A generalized self-consistent model for interfacial debonding behavior of fiber reinforced rubber matrix sealing composites

This paper presents an experimental and numerical study of short-fiber-reinforced rubber matrix sealing composites(SFRC). The transverse tensile stress-strain curves of SFRC are obtained by experiments. Based on the generalized self-consistent method, a representative volume element(RVE) model is established, and the cohesive zone model is employed to investigate the interfacial failure behavior. The effect of interphase properties on the interfacial debonding behavior of SFRC is numerically investigated. The results indicate that an interphase thickness of 0.3 μm and an interphase elastic modulus of about 502 MPa are optimal to restrain the initiation of the interfacial debonding. The interfacial debonding of SFRC mainly occurs between the matrix/interphase interface,which agrees well with results by scanning electron microscope(SEM).     

Unified approach for vibration analyses of annular sector and annular plates with general boundary conditions

This paper presents a unified approach for predicting the free and forced (steady-state and transient) vibration analyses of annular sector and annular plates with various combinations of classical and non-classical boundary supports. In spite of the types of the boundary restraints and the shapes of the plates, the admissible displacement function is described as a modified trigonometric series expansion, and four sine terms are introduced to overcome all the relevant discontinuities or jumps of elastic boundary conditions. Mathematically, the unification of various boundary value problems for annular sector and annular plates is physically realized by setting a set of coupling springs to ensure appropriate continuity conditions along the radial edges of concern. Numerous examples are presented for the free vibration analyses of annular sector and annular plates with different boundary restraints. With regard to the forced vibration analysis, annular sector and annular plates with different external excitations are examined. The accuracy, convergence and numerical robustness of the current approach are extensively demonstrated and verified through numerical examples which involve plates with various shapes and boundary conditions.     

Investigation of springback behavior and process control for stamping of ring-shaped workpiece

Due to the elastic deformation of metal stamping, springback is a serious problem to cause shape deviation and thus reduce precision. The springback behavior of ring-shaped workpiece is investigated in this paper and an auxiliary boss device is proposed to control the springback deformation. A finite element model is developed.The characteristic parameters including boss height, boss angle and boss gap are discussed systematically. It can be concluded that the gap has a positive linear correlation with springback percentage, and the boss angle has an optimal interval of 30°—60° to reduce springback. When the boss height increases, the springback decreases,but the effect weakens when the boss height is larger than 1.0 mm. Then, a response surface analysis is conducted with Design Expert 8.0.5 software and an optimal parameter process window(i.e., boss height from 2.1 to 3.0 mm,boss angle from 53° to 60° and the gap from 0 to 1.2 mm) is obtained. Finally, a set of molds are fabricated and the stamping experiments are conducted. The springback behavior is well controlled. The springback percentage can be decreased from 33% to 6% by using the auxiliary boss device of ring-shaped workpiece.     

Effect of carbon nanotube concentration on cooling behaviors of oil-based nanofluids during the immersion quenching

Oil-based nanofluids including 0.75%—1.75%(mass fraction) carbon nanotubes(CNTs) without any surfactants have been synthesized by a two-step process. The probes machined from 45~# steel with 22 mm diameter and 50 mm length are quenched in the as-synthesized CNT nanofluids for testing the cooling behaviors of the nanofluids. The laser diffraction particle size analyzer, scanning electronic microscope(SEM), X-ray diffractometer and transmission electron microscope(TEM) are used to characterize the quality and distribution of CNTs in the nanofluids. The wettability and viscosity of 30~# oil and oil-based CNT nanofluids are measured by a goniometer at 15℃ and a rotational type viscometer at 40℃, respectively. The results show that the cooling efficiency of the oil-based CNT nanofluids is better than that of 30~# oil. Moreover, the cooling rate of the naonofluids increases with the further increase of the CNT concentration. When the mass fraction of CNTs increases to 1.75%, the cooling rate of the naonofluids reaches a maximum at 760℃ and it is increased by 77.8% as compared to that of base oil. The improved cooling rate of oil by CNTs is mainly due to the uniform distribution and excellent thermal conductivity of CNTs.     

