堆焊熔敷层表面纳米晶层摩擦磨损性能研究

用预压力滚压技术在堆焊修复层表面制备纳米晶层.利用TEM、SEM分析技术研究表面纳米晶层微观结构,利用CETR-3型多功能摩擦磨损试验机考察在干摩擦条件下堆焊层表面纳米晶层的摩擦磨损性能.结果表明堆焊修复层表面经表面纳米化处理后,表面形成厚度约为10μm(晶粒尺寸小于100 nm)的纳米晶层,最表面层平均晶粒尺寸约为10 nm.纳米压痕试验表明纳米晶层的硬度提高,最表面纳米晶层的硬度约为原始堆焊层硬度的3倍.与原始堆焊试样相比,表面纳米化试样的摩擦系数降低了10%,磨损体积降低了25%~30%左右.表面纳米化样品的磨损机制由原始堆焊层的磨粒磨损和黏着磨损转变为磨粒磨损,分析表明晶粒细化导致的高硬度、低塑性是摩擦磨损性能改善和磨损机制改变的主要原因.     

两种晶粒尺寸氧化铝陶瓷滑动磨损表面演化

文中比较研究了两种晶粒尺寸(0.6μm和3.8μm)氧化铝陶瓷在室温干摩擦条件下分别与氮化硅陶瓷对摩时的摩擦磨损性能,发现细晶氧化铝陶瓷(0.6μm)/氮化硅陶瓷摩擦副有较低的摩擦系数和磨损率以及高的磨损转变载荷,而粗晶氧化铝陶瓷(3.8μm)/氮化硅陶瓷摩擦副的摩擦学性能较差.对这两种晶粒尺寸氧化铝陶瓷的磨损表面进行了表征,发现了两种不同的磨损机制和磨损演化规律.在15 N的载荷下,3.8μm氧化铝陶瓷在磨损初期发生了晶粒断裂和拔出,在100 s后开始形成摩擦层,随后摩擦层的面积随着滑动时间的延长而增大,其特征为光滑、有裂纹贯通的机械混合层.0.6μm氧化铝陶瓷在初期的磨损以微凸体磨损和晶界破坏为主,随后出现晶粒断裂和拔出,没有发现机械混合层.本文中讨论了晶粒尺寸效应和磨痕尺寸效应对两种晶粒尺寸氧化铝陶瓷磨损表面演化的影响.     

接触应力对FCB车轮钢组织演变与性能的影响

利用双盘滚动摩擦磨损试验机进行了贝氏体车轮钢的滚动磨损试验,采用扫描电子显微镜(SEM)、电子背散射衍射(EBSD)分析不同接触应力条件下贝氏体车轮钢次表层微观组织演变. 结果表明:在滚动磨损条件下,磨损机制由黏着磨损转变为疲劳磨损,增大接触应力对黏着磨损阶段的磨损量影响不大,但会显著增加疲劳磨损阶段的磨损量;贝氏体车轮钢在塑性变形的过程中,贝氏体铁素板条中位错逐渐增值、先累积形成小角度晶界,而后形成大角度晶界,使贝氏体铁素体发生细化;接触应力的大小影响表层组织的演变,当接触应力增至1 150 MPa时,晶粒细化为超细等轴晶,继续增加接触应力,组织变化并不明显. 接触应力大小会影响贝氏体车轮钢的表面硬度. 接触应力增加使贝氏体车轮钢的表面硬度增高,硬化层深度增大.      

氮合金化堆焊合金往复式摩擦磨损行为的研究

在马氏体不锈钢中引入氮,通过铌、钛固氮制备氮合金化堆焊合金. 利用往复式摩擦磨损试验机测试加氮和未加氮两种堆焊合金在不同载荷(5、10和15 N)下的摩擦磨损性能,研究了其摩擦磨损行为. 结果表明:在摩擦磨损过程中,堆焊合金表面承受周期性载荷,摩擦表面出现明显的切削痕和塑性变形,其磨损机制以磨粒磨损和表面疲劳磨损为主. 氮合金化堆焊合金中,碳氮化物沿马氏体基体、晶界弥散析出,起到了明显的细晶强化和弥散强化作用,增强了基体的塑性变形抗力以及抵御磨粒磨损的能力,使磨损表面切削痕数量更少、深度更浅,抗疲劳剥落现象得到明显改善.      

位移幅值对铜镁合金微动磨损行为的影响

在研制的多功能微动磨损试验机上,开展了不同位移幅值下铜镁合金微动磨损试验,以研究位移幅值对铜镁合金微动磨损行为的影响. 微动过程中记录摩擦系数曲线与F_t-D-N曲线,利用光学显微镜(OM)、扫描电镜(SEM)、能量色散X射线光谱仪(EDS)及三维形貌仪对损伤区域进行了微观分析. 结果显示:随着位移幅值的增加,铜镁合金微动运行状态由部分滑移进入完全滑移,未发现混合滑移状态;部分滑移区中呈现由弹性变形协调逐渐向塑性变形协调转变的趋势. 磨损体积随位移幅值的增加而增加,在完全滑移区中体积损失非常严重. 在弹性变形协调的部分滑移状态下,接触表面损伤轻微,而由塑性变形协调的部分滑移状态下,接触中心出现较大切应力,疲劳裂纹扩展至接触表面导致材料剥落,接触边缘有磨粒磨损和氧化磨损的痕迹. 在完全滑移状态下,接触表面损伤主要为疲劳剥层,磨粒磨损和氧化磨损.      

