regions. A discrete track with the proposed dynamic vibration absorber, which is arranged in continuous or discrete distribution along the rail, is illustrated to study the influences of the rail components on the decay rate and vibration energy level of rails. These calculated results could provide a theoretical basis for the design of the proposed dynamic vibration absorber in controlling the vibration and radiated noise from rails.

A compound track-absorber model with multiple wheels on the rail is employed to study the effects of a rail absorber on the normal wheel–rail contact forces in the frequency domain. Two different absorber models, which are the piecewise continuous absorber and the discrete absorber installed in the middle of the sleeper span, are presented. It can be seen from the calculation results that there are more peaks occurring in the frequency range of 500–1200 Hz due to the wave reflections between the wheels than that of a single wheel–rail interaction. However, these peaks are all suppressed due to the effects of the rail absorber, and there are new peaks appearing at other frequencies while the amplitude of these peaks is relatively small. The peaks in contact force at low frequencies are higher, whereas the peak at pinned-pinned resonance is suppressed.

Based on the finite element method, numerical simulation models of a standard disc spring were built and forcedisplacement curves were obtained under different displacement loads. Then the static loading experiments were conducted by the tensile experimenting machine. The computation model was validated by comparison of the model predictions with the experimental results. The results of the numerical simulation model were in good agreement with the experimental data. Based on the finite element method, models of grooved disc springs were established. The force-displacement and stiffness-displacement curves for the disc springs with different groove configurations were obtained. And the results were verified by the experiment data. The effects of the distribution and number of the grooves on the load variation, the stiffness change, the negative stiffness region in the force-displacement curve were analyzed. The research has good reference value for the design of disc spring with negative stiffness and the application of negative stiffness part in reducing vibration and vibration isolation device.

The dynamic performance of an integrated quasi-zero stiffness (IQZS) isolator which is constructed by a single elastic structure is investigated in this study. This prototype exhibits the characteristics of the best simplicity, high reliability and without friction by using the minimum number of elements. For completeness, the static properties of the IQZS isolator are provided at first. And then, the dynamic behavior is analyzed and the frequency response under harmonic excitation is derived by using an equivalent mechanical model. Frequency response curves (FRCs) are obtained by using the harmonic balance method (HBM) under force excitation condition. Moreover, the dynamic performance of the nonlinear isolator supporting a lumped mass is investigated by using force transmissibility, which are derived by modelling and compared with an equivalent linear system with the same design parameter values. The isolation performance of the nonlinear isolator outperforms the linear counterpart for providing a larger isolation range. The effects of system parameters on the transmissibility are also examined. At last, the comparison between the analytical and experimental results under force excitation shows that the analytical model of the IQZS isolator is accuracy in terms of force transmissibility. The calculation results discussed may provide a theoretical basis for designing this class of IQZS isolator in engineering practice.