Absolute quantum efficiency calibration of analog detectors with twin photon current

Correlated photon is exploited as a tool for absolute quantum efficiency calibration of photon detectors working in the photon-counting regime. We extend the method from photon-counting regime to the absolute calibration of analog regime photon detectors. A revised calibration module is proposed based on balance detection and fluctuation restrictions conditions applied to analog photon detectors. An absolute calibration experimental system is established. This method shows a relative standard uncertainty of 2.1% and a relative deviation of 1% compared with those of the typical photomultiplier quantum efficiency.     

Model testing for ship hydroelasticity: A review and future trends

Conducting model experiments is an effective and reliable way in the investigation of ship hydrodynamic and hydroelastic behaviors. A survey of model testing techniques for ship hydroelasticity and its prospect are presented in this paper. The research highlights with respect to ship hydroelasticity and key points in model testing are summarized at first. Then testing techniques including laboratory tank test and full-scale sea trial are reviewed, and both their advantages and disadvantages are analyzed comprehensively. Based on the conventional testing approaches, a state-of-the-art testing approach which includes performing tests using large-scale model at sea is proposed. Furthermore, recommendations towards the further development of ship hydroelasticity tests are forecasted and discussed.     

Optimal allocation of fleet’s spare parts for system reliability

Allocation of fleet’s spare parts is rarely studied due to its complexity. However, this task is extremely important because the warship’s service level highly relies on the maintenance logistics’ level. In this study, the readiness ratio is proposed as a critical index in measuring the system’s reliability. A well-established mathematical model adopting the optimization method of spare part allocation is also introduced. The objective is to minimize the number of each spare part while satisfying the fleet’s system reliability. The fault tree analysis (FTA) is applied to analyze the system’s failure logic and stratify the units on ship. As a result, the strategy of spare part sharing can be introduced in detail. The solution algorithm is developed, and the simulation experiments to obtain the key parameters are conducted. The proposed model and algorithm are applied to an actual fleet of two warships, and results show that the method above is feasible and can be directly applied into practice.     

Pedestrian crosswalk overflow violation in China: Characteristics and countermeasure

The phenomenon that pedestrians do not walk in the crosswalk during pedestrian green is defined as overflow violation, which is illegal but common. Broadly varying crossing positions at far-side cross-section may result in widely distributed conflict points with left-turning and right-turning vehicles, which may cause the occurrence of severe conflicts. This paper proposes a model to estimate the overflow pedestrians’ crossing positions at the far-side cross-section of signalized crosswalk, which enables us to better understand pedestrian overflow violation behavior and finally facilitate their safety. After analysis, the intersection geometry and destination are determined as the critical factors causing pedestrians to overflow. And then, Weibull distribution is employed to describe the stochastic characteristics of overflow pedestrians’ crossing position distribution at the far-side cross-section. A crossing position distribution model which takes the crosswalk length, width and distance between crosswalk and destination into account is developed. The established model is validated by comparing the observed pedestrian crossing positions with the estimated crossing positions. The validation results suggest that the established model is capable of being adopted to estimate the overflow pedestrians’ crossing positions at far-side cross-section. Based on the model, countermeasure for overflow violation can be put forward to prevent pedestrians from walking outside the crosswalk.     

On-line adaptive repetitive controller for power factor correction systems

When the fundamental frequency is shifting, it is hard for traditional repetitive controller to work at the resonant frequencies. In this paper, a novel adaptive repetitive controller for power factor correction systems is proposed to suppress the current harmonics. Through the controller, the shifting sampling times of the repetitive controller in a fundamental period can be obtained. Mathematical analysis, simulations and physical experiments have validated the effectiveness of the adaptive repetitive controller.