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42CrMo steel is widely used in ultrahigh-strength structures such as low-speed heavy-duty gears. Mastering the fatigue crack propagation law has important significance for predicting structural fatigue life. Firstly, the fatigue crack propagation experiment is used to obtain the upper and lower thresholds value of type I fatigue crack propagation of 42CrMo steel compact tensile specimen under the alternating load of stress ratio R = 0.1. The Paris formula describing the relationship between the fatigue crack propagation rate and the crack tip stress intensity factor between the upper and lower thresholds value is obtained. Scanning electron microscopy was used to observe the microscopic features of different stages of fatigue fracture. The results show that the twin boundary can provide a place for crack initiation; the defects in the material can promote the initiation and extension of fatigue cracks. The fatigue crack propagation of 42CrMo steel compact tensile specimens was numerically simulated by the finite element method. The relationship between the crack tip stress intensity factor and the crack length was obtained. The analysis results show that the crack tip stress intensity factor calculated by the plane finite element method differs slightly from the experimental results during the stable extension stage. After correction, the correlation coefficient between the numerical simulation correction value and the crack tip stress intensity factor value obtained by the experiment is 0.9926. Finally, the fatigue crack propagation rate corresponding to the crack tip stress intensity factor in the finite element results is calculated by the Paris formula and briefly analyzed. Compared with the experimental results, it shows that the numerical simulation is consistent with it, indicating the accuracy of the numerical simulation method, which can effectively predict the initiation and propagation of fatigue cracks in 42CrMo steel compact tensile specimens.

In this work, the α-MnO2 and α-MnO2/activated carbon composite were prepared by a facile hydrothermal method. Effects of reaction time (1–12 h) and MnO2 loading (10–70%) on structure and electrochemical performances for materials were studied. Samples were analyzed by X-ray diffraction, scanning electron microscope, galvanostatic charge/discharge, cyclic voltammetry and Mott-Schottky testing. A growth model was used to describe the development mechanism of α-MnO2, and MnO2 samples prepared at 6–12 h displayed the actiniaria-shaped structure. The MnO2 electrode at 6 h exhibited the largest specific capacity of 629.2 C/g in K2SO4 electrolyte. After incorporation of carbon, the composite expressed low resistance and large carrier concentration than single MnO2. Due to good conductivity of carbon, the capacity of MnO2/carbon was up to 977.4 C/g (55.3% higher than MnO2). After 3000 cycles at 0.2 A/g, the MnO2/carbon exhibited higher capacity retention of 81.3% than 56.2% for MnO2. It indicated that the α-MnO2/activated carbon showed potential application as electrode material for supercapacitor.

Fuel spray nozzle is an important part of automobile engine. Its performance heavily affects engine performance and engine power. Therefore, the study of fuel spray nozzle detection system and detection method has direct significance for improving engine performance. This paper developes a device to test spray form from fuel spray nozzle. Firstly, an externally-triggered industrial camera is used to collect the spray image of the fuel spray nozzle, combined with OpenCV image processing. Then, the spray form parameters of the fuel spray nozzle, including the spray angle, deflection angle and spray distance, are calculated. Finally, the quality of the spray can be evaluated by the obtained Euclidean distances. Experiments have proved that the system can complete the detection of fuel injectors.

Alertness is the state of attention by high sensory awareness. A lack of alertness is one of the main reasons of serious accidents. Traffic accidents caused by driver’s drowsy driving have a high fatality rate. This paper presents an EEG-based alertness detection system. In order to ensure the convenience and long-term wearing comfort of EEG recordings, the wearable electrode cap will be the principal choice in the future, and the selection of channels will be limited. We first built a 3-D simulated driving platform using Unity3D. Then, we perform an experiment with driving drift task. EEG signals are recorded form frontal and occipital regions. We select data segments using the driving reaction time, classify the state of alertness with a support vector machine (SVM), and select the optimal combination of channels with minimum number of channels. Our results demonstrate that alertness can be classified efficiently with one channel (PO6) at accuracy of 93.52%, with two channels (FP1+PO6) at 95.85% and with three channels (FP1+PO6+PO5 and FP1+PO6+POZ) at 96.11%.

