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关键词： 制动盘   摩擦磨损   服役损伤   第三体膜  

摘要： 在服役过程中制动盘承受着剧烈的摩擦制动作用,故制动盘材料摩擦磨损性能决定着列车制动性能的优劣。文章分别对带热疲劳裂纹、带热斑和无热损伤的制动盘材料进行摩擦磨损试验。结果表明:无损伤的制动盘材料与闸片有较好的摩擦匹配性,制动盘材料表面形成连续、致密的第三体膜,摩擦因数稳定;热斑损伤会使摩擦副的摩擦因数和磨损率升高,制动盘材料表面第三体膜出现明显剥落;热疲劳裂纹会使摩擦副的平均摩擦因数显著降低和波动,热疲劳裂纹会破坏第三体膜的连续性和均匀性,摩擦过程中形成的磨屑会在裂缝内堆积,使制动盘材料出现增重现象。

关键词： input constraints   mechanical systems   output-feedback continuous control   strict Lyapunov functions   uniform finite-time tracking  

摘要： An output-feedback finite-time/exponential tracking continuous control scheme for mechanical systems with constrained inputs is proposed. The developed controller has a velocity-free saturating-proportional saturating-derivative type structure, inducing damping through a dirty-derivative based auxiliary dynamics. Special well-defined functions that coat the error correction actions of the control scheme give the required shaping for the concerned type of convergence and input saturation avoidance. The type of convergence is determined through the choice on the values of specific control parameters. Differently to similar previous approaches for state-feedback tracking or output-feedback regulation, the control parameters that determine the trajectory convergence are not restricted to satisfy a fixed equivalence relation but rather a wider comparative one. This expands the spectrum of finite-time convergent trajectories that may be induced, and further gives the option of an additional (unconventional) type of exponential stability (in addition to the conventional one). The closed-loop analysis is supported through suitable strict Lyapunov functions. Experimental tests on a 3-degree-of-freedom robot manipulator further support the contributed result.

关键词： clay   irradiation   microstructure   UHMWPE   wear resistance   gamma-ray  

摘要： Ultra-high molecular weight polyethylene (UHMWPE)/illite-smectite interstratified clay minerals (ISIC) composites were irradiated by gamma-ray in air and N-2 at 75 kGy. The abrasion-resistance of composites were studied via a ring-on-ring friction tester under dry friction conditions. Compared with virgin UHMWPE, the friction coefficient and wear rate of UHMWPE filled with 0.5 wt% ISIC powders and irradiated by gamma-ray in N-2 could be further reduced by near 3.1% and 88.0%, respectively. The worn surfaces of the UHMWPE/ISIC composites irradiated in N-2 were relatively smooth after dry friction. The composites exhibited relatively high wear resistance. ISIC powders can play the role of heterogeneous nucleation and induce the crystallization of UHMWPE, thereby improving the abrasion-resistance. The linear molecular chain of UHMWPE was transformed into a three-dimensional crosslinked structure after irradiation, which can effectively enhance the plastic deformation resistance and then improve the tribological properties. The results show that low filling amount of ISIC powders and gamma-ray irradiation in N-2 are effective strategies to improve abrasion resistance of UHMWPE.

关键词： Abrasion-resistant steel   Boron   DTA   Thermo-Calc  

摘要： Special wear-resistant steels are essential in applications with extreme abrasion conditions. Main applications of low-alloyed, weldable abrasion-resistant steels are found in mining, agriculture, and elsewhere. They are normally produced via continuous casting process and then hot rolled into heavy plates of desired thickness and width. This paper focuses on the strand casting part where the solidification interval of boron 500HB steel is studied through DTA heating curves and compared with thermodynamic predictions using Thermo-Calc (TCFE7 and TCFE9 database) and JMatPro with internal database General steel. Liquidus temperatures measured from the second heating curve are in good agreement with the thermodynamic approach using both commercial software. Additionally, the invariant peritectic temperature was experimentally determined and a reasonable agreement is achieved with predictions. All databases revealed a similar solidus temperature if the calculation was performed without boron included. By including 23 ppm of boron into the calculation, only one commercial software predicted the solidus temperature in good agreement with the measured value determined by DTA, the other result differed significantly. This study shows that important variation of the predicted metallurgical length in the strand slab caster exists if the solidus position is estimated using thermodynamic prediction. As the studied samples were taken directly from an industrial plate, a qualitative evaluation of micro-segregation through the cross-section of the thickness was also done and taken into account with thermal analysis.

