Research on damage of 3D random aggregate concrete model under ultrasonic dynamic loading

Lixiao Wang,Qidong Chen,Xin Liu,Bin Zhang,Yichen Shen 사단법인 한국계산역학회 2020 Computers and Concrete, An International Journal Vol.26 No.1

Concrete are the most widely used manmade materials for infrastructure construction across the world. These constructions gradually aged and damaged due to long-term use. However, there does not exist an efficient concrete recycling method with low energy consumption. In this study, concrete was regarded as a heterogeneous material composed of coarse aggregate and cement mortar. And the failure mode of concrete under ultrasonic dynamic loading was investigated by finite element (FE) analysis. Simultaneously, a 3D random aggregate concrete model was programmed by APDL and imported into ABAQUS software, and the damage plastic constitutive model was applied to each phase to study the damage law of concrete under dynamic loading. Meanwhile, the dynamic damage process of concrete was numerically simulated, which observed ultrasonic propagating and the concrete crushing behavior. Finally, the FE simulation considering the influence of different aggregate volume and aggregate size was carried out to illustrate the damage level of concrete.

Improved Four-channel PBTDPA Control Strategy Using Force Feedback Bilateral Teleoperation System

Xin Gong,Lixiao Wang,Yuanyuan Mou,Haili Wang,Xiaoqian Wei,Wenfeng Zheng,Lirong Yin 제어·로봇·시스템학회 2022 International Journal of Control, Automation, and Vol.20 No.3

Bilateral teleoperation robots with force feedback enable humans to accomplish these tasks without exposing them to these hazardous environments. Its stability and transparency describe the performance of bilateral teleoperation systems with force feedback. Bilateral teleoperation with force feedback enables humans to combine tactics with optesthesia. However, the force feedback may lead to bilateral teleoperation instability if the communication channels’ time delay exists. The instability of bilateral teleoperation with force feedback, which is brought in by the time delay, has become one of the complicated problems researchers need to solve. Transparency is one of the leading design objectives of the teleoperation system. There are two evaluation criteria for transparency: the accuracy of the position followed by the master mechanical arm and the accuracy of the feedback received by the slave arm from the master arm. The main content of this paper is as follows: 1) This paper researches and summarizes the control structures and control algorithms of several well-developed force-feedback bilateral teleoperation systems and decides to improve the PBTDPA algorithm, which aligns with practical application requirements. 2) The fourchannel structure makes the transparency of force-feedback bilateral teleoperation systems perfect in theory. This paper uses the four-channel structure combined with the PBTDPA algorithm to improve the transparency of the approach. 3) Moreover, the delay predictor is used to improve the four-channel power-based time domain passivity approach (PBTDPA) control strategy. The delay differential predictor is added to the communication channel. The delay change rate differential predictor can estimate the communication channel’s delay change rate instead of the maximum delay change rate to improve transparency. The simulation experiment of the improved control strategy was carried out. The results show the excellent performance of our design.

Fault diagnosis of rolling bearing under limited samples using joint learning network based on local-global feature perception

Bin Liu,Changfeng Yan,Zonggang Wang,Yaofeng Liu,Lixiao Wu 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.7

Deep learning is widely used in the field of rolling bearing fault diagnosis because of its excellent advantages in data analysis. However, in practical industrial scenarios, the capability of intelligent fault diagnosis (IFD) method is still affected by two problems: (1) The signal samples provided for network learning are limited; (2) Fully extracting feature information from the original data is difficult. To address the above issues, a novel fault diagnosis method using joint learning network (JLNet) based on local-global feature perception is proposed. The method enhances the learning mechanism of fault signal through the local information dynamic perception subnetwork, which dynamically distinguishes between local impulse segment and normal signal segment. Then, a global channel attention mechanism (CAM) is used to guide the assignment of weights, which helps bidirectional gated recurrent unit (BiGRU) to learn advanced discriminative features. The feature information of the original signal is thoroughly mined through local-global comprehensive perception, thus realizing efficient diagnosis. In addition, the variation of the characteristics of each layer is analyzed by visualization, which improves the interpretability of the network. Finally, experiments are conducted using two different datasets, and the results show that JLNet has a better diagnostic effects and robustness.

Characteristics of vibration response of ball bearing with local defect considering skidding

Yu Tian,Changfeng Yan,Yaofeng Liu,Wei Luo,Jianxiong Kang,Zonggang Wang,Lixiao Wu 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.11

The occurrence and aggravation of local defects in ball bearings are closely linked to the skidding behavior of the ball. Previous studies have given less attention to investigating the impact of localized defects on the problem of bearing skidding. To investigate the dynamic response of defective bearings due to skidding, a dynamic model of the ball bearing is developed that considers various factors, including self-rotation, revolution, and radial motion of the ball, as well as the contact forces and friction forces of ball/cage and ball/race, time-varying displacement excitation, and elastohydrodynamic lubrication (EHL). Experimental signals collected from a machinery fault simulator test rig are used to validate the accuracy of the proposed model. The impact of race defects on the vibration characteristics of the bearing is analyzed, and the patterns of variation in contact and friction forces within one cycle of inner race rotation are described. The results indicate that the presence of defects intensifies the force fluctuation of the ball and causes it to deviate from its normal rolling condition. By comparing the skidding characteristics of a healthy bearing with a defective one under slippage, local defects will increase the skidding ratio of bearings. The proposed model can investigate the impact of race defects on the vibration response of ball bearings under the skidding condition.

Convenient and Robust Route to Photoswitchable Hierarchical Liquid Crystal Polymer Stripes via Flow-Enabled Self-Assembly

Li, Xiao,Li, Bo,He, Ming,Wang, Wei,Wang, Tianjie,Wang, Aurelia,Yu, Jiwoo,Wang, Zhonglin,Hong, Suck Won,Byun, Myunghwan,Lin, Shaoliang,Yu, Haifeng,Lin, Zhiqun American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.5

<P>Hierarchically arranged stripes of photoswitchable liquid crystal polymers (LCPs) containing azobenzene moieties were conveniently crafted via a flow-enabled self-assembly (FESA). Interestingly, by subjecting a drop of LCP solution to dry in a restricted geometry comprising two nearly parallel plates with a stationary upper plate and a movable lower plate that programmably traveled in a 'stop -and-move' manner during the FESA process, photoswitchable LCP stripes were yielded, displaying two modes of deposition, namely, periodic primary stripes of large dimensions and regularly spaced secondary stripes of small dimensions situated between adjacent, primary stripes (i.e., forming hierarchical LCP stripes). Notably, these hierarchical azobenzene moieties-containing stripes demonstrated sequential photoinduced reversible phase transition (i.e., photoswitching) due to the thickness difference between primary and secondary stripes. A UV light-induced expansion effect. was observed on the LCP stripes. Clearly, such rapid creation of hierarchical stripes by FESA represents a robust means of organizing polymers, nanoparticles, colloids, DNA, etc. into complex yet ordered patterns over a large area in a simple and controllable manner for potential use in surface relief grating, photoactuators, photoswitchable devices, antifake labels, etc.</P>