With the increase of excitation, the nonlinear energy sink (NES) will cause the controlled system to produce high branch response and lead to sudden failure. Increasing the mass of the NES can prevent the generation of high branch within a certain range, but high-precision instruments such as aerospace have strict requirements for additional mass. A parallel NES (PNES) is proposed to improve the robustness without increasing the mass. The slow flow equations of the system are derived by using complexification-averaging (CX-A) method, and the vibration suppression performance of the PNES is analyzed from the frequency domain. Compared with purely cubic stiffness NES (CNES), it is found that PNES has better performance near the main resonance. And it is not easy to produce high branch response under the same excitation intensity. Finally, the performance of PNES and CNES is compared by numerical method from time domain and energy spectrum. The results show that when PNES is attached, the attenuation time of the controlled system is shorter under impact excitation, much more, the controlled system has a smaller energy amplitude near the main resonance under harmonic excitation.

In this paper, the ballistic damage mechanism and residual bearing capacity of ceramic/backing plate armor were investigated. First, a series of lightweight armors were prepared, consisting of ceramic and ultra-high molecular weight polyethylene fiber-reinforced resin matrix composite (UHMWPE) plates, and were wrapped in a high-strength fabric. Then, the ceramic/UHMWPE armors were hit by one or two bullets, and finally subjected to compression testing. The results showed that the main failure mode of integral ceramic/UHMWPE armors was ceramic brittle fracture. Many zigzag patterns on the compression curve indicated that the specimens had undergone the stages of crack propagation, ceramic fragment reorganization, plastic deformation of UHMWPE backing plate, interlaminar tearing, and overall fracture. The failure of spliced ceramic/UHMWPE armors was mainly due to the dislocation between ceramic sheets; the smooth compression curves indicated that there was no recombination of ceramic fragments and obvious interlayer debonding during the compression. Under the maximum load, each ceramic/UHMWPE armor with ballistic damage did not suddenly break and fail. The structure and thickness of ceramic plates all had an impact on residual strength: under the same structure, the greater the thickness, the greater the residual strength, but the relationship between them was not linear; under the same thickness, the residual strength of the spliced ceramic/UHMWPE armor was higher. The residual strength was also related to the number of shots: after two bullets hit, its value was only one-third of that after one bullet hit.

The dynamics and vibration reduction performance of bistable nonlinear energy sink (BNES) are studied in this paper. First, the negative stiffness of BNES is realized by geometric nonlinearity, and the dynamics model of the system is established. The slow flow equation of the system under 1:1 main resonance is analyzed based on the complexification-averaging (CX-A) method, and the boundary conditions of saddle node bifurcation and Hopf bifurcation are analyzed. Second, the slow invariant manifold (SIM) of the BNES is studied based on multiscale analysis, and the excitation threshold of strongly modulated response (SMR) is analyzed; the analysis results are verified by the numerical method. The results show that the analytical solution is highly consistent with the numerical solution, and the error is less than 1%. Finally, the influence of structural parameters on the vibration reduction performance is analyzed and optimized. The vibration reduction performance of BNES and CNES is compared, and the results show that the BNES has better vibration reduction performance in the full frequency band.

The absorbing effect of traditional dynamic vibration absorber (TDVA) is satisfactory only when the natural frequency is close to the excitation frequency. For this defect, a semi-active vibration absorber is designed with magnetorheological elastomer (MRE) as a stiffness element, that its stiffness can be controlled by magnetic field, to widen the frequency band of the absorber. Theory and experiments show that reducing the damp of the absorber can improve the performance of the absorber at the anti-resonance point, but it will cause the vibration of the controlled system at the new resonance point, which caused by the addition of a DVA, to be more intense. For this problem, the compatibilizer: silane coupling agent KH570, is added to the preparation of MRE to reduce material damping, at the same time, the stiffness control strategy is used to eliminate the resonance of the controlled system caused by the addition of DVA. The final experimental results show that the frequency band of vibration reduction has been broadened effectively and the vibration reduction performance has been improved considerably. Moreover, the resonance has been eliminated very well.

In order to improve the ride comfort of the passenger vehicles, an improved MR damper is designed. The magnetic pole of the damper is sinusoidal, whose effective length can be controlled by the magnetic field. In this way, the flow area of MR fluid can be controlled. The mechanical analysis of the proposed MR damper is carried out and the theoretical analysis results show that the proposed damper can meet the damping force requirements of vehicles under various driving conditions. Half car models are established, simulation analysis is carried out under random excitation, the evaluation parameters such as body acceleration and pitch angle are analyzed comprehensively. The results show that the proposed damper is more conducive to improve the ride comfort of the vehicle.

Nonlinear energy sink (NES) can transfer energy efficiently and unidirectionally through target energy transfer (TET). However, its performance is sensitive to the excitation intensity. When the excitation is lower than the trigger threshold, the performance of NES will be greatly reduced. When the excitation exceeds the trigger threshold, its performance will decrease with the increase of the excitation. At the same time, strong excitation may lead to high branch response of the linear oscillator (LO) under harmonic excitation, which will make the vibration worse. In view of those, NES with negative stiffness is proposed to improve the vibration reduction performance under low disturbance. Meanwhile, 2DOF parallel nonlinear energy sink (PNES) is used to ensure the performance under strong excitation. Two important indexes of bistable NES (BNES), the threshold of the transition from intra-well periodic vibration to inter-well chaotic vibration, and the strongly modulated response (SMR) trigger threshold of BNES, are analyzed in this paper. The parameters of bistable parallel nonlinear energy sink (BPNES) are optimized, and the vibration performance of BPNES and cubic stiffness NES (CNES) is compared. The analysis results show that, the performance of BPNES is better than that of CNES under both impulse and harmonic excitation.