Journal of Mechanical Science and Technology

Pham, Duy-Binh; Huang, Shyh-Chour

doi: 10.1007/s12206-024-2203-5pmid: N/A

In response to the growing demand for sophisticated engineering applications, this study introduces a novel lattice metamaterial inspired by the lotus root shape, designed to simultaneously possess energy absorption and vibration mitigation properties. A lattice structure composed of 3×3×3 unit cells was developed and numerically analyzed to evaluate its energy absorption and vibration isolation capabilities. The proposed structure was fabricated using additive manufacturing technique and subjected to experimental testing to validate the numerical findings. Notably, the addition of struts to the lattice structure yields low-frequency vibration mitigation features. Furthermore, a comprehensive exploration of geometric parameters through numerical and experimental analysis provides valuable insights for tailoring the structure's performance. A graded lattice metamaterial is designed to further enhance energy absorption and vibration mitigation performance. The findings of this study suggest an effective approach for designing multifunctional metamaterial structures capable of addressing diverse engineering challenges.

Panghal, Harish; Kumar, Awadhesh

doi: 10.1007/s12206-024-0513-2pmid: N/A

This study investigates the potential of incorporating recycled fine aggregates (RFA) into sustainable concrete. In this research, a conventional compaction technique is utilized to establish the order of compressive strength and, consequently, to assess particle packing density in terms of weight within a specific cylindrical volume and evaluate workability, compressive and flexural strengths, splitting tensile strength, elasticity modulus, and microstructural properties (analyzed through XRD, SEM, and EDAX). The study found that RFA can improve concrete properties, hardened characteristics, and microstructure up to an optimum 25 % RFA replacement threshold (RFA 25). Beyond this value, concrete strength and microstructure deteriorate. RFA 25 exhibits significantly higher compressive (14.75 %), flexural (6.61 %), and splitting tensile (13.14 %) strengths compared with the reference concrete, along with a 5.71 % decrease in the modulus of elasticity. Lower replacement levels promoted pozzolanic reactions, enhancing strength through additional hydration products, whereas higher replacements reduced strength.

Rong, Yu; Dou, Tianci; Zhang, Xingchao

doi: 10.1007/s12206-024-0528-8pmid: N/A

In this work, we address the issue of insufficient accuracy in the gradient projection algorithm and propose a closed-loop control dynamic obstacle avoidance algorithm that relies on a machine learning objective function. We initially establish a reasonable objective function and employ the gradient descent algorithm to enable dynamic obstacle avoidance in each bar. We then separate the end trajectory of the manipulator into multiple trajectory points and use the actual and expected positions of the end as the starting and ending points to significantly enhance the end tracking accuracy of the manipulator. Finally, we conduct simulation and real experiments on planar four degrees-of-freedom redundant manipulators to validate the efficacy of the algorithm. Moreover, the algorithm is proven to be applicable to dynamic obstacle avoidance under various trajectory tracking scenarios. It also exhibits advantages, such as smooth and continuous avoidance states and low computational costs.

Tian, Shengli; Wang, Zhiwen; Zhao, Xingxin; Dong, Shaojiang

doi: 10.1007/s12206-024-2202-6pmid: N/A

The dynamic support stiffness (DSS) of assembled bearings in high-speed motorized spindles (HSMSs) is the main factor affecting the rotor’s operating stiffness which, in turn, directly affects the machining accuracy of HSMSs. This paper establishes a thermo-mechanical coupled quasi-static model of the DSS of assembled bearings, providing a theoretical model for analysing the combined effects of preloading method, assembly form, thermal expansion and external load. An experimental method is designed to quantitatively measure the DSS of assembled bearings in HSMSs. By combining the modelling with experimental measurements, the effects of radial force and speed on the radial and axial DSS of the assembled bearings in an HSMS are investigated. The results show that the radial DSS of the front and rear bearings increases with radial force and decreases with speed; while the axial DSS of the front bearings decreases with radial force and speed, and the axial stiffness of the rear bearings is less affected by the radial force and speed under the condition of constant-pressure preload. The proposed experimental device can accurately measure the DSS of assembled bearings at speeds of up to 30000 r/min. This study provides a new theoretical model and experimental method for the estimation and quantitative measurement of DSS in assembled bearings in HSMSs.

Ying, Qihui; Jia, Zhixin; Wang, Xing; Liu, Lijun; Li, Jiqiang; Rong, Di

doi: 10.1007/s12206-024-0515-0pmid: N/A

Composite materials are an effective way to realize the lightweighting of automobiles. The molding process parameters have significant effects on the mechanical properties of the products. In this paper, continuous glass fiber reinforced polypropylene plastics (CGFRPP) laminated boards were prepared through compression molding. The influence of process parameters on the mechanical properties of CGFRPP products was investigated. The material preheating temperature was found to have the greatest influence by the extreme difference analysis method. Typical products were selected for microscopic observation to investigate the microscopic mechanism of the influence of material preheating temperature on CGFRPP products. The results show that the optimal process parameters for compression molding are 95 °C, 570 kN, 90 s, 9 mm/s, 195 °C and 600 s for mold temperature, compression pressure, holding time, mold-closing speed, material preheating temperature, and material preheating time, respectively. Afterward, a confirmation test was performed to validate the optimum parameters.

