铁基形状记忆合金防松螺母防断机理的数值分析

由于铁基形状记忆合金材料本身的特殊性能,由其制成的螺母所组成的螺栓联接中,不仅螺纹副之间的自锁摩擦力矩有所提高,而且轴向载荷在各螺纹齿间分布的均匀性也得以改善,从而有效地防止了螺纹联接松动、松脱及疲劳断裂等失效现象的发生。主要对这种新型螺母的防断机理进行了分析,建立了螺栓联接载荷分布的计算模型,并通过与普通螺栓联接的比较,对这种新型螺母的防断性能进行了评价。     

螺栓连接的质量控制

分析了螺栓连接产生松动的原因，并阐述了标定板手法和螺母转角法丙种控制螺栓连接质量的方法。     

输电铁塔双螺母防松螺栓横向振动试验研究

螺栓松动是强风区和舞动区输电铁塔横担损坏的主要原因,通过开展三种型式输电铁塔双螺母螺栓的横向振动试验,获得了双螺母螺栓的预紧力时程曲线,分析了上、下螺母安装扭矩比例对螺栓预紧力衰减特性的影响规律。下螺母与上螺母安装扭矩之比为25%时,普通双螺母螺栓的防松性能最佳。完成了输电铁塔横担在舞动工况下的横向振动试验,确定了铁塔横担螺栓松动顺序和松动位置的分布规律。舞动荷载作用下横担下平面螺栓易发生松动,其中下平面主材与固定端连接螺栓、横担端部挂点处杆件连接螺栓的松脱现象最为严重,建议设计时进一步提高横担下平面主材及斜材连接螺栓的防松性能。     

水表连接黄铜螺母断裂分析

居民住宅内与水表连接的黄铜螺母发生断裂,造成管路泄漏.采用宏、微观检验方法对失效螺母进行了分析.结果表明,黄铜材料中含有较多的铅,使金属基体脆化并在晶界上存在脆性共晶体网膜,加上金属中还存在孔洞、缩松等铸造缺陷,是造成螺母断裂的主要原因.     

钛合金螺母开裂原因分析

钛合金螺母在使用过程中发生了开裂,采用化学成分分析、金相分析、微观观察等方法对开裂螺母进行了分析。结果表明螺母的开裂是由于应力腐蚀造成的,并提出改进措施。     

螺纹摩擦对螺栓轴向力-伸长量特征曲线的影响

基于超声波技术,通过对螺栓进行拉伸试验,研究了不同外载下螺栓轴向力-伸长量特征曲线的差异,分析了螺纹摩擦对螺栓轴向力-伸长量特征曲线的影响。结果表明:螺栓的单向拉伸与扭转拉伸因受到的载荷方向不同而导致其屈服点不同;螺栓前期拧紧标定过程中螺纹摩擦对螺栓轴向力有很大影响,会影响后续子系统螺栓夹紧力的大小;不同的螺纹摩擦状态导致拧紧过程中螺栓轴向应变速率不同,会产生不同的特征曲线,且螺纹摩擦因数越大,扭转应力就越大,螺栓屈服点就越低;若能保证轴向拉伸速度相同,不管是涂层之间的正常螺纹摩擦还是使用机油降低摩擦,获得的特征曲线斜率是相同的;无涂层的金属间摩擦会导致螺纹尖端产生塑性变形,形成的特征曲线弹性段斜率有较大差异。     

发动机螺母零件质量分析研究

飞机发动机的某组合件上的螺母,工人在装配过程中发现自制螺母与外购的螺母有差异,自制零件螺纹装配时对相配件的伸长量不合格,明显比外购零件低,性能不稳定,因此主要研究对象是内螺纹,该零件螺纹的加工方法采用的是在立钻上丝锥攻制内螺纹。故从自制螺母零件的设计要求、执行标准入手,对加工螺纹的方法选择、工装选定、检测等与螺纹加工和测量过程相关的因素分析研究,通过大量数据测量、分析找到影响螺母加工质量的原因,并调整底孔尺寸后加工的零件,经过测量和验证,制造水平超过外购零件。     

