On the Bump Tests of Cracked Shafts Using Acoustic Emission Techniques

An investigation about the application of Acoustic Emission (AE) techniques to analyze the dynamic response of different cracked shafts rendered in bump tests is presented in this work. The experimental apparatus devised for this work complies of six shafts with different transverse crack sizes and a high-frequency data acquisition system. The AE signals generated in the bump tests performed on the different cracked shafts are captured by a wideband AE transducer. Those signals are treated by using statistical moments, wavelet transforms, and frequency- and time-domain procedures. A transverse crack of predetermined depth is etched into each shaft. The experimental results show that the values of kurtosis and skewness estimated for the AE signals can be used to identify the crack size.

DIAGNOSTICS OF FATIGUE CRACK IN ULTERIOR PLACES OF LARGER-SCALE OVERLOADED SUPPORTING SHAFT BASED ON TIME SERIES AND NEURAL NETWORKS

To improve the diagnosis accuracy and self-adaptability of fatigue crack in ulterior place of the supporting shaft, time series and neural network are attempted to be applied in research on diag-nosing the fatigue crack’s degree based on analyzing the vibration characteristics of the supporting shaft. By analyzing the characteristic parameter which is easy to be detected from the supporting shaft’s exterior, the time series model parameter which is hypersensitive to the situation of fatigue crack in ulterior place of the supporting shaft is the target input of neural network, and the fatigue crack’s degree value of supporting shaft is the output. The BP network model can be built and net-work can be trained after the structural parameters of network are selected. Furthermore, choosing the other two different group data can test the network. The test result will verify the validity of the BP network model. The result of experiment shows that the method of time series and neural network are effective to diagnose the occurrence and the development of the fatigue crack’s degree in ulterior place of the supporting shaft.

自密实高抗裂混凝土在盾构隧道工作井侧墙中的应用

采用明挖顺作法施工的盾构隧道工作井侧墙位于由维护结构、环框梁、底板及模板组成的密封空间内,其受到的约束作用强,施工难度大,容易因混凝土收缩开裂及浇筑不密实导致渗漏。依托在建的江阴靖江长江隧道工程,在室内研究的基础上,通过现场系列模型试验,比较了采用不同混凝土材料及施工工艺时混凝土结构的密实性。模型试验及工程应用结果表明,采用自密实高抗裂混凝土,结合布料工艺、浇筑速率、分层浇筑静置时间的控制,并辅以必要的振捣,可保证混凝土浇筑密实,进一步结合抗裂温控措施,可消除混凝土收缩裂缝,避免工作井侧墙出现渗漏。

盾构井底板混凝土温控参数敏感性分析

以珠江三角洲水资源配置工程的典型盾构井底板为例,采用saptis三维有限元软件,进行浇筑温度和通水冷却温控参数敏感性分析。结果表明,高温季节降低浇筑温度有利于控制混凝土内部最高温度,浇筑温度每增高1℃,内部最高温度增加约0.79℃,建议将浇筑温度降低至23℃;优化通水冷却参数(加密冷却水管,降低通水水温,适当延长通水时长)能达到良好的温控防裂效果。

富水砂土地层中斜井井筒地面注浆堵水技术

为了有效降低富水砂-土地层结构对煤矿斜井井筒造成的不均匀沉降和破坏作用,以榆神矿区西部某矿副斜井井筒涌水治理为例,在充分分析井筒涌水特征和治理条件的基础上,利用井筒周圈砂土地层与裂隙间的可注浆差异性,通过现场注浆试验及施工验证,创新性地采用地面垂直钻孔,在钻孔点位距离单层结构井壁0.6~0.8 m的平面位置和进入井筒底板片石碎石垫层0.2~0.5 m的注浆层位上,利用φ108 mm的注浆孔径,以不大于1 MPa的注浆压力和高浓度水泥单液浆(0.7∶1~1∶1)、水泥-水玻璃双液浆(水玻璃体积占比1%~5%),直接对井筒底板片石垫层进行注浆治理,实现了对井筒底板及井壁四周裂隙的高效封堵。经地下水水位恢复检验,原井筒裂缝出水地带已再无明水涌出,治理段井筒的涌水量显著降低,表明该注浆堵水技术在解决我国西北部区域因松散砂土地层不均匀沉降而导致的井筒涌水治理方面具有一定的适用性。