关键词： 航空发动机  

ISBN: (纸本)9787030706942

摘要： 本书针对航空发动机机械系统中附件传动系统、滚动轴承、滑油系统和密封四部分内容进行系统介绍。从基本概念出发，对机械系统各部分涉及的结构形式、设计要求、设计方法、分析流程、应用设计案例、试验验证、发展展望及新技术等进行全面论述，充分结合典型发动机相关设计实践。

关键词： Mechanical systems   Adaptive control   Uncertainty   State feedback   Stability analysis   Safety   Mobile robots   Adaptive control   nonlinear mechanical systems   output constraints   shared control   state feedback  

摘要： This work develops two kinds of adaptive state feedback shared-control algorithms for a class of nonlinear mechanical systems in the presence of output constraints described by a set of linear inequalities. The parametric uncertainties and unknown external disturbances in the dynamical model are compensated by the proposed adaptive control laws for the feedback controller. In particular, an adaptive fixed-time state-feedback control law is also developed after the classical robust adaptive state-feedback control law design. The properties of the closed-loop shared-control systems are studied by using Lyapunov method. Simulation results demonstrate the effectiveness of the proposed approach.

关键词： abrasion volume   cliff recession   growth of beach   evolution of abrasion coast  

摘要： Abrasion of coasts is considered, the destruction of which is accompanied by extraction of sediments capable of forming a beach (sand, gravel, pebble). The behavior of such a type of coast is controlled by the feedback between the abrasion rate and volume of growing beach. The suggested evolutionary model leads to conclusion that abrasion should decay exponentially with time. The duration of the process may be measured in decades, centuries, or millennia depending on the fraction of beach-forming material incoming from the cliff. A rise in relative sea level contributes to an increased duration of abrasion. To predict the yearly volume of cliff abrasion, the approach by Larson et al. [15] is applied, taking into account the difference between the elevation of the beach and height of wave runup. The computational formula includes an empirical coefficient, which is estimated from data on the coasts of the Kama water-storage basin and Sea of Okhotsk (where the tide plays a significant role in cliff abrasion). It is shown that a comparatively small-scale beach fosters a substantial decrease in the abrasion volume. Abrasion of a submerged coastal slope is determined by both the cliff abrasion rate and "closure depth" concept.

关键词： exponentially stable   mechanical systems   nonholonomic constraints   speed observer  

摘要： In this article, a novel globally exponentially convergent velocity observer for a class of mechanical systems with l nonholonomic constraints is presented. Through using a special coordinate transformation, the constrained system is converted into the integral cascade Euler-Lagrange form, which could avoid solving partial differential equations and eliminate the influence of the constraint force when reconstructing the speed information. The proposed observer has a simple structure and lower dimensions compared with other globally exponentially stable observers by using dynamic scaling and gain filtering. The simulation results demonstrate the stability and effectiveness of proposed reduced-dimensional observer.

关键词： 露天采矿设备   机械零件   损坏形式   修复措施  

摘要： 当前市场经济持续进步发展,各个产业的技术都得到了一定提高,对有色金属的需求有所提高.因此,要充分利用露天采矿设备,保证采矿设备的质量.本文探讨了露天采矿设备机械零件主要的损坏形式和修复方法,研究了露天采矿设备机械零件损坏现象的改善措施,旨在提高露天采矿设备的运行质量,保证金属矿物的开采水平,改善矿业发展.

关键词： Marine policy   Maritime industry   Plastic lifespan   Polypropylene   Polysteel   Secondary microplastic   Synthetic fibres  

摘要： While land-based sources of plastic pollution have gained increasing attention in recent years, ocean-based sources have been less well studied. The aim of this study was to compare a variety of ropes (differing in age, wear surface and material) to quantify and characterise the production of microplastic during use. This was achieved by simulating, in laboratory and field experiments, rope hauling activity which is typically performed on board maritime vessels, such as fishing boats. Microplastic generation was quantified by collecting fragments that were released as a consequence of abrasion. Notably, we show that microplastic fragments generated from rope wear during use were characteristically irregular in shape, rather than fibrous such as those assigned to syn-thetic rope by previous studies. Therefore, we suggest that some of the plastic fragments found in the marine en-vironment may have been falsely attributed to land-based sources but have in fact arisen form the abrasion of rope. Our research found that new and one-year old polypropylene rope released significantly fewer microplastic fragments (14 +/- 3 and 22 +/- 5) and less microplastic mass (11 +/- 2 and 12 +/- 3 mu g) per metre hauled compared to ropes of two (720 +/- 51, 247 +/- 18 mu g) or ten (767 +/- 55,1052 +/- 75 mu g) years of age. We show that a substantial amount of microplastic contamination is likely to directly enter the marine environment due to in situ rope abra-sion and that rope age is an important factor influencing microplastic release. Our research suggests the need for standards on rope maintenance, replacement, and recycling along with innovation in synthetic rope design with the aim to reduce microplastic emission. (c) 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://***/licenses/by/4.0/).