铁路货车钩缓装置钩尾扁销螺栓断裂原因分析

铁路货车钩缓装置中的钩尾销螺栓在螺杆近方头一侧根部位置发生断裂。采用微观分析方法分析了该螺柱断裂原因。综合分析表明：该断裂螺栓方头一侧可能仅局部加热后锻打成四方头,并发生过热,造成在方头一侧的螺柱根部形成马氏体组织和魏氏体组织过渡的U型区域。不良组织的存在增大了钢的脆性,冷加工性能大大降低,在U型区域和螺柱表面交界处萌生了微细裂纹。当钩尾扁销螺栓在列车运行过程中受到过大的冲击时,该螺栓上的微细裂纹在螺栓靠近方头一侧存在的沿轴向的拉应力和螺栓正常紧固力的合力联合作用下张开并迅速扩展,造成螺栓断裂。     

不锈钢U形螺栓的断裂原因

某S30408不锈钢U形螺栓使用约0.5 a(年)后就发生了断裂。通过化学成分分析、硬度测试、拉伸试验、金相检验、非金属夹杂物测试、断口分析及能谱测试等方法对该U形螺栓的断裂原因进行了分析。结果表明:该S30408不锈钢U形螺栓在冷加工硬化时产生了残余应力,后又叠加了工作应力,再加上在潮湿的腐蚀环境下工作,螺栓发生了应力腐蚀开裂,裂纹不断扩展最终导致该U形螺栓断裂。     

风力发电机叶片连接用高强度螺栓断裂原因

XE112-2000型风力发电机叶片连接用高强度螺栓在服役过程中频繁断裂,通过宏观观察、金相检验、力学性能测试及化学成分分析等方法对螺栓的断裂原因进行了分析。结果表明:螺栓断裂形式为腐蚀疲劳断裂,主要原因是螺栓的螺纹成形工艺为先调质后滚压成形,螺纹外侧表面受到挤压,导致螺纹顶部受到相反的拉应力作用,此外,又因为螺栓受到加工硬化的影响,产生较大的残余拉应力,增加了产生微裂纹和表面缺陷的可能,导致在螺纹顶部偏中心处产生了应力腐蚀裂纹。在之后的服役过程中,由于疲劳作用,裂纹处产生应力集中,导致裂纹快速扩展,最终螺纹发生腐蚀疲劳断裂。     

发动机凸轮轴正时带轮紧固螺栓断裂原因分析

某汽车发动机凸轮轴正时带轮紧固螺栓在台架耐久试验中发生断裂。通过宏观检验、化学成分分析、硬度测试、金相检验以及断口分析等方法对螺栓的断裂原因进行了分析。结果表明:该紧固螺栓的断裂模式为疲劳断裂;螺栓未紧固到设计要求的预紧力,导致其在使用过程中发生松动,在交变应力作用下螺栓螺纹旋合部位萌生裂纹,最终导致螺栓发生疲劳断裂。     

某核电站凝汽器密封结构用镍铝青铜螺栓断裂原因

某核电站凝汽器密封结构用镍铝青铜螺栓发生断裂现象,采用宏观观察、化学成分分析、扫描电镜分析、力学性能测试、金相检验等方法对螺栓断裂的原因进行分析。结果表明：螺栓在潮湿的NH₃环境下发生了应力腐蚀开裂;断裂螺栓在服役过程中受到不均匀的应力载荷,使表面应力腐蚀倾向变大,且螺栓长期处于自身应力腐蚀敏感介质中,在二者的耦合作用下,应力腐蚀裂纹萌生;裂纹沿残余应力较高的相界区域向内扩展,最终导致螺栓发生断裂。     

制动器螺栓复合应力下的失效分析

用手制动拉索和制动器螺栓将装运的面包车固定在平板车上，到达目的地后发现制动器螺栓出现松动和断裂现象。在运输过程中，制动器螺栓不仅承受上下振动方向高频率低应力而形成的双向弯曲状态，而且又要承受前后方向的低频率高应力而形成的单向弯曲状态。通过受力分析并结合扫描电镜对断口形貌和显微组织的观察，在螺栓齿根发现多处疲劳源，在扩展阶段，出现疲劳辉纹和大量二次裂纹，最终在拉应力作用下形成撕裂台阶而断裂。     

