烟气轮机叶片断裂原因分析

某炼化厂烟气轮机一动叶片断裂引起停机事故.通过断口宏观、微观观察和叶片金相检验对叶片断裂原因进行分析,结果表明:叶片断裂性质为微动疲劳,叶片榫头与轮盘榫槽装配不良导致局部应力过大产生微动磨损是引起疲劳断裂的主要原因.     

某钢制螺钉断裂失效分析

某液压缸盖紧固用螺钉在进行试验时发生断裂。采用外观检查、断口宏微观观察、金相检验和硬度测试等方法对两枚断裂失效螺钉进行了分析。结果表明,螺钉A失效性质为过载断裂,其断裂原因主要与装配时拧紧力过大从而产生了扭转剪切开裂损伤有关;螺钉B失效性质为疲劳断裂,其断裂原因主要与螺钉B表面存在脱碳层导致疲劳强度大幅降低有关,且在装配时发生倾斜,螺钉一侧存在附加拉应力,对疲劳失效也有一定的促进作用。建议严格控制热处理工艺和装配过程力矩大小,并加强螺钉孔和螺钉的加工精度控制。     

钛合金螺钉脆性断裂原因分析

钛合金螺钉在装配过程中发生断裂失效,对装配和模拟扭转试验过程中断裂的钛合金螺钉断口进行了宏微观观察和能谱成分分析,对同批次螺钉进行了应力持久试验,对失效钛合金螺钉的金相组织进行了检查.结果表明,螺钉的断裂性质相同,均为脆性断裂;螺钉断裂的主要原因是存在内部缺陷,而与氢致脆性断裂的关系不大;螺钉的内部缺陷可能是在锻造过程后期由于某种偶然因素造成了原始β晶界开裂所致.     

双耳托板螺钉断裂原因分析及改进措施

双耳托板螺钉装配过程中在托板与杆部结合处发生断裂。对断裂螺钉进行断口形貌分析,确定断裂性质为过载断裂;对同批次螺钉进行了金相、硬度、拉力试验、楔负载试验以及模拟安装试验,结果表明,螺钉断裂原因主要与断裂位置流线密集有关,同时热处理制度不匹配和流线被切断对断裂有促进作用。针对螺钉断裂有关原因提出了改进冷镦工艺、调整热处理制度和优化头(托板)杆加工工艺等改进措施,并对改进效果进行了验证,结果表明改进有效,新工艺加工的螺钉装配过程未再发生相同断裂现象。     

冷轧机轴承的失效分析

冷轧机使用一段时间后第四滚子组的销子发生断裂失效现象。采用扫描电镜、金相、硬度、化学成分测试对失效件进行了综合分析。结果表明,滚子与外圈不良接触导致其接触部位产生磨损,滚子内的固定销承受较高的扭转应力并使其发生疲劳断裂。     

20钢吊环螺钉断裂分析

通过对20钢吊环螺钉的宏观检查、化学成分、金相显微组织、断口形貌以及断口微区成分等进行分析,确定了吊环螺钉的断裂原因。结果表明:吊环螺钉断裂的性质为脆性断裂,吊环螺钉装卡不当、螺纹处加工质量不高以及材质上的不足是吊环螺钉断裂的主要原因。     

M3×10 mm十字槽沉头螺钉断裂分析

某发射装置中的1Cr17Ni2钢M3×10 mm十字槽沉头螺钉,在使用中发生断裂。为了确保该发射装置可靠运行,对该螺钉断裂展开了分析和研究。观察了金相组织、测试了硬度,其均符合HB1-206-2002标准要求。通过体视镜对螺钉断口及未断裂螺钉十字槽进行了宏观形貌观察,发现断裂部位存在锈蚀痕迹,而未断裂螺钉十字槽底部已出现裂纹。进一步对断口微观形貌进行了观察与分析,发现断口无明显塑性变形痕迹。能谱分析结果显示,断口区域存在大量Cl~-,可判断失效原因为应力腐蚀破坏。建议调整冲压工艺、降低表面拉应力,避免出现应力腐蚀现象,确保发射装置运行可靠性。     

精冲凸模根部断裂的失效分析

利用扫描电镜对精冲凸模的断口进行微观分析,借助有限元软件对模具进行计算,得到凸模上的应力分布情况。结果表明:凸模根部为脆性疲劳断裂,螺纹孔处的应力集中导致该螺钉固定式凸模发生断裂。     

PDC钻头不良工况分析

PDC钻头已经得到了广泛应用,但在硬地层及复杂地层钻进时,钻头寿命短,钻速低。基于ANSYS软件对PDC钻头在致密砂岩中钻进时的正常工况及不良工况的瞬态接触仿真分析,比较了各种工况下PDC钻头的应力云图。发现不良工况会导致PDC钻头局部受到集中应力的作用,这些集中力大于或远大于正常钻进时钻头受到的最大应力。长时间的不良工况会导致钻头损坏,造成进尺缓慢或无进尺。     

镀锌螺钉断裂失效分析

采用宏微观断口形貌分析、化学成分分析、金相组织分析、力学性能测试等方法,分析了镀锌螺钉断裂的原因.结果表明:搓牙工序中在牙根部位产生的微裂纹是导致螺钉发生最终断裂的主要原因,螺钉具有较高的脆性是导致螺钉发生最终断裂的重要原因.     