联轴器传动轴断裂原因

某型号联轴器传动轴在使用过程中发生断裂现象。采用宏观观察、化学成分分析、力学性能测试、扫描电镜分析、金相检验、热酸蚀试验等方法分析了该传动轴断裂的原因。结果表明:传动轴内部存在白点缺陷,材料中存在较多的硫化物和呈沿晶特征的二次裂纹;氢原子在硫化物附近聚集,形成氢陷阱,在组织和内应力的共同作用下,裂纹在氢陷阱部位萌生并扩展,形成氢致裂纹,最终导致传动轴断裂。

齿轮轴的失效分析

FM8T钢齿轮轴在使用中早期开裂。对开裂的齿轮轴进行了断口分析、金相检验、硬度测定和化学成分分析。结果表明:FM8T钢齿轮轴有效硬化层深度偏浅,且表层有非马氏体组织,承载性能下降;有严重的非金属夹杂物,力学性能较差。这两个因素导致了齿轮轴扭转疲劳开裂。

煤矿立井混凝土井壁裂缝修补技术

通过对煤矿立井混凝土井壁裂缝产生原因的分析,针对不同性质的裂缝进行了系统分类,并提出了相应的修补措施。这些措施消除了井筒整体结构存在的安全隐患,并显著提高了井壁结构的耐久性能和防水性,可为类似工程设计及施工提供有益参考。

往复式天然气压缩机主驱动电机轴裂纹分析

针对往复式天然气压缩机主驱动电机轴裂纹故障进行了失效分析,通过对该压缩机组在故障前的运行工况分析、扭振分析复核、外观分析、裂纹电镜扫描分析、金相分析、机械性能分析、化学分析等找出了引起电机轴产生裂纹的原因。分析结果表明:电机轴表面存在一层厚度1.7 mm左右的堆焊层,该电机轴表面的堆焊层是引起本次压缩机主驱动电机轴产生裂纹的直接原因。

挤压脱水机减速器空芯轴开裂的分析与对策

对某合成橡胶装置挤压脱水机进行检修时发现减速器空芯轴开裂和输出齿轮内孔磨损的问题。分析显示,导致上述问题的原因为:减速器空芯轴材料的抗疲劳能力不足,诱发了空芯轴的开裂;机组生产干胶时,长期在中低负荷条件下运行,同时,螺套的设计布局不够合理以及螺套与笼体间隙偏小,造成螺套与笼体的刮磨,从而引发了机组的异响和振动;在交变载荷、异常振动和润滑油元素聚集的共同作用下,加快了空芯轴的疲劳开裂。空芯轴与输出齿轮为间隙配合,空芯轴的开裂使两者间的微运动加剧,并最终导致输出齿轮内孔的磨损。考虑到输出齿轮内孔的磨损程度在可控范围内,因此,对输出齿轮内孔和齿面采用了修复的处理方案。而开裂的空芯轴则需要更换新轴。新的国产化空芯轴选用机械性能更好的34CrNi3Mo并优化了热处理工艺,与修复后的输出齿轮内孔配对加工。此外,还优化了螺套的布局,适当减小了螺套的外径并提高了机组的运行负荷,以使挤压脱水机的运行更加安全稳定。

某型电机轴开裂原因

某型电机在使用过程中振动异常,停机检查发现电机轴表面存在裂纹。采用宏观观察、化学成分分析、金相检验、力学性能测试、扫描电镜分析等方法研究了该电机轴开裂的原因。结果表明:电机轴断口呈多源疲劳快速扩展特征形貌;堆焊工艺不当,使堆焊层硬度较低,且形成了脆性较大的自回火马氏体;在运转过程中,电机轴主要承受扭转载荷,轴表面所受应力最大,因此优先在轴表面堆焊层形成微裂纹,裂纹在扩展过程中汇聚形成多源疲劳,并在扭矩作用下裂纹呈八字形扩展,最终导致电机轴发生开裂现象。

