螺栓摩擦系数对连接松动性能影响的实验研究

松动是螺纹连接最常见的失效形式之一。论文从理论上分析了摩擦系数对螺栓连接松动性能的影响,并进行试验验证。利用螺栓摩擦性能试验机,测量了不同润滑条件下螺纹摩擦系数和螺母支承面摩擦系数;利用紧固件横向振动试验机,测试了横向循环载荷条件下,不同润滑状态的螺栓连接松动情况。经验证,螺栓摩擦系数越大越有利于防松。     

碳/碳编织复合材料连接结构的拉脱性能分析

对碳/碳(C/C)编织复合材料沉头螺栓与凸头螺栓连接结构在面外载荷下的拉脱强度进行试验和数值研究。测试不同螺栓形式及沉头角度的C/C编织复合材料螺栓连接结构在面外载荷下的失效模式和拉脱性能。结果显示，螺栓形式对结构的拉脱性能有显著的影响，凸头螺栓的载荷位移曲线有明显的线性阶段，接近于脆性失效，沉头螺栓的载荷位移曲线为非线性，表现为双峰值，其更接近于塑性失效。采用ABAQUS建立了基于Hashin失效准则的连接结构非线性接触模型，有效预报了C/C编织复合材料连接结构的失效模式及载荷-位移曲线。得到C/C编织复合材料连接结构渐近损伤过程及失效机理，给出连接参数(螺栓形式、沉头角度和约束面积)对拉脱失效的影响机制。随着沉头螺栓角度的增加，结构的拉脱失效载荷先增加，后降低，在110°附近达到极值，约束区域尺寸变化导致凸头螺栓的失效模式由剪切失效转变为弯曲失效。     

新型防松螺纹副

新型防松螺纹副是由标准螺栓配防松螺母(单向或双向)或由防松螺栓配标准螺母组成的,它的结构特点是防松螺母或防松螺栓的牙底有一与螺母或螺栓轴线成30°的承载斜面。与现行的各种防松方法相比,主要表现在它既防松可靠又结构简单,简述如下。 1.防松螺母 防松螺母的牙底有一与轴线成30°的承载斜面,它与标准螺栓紧固后的情况如图1所示。美国EMUGE有限公司将这种防松方法在原西德学者G.Junker的横向振动测试装置上进行测试,结论为该种防松方法永不松动,而标准螺纹副则在60s后完全松动。美国麻省理工学院副教授、工学博士P.N.Nayak对旋合段螺纹牙上的载荷进行了计算,结论为防松螺纹副其螺纹牙上的载荷是分散在每个螺纹牙上,而标准螺纹副其螺纹牙上的载荷是集中在靠近支承面的一两个螺纹牙上。Nsyak还进一步阐明,正是由于这种分散的载荷分布,才使得防松螺母不易发生径向窜动,因此具备了防松性能。西安交通大学将防松螺母立题研究,做了大量的实验,充分肯定了它的防松性能。     

热-力耦合作用下螺栓连接松动行为研究

为研究高温环境下螺栓连接结构松动行为，开展温度和横向振动载荷耦合作用下螺栓连接结构的松动行为及防护方法研究。利用光学显微镜、白光干涉三维形貌仪、扫描电子显微镜分析螺纹表面的损伤形貌，揭示其磨损机制；结合动力学响应分析，研究螺栓连接结构的松动行为。试验结果表明：随着温度的升高，螺栓连接结构因变形不一致导致构件之间的相对运动加剧，在相同横向交变位移载荷下，螺栓表面的磨损更加严重，螺栓连接结构松动程度增大；在室温条件下，DLC涂层螺栓/螺母和CrAlN涂层螺栓/螺母连接结构具有良好的防松性能。     

紧固件防松性能定量评价方法

工程领域一直都缺少对紧固件防松性能进行定量评价的方法,针对该问题,基于现有的横向振动试验方法,改进了横向振动试验设备,提出以导致旋转松动的临界横向力作为评价防松性能的定量指标,并给出了具体的试验方法和数据获取方法.基于所提的方法,对弹簧垫圈、楔形螺母和偏心双螺母的防松性能进行了定量测试与对比,在本研究试验条件下,得出以下结论:①弹簧垫圈没有防松性能;②相同预紧力下,相比普通螺纹连接,使用楔形螺母后防松性能最多提升了117％;③相同预紧力下,相比普通螺纹连接,使用偏心双螺母后防松性能最多提升了125％;④在高预紧力条件下,使用楔形螺母和偏心双螺母后防松性能和普通螺纹连接的防松性能相差不大.     