7075-T73铝合金高锁螺母断裂原因

7075-T73铝合金高锁螺母在装配时发生纵向断裂。通过宏观观察、扫描电镜分析、能谱分析以及金相检验等方法,结合生产工艺和零件复查结果,对高锁螺母的断裂原因进行了分析。结果表明:原材料中存在氧化铝夹杂,在装配应力作用下裂纹起源于氧化铝夹杂处,并沿厚度方向扩展,最终导致高锁螺母断裂。建议增加原材料缺陷检查工序以及严格执行无损检测工艺,避免此类故障再次发生。     

调整螺母裂纹成因分析

调整螺母在调质处理后探伤时发现有裂纹,采用宏观检验、化学成分分析、金相检验等方法对其开裂原因进行了分析。结果表明：该批调整螺母开裂是由于明显的带状偏析和较多的夹杂物引起的淬火裂纹,同时由于回火温度过高,使得裂纹两侧脱碳出现网状铁素体。     

HB4-49收紧螺母开裂原因

通过理化检验、仿真分析和装配拧紧试验等方法，对HB4-49收紧螺母的开裂性质和原因进行了分析。结果表明：该螺母开裂的原因为拧紧力矩过大。     

Experimental results and finite-element predictions of the effect of nut geometry, washer and Teflon tape on the fatigue life of bolts

The effect of nut geometry, curved spring washer and a sealing material (Teflon tape) on the fatigue life of M12 and M16 ISO bolts was investigated. This was accompanied by the study of the axial and bending stress distribution in threads by numerical simulation of bolt and nut connections using the finite‐element method. The experimental results showed that the highest fatigue life is achieved for a slotted tapered nut. The presence of a spring washer also increases the fatigue life, providing that the correct tightening torque is applied to produce a pretension in the bolt. The use of Teflon tape as a filling material between engaging threads of the bolt and nut is shown to significantly increase the fatigue life. On the whole, the highest fatigue life is obtained for a slotted tapered nut using washer. Four fracture mechanisms were observed for bolt–nut connections during the fatigue tests.     

航天器结构用不同材质的侧面销钉和螺母组件的耐蚀性能研究

目的 针对航天器结构用不同材质的侧面销钉和螺母组件在实际的使用工况下极易出现腐蚀与咬死的问题,对不同材质的侧面销钉和螺母组件的耐蚀性能进行研究。方法 分别在高量级腐蚀条件和低量级腐蚀条件下,采用重复拧紧试验方法,对侧面销钉和螺母开展耐腐蚀性能、防咬死性能研究。结果 在高量级腐蚀条件下,无表面处理的30CrMnSiA侧面销钉+TC4螺母组件在经历12 h腐蚀试验后,其表面发生了100%的腐蚀;经历过重复拧紧试验的30CrMnSiA(表面镀镍)侧面销钉+TC4螺母组件,在经历12 h腐蚀试验后,其表面腐蚀面积＞50%;未经历重复拧紧试验的30CrMnSiA(表面镀镍)侧面销钉+TC4螺母组件,在经历12 h腐蚀试验后,其腐蚀面积约为25%~50%。在低量级腐蚀条件下,经历重复拧紧试验和未经历重复拧紧试验的30CrMnSiA(表面镀镍)侧面销钉+TC4螺母组件均未发生表面腐蚀,而30CrMnSiA(无镀镍)侧面销钉+TC4螺母组件的腐蚀面积为25%~50%。镀镍处理可以显著提高30CrMnSiA侧面销钉的耐腐蚀性能。结论 经过镀镍表面处理的30CrMnSiA侧面销钉比经过表面钝化处理的1Cr17Ni2侧面销钉具有更好的耐蚀性能、防咬死性能和环境适应性。重复拧紧虽然对镀镍侧面销钉的耐腐蚀性能有影响,但重复拧紧后的侧面销钉和螺母组件的耐蚀性能仍优于无镀镍处理的侧面销钉和螺母组件。30CrMnSiA镀镍侧面销钉+ TC4螺母的组件通过了低量级实际工况的盐雾试验考核。     