钛合金筋板件等温局部加载模具应力分析

等温局部加载成形技术为航空航天复杂筋板类大型整体构件的成形提供了一种新的途径,但由于构件尺寸大,其成形温度高、时间长、载荷大等工艺特点,对模具提出了更高的要求。文章针对TA15钛合金典型环形高筋薄腹特征结构件等温局部加载成形,分析了等温局部加载模具的结构特点和可能的失效形式,并在此基础上采用DEFORM 3D有限元软件,对成形时模具应力进行了研究,获得了模具载荷和应力分布规律,并进一步分析了模具凹圆角半径和锻件筋条宽度对模具应力的影响。结果表明,等温局部加载成形模具的失效形式,主要为应力集中引起的脆性断裂;加载分区边界附近模具应力较小,离分区边界越远模具应力越大,且应力峰值出现在宽度较小的环形筋型腔凹角处;模具型腔各部分材料填充能力的不一致,是导致模具应力不均匀、局部出现应力集中的主要原因;增大模具凹圆角半径,模具应力降低程度较小,而通过合理的锻件几何尺寸设计,可以改善模具型腔的充填性,能更有效地降低模具应力的不均匀性和应力峰值。文章的研究结果可为等温局部加载成形模具的设计提供参考。     

Torsional Fatigue Cracking and Fracture Behaviors of Cold-Drawn Copper:Effects of Microstructure and Axial Stress

The fatigue cracking and fracture behavior of cold-drawn copper subjected to cyclic torsional loading were investigated in this study.It was found that with increasing stress amplitude,the fracture mode of cold-drawn copper gradually changes from a shear fracture on transverse maximum shear stress plane to a mixed shear mode on both transverse and longitudinal shear planes and finally turns to the shear fracture on multiple longitudinal shear planes.Combining the cracking morphology and the relationship between torsional fatigue cracking and the grain boundaries,the fracture mechanism of cold-drawn copper under cyclic torsional loading was analyzed and proposed by considering the effects of the microstructure and axial stress caused by torsion.Because of the promotion of the grain boundary distribution on longitudinal crack propagation and the inhibition of axial stress on transverse crack grown,the tendency of crack propagation along the longitudinal direction increases with increasing stress levels.     

MECHANISM ANALYSIS OF THICKNESS EFFECT ON MIXED MODE I／II FRACTURE OF LC4-CS ALUMINUM ALLOY

Mixed mode I//II fracture experiments of LC4-CS aluminum alloy were conducted by using tension-shear specimens with thicknesses of 2, 4, 8 and 14mm. Fracture mechanisms of thickness effect on mixed mode I//II fracture were first examined from fracture surface morphology to correlate with the macroscopic fracture behavior and stress state. It is found that specimen thickness has a strong influence on mixed mode fracture. As thickness varies from thin to thick the macroscopic fracture surfaces appear the characteristics of plane stress state (2mm, 4mm-thick specimen), three-dimensional stress state (8ram-thick specimens), and plane strain state (14mm-thick specimens), respectively. The specimens of all kinds of thicknesses are typical of tensile type failure under mode I loading condition and shear type failure under mode II loading condition. Two distinct features coexist on the fracture surfaces under mixed mode loading conditions, and the corresponding proportion varies with loading mixity. Void-growth processes are the failure mechanism in both predominately tensile and shear-type fractures. The size and depth of dimples on the fracture surface vary greatly with thickness. Therefore, it is extraordinary necessary to take into account the thickness effect when a mixed mode fracture criterion is being established.     

MECHANISM ANALYSIS OF THICKNESS EFFECT ON MIXED MODE Ⅰ/Ⅱ FRACTURE OF LC4-CS ALUMINUM ALLOY

Mixed mode Ⅰ/Ⅱ fracture experiments of LC4-CS aluminum alloy were conducted by using tension-shear specimens with thicknesses of 2, 4, 8 and 14mm. Fracture mechanisms of thickness effect on mixed mode Ⅰ/Ⅱ fracture were first examined from fracture surface morphology to correlate with the macroscopic fracture behavior and stress state. It is found that specimen thickness has a strong influence on mixed mode fracture. As thickness varies from thin to thick the macroscopic fracture surfaces appear the characteristics of plane stress state (2mm, 4mm-thick specimen), threedimensional stress state (8mm-thick specimens), and plane strain state (14mm-thick specimens), respectively. The specimens of all kinds of thicknesses are typical of tensile type failure under mode I loading condition and shear type failure under mode Ⅱloading condition. Two distinct features coexist on the fracture surfaces under mixed mode loading conditions, and the corresponding proportion varies with loading mixity. Void-growth processes are the failure mechanism in both predominately tensileand shear-type fractures. The size and depth of dimples on the fracture surface vary greatly with thickness. Therefore, it is extraordinary necessary to take into account the thickness effect when a mixed mode fracture criterion is being established.     