轴向振动工况下切槽式螺母的防松性能研究

针对全扭矩工况(螺栓预紧力矩均为设计值)、欠扭矩工况(螺栓预紧力矩均为设计值的20%)和部分欠扭矩工况(其中一组对角螺栓预紧力矩为设计值,另一组对角螺栓预紧力矩为设计值的20%),系统开展了轴向振动载荷作用下切槽式螺母的防松性能研究;全扭矩工况下研究了切槽处裂纹对切槽式螺母防松性能的影响,利用体式显微镜(OM)和扫描电子显微镜(SEM)等微观分析设备分析裂纹的扩展情况。结果表明:在三种预紧工况下,全扭矩时螺母具有良好的防松性能,但在欠扭矩和部分欠扭矩工况下螺母的防松性能降低,且后者更为严重;螺栓的松动过程可分为两个阶段:第一阶段是螺栓轴向力快速下降,原因是材料发生塑性变形和螺纹接触面应力重新分布;第二阶段是螺栓残余预紧力缓慢下降,原因是螺纹接触面发生微动磨损。此外,切槽处裂纹会降低螺母防松性能,通过微观分析表明裂纹试验后出现明显扩展。     

双螺母防松及其力关系

机器设备中的螺纹连接用得很多。设备在运行时的振动、冲击、温度变化等原因会影响到螺纹连接的紧固性和可靠性。因此,为保证安全,就得认真考虑螺纹连接的强度和防松问题。螺纹连接的防松方法颇多,而双螺母锁紧是目前广泛采用的一种,尽管它还有某些不足之处。本文研究双螺母防松的有关机理,探讨正确使用这种连接的方法。先观察一下双螺母防松的可能操作过程,当用外力偶矩M_(Z1)施加在第一个螺母(主螺母)上时,无疑在螺栓与螺母啮合牙间,因弹性变形关系而产生一个相应R_1大小的压紧力〔图1(a)、(b)〕。此时,螺栓的轴向拉力和螺母与被连接件接触表面间的     

实用可靠的双螺母防松装置

实用可靠的双螺母防松装置新余钢铁有限公司设计院（３３６５０１）袁道幸《机械》１９９０年第１期刊文《双螺母防松及其力关系》，我厂采用文中所述操作方法，对顶双螺母的防松效果确有所改善，但对于在剧烈振动、高温环境下工作的设备，螺母的松脱失效现象仍很频繁，设...     

螺栓摩擦系数对连接防松影响的有限元分析

螺栓连接受横向振动载荷一段时间后,容易出现连接松动,夹紧力衰退,夹紧失效等现象.国内鲜见钎对螺纹连接松动现象的有限元仿真,文中利用ABAQUS有限元软件建立了螺栓连接模型,对连接松动过程进行仿真.以建立的松动模型为基础,通过对比几组螺栓连接的防松特性,得到了螺栓连接摩擦系数越大其防松性能越佳的结论,该结论与螺栓连接的摩擦力矩防松机理相吻合.     

介绍一种强抗振型防松螺母

目前,国内使用的紧固螺母大多为一般普通螺母或用双普通螺母自锁以防松,或用弹簧垫圈等来防松.但对于强振动机械设备,如振动出矿机、振动运输机等,普通螺母是很难防松的,为此,我们经过多次对普通螺母现场失效分析,设计试制了一种强振型防松螺母,如图1所示,现经广西大厂铜坑铜矿、铜陵有色凤凰山铜矿等振动出矿机、振动运输机中与振动电机联结试用,防松效果良好,基本上消除了螺栓松动现象,很受工人们的欢迎.     

Investigation on Tribological Behavior of Advanced High Strength Steels: Influence of Hot Stamping Process Parameters

In order to investigate the friction and wear behavior of high strength steel in hot stamping process, a hot strip drawing tribo-simulator is developed and the friction coefficient, which is an important parameter in the finite element modeling, is measured. The results have shown that the friction coefficient remains almost unchanged until temperature reaches 500 °C. It then increases sharply as temperature is increased from 500 to 600 °C. It has also been shown that the friction coefficient decreases as the drawing speed increases. The change in the dominate wear mechanism as the temperature and the drawing speed increases has been identified from SEM analyses of the worn surface. The dominate wear mechanism is the groove cutting at temperatures between room temperature and 500 °C, which changes to the adhesive wear at temperatures above 500 °C. The main wear mechanism is the adhesive wear at 25 mm/s, which changes to the slight groove cutting at 75 mm/s.     

Improving the life and sealing of bolt joints in aircraft

New bolts with a countersunk head are considered. The bolts extend joint life, while maintaining the required air-tightness and surface quality.     

