Journal of Mechanical Science and Technology最新文献

This article designs a suction cup adjustment mechanism for board conveyors, which has solved the problem of poor equipment adaptability caused by different shapes and sizes of bamboo and wood shaped boards during transportation. Firstly, a kinematic model of the mechanism was established by combining graph theory with closed-loop vector method, and its kinematics were systematically studied, including position, velocity, acceleration, and singular position, and the influence of main structural parameters on the motion behavior of the mechanism was discussed. Secondly, the dynamic model of the mechanism was established using the principle of Jean le Rond d’Alembert, and the driving force and internal forces acting on each component were obtained. Then, numerical simulation verification including kinematic and dynamic models was completed. Finally, the effectiveness of the mechanism was verified through the experiment of grasping heterogeneous boards. This study will lay a solid theoretical foundation for the application of this new type of heterogeneous boards suction cup gripper.

This paper presents an improved analytical formulation for analyzing the sliding friction torque in cylindrical roller bearings (CRBs), which are renowned for their outstanding radial load-carrying capacity. Although sliding friction in CRBs typically employs a minor heat source during rotation, its association with the roller-bearing starting torque is vital. In particular, their impact is substantial at higher rotational speeds when the centrifugal forces come into play. The intricacy lies in the manifestation of sliding friction torque between the rollers and races, stemming from non-uniform surface deformation. Two key aspects of the CRB sliding friction torque are considered in this study, the differential sliding friction torques caused by roller rotation and roller orbital motion. Additionally, a computational method for evaluating sliding friction based on pure rolling lines (PRLs) in the race contact area is introduced. This method incorporates an innovative updating algorithm that provides more precise insights into PRLs and sliding friction torque. The effectiveness of the proposed approach was then established through a comparative analysis of the empirical formulas provided by bearing manufacturers. This comparison underscores the potential of the method as a useful tool for comprehending and quantifying sliding friction torque within CRBs.

This paper presents design method for a tuned liquid damper (TLD) to improve the stability of measurement system based on a spar buoy. Firstly, a TLD was designed utilizing the double-partition hull structure of spar buoy, and the theoretical natural sloshing frequency for this design was calculated. Next, an experimental study was conducted to verify the theoretical calculations. The experimental results showed that the natural sloshing frequency increased with the height of the fluid free-surface, and the values are in close agreement with the theoretical calculations. Finally, the TLD was installed to a free-drifting structure at sea, and the dynamic behavior reduction effect was experimentally verified. The results showed that the behavior of the structure is significantly reduced after the TLD is installed, especially for the behavior above 4 cm. The main contribution of this study is the integration of a TLD into the existing structure of the spar buoy, which enhances stability without compromising buoyancy. However, this approach is limited by the shape and volume constraints of the TLD, making it less effective across all wave-induced frequencies. Further research is required to extend its applicability to a broader range of maritime conditions.

To address the difficulty in evaluating the damage effect of missile target attacked by fragmented warheads, this paper proposes a new damage assessment method. In this paper, the damage to the missile target is regarded as the result of the continuous action of multiple layers of warhead fragments at multiple times. Based on this damage mechanism, sample data is formed using the characteristic parameters of warhead fragments, by introducing intuitionistic fuzzy neural network (IFNN), a new missile target damage effect evaluation model based on IFNN is established. Finally, training and testing are conducted on the data of actual missile target intersection damage tests, and the results are compared with other target damage evaluation methods. The results show that this evaluation method can effectively obtain the damage value of the missile target, and the evaluation model has good generalization ability. This provides ideas for developing a new method to evaluate the static or dynamic damage effectiveness of intelligent ammunition.

Early defect identification in laser-directed energy deposition (L-DED) additive manufacturing (AM) is pivotal for preventing build failures. Traditional single-modal monitoring approaches lack the capability to fully comprehend process dynamics, leading to a gap in multisensor monitoring strategies. This research proposes a novel in-situ monitoring method using a multi-sensor fusion-based digital twin (MFDT) for localized quality prediction, coupled with machine learning (ML) models for data fusion. It investigates acoustic signals from laser-material interactions as defect indicators, crafting a ML-based pipeline for rapid defect detection via feature extraction, fusion, and classification. This approach not only explores acoustic features across multiple domains, as well as coaxial melt pool images for ML model training, but it also introduces a novel MFDT framework that combines data from coaxial melt pool vision cameras and microphones, synchronized with robotic movements, to predict localized quality attributes. The key novelty in this research is the exploration of intra-modality and cross-modality multisensor feature correlations, revealing key vision and acoustic signatures associated with varying process dynamics. A comprehensive understanding of how multi-sensor signature varies with process dynamics improves the effectiveness of the proposed multi-sensor fusion model. The proposed model outperforms conventional methods with a 96.4 % accuracy, thereby setting a solid foundation for future self-adaptive quality improvement strategies in AM.

