摘要：Traditional passive vibration absorbers are effective only when their natural frequencies are close to those of the excitations. To solve this problem, a vibration absorber with time-delayed feedback control is proposed to suppress vibration of the primary system under excitation with changing frequency. Firstly, the mechanical model of the delay coupled system is established. Then, the displacement transfer ratio of the system is obtained. The stability of the system is analyzed since delay may result in destabilization. Next, in order to design the control parameters, the vibration absorption performances of the proposed time-delayed vibration absorber are studied. The vibration absorption region is shown. The results show that time-delayed feedback control is able to change the response of the system. The effective vibration absorption frequency band is adjustable by tuning the control gain and time delay. The effective frequency band can be widened when choosing appropriate control parameters. The vibration absorption performances can be greatly improved by the time-delayed absorber. In addition, the optimum control parameters are obtained. Finally, the experimental prototype is constructed. Several tests with different control parameters are taken. The experimental and analytical results match quite well.

摘要：陶瓷复合装甲主要由陶瓷层和背板层组成,广泛应用于冲击防护.然而,目前仍缺乏背板层在提高陶瓷复合装甲系统防弹性能方面的定量认识和分析.本文以B4C/UHMWPE双层装甲体系为例,从理论上系统地研究了UHMWPE层在提高陶瓷复合装甲弹道阻力方面的增强机理和适合UHMWPE厚度的选取.开发并验证了预测双层装甲系统剩余速度的理论模型.具体而言,分别从理论上获得与塑性、断裂和摩擦相关的耗散能以及由弹性应变能和动能组成的储存能.理论结果表明,随着UHMWPE层厚度的增加,耗散能单调增加,而储存能则先增加后减少,并会出现一个转折点,这是由于储存能的主导机制由系统固有的最大储存能转变为剩余动能.此外,对于给定的弹道阻力,根据存储能的转变提出了为降低面密度的最佳UHMWPE厚度的参考值,这与陶瓷厚度、冲击速度和弹丸质量有关.本文的研究有助于指导陶瓷复合装甲的轻量化设计.

摘要：The application of hard/soft composite structure in personnel armor for blast mitigation is relatively practical and effective in realistic protection engineering,such as the shell/liner system of the ***,there is still lacking a reliable experi-mental methodology to effectively evaluate the blast mitigation performance when the structure directly contacts the protected target,which limits the development of protection *** this paper,we proposed a new method to evaluate experi-mentally and numerically the blast mitigation performance of hard/soft composite *** blast mitigation mechanism is *** hard/soft structures were composed of ultra-high molecular weight polyethylene(UHMWPE)composite and expanded polyethylene(EPE)*** field explosion experiment,a 7.0 kg trinitrotoluene(TNT)spherical charge is used to generate blast waves at a 3.8 m stand-off distance.A pressure test device is designed to support the tested structure and measure the transmitted blast pressure pulses after passing through the *** results indicate that the hard/soft structures can mitigate the blast pressure pulse into the triangular pressure pulse,through making the pulse profile flatter,reducing the pressure amplitude,and delaying the pulse arrival ***,the combination of 7 mm UHMWPE composite and 20 mm EPE foam can reduce the blast pressure amplitude by 40%.Correspondingly,the finite element simulation is also carried out to understand the blast mitigation *** numerical results indicate that the regulation for blast pressure pulses mainly complete at the hard/soft interface,which is attributed to the reflection of pressure waves at the interface and the deformation of the soft layer compressed by the hard layer possessing kinetic ***,based on these analyses,the corresponding theoretical model is proposed,and it can well explain the experimental and numerical *** study is meaningful for e

摘要：A novel vibration isolation device called the nonlinear energy sink(NES)with NiTiNOL-steel wire ropes(NiTi-ST)is applied to a whole-spacecraft *** NiTi-ST is used to describe the damping of the NES,which is coupled with the modified Bouc-Wen model of *** NES with NiTi-ST vibration reduction principle uses the irreversibility of targeted energy transfer(TET)to concentrate the energy locally on the nonlinear oscillator,and then dissipates it through damping in the NES with *** generalized vibration transmissibility,obtained by the root mean square treatment of the harmonic response of the nonlinear output frequency response functions(NOFRFs),is first used as the evaluation index to analyze the whole-spacecraft system in the *** optimization analysis of the impact of system responses is performed using different parameters of NES with NiTi-ST based on the transmissibility of ***,the effects of vibration suppression by varying the parameters of NiTi-ST are analyzed from the perspective of energy *** results indicate that NES with NiTi-ST can reduce excessive vibration of the whole-spacecraft system,without changing its natural ***,the NES with NiTi-ST can be directly used in practical engineering applications.