Deformation behaviour of closed-cell aluminium foams in tension

The mechanical behaviour of commercially available ALPORAS aluminium foam with two different densities was studied under tension loading. In addition to the common stress–strain measurements, local deformation, notch-opening displacement and damage evolution were determined. The deformation characteristics deviated from those observed in aluminium foams under compression. No deformation bands or plastic instabilities could be observed in tension, which are very frequent in compression of metallic foams. Four regimes were evident in the stress–strain curves and deformation maps: the linear elastic regime, the plastic regime with no significant crack initiation and propagation, the regime of formation of a fracture process zone and, finally, the regime of fracture, where a main crack propagates through the specimen and leads to failure. The fracture strain was only a few per cent, with the higher-density foam showing a larger fracture strain, and the plastic Poisson's ratio was about 0.35. The notched specimens showed increasing fracture strengths in terms of the net section stress with increasing notch depth. It is suggested that a change in stress state, caused by a non-vanishing Poisson's ratio, in front of the notch tip creates an increase of the fracture strength similar to the behaviour in ductile bulk metals.     

直升机尾桨连杆组件失效分析

直升机在飞行降落时尾桨操纵连杆发生断裂,对断裂的尾桨连杆组件损伤及磨损情况进行外观检查,宏微观观察分析连杆断口,并对连杆的材料成分、金相组织和硬度进行检查。结果表明：连杆的断裂性质为疲劳断裂,疲劳起源于螺纹根部,疲劳区占断口总面积80%以上;连杆端部的球轴承产生了异常的磨损。分析认为：由于连杆端的球轴承产生了异常的磨损,导致其对连杆的限位功能不良,连杆发生轻微偏转使连杆上形成了附加的弯曲应力。该应力与连杆上的工作应力叠加,造成连杆发生了疲劳断裂。此外,对连杆硬度的检测表明连杆的硬度仅为HRC 22.7,说明其强度较低,疲劳抗力较差,也是连杆容易发生疲劳断裂的原因。     

循环式行星滚柱丝杠副的热力耦合特性研究

为了研究循环式行星滚柱丝杠副在不同轴向载荷和不同工作温度下的变形和接触应力分布规律,以循环式行星滚柱丝杠副中的丝杠为研究对象,采用热力耦合仿真方法,建立了循环式行星滚柱丝杠副的有限元模型,研究不同工况下滚柱丝杠副的轴向载荷和工作温度使丝杠产生的变形和接触应力规律.对比轴向载荷、工作温度、热力耦合3种工况下丝杠的变形和接...     

燃气轮机低压压气机转子叶片断裂分析

某型燃气轮机运行近1 000 h后,发生2片低压压气机转子叶片脱榫断裂和同级多片榫头裂纹故障。通过对断裂和裂纹叶片外观观察、断口分析、化学成分分析、硬度检测和金相检验等手段,确认了断裂和裂纹叶片失效模式相同,均属振动疲劳断裂,盘和叶片配合不良引起微动磨损是该级叶片早期振动疲劳断裂的主要原因。盘、片配合不良主要是由于配合面间无防磨损涂层,在应用过程中产生氧化和磨损引起的;通过盘和叶片榫齿配合面涂干膜润滑,有效解决了盘片配合面微动磨损问题。     

Study on dynamic fracture behavior of TA15ELI ahoy under mode-Ⅱ loading by caustics method

The dynamic fractttre behavior of TA15ELI alloy with lath-like microstructure was studied by caustics method. Specimens with double-side pre-notch were tested under the plane-stress condition at mode-Ⅱ loading with a drop hammer system. Caustics information recorded in films illustrated the histories of both crack length and stress intensity factor. The dynamic fracture toughness and crack growth velocity of mixed feature of mainly plastic mode for TA15ELI alloy in dynamic mode-Ⅱ fracture. Shear localization was observed in the vicinity of the crack initiation area.     

加载方式对铸铁断口形貌的影响

铸铁断口形貌主要受其内部结晶组织和加载方式的影响，铸铁基体和石墨出现的不同形貌是被不同的加载方式所控制的，石墨在不同方式应力影响下，随着基体的拉伸，扭转或压缩而变形，挤出或破碎，呈现出不同的断裂形貌，这种形貌特征有助于判别加载方式的类别，明确铸铁断裂的机理，是失效分析的重要手段。