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In modern tunnel construction, TBM (Tunnel Boring Machine) plays a very important role. In response to the needs of tunnel wall reinforcement and TBM automated construction for tunnel construction, a shotcrete mechanism mounted on the TBM is designed. In order to evaluate the kinematic performance of the mechanism, this paper studies the forward and inverse kinematics and spatial architecture of the TBM shotcrete robot. Firstly, based on the D–H parameter method, the number of joints and links is determined and structural analysis is performed to obtain the robot's forward kinematics equation, achieving the mapping between joint space and pose space. Then, by determining the joint variables, the mapping of the end tool in Cartesian space is achieved. Finally, based on the Monte Carlo random sampling method, the workspace of the robot is constructed, and its reachability and flexibility within the robot workspace are evaluated. The performance of the device is verified by building a prototype, which meets the requirements well. Through the research in this paper, it can provide theoretical basis and guidance for the design and control of the shotcrete robot. [ABSTRACT FROM AUTHOR]

Timely and effective feature extraction is the key for fault diagnosis of rolling element bearing (REB). However, fault feature extraction will become very difficult in the early weak fault stage of REB due to the interference of strong background noise. To solve the above difficulty, a two-stage feature extraction method for early weak fault of REB is proposed, which mainly combines feature mode decomposition (FMD) with a blind deconvolution (BD) method. Firstly, based on the impulsiveness and cyclostationary characteristics of the vibration signal of faulty REB, FMD is used to decompose the complex original vibration signal into several modes containing single component. Subsequently, the sparse index (SI) is calculated for each mode, and the mode containing sensitive fault feature is selected for further analysis. Subsequently, apply the deconvolution method on the selected mode for further enhancing the impulsive characteristic. At last, traditional envelope spectrum (ES) analysis is applied on the filtered signal, and satisfactory fault features are extracted. Effectiveness and advantages of the proposed method are verified through experimental and engineering signals of REBs. [ABSTRACT FROM AUTHOR]

To solve the difficulty in weak fault detection of rolling element bearing (REB), a fusion method by combining robust empirical mode decomposition (REMD) with adaptive maximum second-order cyclostationarity blind deconvolution (AMCBD) is proposed in the paper. The advantage of REMD in determining the optimal iteration number of a sifting process and the advantage of AMCBD in setting the key parameter (targeted cyclic frequency or fault period) appropriately are utilized comprehensively by the proposed method. Firstly, in view of the multi-component and modulation characteristic of the vibration signal of REB, REMD is used to extract the useful component from the multi-component and modulated signal. Then, AMCBD is used to process the selected useful component to further highlight the cyclostationary and impulse characteristics of the vibration signal of faulty REB. Compared with traditional maximum second-order cyclostationarity blind deconvolution (MCBD) method, AMCBD has the advantage of no needing prior knowledge of the faulty REB such as the targeted cyclic frequency or fault period. At last, envelope spectral (ES) is applied on the signal handled by AMCBD and satisfactory fault extraction feature result is obtained. Effectiveness of the proposed method is verified through simulated, experimental, and engineering signals, and its superiority is also presented through comparison study. [ABSTRACT FROM AUTHOR]

In this work, alumina ceramic was bonded to itself with composite foils (Ti/Cu/Ni/Cu/Ti). The thermodynamics analysis indicates that Ti-Cu liquid firstly formed and reacted with alumina to produce Ti 3 Cu 3 O reaction layer. Meanwhile, the consumption of element Ti within the Ti-Cu liquid by Ni interlayer optimized the microstructure of the joint. By thickening Ni interlayer from 0 µm to 100 µm at 1020 ℃, the joints' strength could be significantly improved by 130.6%. While the joints' strength decreased with the decomposition of reaction layer at the brazing temperature higher than 1020 ℃. The FE simulations show that the high-level stress concentration within the reaction layer could be ameliorated by Ni interlayer effectively, which was in accordance with the corresponding fracture characteristics. Although the joint's strength could be improved to 203.9 MPa by using 300 µm Ni interlayer, its improvement rate was limited with Ni interlayer constantly thickening. [ABSTRACT FROM AUTHOR]

In this paper, AlN ceramic was directly joined to copper without active brazing filler metal. By exerting the nanosecond laser irradiation on the AlN surface, the AlN ceramic was thermally decomposed to aluminum and the surface was metalized. The as-metalized AlN ceramic was successfully joined to copper through the eutectic reaction between aluminum and copper. The effect of the groove interface structure fabricated with various laser scanning speeds on the mechanical and heat transfer properties of AlN/Cu joints was investigated. The joints obtained optimal shear strength and thermal diffusivity of 10.64 MPa and 51.75 mm2/s at the scanning speed of 250 mm/s. The micro groove structures of the interface contributed to the enhancement of mechanical and heat transfer properties of joints. The approach of laser-irradiation assisted joining proposed in this paper provided a novel thought for the fabrication of metal/ceramic composite structures. [ABSTRACT FROM AUTHOR]