摘要：The spinodal decomposition method emerges as a promising methodology,showcasing its potential in exploring the design space for metamaterial ***,spinodal structures design is still largely limited to regular structures,due to their relatively easy parameterization and *** predicting the mechanical properties of 3D spinodal membrane structure remains a challenge,given that the features of the membrane necessitate adaptive mesh through the modelling *** paper proposes an integrated approach for morphological design with customized mechanical properties,incorporating the spinodal decomposition method and adaptive coarse-grained modeling,which can produce various morphologies such as lamellar,columnar,and cubic ***-periodic parameterβand orientational parameterΘ(θ_(1),θ_(2),θ_(3))are identified to achieve the optimal goal of anisotropic mechanical *** analysis is conducted to reveal the correlation between the customized spinodal structure and mechanical *** work provides an integrated approach for morphological variation and tuning mechanical properties,paving the way for the design and development of customized functional materials similar to 3D spinodal membrane structures.

摘要：In this study,a high impact resistant multi-layered composite consisting of continuous carbon fibre/nylon(CCF)and short carbon fibre/nylon(SCF)layers is developed via 3D printing *** effect of CCF/SCF layers configuration on the impact resistance is investigated by low-velocity impact test,and the impact failure mechanism of the 3D printed composites is explored by microscopic observations and finite element(FE)simulation *** results show that the 3D printed multi-layered composite with SCF layers distributed in the middle(HFA)exhibits higher impact resistant performance than the specimens with alternating SCF/CCF layers(HFB)and CCF layers distributed in the middle(HFC).The effect of CCF/SCF layers proportion on the impact performance is also studied by FE simulation,and the results show that the specimen with a CCF/SCF proportion of 7.0 exhibits the highest impact strength.

摘要：Inspired that the neck structure can stabilize the head from body movements and external dynamic vibration by the role of intervertebral disc and surrounding muscles,a novel multi-layer structure with nonlinear elastic components is proposed in this *** proposed structure is expected for loading the weight of the end effector and isolating bending vibration with lowfrequency in the range of 0.1 Hz to 1 ***,considering the loading,the potential energy,restoring force,and structural configuration in axial direction are ***,the dynamical restoring force and stiffness for bending are modelled for different structural parameters and configurations after the axial *** to the functions of the proposed structure required in applications including loading capacity and bending vibration isolation effectiveness,design criteria are carried *** to the realization of high-order quasi-zero stiffness property,the effective isolation band for bending vibration can be extended from about 0.08 *** addition,based on the proposed design criteria,the constructed multi-layer structure displays remarkable dynamical stabilization effectiveness in ultralow frequency *** proposed structure not only provides the biological explanations for car sickness,nausea,and airsickness of humans,but also solves the bottleneck techniques in bioinspired nonlinear isolation structural design for transverse dynamical stabilization,which has remarkable potential applications in the fields of mechanical arm,sensors in satellite etc.

摘要：本文分别通过双悬臂梁(DCB)实验与数值模拟,研究了不同短纤维插层(包括短纤维种类、短纤维长度与插层面密度)对亚麻纤维增强复合材料I型层间断裂韧性的影响规律.DCB试验结果表明,当插层为5mm长度、25g/m^(2)面密度的短碳纤维插层时,复合材料1型层间断裂韧性达到2.322kJ/m^(2),取得最大提升幅度80.7%,短纤维桥联与亚麻连续纤维多层级破坏为其主要增韧机理。在此基础上,采用五参数控制的三线性内聚力单元,建立了数值仿真模型。实验与数值模拟结果的对比分析揭示了短纤维插层属性与内聚力模型参数之间的定量关系,可为植物纤维增强复合材料短纤维插层增韧设计提供参考依据.

摘要：Variable stiffness composite laminates(VSCLs)are promising in aerospace engineering due to their designable material properties through changing fiber angles and stacking *** to control the thermal postbuckling and nonlinear panel flutter motions of VSCLs,a full-order numerical model is developed based on the linear quadratic regulator(LQR)algorithm in control theory,the classical laminate plate theory(CLPT)considering von Kármán geometrical nonlinearity,and the first-order Piston *** critical buckling temperature and the critical aerodynamic pressure of VSCLs are parametrically *** location and shape of piezoelectric actuators for optimal control of the dynamic responses of VSCLs are determined through comparing the norms of feedback control gain(NFCG).Numerical simulations show that the temperature field has a great effect on aeroelastic tailoring of VSCLs;the curvilinear fiber path of VSCLs can significantly affect the optimal location and shape of piezoelectric actuator for flutter suppression;the unstable panel flutter and the thermal postbuckling deflection can be suppressed effectively through optimal design of piezoelectric patches.

摘要：通过分子动力学模拟研究了纳米多晶316L奥氏体不锈钢在不同峰值应力下的高温蠕变变形行为和蠕变机制.数值模拟结果表明纳米多晶316L奥氏体不锈钢的高温蠕变变形是由位错、晶粒内部和晶界扩散以及晶界滑移之间的交互作用引起.在初始蠕变和稳态蠕变阶段,纳米多晶316L奥氏体不锈钢高温蠕变的主导性机制是晶粒内部和晶界的扩散以及晶界的滑移.在加速蠕变阶段,一些晶界被摧毁后,位错滑移成为纳米多晶316L奥氏体不锈钢的主要蠕变机制.这项工作旨在揭示纳米多晶316L奥氏体不锈钢的高温蠕变机理,为增强型抗蠕变316L奥氏体不锈钢的设计和制造提供指导.