A computational methodology to model and analyze planar rigid mechanical system with stick–slip friction in revolute clearance joint is presented. In this work, the LuGre friction model, which captures the Stribeck effect and spring-like characteristics for stiction, is employed to estimate the stick–slip friction in revolute clearance joint. A hybrid contact force model, combining Lankarani–Nikravesh model, and improved elastic foundation model, is used to establish contact model. The generalized-α method, which can dissipate the spurious high-frequency responses caused by the strongly nonlinear contact force and friction in numerical simulation, is adopted to solve the equations of motion and make the result closer to the physics of the problem. A slider-crank mechanism with revolute clearance joint based on LuGre friction model and modified coulomb friction model are simulated, respectively, and utilized to discuss the influences of the Stribeck effect and stiction on dynamic behavior of the mechanism. Different test scenarios are considered to investigate the effects of the clearance size and friction coefficient on the dynamic response of the mechanism. The results show that the mechanism based on LuGre friction model has better energy dissipation characteristics, while there are stiction phenomena of the contacting surfaces in many cases. When the relative velocity is zero or close to zero, the contact force of mechanism based on the LuGre friction model is significantly lower than that based on the modified coulomb friction model. Clearance size and friction coefficient obviously affect dynamic behavior of the mechanism.

Nonlinear phononic crystals are receiving increasingly greater attention in the field of sound absorption and vibration reduction. In this paper, we use the perturbation method to investigate elastic wave propagation in one-dimensional discrete local resonance nonlinear phononic crystals. The nonlinear force on the inner resonator is expressed in the form of a linear part plus a cubic nonlinear fluctuation. By combining Bloch wave theory and the perturbation method, the nonlinear dispersion relation is obtained by a first-order approximate analytical solution. The results show that the band’s cut-off frequency is not only affected by the degree of nonlinearity but is closely related to the wave amplitude. In addition, the finite element method is used for comparison and verification. Finally, an application example of a wave filter is provided based on the nonlinear characteristics.

An experiment of face milling of Invar36 was conducted by using coated carbide insert, the microhardness was tested and the metallographic structure was observed to figure out the principles of work-hardening. The results showed that the depth of work-hardening ranges from 80μm to 160μm among the parameters selected in the experiments. The degree and the depth of work-hardening were significantly affected by the axial depth of cut and feed per tooth. The degree and the depth of work-hardening showed a tendency to increase with the increase of the axial depth of cut and feed per tooth. Compared with the axial depth of cut and feed per tooth, cutting speed had less influence on the degree and depth of work-hardening. The degree and depth of work- hardening decreased slowly with the increase of cutting speed. Metallographic observation showed that work-hardening layer consisted of the thermal force influenced layer and the force influenced layer, while the amorphous metallographic structure was observed in the thermal force influenced layer, and lattice distortion was observed in the force influenced layer.

A miniaturized circularly polarized microstrip antenna with a short circuit strip for Radio-Frequency identification (RFID) reader is proposed in this paper. The size of the miniaturized antenna is realized by the capacitive load provided by the connection between short-circuit strip and ground. The overall size of the antenna is 80mm×80mm×1.6mm(0.24λ×0.24λ×0.0048λ). Simulated results prove that the impedance bandwidth of this antenna (where return loss below -10 dB) is 19 MHZ (894-913 MHZ), and its axial ratio below -3 dB is 11 MHZ (897-908 MHZ), and the peak gain is -5.6 dBi across the bandwidth.