The weak stiffness and strength of materials with negative Poisson’s ratio limits their application. In this paper, three types of novel lattices with negative Poisson’s ratio are proposed to improve not only stiffness and strength but also energy absorption capacity by embedding different ribs into a classic re-entrant structure. Unit cell analyses show these novel lattices have significantly increased Young’s modulus along the loading direction, and Type C can maintain sufficient negative Poisson’s ratio performance compared with the base lattice. In addition, the novel lattices exhibit higher yield stress, plateau stress and densification strain extracted from quasi-static compressive simulation. The lattices are prototyped by laser-based additive manufacturing and tested in quasi-static experiments, which show the experimental data match the numerical results within an error of margin. The work signifies the prospect of lattices with negative Poisson’s ratio in enhancing engineering-applicable structures, and indicates the potential of structural topology optimization in more sophisticated designs.

In recent years, the research of nonlinear energy sink on low-frequency noise control has become a hotspot. By adding a nonlinear energy sink into one primary system, it is possible to obtain the significant target energy transfer characteristics. The target energy transfer can be defined for which the vibration energy of the primary structure is irreversibly transferred to the nonlinear energy sink, quickly concentrated in the nonlinear energy sink and dissipated by the nonlinear energy sink damping. This method has significant advantages to control the broadband low-frequency noise inside the transportations (such as cars, trains, airplanes, etc.). Compared with traditional noise reduction methods such as adding the damping and acoustical materials, the nonlinear energy sink has a simple and lightweight structure. The paper reviews the nonlinear characteristics of the nonlinear energy sink, the main theoretical research methods and the applications of vibration and noise control, and discusses the application of the nonlinear energy sink for the control of low-frequency noise inside the three-dimensional acoustic cavities, which provides the reference and guidance for the low-frequency noise control inside the acoustic cavities of the mean of transportation.

As a new approach to passive sound control in low-frequency domain, the targeted energy transfer (TET) phenomenon has been investigated inside a three-dimensional (3D) acoustic cavity by considering a two degrees-of-freedom (DOF) system with an acoustic mode and a membrane nonlinear energy sink (NES). The beginning of TET phenomenon of the 2DOF system and the desired working zone for the membrane NES have been defined. In order to enhance the robustness and the effective TET range in acoustic cavities, a 3DOF system with two membranes and one acoustic mode is studied in this paper. We consider two different membranes and two almost identical membranes to analyze the TET phenomenon, respectively. The desired working zone which was obtained by the 2DOF system is applied to analyze the 3DOF system. We observe that two membranes can enlarge the desired working zone.

As a new approach to passive noise control in low frequency domain, the targeted energy transfer (TET) technique has been applied to the 3D fields of acoustics. The nonlinear membrane absorber based on the TET can reduce the low frequency noise inside the 3D acoustic cavity. The TET phenomenon inside the 3D acoustic cavity has firstly investigated by a two degrees-of-freedom (DOF) system, which is comprised by an acoustic mode and a nonlinear membrane without the pre-stress. In order to control the low frequency broadband noise inside 3D acoustic cavity and consider the influence of the pre-stress for the TET, a general model of the system with several acoustic modes of 3D acoustic cavity and one nonlinear membrane is built and studied in this paper. By using the harmonic balance method and the numerical method, the nonlinear normal modes and the forced responses are analyzed. Meanwhile, the influence of the pre-stress of the nonlinear membrane for the TET is investigated. The desired working zones of the nonlinear membrane absorber for the broadband noise are investigated. It can be helpful to design the nonlinear membrane according the dimension of 3D acoustic cavity to control the low frequency broadband noise.