接触载荷对钢丝微动磨损行为影响的研究

以6×19点接触式提升钢丝绳为研究对象,在自制的微动摩擦磨损试验机上开展钢丝微动磨损的实验研究,考察在不同接触载荷下钢丝的微动磨损行为,采用S-3000N型扫描电镜观察钢丝的磨损形貌并分析其微动损伤机理.结果表明:在接触载荷为9～29 N范围内,微动摩擦力(Ft)-位移幅值(D)曲线随循环周次的变化表明钢丝运行于混合区,并随着接触载荷的增加,钢丝间接触应力增加;在微动磨损初期钢丝间的摩擦系数均较低,之后逐渐增加并趋于稳定;其稳定摩擦系数随着钢丝间接触载荷的增加而降低,接触载荷为9 N时的摩擦系数最大,约为1.25,而29 N的摩擦系数约为0.57;钢丝间的接触载荷增加,钢丝表面接触疲劳的几率增大,出现磨屑疲劳脱落的痕迹和疲劳微裂纹,其损伤机制主要表现为磨粒磨损、疲劳磨损和摩擦氧化.     

制备工艺对MoS_2粘结固体润滑涂层微动磨损寿命的影响

在不同载荷和位移振幅条件下,考察了2种基体材料表面MoS2粘结固体润滑涂层的微动磨损性能,深入分析了基体表面预处理、涂层厚度及涂层固化温度等对涂层微动磨损寿命的影响.结果表明,通过提高基体材料硬度、增加涂层厚度、对基体表面进行喷砂预处理以及对涂层进行高温固化等均可不同程度地提高涂层的微动磨损寿命,其中高温固化对涂层磨损寿命的影响最显著;而基体表面喷砂处理对高温固化涂层磨损寿命的影响减弱.喷砂42CrMo基体表面涂覆的经高温固化的厚16±1μm的MoS2粘结固体润滑涂层的抗微动磨损性能最佳.     

制备工艺对MoS2粘结固体润滑涂层微动磨损寿命的影响

在不同载荷和位移振幅条件下,考察了2种基体材料表面MoS2粘结固体润滑涂层的微动磨损性能,深入分析了基体表面预处理、涂层厚度及涂层固化温度等对涂层微动磨损寿命的影响.结果表明,通过提高基体材料硬度、增加涂层厚度、对基体表面进行喷砂预处理以及对涂层进行高温固化等均可不同程度地提高涂层的微动磨损寿命,其中高温固化对涂层磨损寿命的影响最显著;而基体表面喷砂处理对高温固化涂层磨损寿命的影响减弱.喷砂42CrMo基体表面涂覆的经高温固化的厚16±1μm的MoS2粘结固体润滑涂层的抗微动磨损性能最佳.     

载荷对304不锈钢微动磨损性能的影响

采用SRV-IV微动摩擦磨损试验机,研究了在干摩擦和水介质润滑条件下,载荷对304不锈钢微动磨损行为的影响,用扫描电子显微镜(SEM)和X射线能谱(EDS)对磨损表面形貌和成分进行分析.结果显示:载荷和介质对微动摩擦行为和磨损机理有显著影响.在干摩擦下,载荷明显改变了微动运行区域,当载荷增大到50 N时微动运行区域由滑移区变为部分滑移区.摩擦系数和磨痕深度随着载荷的增加依次减小.磨损机理由黏着、磨粒和氧化磨损转变为局部疲劳和轻微氧化.同干摩擦相比,由于水介质的润滑和冷却作用,表面黏着被抑制,摩擦系数显著减小,两接触面间易滑移,部分滑移区消失.随载荷的增大磨痕深度增大,因腐蚀与磨损的交互作用,在海水中的磨痕深度比去离子水中略大.磨损机理主要为磨粒磨损和轻微的腐蚀磨损.     

金属橡胶隔振构件中不锈钢丝的微动摩擦磨损性能研究

以金属橡胶隔振构件疲劳试验数据为基础,将柱-块摩擦样品表面刻槽以嵌入并固定钢丝,在SRV高温摩擦磨损试验机上评价φ0.3 mm的冷拉拔1Cr18Ni9不锈钢钢丝在不同载荷下的微动摩擦磨损性能,用激光扫描共焦显微镜对其磨痕表面进行分析.结果表明:冷拉拔不锈钢丝的表面粗糙度Ra值为3.447μm;在磨损初期阶段,需要约28s打磨其表而的凹凸体;由不锈钢丝"微动单元"的摩擦曲线可以将其磨损过程划分为表面打磨、接触面黏着、第三体床形成以及稳定磨损4个阶段,其中稳定磨损阶段的摩擦系数相对平稳,磨痕表面光滑程度高于基体的原始表面,磨痕深度介于50～60μm之间.     