Driven by the growing requirements for long-distance tunnels, autonomous steering control is a productive research to surpass the limitations of manual operation in steering control of tunnel boring machines (TBMs). However, existing reviews have not yet systematically discussed it from the perspective of hierarchical control. Besides, they mainly focused on how to use artificial intelligence to accomplish this task, while neglecting the knowledge-based studies. Therefore, based on the definition of hierarchical control, this paper surveys a wide range of literature on autonomous steering control from three aspects: 1) Perception layer acquires information about attitude deviation, geological conditions, and shield tail clearance; 2) Decision layer gives appropriate commands for thrust system, making the actual tunnel axis approach the designed one; 3) Execution layer designs feedback-based controllers to ensure the hydraulic cylinders accurately implement those commands. Ultimately, some future directions are highlighted to improve the efficiency and stability of tunneling. [Display omitted] • Autonomous steering control for TBM is discussed from the perception, decision, and execution layers. • Perception layer discusses how to acquire attitude deviation, geological conditions, and shield tail clearance. • Decision layer concerns with giving appropriate commands to thrust system by data-driven or knowledge analysis. • Execution layer pays attention to the control algorithms to achieve accurate tracking of the preset trajectories. [ABSTRACT FROM AUTHOR]

This study focuses on configuration and dimension optimization of cutter disassembly mechanism. Firstly, a cutter disassembly mechanism configuration is proposed with four components and simple actions, based on the theory of inventive problem solving (TRIZ) contradiction solutions. Furthermore, a comprehensive dimension optimization strategy was developed, including non-dimensional normalization model, kinematic performance atlases and fuzzy comprehensive evaluation method. Then, the optimal relative dimension of crucial parameters was obtained. Combined with the assembly relationship between components, dimension of all parameters was designed for cutter disassembly mechanism. The locking and disassembling process simulation was provided to illustrate the feasibility of the mechanism. The results show that the angular velocity is very smooth and the locking and disassembling actions are realizable without interference for optimized cutter disassembly mechanism. The effectiveness of the configuration and dimension optimization method is validated. [ABSTRACT FROM AUTHOR]

Pedestrian detection, as a research hotspot in the field of computer vision, is widely used in many fields, such as automatic driving, video surveillance, robots and so on. In recent years, with the rapid development of deep learning, pedestrian detection technology has made unprecedented breakthroughs. However, it fails to saturate pedestrian detection research, and there are still many problems to be solved. This study reviews the current research status of pedestrian detection methods based on deep learning. In the first place, we summarised the research results of two stage and one stage pedestrian detection based on deep learning, also summarised and analysed the improvement methods. Meanwhile, we focused on the occlusion and multi‐scale problems of pedestrian detection and discussed the corresponding solutions. At last, we induced the pedestrian detection datasets and evaluation methods and prospected the development trend of deep learning in pedestrian detection. [ABSTRACT FROM AUTHOR]

In order to improve the pipeline transport performance of slurry shield circulation system, a bionic pipeline with transverse protuberances structure similar to sand ripples in desert is used for stones transport pipeline of slurry circulation system. Based on the theory of CFD-DEM (Computational Fluid Dynamics-Discrete Element Method), the numerical calculation model of fluid-particle coupling of the bionic pipeline is established, and the experimental platform of the slurry circulation system is set up to verify the validity of the numerical calculation model. The pipeline transport characteristics of the ordinary smooth straight pipeline was compared with the bionic pipeline. The findings show that the bionic pipeline has the optimal pipe conveying performance, which reduces the number of stones accumulation in the pipeline by about 35% compared with that of the ordinary smooth straight pipeline. The single factor analysis was used to investigate the influence laws of different geometric parameter structures on the flow field and stone distribution of the bionic pipeline. [Display omitted] • The bionic pipe with transverse protrusion is applied to mud-water circulation pipe. • The slag carrying performance of pipeline was evaluated by CFD-DEM method. • The relationship between the structure parameters and the slag carrying performance of the pipeline is studied. • The conveying performance of the bionic pipe reduces the number of stones in the ordinary pipe by about 35% [ABSTRACT FROM AUTHOR]

