Abstract To study the stress and strain of the tail beam and the change of the movement state when coal gangue particles impact the tail beam of the hydraulic support, coupled with the differences of impact results between coal rocks with different materials, this paper uses the method of joint simulation by Hypermesh and Workbench. Firstly, using the software Hypermesh to pre-process the impact model, and then importing the grid file into the finite element analysis software workbench. Finally, using the Explicit Dynamic module of Workbench to simulate and analyze the impact behavior of different coal gangue particles. The results show that, compared with gangue, the stress and strain, as well as the dynamic response of the metal plate caused by coal is smaller. This study can provide a reference for the study of dynamic characteristics of hydraulic support, and a research basis for the realization of coal gangue vibration identification method.
The helicoids pushing chain mechanism is a novel telescopic mechanism used to push target from one position to another rapidly. The structure of the telescopic mechanism is developed and the basic design criteria are given. The position precision of the pushing chain influenced by various factors is very important to accomplish the task of pushing target. The mathematical model of position precision under the static condition is established in order to forecast the final effects and achieve some desired results by the machining. The influence of each factor is obtained through the numerical simulation. Furthermore, the bended deformation of the extended chain is calculated using the mechanics of materials method. According to the influences and the bended deformations, an error compensation method for a certain pushing distance is proposed so as to improve the position precision of chain head and achieve a satisfactory shape of the extended part. This research provides theoretical and methodological guidance for controlling machining errors and manufacturing of the pushing chain.
The dynamic characteristics of bolt connections will directly affect the response of structures under vibration.First,the scope of the connection area of bolt connections with preload was analysed.Then,the finite element model of bolt connections with preload was established by nonlinear static analysis of finite element method,so the maximum stress region of bolt connections was obtained and the region was defined as the equivalent contact area of bolt connections.The equivalent contact area was glued together to simulate the connect area of bolt connections,which changed the nonlinear problem of bolt connections to linear.Furthermore,the finite element modal analysis of the equivalent contact model and the Gang Hua contact model was proceeded,the dynamic characteristics of the two models were obtained;Finally,both the results of finite element modal analysis with experimental modal analysis were compared and the validity of the method in simulating bolt connections was verified.
Optimization design for SHPS is investigated in this paper.Through finite element analysis, SHPS with torsional load on the upper beam and base together is determined as the optimization object.The distance between the cross-section of the live column and the top end of the outer cylinder of the adjustment jack P1, the horizontal distance between axis of lug and rear linkage P2, and the angle P3 of the inclined ramp are chosen as the variable quantity, and the maximum von-Mises stress and maximum total deformation are chosen as evaluation indexes, the size range of each variable is defined in ANSYS WORKBENCH (AW).AW implements force analysis and Solidworks reconstructs the optimization object within the variable range.Two pieces of software jointly implement the continuous modeling and simulation automatically to achieve the 3 factors and 2 levels central composite design experiment of the optimization object.The simulation results after each model reconstruction are recorded in AW.The effects of three selected variables on evaluation indexes are studied and the optimum structure of SHPS is determined.Compared with the original design, the two evaluation indexes decreased by 2,37% and 2,40% respectively, which improves the supporting ability of SHPS efficiently.
The wheeled chassis, which is the carrying device of the existing handling robot, is mostly only suitable for flat indoor environments and does not have the ability to work on outdoor rugged terrain, greatly limiting the development of chassis driven handling robots. On this basis, this paper innovatively designs a four-wheel-driving Ackerman chassis with strong vibration absorption and obstacle surmounting capabilities and conducts performance research and optimization on it through quantitative experiments and dynamic simulation. Firstly, based on the introduction of the working principle and structure of the four-wheel-driving Ackerman carrier chassis, a multi-sensor distributed dynamic performance test system is constructed through the analysis of the chassis performance evaluation index. Then, according to the quantitative operation experiment of the chassis, the vibration and acceleration characteristics of the chassis at different positions of the chassis, the amount of slip and straightness of the chassis under different running distance, and the operating characteristics of the chassis under different road conditions and different damping springs conditions were analyzed respectively, which verified the rationality of the chassis design. Finally, by constructing the chassis dynamics simulation model; the influence law of chassis structure; and performance parameters such as chassis wheelbase, guide rod structure, and parameters, wheel friction coefficient and assembly error on the dynamic characteristics of the chassis is studied, and the optimal structure of the four-wheel-driving Ackerman chassis is determined while it is verified based on the simulation results. The research shows that the four-wheel-driving Ackerman chassis has good vibration performance and stability and has strong adaptability to different roads. After optimization, the vibration performance, stability, amount of slip, and straightness of the chassis structure are significantly improved, and the straightness is reduced to 0.399%, which is suitable for precise carriage applications on the chassis. The research has important guiding significance for promoting the development and application of wheeled chassis.
This study investigated the fretting fatigue behavior and mechanism of 35CrMoA steel of different contact stresses under diamond and square loading paths in the form of curved surface contact. The results show that multiple crack sources will initiate on the subsurface of the specimen under the combined effect of contact stress and cyclic stress. Under low contact stress, only one crack source dominates, causing the instantaneous fracture zone to be biased to the other side of the main crack source. Under high contact stress, the crack sources in both fretting zones play a dominant role, making the shape of the instantaneous fracture zone into a nearly circular shape with better symmetry; At the beginning of the fretting fatigue, cracks only propagate in the cross-section where they form. When they propagate to a certain depth, a component that propagates in the longitudinal direction will be generated.
This article proposes a hybrid multi-dimensional features fusion structure of spatial and temporal segmentation model for automated thermography defects detection. In addition, the newly designed attention block encourages local interaction among the neighboring pixels to recalibrate the feature maps adaptively. A Sequence-PCA layer is embedded in the network to provide enhanced semantic information. The final model results in a lightweight structure with smaller number of parameters and yet yields uncompromising performance after model compression. The proposed model allows better capture of the semantic information to improve the detection rate in an end-to-end procedure. Compared with current state-of-the-art deep semantic segmentation algorithms, the proposed model presents more accurate and robust results. In addition, the proposed attention module has led to improved performance on two classification tasks compared with other prevalent attention blocks. In order to verify the effectiveness and robustness of the proposed model, experimental studies have been carried out for defects detection on four different datasets. The demo code of the proposed method can be linked soon: http://faculty.uestc.edu.cn/gaobin/zh_CN/lwcg/153392/list/index.htm.
In order to improve automotive passive safety performance, a single rod cylinder magnetorheologicaldamper that applied to the front energy-absorbing structure is proposed and optimized. By means of Bingham -plastic nonlinear flow modified model （BPM）, taking the maximum damping force and the damping dynamicrange as the optimization goals to avoid the design limitation under the high impact condition, the NSGA-Ⅱ algo-rithm of modeFRONTIER is used to design the structural parameters of magnetorheological damper for multi-objec-tive optimization. Optimization results showed that the maximum damping force and the clamping dynamic rangeare inversely proportional, the optimization algorithm that used made it impossible for two optimization objectivesto achieve the optimal at the same time, only to choose the optimized solutions that meet the conditions from allthe Pareto solutions, the magnetic field distribution of optimized magnetorheological damper is more concentratedand reasonable.
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