9FA燃机过渡段用螺栓断裂分析

某国产9FA燃机过渡段用螺栓在运行较短时间后发生断裂。采用化学成分分析、力学性能测试及金相检验等方法对螺栓断裂的原因进行了分析。结果表明：由于螺栓螺纹边缘部位凹凸不平造成大量的应力集中而形成微裂纹,在不断的热循环过程中,受热应力的作用微裂纹不断地扩展,直至剩余截面不能再承担负荷而导致螺栓的断裂。     

发电机组轮毂变桨轴承螺栓断裂原因分析

某风力发电公司的变桨轴承螺栓在使用半年后发生断裂。采用金相检验、化学成分分析、硬度测试及断口分析等方法对该螺栓断裂的原因进行了分析。结果表明:裂纹起源于螺帽与螺杆连接的R角处,该处为应力集中部位,在螺栓松动后,垫片在交变载荷的作用下不断撞击螺栓R角处并在螺杆表面造成损伤,当损伤达到一定程度后,再加上螺杆表面存在脱碳现象,造成表面裂纹的萌生,裂纹在交变载荷的作用下扩展,导致螺栓发生疲劳断裂。     

某压缩机内部活塞与滑阀连接螺栓断裂失效分析

某螺杆压缩机内部活塞与滑阀之间的连接螺栓在使用过程中仅运行2 500h即发生断裂。采用化学成分分析、宏观观察、光学显微镜和扫描电镜观察等方法对连接螺栓的断裂原因进行了分析。结果表明:导致连接螺栓断裂的主要原因是螺栓装配服役期间承受附加弯曲应力,在交变应力的共同作用下于应力集中的齿根周边过早萌生裂纹并疲劳扩展,最终造成螺栓断裂。     

10.9级高强螺栓头部断裂原因分析

通过宏观检验、化学成分分析、力学性能试验、金相检验及能谱分析等方法对10.9级高强螺栓断裂原因进行了分析。结果表明:在螺栓镦头成型工序中,头部R角部位产生折叠微裂纹,形成了早期裂纹源;在服役过程中,螺栓长期受交变工作应力作用,使得微裂纹进一步扩展,最终导致高周疲劳断裂。最后提出了相应的预防措施。     

汽轮机末级叶片断裂原因分析

某机组低压末级叶片在运行过程中发生断裂。采用化学成分分析、力学性能检测和显微组织检验及用X射线法分析叶片的残余应力等方法对断裂叶片进行了分析。结果表明：疲劳裂纹起源于一个机械缺口,裂纹源在交变应力和残余应力的共同作用下不断扩展,导致叶片疲劳断裂。     

Failure Investigation on Inducer Blades of Locomotive Turbocharger

Damage to varying degrees including fracture, cracking, and scraping occurred on inducer blades used in a locomotive turbocharger which had run for 3626 km. The blade fracture was formed by the propagation of axial and radial cracks forming an L-shape. Fractography investigation indicates that the axial fracture mode of the blade was by fatigue. The radial fracture was formed by one instantaneous crack. A strike dent was present on the leading edge of the fractured blade and this dent became the initiation site of fatigue crack. Failure of other blades was subsequent to the original fracture.     

循环泵法兰螺栓断裂分析

通过金相检验、断口分析和化学成分分析等方法对循环泵法兰螺栓的断裂原因进行了分析。结果表明：螺栓早期断裂失效的主要原因是材料使用有误,加上受海水中的氯离子腐蚀引起奥氏体不锈钢螺栓产生应力腐蚀裂纹并扩展所致。     

Bimodular behaviour and crack closure in compression in a brittle material

A vibrating beam method was used to determine the elastic modulus of graphite rods. The frequency and apparent modulus were determined as a function of compressive end-loading. Following fracture of the rod, the frequency and apparent modulus were decreased. At a compressive end-loading of about 0.83 MPa (120 p.s.i.), crack closure was sufficient for the fractured rod to behave similarly in vibration to the unfractured rod. Thus, the fractured material behaves in a bimodular fashion and crack closure can be achieved to enable unimpeded stress transfer across the fracture surface during vibration.     