Feng, Xiguang; Kim, ByeongGeon; Park, Kyoung-Su

doi: 10.1007/s12206-024-0501-6pmid: N/A

Transcranial direct current stimulation (tDCS) is a noninvasive method of brain modulation that is increasingly used to treat neuropsychiatric disorders and enhance cognitive capacity. Computational modeling provides a valuable tool for designing and analyzing current stimulation devices for the treatment of neurological disorders and diseases. Here we use a three-dimensional finite element model (FEM), we constructed a simulation model and verified the results by reference to experimental data. A multi-layer sponges’ design with step conductivity was presented to reduce the crowded current density distribution and investigated the influencing factors, we identified relevant factors and used them to optimize the sponge. We optimized the sponge design by optimizing the sponge’s stepped conductivity and the thickness. We found that by using the stepped sponge design, the model could meet the impedance matching between the last sponge layer and the skin surface.

Kim, Moojae; Kim, Sangjo; Kim, Donghwa; Lee, Changhoon

doi: 10.1007/s12206-024-0520-3pmid: N/A

Gas turbine pre-swirl systems has been known to provide smooth cooling air to rotating turbine blades for prevention of thermal damage caused by high turbine inlet temperatures. The performance of the pre-swirl system depends on the shapes of its components, such as the pre-swirl nozzle and receiver hole. This study focused on obtaining the optimal shape of a pre-swirl nozzle that minimizes aerodynamic losses. To determine the optimal shape with minimal design parameters, we modeled the nozzle vane using piecewise cubic functions in three segments to satisfy the given geometric constraints. The optimization results indicated that the nozzle discharge coefficient increased when the second and third segments were positioned closer to the throat area. Even simpler shapes, such as a cubic function in one or two segments with less smooth connections between the segments, were tested for comparison. Although the simplest shape using one segment yielded the best performance, all considered shapes were proposed as candidates for the optimal shape in the general design of the pre-swirl nozzle vane.

Li, Fenqiang; Wang, Qianting; Shu, Jiawei; Chen, Hao; Li, Hui

doi: 10.1007/s12206-024-2205-3pmid: N/A

iSoldering_wetting software was used to simulate the solder wetting process in laser soldering. Based on the simulation, the range of process parameters was initially determined, and the orthogonal experimental method was used to study the impact of each process parameter on solder wetting and connection quality. Then, the components were connected to the printed circuit board (PCB) using laser soldering equipment, and the welding seam morphology was analyzed to verify the reliability of the software. Pull-out experiments were carried out to test their connection strength using a universal testing machine. The results show that the simulation of the solder wetting process using iSoldering_wetting software is reliable. Laser power 16 w, wire speed 10 mm/s, and welding time 0.7 s are the process parameters with the best wettability of Sn-based solder, and the connection strength between the component and PCB is the highest using these process parameters.

Fan, Chunming; Liao, Yucheng; Han, Chuanjun

doi: 10.1007/s12206-024-0538-6pmid: N/A

In the process of drilling or repairing oil and gas wells, sudden blowout fires may lead to huge economic losses, personnel injuries and environmental damage. In order to understand the effects of flame changes and high temperatures on the surrounding environment and human body during the blowout fire, a simulation model was established to analyze the situation according to the different blowout volumes and wind speeds. The results show that the increase of the blowout volume will aggravate the burning degree of the flame, and the larger the blowout volume, the more likely the flame vortex will occur. The wind speed tilts the flame, changing the shape of the flame, which affects the flame burning. When rescuing and repairing without precautions, the flame temperature and radiation will cause burns or even death to emergency responders in a very short period of time.

Chen, Shuai; Lu, Yue; Hu, Yawen; Wang, Zheng; Tao, Tingfang; Cui, Hongbo

doi: 10.1007/s12206-024-0511-4pmid: N/A

Friction stir welding of 7075 aluminum alloy plate with a thickness of 10 mm was carried out with a self-designed stirring tool, and after welding, an irregular transitional zone between the tool shoulder zone and the nugget zone, known as the turbulent zone, was discovered on the advancing side of the weld. The formation mechanism of the turbulent zone was analyzed by observing the transverse and longitudinal sections of the joint cross section. The grain size, the degree of dynamic recrystallization, the misorientation angle distribution in the turbulent region were evaluated by electron backscatter diffraction (EBSD). The grain size in the turbulent zone is large with an average grain size of 2.98 μm. The proportion of substructure is as high as 75.1 %, which makes the hardness value higher than that of other areas of the weld. In addition, layered tensile mechanical test results show that the tensile strength of the turbulent zone layer (342 MPa) is comparable to that of the central layer of the weld nugget zone (345 MPa).