Experimental and computational investigations of thermal modal parameters for a plate-structure under 1200 °C high temperature environment

When a hypersonic aircraft flies at a high Mach number, the plate-like attitude control structures, such as the wings and rudders, will be exposed to an extremely high-temperature environment. To obtain the thermal modal parameters of a structure that are difficult to measure, a high-temperature transient heating test system and a vibration test system were combined to establish a test system that can perform the thermal/vibration test at 1200 °C. Infrared radiation heating was employed to generate a controlled time-varying high-temperature environment, and an exciter was used to exert vibration excitation on the free end of the cantilever rectangular plate. A self-developed extension configuration of a high-temperature-resistant ceramic pole was used to transfer the vibration signals of the structure to a non-high temperature zone, and the acceleration sensors were applied to identify the vibration signals. The test data were analyzed using a time-frequency joint analysis technique, and next, the key vibration characteristic parameters of structure in a thermal-vibration coupled environment up to 1200 °C (e.g., the modal frequency and modal vibration shape) were experimentally obtained. In addition, the numerical simulation on the thermal modal characteristics of a rectangular plate was performed. The calculated results coincide favorably with the test results, verifying the credibility and effectiveness of the experimental methods. The research results can provide an important basis for the dynamic performance analysis and safety design of structure under high-temperature thermal-vibration conditions for hypersonic flight vehicles.     

FDM 3D打印聚醚醚酮零件摩擦磨损特性研究

为研究3D打印各向异性对摩擦性能的影响，通过熔融沉积成型（FDM）制备了0°、45°、90° 3种打印角度的聚醚醚酮(PEEK)试样，研究3种不同打印角度及载荷变化对PEEK试样摩擦学性能及磨损机制的影响。利用MFT-5000摩擦磨损试验机对PEEK材料进行室温水润滑下的往复滑动摩擦试验，用超景深显微镜观察磨损后表面形貌。试验结果表明：不同载荷下3种打印角度试样的摩擦因数由大到小依次为0°试样、90°试样、45°试样，磨损率由大到小依次为90°试样、45°试样、0°试样；随着载荷的增大，3种不同打印角度试样的摩擦因数均呈现下降趋势，磨损率则呈现上升趋势；PEEK磨损机制是黏着磨损以及疲劳磨损引起的表层脱落。     

Tribological and electrical properties of nanocrystalline Cu films deposited by DC magnetron sputtering with varying temperature

Cu films were deposited on Si substrates by direct current (DC) magnetron sputtering at three different substrate temperatures such as room temperature (RT), 100 °C and 200 °C. Possible mechanisms for substrate temperature dependent microstructure evolution in Cu films are discussed in this paper. Enhanced mechanical properties such as high hardness, high elastic modulus, low friction coefficient and high wear resistance of the films were obtained at deposition temperature of 100 °C. However, high friction coefficient as well as high wear rate was measured in films deposited at room temperature and 200 °C.     

A study of living plant specimens by low-temperature scanning electron microscopy

Young fresh Tradescantia reflexa stamen hair cells were used to clarify the optimal conditions for direct viewing and taking photographs with a scanning electron microscope (SEM) equipped with a cryo-system. The rate of protoplasmic streaming in the cells was measured under an optical microscope after examining and photographing them in the SEM over a period of a few minutes. Almost the same rate of streaming (5.5 μm/second, 20°C) was observed in nonirradiated control cells and irradiated cells photographed in the SEM using an accelerating voltage of 10 kV with the cryo-stage at a temperature of – 15°C. (The specimen holder and specimen were not at this temperature, but, rather, probably somewhat higher.) Fresh plant organs, tissues, and cells were also tested under the same conditions. The fine structure was well preserved in detail. The procedures were as follows: (1) prompt attachment of fresh plant materials on an aluminum specimen holder with double-faced adhesive Scotch tape or a small amount of plastic adhesive for woodcraft; (2) setting the holder on the cryo-stage cooled to –15°C in advance and rapid evacuation; and (3) quick SEM examination and photography (within several minutes). The advantages of this method are summarized as follows: (1) high possibility of viewing living materials; (2) minimal artifacts: freedom from chemical fixation and additional procedures utilized in ordinary SEM specimen preparation; and (3) simplicity, speediness, and economy in preparation for viewing. Since the specimens were not likely to be frozen during quick examination and photography, this method might well be called “low-temperature SEM” (LT-SEM) as distinguished from “cryo-SEM”.     

Why low temperature embedding for X-ray microanalytical investigations?