50CrVA扭杆断裂原因分析

对断裂的50CrVA扭杆进行断口宏微观观察、金相组织检查、硬度测试及疲劳强度校核.疲劳强度校核结果说明扭转载荷过大是扭杆疲劳断裂的主要原因.材质分析显示扭杆中含有大尺寸富Zn夹杂物,它促进了疲劳裂纹的萌生,缩短了扭杆的疲劳寿命.     

飞机舵机失效分析及首断件判定

某飞机舵机在地面随机振动试验后其电传功能失效,分解发现其中的电门支架和传感器支架均已断裂。采用断口分析、化学成分分析、硬度测试和金相检验等手段对该舵机失效原因及首断件进行了分析。结果表明:电门支架为该失效舵机各断裂件中的首断件,电门支架断裂的主要原因是其断裂处在振动试验前就已存在裂纹;舵机失效过程为电门支架首先发生准解理断裂后,其中一块断口由于失去固定作用对传感器支架产生撞击,进而又引起传感器支架发生疲劳断裂。     

室温大气环境下过时效态3J21合金疲劳行为

在MTS万能实验机上对室温大气环境下过时效态3J21合金的疲劳行为进行研究,并采用扫描电镜(SEM)对宏观断口及微观断口进行分析.结果表明,过时效态3J21合金的疲劳裂纹呈穿晶扩展和沿晶扩展,且沿晶扩展的比例较大,疲劳裂纹萌生寿命短,扩展途径相对平直,扩展速率大,裂纹扩展抗力小,疲劳寿命低;过时效态3J21合金疲劳断口...     

Fracture characteristics of a particulate-reinforced metal matrix composite

The effect of particulates on the failure mechanism of an Al-Mg-Si alloy 6061 with 20% angular alumina particles was studied. Fracture toughness tests were conducted on compact tension peak-aged specimens. The interaction of the reinforcement phase with the crack was investigated by optical microscopy and scanning electron microscopy, both on the surface and in the mid-thickness of the fractured specimen. It is shown that the fractured particles ahead of the crack tip, in particular the larger particles, play an important role in the void-initiation phase of the fracture process. Particle size and aspect ratio determine the likelihood of fracture. Some differences in the failure mechanisms have been observed between the mid-thickness and the surface of the specimen because of the difference between plane strain and plane stress fractures.     

Crack tip damage development and crack growth resistance in particulate reinforced metal matrix composites

A study of crack tip damage development and crack growth resistance of aluminium 359/20% V_f silicon carbide and aluminium 6061/20% V_f Micral^Tm particulate reinforced metal matrix composites has been conducted. Observations of crack tip process zone development at the specimen surface have been compared with the results of fractographic examination of the centre of the specimen. Both materials were found to fracture by a process of void nucleation, growth and coalescence. Void nucleation was found to be by fracture or debonding of reinforcement particles, and/or fracture or debonding of secondary matrix particles. The preferred mode of void nucleation was found to vary depending on the constituents of the PR MMC and even the heat treatment state of the material. It was found that in these materials fractured particles identified on the fracture surface fractured during loading rather than being pre-cracked during fabrication. It was further found that observations of damage development from the specimen surface did not necessarily reflect the mechanisms prevailing in the specimen bulk. Under plane strain conditions, both materials were found to exhibit decreasing crack growth resistance as crack extension proceeded, due to the “anti-shielding” effect of damage accumulated in the process zone ahead of the crack tip. In thin specimens of the Comral-85 composite, however, dramatically improved toughness was obtained, and K_R curves have been obtained for such specimens. The method of measuring crack length was found to have a profound effect on the K_R curve; it was concluded that the K_R curve determined using the crack length measured at the specimen surface best reflected the true crack growth resistance of these materials.     

Analysis of the fracture of a turbine blade on a turbojet engine

The fracture on a turbine blade of a turbojet engine has been investigated to see the cause of crack initiation. The fractured turbine blade did not seem to have suffered any damages by foreign objects. The turbine blade had initially cracked by a fatigue mechanism over a period of time and then fractured by the overload at the last moment.The crack initiated at the subsurface or close to the surface and showed the cleavage-like features. The segregated area of Ti and Mo, caused usually by improper manufacturing process, is found by the microstructure and EDX analysis of the blade. The crack initiated at this area and was due to the stress concentration at the segregation of Ti and Mo near the blade surface.