The 7th International Conference on Fluid Mechanics May 24-27,2015,Qingdao,China

正http://www.icfm7.org First Announcement and Call for PapersThe objective of International Conference on Fluid Mechanics(ICFM)is to provide a forum for researchers to exchange new ideas and recent advances in the fields of theoretical,experimental,computational Fluid Mechanics as well as interdisciplinary subjects.It was successfully convened by the Chinese Society of Theoretical and Applied Mechanics(CSTAM)in Beijing(1987,     

INFORMATION FOR CONTRIBUTORS

Contributions： The Journal, Acta Mechanica Solida Sinica, is pleased to receive papers from engineers and scientists working in various aspects of solid mechanics. All contributions are subject to critical review prior to acceptance and publication.     

Preface

This special issue of PARTICUOLOGY is devoted to the first UK-China Particle Technology Forum taking place in Leeds, UK, on 1-3 April 2007. The forum was initiated by a number of UK and Chinese leading academics and organised by the University of Leeds in collaboration with Chinese Society of Particuology, Particle Technology Subject Group （PTSG） of the Institution of Chemical Engineers （IChemE）, Particle Characterisation Interest Group （PCIG） of the Royal Society of Chemistry （RSC） and International Fine Particle Research Institute （IFPRI）. The forum was supported financially by the Engineering and Physics Sciences Research Council （EPSRC） of United Kingdom,     

基于鲁棒滤波的捷联导引头视线角速度估计方法

针对捷联导引头无法直接获取视线角速度等信息的问题,研究了鲁棒滤波在大气层外飞行器捷联导引头视线角速度估计中的应用。为了建立非线性滤波估计模型,考虑目标视线角速度的慢变特性,采用一阶马尔科夫模型建立了状态方程;推导了视线角速度的解耦模型,并建立了量测方程;考虑到实际应用中存在系统噪声统计特性失准的问题,基于Huber-Based鲁棒滤波方法,设计了视线角速度滤波器,并完成了基于Huber-Based滤波方法和扩展卡尔曼滤波方法的数学仿真。仿真结果表明Huber-Based滤波方法的视线角、视线角速度及视线角加速度估计精度分别达到0.1140'、0.1423'/s、0.0203'/s2,而扩展卡尔曼滤波方法的视线角、视线角速度及视线角加速度估计精度仅分别为0.6577'、0.6415'/s、0.0979'/s~2。仿真结果证明了该方法可以有效地估计出相对视线角速度等信息,并且在非高斯噪声的条件下,依然可获得较高的估计精度,具有一定的鲁棒性。     

Guide for authors

正Each of the sections below provides essential information for authors.We recommend that you take the time to read them before submitting a contribution to Acta Mechanica Sinica.We hope our guide to authors may help you navigate to the appropriate section.How to prepare a submission This document provides an outline of the editorial process involved in publishing a scientific paper in Acta Mechanica     

Use specification of multiscale materials for life spanned over macro-, micro-, nano-, and pico-scale

Multiscale material intends to enhance the strength and life of mechanical systems by matching the transmitted spatiotemporal energy distribution to the constituents at the different scale, say—macro, micro, nano, and pico,—, depending on the needs. Lower scale entities are, particularly, critical to small size systems. Large structures are less sensitive to microscopic effects. Scale shifting laws will be developed for relating test data from nano-, micro-, and macro-specimens. The benefit of reinforcement at the lower scale constituents needs to be justified at the macroscopic scale. Filling the void and space in regions of high energy density is considered.Material inhomogeneity interacts with specimen size. Their combined effect is non-equilibrium. Energy exchange between the environment and specimen becomes increasingly more significant as the specimen size is reduced. Perturbation of the operational conditions can further aggravate the situation. Scale transitional functions and/or f_j/j+1 are introduced to quantify these characteristics. They are represented, respectively, by , and (f_mi/ma,f_na/mi,f_pi/na). The abbreviations pi, na, mi, and ma refer to pico, nano, micro and macro.Local damage is assumed to initiate at a small scale, grows to a larger scale, and terminate at an even larger scale. The mechanism of energy absorption and dissipation will be introduced to develop a consistent book keeping system. Compaction of mass density for constituents of size 10⁻¹², 10⁻⁹, 10⁻⁶, 10⁻³ m, will be considered. Energy dissipation at all scales must be accounted for. Dissipations at the smaller scale must not only be included but they must abide by the same physical and mathematical interpretation, in order to avoid inconsistencies when making connections with those at the larger scale where dissipations are eminent.Three fundamental Problems I, II, and III are stated. They correspond to the commonly used service conditions. Reference is made to a Representative Tip (RT), the location where energy absorption and dissipation takes place. The RT can be a crack tip or a particle. At the larger size scales, RT can refer to a region. Scale shifting of results from the very small to the very large is needed to identify the benefit of using multiscale materials.