Freeze-drying followed by infiltration with resin and polymerization by UV light at low temperatures and under constant vacuum conditions is an alternative tissue preparation technique for microprobe analysis. Embedding is carried out with the nonpolar low-temperature embedding resin (Lowicryl HM20) which allows infiltration and polymerization at temperatures down to ?50°C. Sections of low temperature embedded material can be cut dry at ?60°C or at room temperature. Sectioning at low temperatures is an alternative for preparations that are difficult to cut at room temperature. The morphological preservation is adequate for the identification of structures such as mitochondria, lysosomes and different types of endoplasmic reticulum in liver cells. Some physical properties of Lowicryl resins, such as mass loss under the electron beam and high contrast, are positive characteristics for the analysis of semi-thick sections. No significant differences in the elemental composition could be detected between tissue which was freeze-dried or freeze-substituted prior to embedding. Freeze-drying is less time consuming. By avoiding contact with organic solvents the risks of ion loss and redistribution are diminished. In contrast to freeze-dried thin cryosections, low temperature embedded material can be sectioned for light microscopy and areas of interest chosen for further thin sectioning. This is of great importance in work with tissues with complicated morphology and heterogeneous cell populations. The initial preparative step—the cryofixation— determines to a high degree the morphological preservation of freeze-dried and embedded tissue.     

Effect of temperature on the magnetic abrasive finishing process of Mg alloy bars

Experiments were conducted to evaluate the effect of temperature during magnetic abrasive finishing of Mg alloy bars. A magnetic abrasive finishing process is an unconventional finishing technique that has been used to achieve high-quality surfaces with dimensional accuracy. In this study, a Mg alloy bar, which is widely used in automobiles, aircraft, IT, and the defense industry, was chosen as a cylindrical workpiece. The workpiece was then finished with a magnetic abrasive finishing process at three different temperatures, i.e., a cryogenic temperature, room temperature, and high temperature. In the cryogenic temperature condition, liquid nitrogen and argon gas were used as the cryogenic cooling gases in the finishing process; the results from this treatment were compared with those obtained at room temperature and high temperature conditions. At the room temperature condition, the finishing process of the cylindrical workpiece was performed at 24 °C. To carry out the high temperature condition, a hot air dryer was used to maintain a finishing temperature of 112 °C. The experimental results show that the room and cryogenic temperatures could yield excellent performance in terms of the surface roughness. However, in terms of the removal weight and change in diameter, the high temperature condition was found to be superior. In the present research, the improvements of the surface roughness (Ra) at room temperature (24 °C) and cryogenic temperature (-120 °C) conditions were 84.21 % and 55 %, respectively.

     

Deformation and energy absorption of aluminum foam-filled tubes subjected to oblique loading

Research to quantify the energy absorption of empty and foam-filled tubes under oblique loading with different loading angles and geometry parameters was carried out. Tests on circular tubes made of aluminum alloy AA6063 under quasi-static axial or oblique loading were performed. The collapse behavior of empty, foam-filled single and double tubes was investigated at loading angles of 0°, 5°, 10° and 15° with respect to the longitudinal direction of the tube. The tubes were fixed at both ends and oblique load was realized by applying a load at the upper end of a pair of specimens. When the foam-filled tubular structures subjected to oblique quasi-static loading, some new deformation modes, such as spiral folding mode, irregular extensional folding mode and irregular axi-symmetric or diamond deformation mode, were identified and ascribed to the bending of tubes and shearing of foam filler, as well as the interaction between the tubes and the foam. The energy absorption characteristics of empty and foam-filled single and double tube structures with respect to the load angle and wall thickness are determined. It is found that the energy-absorbing effectiveness factors of the circular tube structures with aluminum foam core are significant higher than those of the empty tubes and the energy absorption capacity of the foam-filled double tubes is better than that of the empty and foam-filled single tubes.     

Tribological Properties of Friction Pairs in Lubricant Contaminated with Particles under High Temperature

A liquid–solid lubricant with sand particles of different sizes and concentrations is prepared in advance. The viscosity of the lubricant is measured by a capillary viscometer to determine its relationship to the concentration or size of the sand particles. The relationships between friction and concentration or size of the sand particles are also identified with a UMT2 tribometer. Results indicate that the size of sand particles plays an important role in the lubrication performance; when the size of sand particles is 1–5 μm, the friction coefficient of the liquid–solid lubricant is reduced at low concentration and low load. Contaminant concentration greatly influences the tribological behavior of such a lubricant. The failure probability of the part surface decreases with a reduction in particle concentration; moreover, a high temperature aggravates the friction and wear of this surface. The friction coefficient is 0.14 at 200°C, which is well above the friction coefficient at room temperature (0.078), and the wear volume also increases by 30% compared to the normal temperature. When the temperature is 300°C the wear volume is two times that under room temperature.