某型发动机锥齿轮轴承外圈开裂故障分析与解决方案研究

本文通过对某型涡轴发动机锥齿轮轴承设计、工艺、加工、装配和冶金分析,确认锥齿轮轴承开裂是轴承外圈安装边转接R处有重熔层,提出了对锥齿轮轴承外圆面采用修锉加抛光、安装平面交接R处采用砂轮修磨加抛光的工艺方法等改进措施。制定了外场更换锥齿轮轴承操作规程,对同类型轴承排故具有一定的参考价值。

FATIGUE LIVES FOR INDUCTION HARDENED SHAFTS MATERIALS ACCORDING TO THE ENVIRONMENTAL TEMPERATURES

Rotary bending fatigue tests were carried out with two kinds of materials, S43C and S50C, using the front engine and front drive shaft （FF shaft） of vehicle. The specimens were induction hardened about 1.0mm depth from the specimen surface, and the hardness value on the surface was about HRC56-60. The tested environment temperatures were -30, 25 and 80℃ in order to look over effect of the induction hardening and the environmental temperatures on the fatigue characteristics. The fatigue limit of induction hardened specimens increased more about 45% than non-hardened specimens showing that the endurances of S43C and S50C were 98.1 and 107.9MPa in non-hardened samples, 147.1 and 156.9MPa in hardened samplesrespectably. The maximum tensile and compressive stress on the small circular defect was about ＋250 and -450MPa respectively when circular defect is situated on top and bottom. The fatigue life increased 80, 25 and -30℃ in order regardless of hardening. In comparison of the fatigue lives on the basis of tested result at 25℃, the fatigue lives of non-hardened specimens decreased about 35%, but that of hardened specimens decreased about only 5% at 80℃ more than at 25℃. And fatigue life of non-hardened and hardened specimens were about 110% and 120% higher at -30℃ than that of 25℃. Based on the result of stress distribution near the defect, the tensile and compressive stress repeatedly generated by load direction were the largest on the small circular defect due to the stress concentration.

催化裂化三机组能效实时计算与应用

催化裂化装置三机组能效计算影响因素众多、耦合作用强,结合主风机、烟气轮机的动力学、热力学性质以及电机特性,构建了能效计算模型,可实现三机组能效的实时计算。以某催化裂化装置为例,进行了能效计算的验证,并对机组能效的影响因素进行了分析,结果表明:通过设计、操作与维护协同优化,提高有效烟气流量、温度和压力,降低烟机背压,采用高效叶片,减少烟机结垢,优化主风机设计选型等措施均可有效提升三机组能效。

An Improved Coupled Dynamic Modelling for Exploring Gearbox Vibrations Considering Local Defects

Gearbox is a key part in machinery,in which gear,shaft and bearing operate together to transmit motion and power.The wide usage and high failure rate of gearbox make it attract much attention on its health monitoring and fault diagnosis.Dynamic modelling can study the mechanism under different faults and provide theoretical foundation for fault detection.However,current commonly used gear dynamic model usually neglects the influence of bearing and shaft,resulting in incomplete understanding of gearbox fault diagnosis especially under the effect of local defects on gear and shaft.To address this problem,an improved gear-shaft-bearing-housing dynamic model is proposed to reveal the vibration mechanism and responses considering shaft whirling and gear local defects.Firstly,an eighteen degree-of-freedom gearbox dynamic model is proposed,taking into account the interaction among gear,bearing and shaft.Secondly,the dynamic model is iteratively solved.Then,vibration responses are expounded and analysed considering gear spalling and shaft crack.Numerical results show that the gear mesh frequency and its harmonics have higher amplitude through the spectrum.Vibration RMS and the shaft rotating frequency increase with the spalling size and shaft crack angle in general.An experiment is designed to verify the rationality of the proposed gearbox model.Lastly,comprehensive analysis under different spalling size and shaft crack angle are analysed.Results show that when spalling size and crack angle are larger,RMS and the amplitude of shaft rotating frequency will not increase linearly.The dynamic model can accurately simulate the vibration of gear transmission system,which is helpful for gearbox fault diagnosis.