Constant amplitude loading fatigue tests were carried out for 7075/2A12 dissimilar aluminum alloy friction stir welding (FSW) lap joints, and the fatigue fracture characteristics were observed accordingly. Experimental observation suggested that the effective lap sheet thickness had a salient effect on the fatigue strength of the specimen. Specimens tend to fail at the lower sheet thickness under low relatively loading, while fail at the hook root at higher loading. There exists a competition between the two failure cases, and the fracture site changes with loading levels. The stress/strain at the periphery of the weld nugget were discerned by elastic and elasto–plastic finite element analyses respectively, which were then utilized to evaluate the fatigue life by local life prediction approaches and notch stress methods. Two widely used local stress approaches, the Morrow’s modified Manson-Coffin (MMC) damage model and the Smith-Watson-Topper (SWT) damage model both could give reasonable results relatively close to experimental lives within the low cycle life regime. The notch stress method could give relatively closer life in the high cycle life regime.

In order to suppress the influence of uncertain disturbances on the trajectory tracking of hydraulic manipulator, a composite control strategy for the cutting electro-hydraulic driving system (CEHDS) of the tunneling robot is presented, which synthesizes the advantages of neural networks technique, recursive backstepping and adaptive control theory. The Lagrangian model with actuator dynamics is derived based on the practical tunneling robot. The back-stepping method is utilized for the strictly feedback state-space model. To address the matched and unmatched lumped uncertainties, the radial-basis-function neural networks (RBFNNs) are employed to approximate the unmatched term which contains the nonlinear friction torque and external cutting load in the mechanical subsystem. The nonlinear disturbance observer (NDOB) is utilized to estimate the matched lumped uncertainty in the hydraulic subsystem. Simultaneously, the adaptive robust mechanism is proposed to compensate the residual disturbances. Based on the Lyapunov theorem, the stability and the bounded tracking error of the CEHDS are obtained. The simulation and experimental results validate the effectiveness of the proposed method in comparison with the common backstepping and PID-controller approaches.

This study proposed two designs of padded patient specific wrist cast as an alternative using the 3D printing thermoforming production technique. These designs were printed as a flat structure with and without hinge joints. The casts were 3D printed with polylactic acid (PLA) filament as the main structure and thermoplastic polyurethane (TPU) as the padding material. The casts were fitted to the subject’s wrist by thermoforming the printed structure. The strength of the proposed structure was analyzed using finite element analysis (FEA) during the design stage to estimate the mechanical properties of the proposed cast such as local displacement under a specific load, stress and safety factor. The thermoforming tests of the proposed designs at various temperatures were conducted experimentally to observe any crack and delamination after thermoforming. The design with hinge joint was selected based on its proper post-thermoforming fit as a functional wrist cast.

This study investigated the optimal autofrettage pressure and design method for improving the fatigue life of an ultra-high-pressure hydrogen valve attached to an ultra-high-pressure hydrogen storage vessel, which is responsible for the supply and control of hydrogen gas. The theoretical values calculated by the theoretical equation for determining the hoop residual stress formed by autofrettage pressure in a circular cylinder and the analytical values of the hoop residual stress obtained through finite element analysis of the autofrettage process in a porous circular cylinder using the commercial finite element analysis program ANSYS Workbench were well matched. Based on the analysis technique obtained for the porous circular cylinder, a quantitative target lifespan was examined for the ultra-high-pressure hydrogen valve with the shape of a porous circular cylinder, considering the maximum pulse pressure. As a result, the previously manufactured ultra-high-pressure hydrogen valve did not meet the quantitative target lifespan. To address this, the optimal values of displacement at specific locations where fatigue failure occurs and autofrettage pressure were designed using response surface methodology (RSM). Through this, fatigue life of 172710 cycles more than 150000 cycles (quantitative target lifespan) was obtained.

Carbon steel piping and tubing can be degraded by hydrogen uptake. The hydrogen permeation method is commonly applied to testing and qualification steel in response to hydrogen atom diffusion. Cyclic voltammetry (CV) has recently been proposed because it is a more straightforward method than permeation. A comprehensive study was conducted to investigate whether these two methods are comparable. A model alloy of SA 210 grade was studied. The study involved preparing specimens with varying microstructures through different heat treatments. Subsequently, metallographic analysis was conducted on each microstructural variation, followed by mechanical testing to evaluate the changes obtained before and after the hydrogen absorption test. The CV method consisted of three steps: CV before H absorption to search for a reference voltammogram, H charging, and CV after H absorption to determine the after-charge voltammogram. Electrochemical hydrogen permeation tests were performed in a Devanathan–Stachursky double cell. A comparison of the CV and permeation methods revealed that they show pretty similar results in evaluating the interaction between steel and hydrogen. Permeation methods provide quantitative results, while CV offers more qualitative insights. Both methods show that the quenched steel has the slowest hydrogen diffusion rate compared with those in normalized and base material conditions.