A fuzzy formation control method among a group of distributed robots using only local sensing is proposed. A leading robot moves along a predetermined trajectory, and other robots endeavor to establish and then maintain a given geometric shape by regulating the relative distance and bearing to the leader. The distance to be kept is adjusted by fuzzy logic, which outputs the follower's velocity toward the connecting line of the leader and the follower, and the bearing adjustment is based on fuzzy logic angle controller which outputs the follower's velocity along the moving direction of the leader. The final follower's velocity is acquired by decision-making. The whole formation control system can be achieved without communication. The simulation results show the validity of the proposed approach.

Because the conventional printed circuit board defect detection is slow, a method base on the edge of image is proposed, this method can quickly locate and detect the detects on the circuit board. The algorithm combines gradient direction characteristics of image edge gray, the different characteristics of different defects in standard image and defect image are used to classify the defects, and then identify the type of defects. Experiments show that this method can detect the short circuit, opening, burr, hole and other defects of the circuit board quickly.

In this study, composite [Formula: see text]-MnO2/activated carbon (AC) was prepared by chemical deposition method, and then it was assembled into electrode and electrochemical capacitor. Effects of reaction temperature and MnO2 content were studied. Materials were characterized by X-ray diffraction, scanning electron microscope and electrochemical test. MnO2 prepared at 30[Formula: see text]C was amorphous, and it displayed the high specific capacitance as nearly four times as MnO2 at 80[Formula: see text]C. Due to MnO2 particles which would block carbon pores when its content was too high, the composite containing 30% of MnO2 exhibited the largest specific capacitance of 278.3[Formula: see text]F/g at 0.2[Formula: see text]A/g in K2SO4 electrolyte. The equivalent series resistance and charge transfer resistance of material were only 1.35[Formula: see text][Formula: see text] and 1.41[Formula: see text][Formula: see text], respectively. After 1000 cycles, the capacitance retention was still 91.6%. It indicated that chemical deposition was a facile, low cost and effective method to prepare MnO2/AC with good electrochemical performances.

A kind of interference measurement system with crystal is designed, which is not influenced much by other factors such as vibration for the property of common path. For the distance measurement, the phase of fringes is calculated on the oblique incident holography to avoid effects of fringe curvature, backup and light fluctuation. But the measurement result is affected by the uniformity of the crystal, and another method of adjusting position based on normal incident holography is also discussed. B-splines function is used to calculate zero position in normal incident holography, which is fitted over the patch image around gray extreme points of the stripes obtained by gray projection. Experiment results show that combining the normal and oblique incident holography reduce the repeatability error of the system and improve the measurement precision effectively. DOI: http://dx.doi.org/10.11591/telkomnika.v11i3.2303

With acceleration of the population aging process, the people pay more and more attention on the development of the robot for the elderly. On the basis of technical research and development of service robot positioning technology in recent years, the paper designed the system of the robot for the elderly based on star positioning. The system used ARM9 processor S3C2440 as the core, equipped with IPC and star positioning module and various sensor modules, could complete some assistant works for the old people's living, such as stable walking, environmental monitoring, grasping objects and so on. After tested, the system works well and achieved the design requirements.

In this paper, a new adaptive fuzzy and H∞ control method of robotic manipulators with uncertainties is proposed. The control method combines the fuzzy adaptive control with the H∞ control theory for trajectory tracking of robot manipulators. While establishing the model of the system, the influence of both the modeling errors and the external disturbances can be attenuated to a prescribed level. In addition, it is not necessary for the controller proposed to transform the robotic dynamics into nonlinear systems, and the controller thus obtained does not contain the inverse of matrices and can do without singularities. Based on Lyapunov method, the adaptive learning law is given and H∞ tracking performance is illustrated. The simulation studies on a 2-DOF robot verify the effectiveness of the proposed method.