江阴靖江长江隧道工作井底板混凝土自防水技术与应用

江阴靖江长江隧道是内地最大直径的盾构隧道,其始发工作井底板宽53.6 m,长28 m,厚1.5 m,抗裂防水要求高,但这种一次性现浇大体积混凝土面临着突出的收缩开裂问题。基于多场耦合机制开裂风险评估,从材料与工艺措施两个方面来降低混凝土温度、全过程补偿混凝土收缩变形,实现了对混凝土抗裂性能的精准调控。试验结果表明,混凝土7 d绝热温为43.1℃,且1、7 d比值为48.6%,28 d自生体积膨胀变形202.4με,构件混凝土温升值降低了4℃,温升阶段单位膨胀变形增加了231.2%,单位温降收缩变形减小了15.2%。炎热气候按方案施工的工作井底板混凝土未出现收缩裂缝,达到预期目标。

宽厚板轧机传动轴虎口裂纹产生原因分析

通过对轧机传动轴虎口裂纹分析,发现裂纹首先在传动轴虎口内壁形成,在后期使用过程中逐渐发生疲劳扩展,最终产生脆性断裂。金相组织观察结果表明:裂纹周围组织主要为属于脆性组织的淬火马氏体,回火屈氏体偏少,说明回火工艺不合理;存在残余组织应力,易于在使用过程中开裂。轧制过程中咬钢瞬间电流达到7069 A,比额定电流3096 A高出2倍以上,说明轧制过程中存在主传动轴瞬间冲击载荷过载现象。

1Cr13半马氏体不锈钢短轴热处理后开裂的原因分析

针对某厂1Cr13半马氏体不锈钢短轴热处理后产生裂纹的问题,通过宏观形貌检查、化学成分分析、金相检验、硬度测试和裂纹断口形貌分析等方法对热处理后产生开裂的原因进行分析。结果表明:碳含量略高于标准值、组织中存在较多分布不均匀并且形态控制较差的硫化物夹杂以及由孔隙气道偏析和碳化物聚集偏析形成的偏析线和与淬火后的残余应力是1Cr13半马氏体不锈钢短轴热处理开裂的主要原因,其中以呈细长条状分布的硫化物夹杂和偏析线危害最大。可以通过严格控制钢材的化学成分、夹杂物及偏析线的数量、大小和分布形态与热处理工艺相结合的措施,解决1Cr13半马氏体不锈钢短轴热处理后开裂的问题。

十字轴表面裂纹仿真与材料的断裂韧性试验

针对万向联轴器十字轴结构安全性问题,从表面缺陷裂纹应力强度因子角度分析十字轴断裂情况。建立十字轴三维模型,运用ANSYS WorkBench对十字轴进行静力学分析,找出十字轴轴径圆弧处应力最大。然后在分析后的模型中插入半椭圆形裂纹,进行表面裂纹分析。最后,在低周疲劳试验机上进行三点弯曲试验与柔度法得到十字轴材料的平面断裂韧性。研究结果表明:在十字轴轴径处裂纹大小长半轴半径c=5mm,短半轴半径a=1mm的半椭圆形裂纹得到十字轴应力强度因子大于材料试验的KIC,十字轴出现裂纹断裂。

斜井井筒风积沙段拱部轴向开裂规律研究与治理技术

朱家峁煤矿首次发现主、副斜井井筒拱顶轴向开裂后,即开始进行原因分析和治理的多方案的制定、选择、论证。提出的治理方案主要有地面旋喷注浆加固、深层搅拌桩法、斜井井筒两帮壁后土层压力帷幕注浆法。通过分析井筒受力状态,提出造成井筒拱顶轴向开裂且持续发展的最主要原因是斜井井筒左右两帮土层对井筒的水平支撑反力不足这一观点,经论证后确定了井筒的拱顶轴向开裂段治理技术,对井筒左右两侧土层注浆加固,以提高拱形井壁结构左右两侧土层的水平支撑反力,同时减少左右两侧土层沉降的治理方案。注浆加固后,井筒周围的土层虽然仍会有塑性变形,但变形速率极为缓慢,而且在注浆加固期间挤密加固了地层,一定程度地减小已发生的拱顶裂缝、拱肩裂缝的宽度,并且对井筒开裂段井壁加强支护,从而缓解井壁破裂危险程度。截至目前,朱家峁煤矿3条井筒拱顶开裂段理后稳定,井筒拱顶开裂未见扩大现象。