Contact-reactive brazing was introduced to obtain the high-quality joints between CoCrFeMnNi high entropy alloys (HEA) and Zr alloys using Cu interlayer in a vacuum furnace. The influence of brazing temperature and holding time on the microstructure evolution and mechanical property of HEA/Cu/Zr-3 brazed joints were studied synthetically. The results displayed that the HEA/Cu/Zr-3 joints brazed at 950 °C for 10 min consisted of HEA/Cr-rich(Mn , Fe)ss/Zr(Cr,Mn) 2 /Zr 2 (Cu,Ni) + Zrss+Zr(Cr,Mn) 2 /Zr-3. As the brazing temperature raised, the Zr(Cr,Mn) 2 layer adjacent to HEA thickened, the content of Zrss and blocky Zr(Cr,Mn) 2 phases in brazing seam increased whereas Zr 2 (Cu,Ni) phase decreased. Noticeably, the Cr-rich(Mn , Fe)ss acted as the diffusion barrier at HEA/Zr(Cr,Mn) 2 interface increased with the increasing of brazing temperature/holding time. The shear strength of HEA/Cu/Zr-3 joints was increased first and then diminished with the increasing of brazing temperature/holding time. In particular, the joints brazed at 950 °C for 10 min had the maximum shear strength of 140.1 MPa. Moreover, the cracks started at HEA/Zr(Cr,Mn) 2 interface, and extended along the bulk Zr 2 (Cu,Ni) phase in brazing seam. Furthermore, the finite element analysis demonstrated that the primary concentration of residual stress in HEA/Zr-3 joints was at the interface of Cr-rich (Mn,Fe)ss/Zr(Cr,Mn) 2 , indicating this area was the weaknesses in whole brazed joints. • CoCrFeMnNi high-entropy alloy is successfully brazed to Zr alloy using Cu interlayer. • The joints brazed at 950 °C for 10 min had the maximum shear strength of 140.1 MPa. • The residual stress in joints was primarily concentrated at the Cr-rich(Mn , Fe)ss/Zr(Cr, Mn) 2 interface. [ABSTRACT FROM AUTHOR]

The graphene nanoplates (GNPs) reinforced TiNiCu (53Ti-23.5Ni-23.5Cu, at.%) filler materials (abbreviated as G-TNC) were innovatively developed and adopted in the form of multi-layers (G-TNC/Nb/Ti) to braze laser-modified C f /SiC and GH99. The corresponding typical interfacial microstructure of the joint was studied and its evolution with GNPs content and brazing temperature was elucidated in detail. The joining mechanism demonstrates that the Ti 2 (Ni,Cu) in filler materials firstly melted to be L1 and then dissolved Nb foil to form L2 which was the decisive factor for forming joint. The Ti 2 (Ni,Cu) content was regulated by GNPs, which decreased after increasing GNPs content. With the proper GNPs content of 0.3 wt%, the sound C f /SiC/GH99 joint with maximum average shear strength was obtained and the brazed seam was occupied by ductile Ti(Ni,Cu) + (Nb,Ti)ss with dispersedly distributed (Ti,Nb)C particles. The corresponding strength of joint was 77.9 MPa at room temperature and 67.3 MPa at high temperature (800 °C), which separately increased by 22.8% and 46.3% than that of joints without introducing GNPs. When the GNPs content exceeded 0.3 wt%, the decreased content of L1 caused L2 deficiency, hence, the joint was weakened and its performance was deteriorated. Neither increasing GNPs content nor brazing temperature could optimize the strength of joints. • The GNPs - TiNiCu filler material and the reaction mechanism between it and Nb were clearly studied by SEM, TEM and DSC. • The effective method of combining surface modification and composite brazing was proposed to strengthen joints. • The effect of GNPs and brazing temperature on microstructure evolution and mechanical properties of joints were clarified. • The room temperature and high temperature strength of joint were improved by 22.8% and 46.3% by using 0.3 wt.% G - TNC [ABSTRACT FROM AUTHOR]

• A TBM test-bed and its electro-hydraulic-mechanical dynamic model are established. • A wireless vibration monitoring system was built on the test-bed. • The dynamics model is verified by three typical working experiments. • The excavation parameters on the vibration characteristics of the TBM are studied. The main drive system is the core of a Tunnel Boring Machine (TBM). The force transmission law of this system is extremely complicated, which leads to severe vibration, structural failure, and safety hazards. Therefore, the dynamic analysis and the study of the vibration transmission law of a TBM main system under different working conditions are very important. In this study, a novel testbed for a hard rock TBM main system and a multi-DOF coupling dynamics model were built by considering the external excitations of the cutters, the time-varying meshing stiffness of the gear teeth, the meshing error, the clearance, and the stiffness of the main bearing. A wireless vibration monitoring system was built on the testbed. Experiments under typical working conditions were done to verify the dynamic model. Finally, the dynamic response of the system was analyzed. The results showed that the maximum error of the theoretical and actual dynamic response was 18.1%, and the dynamic model could be used to analyze the vibration of an actual TBM. The vibration law of the testbed was close to the actual TBM, so the testbed could be used for the vibration law analysis of the actual TBM under other working conditions. The study of the vibration law under different working conditions and different digging parameters could be used to guide the intelligent tunneling of the TBM. [ABSTRACT FROM AUTHOR]