常温下MAP对红松仁酸价的影响

研究常温下MAP对红松籽油酸价的影响,为松仁的科学贮藏提供技术参考。研究结果表明MAP可以较好地抑制松仁的酸败,有利于保持松仁的贮藏品质,其中充入100%N2和100%CO2气体的试样在贮藏期间其酸价的变化相对一致,效果相对其他充气方式较好,建议在常温贮藏中使用。     

试飞测试系统压力参数在线校准方法与装置

当前试飞测试系统压力参数的校准主要采取拆卸后在实验室校准的方式,存在校准时间长,多次拆装容易造成接口损坏的问题。为了解决这个问题,研究一种压力参数的在线校准方法,实现了真实工况下的原位比对校准。通过实验获得了标准压力传感器在温度复合情况下的量值特性规律,构建了温度补偿模型,实现了标准压力值的准确获取。研制了由三个不同量程标准压力传感器、环境温湿度和大气压传感器以及在线校准软件等组成的校准装置,通过初步实验验证了校准方法和装置的合理性。该方法可以作为实验室校准的有效补充,降低校准的人力和时间成本,提高飞行试验的效率。     

Experimental analysis of the friction coefficient effect of the zinc‐lamella coated fasteners on bolt preload and tightening moment

Basic parameters of the bolt‐nut joints, which are ones of the most important elements of assembly processes, are the torque, bolt preload and friction coefficients between bolt and nut interfaces. In bolted joints tightened with torque and angle‐controlled method, friction coefficients of the fasteners are highly significant because they affect final torque and bolt preload values directly, creating a large uncertainty in regard to meet the minimum requirements on preloads considering the safety of joints and further systems, in case of this study, the vehicles being assembled. Also, the range of the lower and upper limits of friction coefficients of the coated fasteners affect process quality considerably in bolted joints tightened with torque and angle‐controlled technique. In this study, the effect of the friction coefficients on the bolt preload and final torque values in the vehicle chassis joints, which are created using torque and angle‐controlled tightening, were investigated experimentally. Therefore, bolt specimens which have both low and high friction coefficients, were tightened by the torque and angle‐controlled tightening method especially using high angle torque parameters on the vehicle chassis test bench. The torque and preload values obtained have been compared to each other and correlated in terms of the friction coefficients occurred.     

Corrosion Characterization: Use of Raman Spectroscopy for Failure Analysis

A self-locking nut was received for inspection as part of the IAF’s standard quality assurance procedure. A metallurgical cross section was taken, and upon optical microscopic observation, crack-like defects filled with what appeared to be oxides were observed close to the surface of the nut. In order to determine if the defects are folds created during forging, Raman spectroscopy was used to analyze the oxides. The analysis was based on two important properties of Iron oxides: Different oxides are created at different temperatures, each having distinct Raman spectrum. By comparing Raman spectrums from the literature to the ones obtained experimentally, it was determined that the defects originated in the manufacturing process, most likely during forging.     

Development of an anti-loosening fastener and comparing its performance with different other threaded fasteners

Threaded fasteners are widely used for temporary joining of different components that require occasional disassembling. However, threaded fasteners may have the problem of loosening under vibrating conditions, which may lead to decreasing clamping force and, thereby, a system failure. In the present experimental investigation, anti-loosening ability of various fastening elements, such as conventional nut, nylock nut, flat washer, spring washer, inside and outside serrated washer, is tested with a conventional M16 high-tension steel bolt. A hybrid double nut is used to clamp the plates in which a conventional nut is used to tighten first, and one nylock nut is then placed at the outer side for further tightening. An adhesive-bonded nut is also tested, where an adhesive is placed between bolt and nut threads. All these fasteners are tested in terms of their loosening characteristics. Accelerated vibrating conditions are used for the test on an indigenously made test rig. A split bolt with taper pin is introduced for the first time to reduce loosening of fasteners. The split bolt with taper pin shows considerably good anti-loosening property compared with other threaded fasteners tested in this work.