汽车稳定杆连接杆球头销断裂原因

某汽车稳定杆连接杆球头销发生断裂现象，采用宏观观察、化学成分分析、扫描电镜分析、金相检验、硬度测试等方法分析了其断裂原因，用有限元分析方法进一步分析。结果表明：未对球头销进行调质热处理，导致其力学性能降低，球头销在外界交变载荷的作用下发生了断裂。     

45B钢链轨销轴断裂原因分析

某45B钢链轨销轴在使用过程中发生早期断裂。通过化学成分分析、硬度测试、有效硬化层深度测定、金相检验、断口分析等方法,对销轴的断裂原因进行了分析。结果表明:销轴断裂机制为准解理断裂+韧性断裂的混合型断裂;在使用过程中,45B钢材料中的球状氧化物剥落留下微孔洞形成裂纹源,在弯曲应力的作用下,裂纹源迅速放射扩展,造成销轴早期断裂。     

飞机操纵系统链条销轴断裂分析

某型飞机操纵系统链条销轴在使用中断裂。采用化学成分分析、外观检查、断口分析和表面质量检验等方法对断裂销轴进行了分析,又对有裂纹的销轴与断裂销轴进行了对比分析。结果表明：销轴表面存在原始缺陷,加上链条链板在长期使用中的磨损使得链板间隙增大,导致销轴承受剪切力的同时又承受弯曲载荷,最终导致销轴发生疲劳断裂。     

基于DEFORM的球销旋铆有限元分析

铝合金球头销目前主要应用于汽车行业,其封装技术是实现汽车轻量化和汽车行驶安全的核心技术之一。由于影响球头销的封装因素复杂,致使封装完成后组件的质量很难得到保证。在这种情况下,文章主要采用DEFORM-3D有限元软件进行球头销旋铆成形模拟分析,并进行试验验证,通过对比得出铆模拟结果与试验结果吻合较好,可以采用模拟方法对旋铆工艺进行研究分析。同时,研究在旋铆头一定的情况下,球座的几何形状对球头销封装质量的影响,通过正交分析法和极差分析法对数据进行分析处理,得出影响球头销封装质量的主次关系,从而保证球头销封装情况良好,符合使用条件。     

挖掘机销轴断裂分析

利用宏观检验、断口分析、化学成分分析、金相检验以及硬度检测等方法,对42CrMo钢挖掘机销轴的断裂原因进行了分析。结果表明:销轴断裂为双向弯曲疲劳断裂。由于销轴表面存在较脆的白亮层ε相,且白亮层分布有较严重的疏松,增加了销轴表面的脆性,使销轴表面形成了较多的微裂纹,导致了疲劳裂纹的萌生;销轴的渗氮层深度和硬度偏低也降低了销轴的疲劳强度,加速了疲劳裂纹的扩展,最终使销轴发生早期疲劳断裂。     

某电动泵传动轴断裂原因分析

某电动泵传动轴在使用过程中发生早期断裂,采用断口分析、金相检验、硬度测试、化学成分分析、表面质量检查等方法对传动轴断裂的原因进行了分析。结果表明:该传动轴的断裂模式为疲劳断裂;由于电火花加工工艺设置不当,使传动轴的销孔表面产生了微裂纹,在交变载荷作用下,微裂纹不断扩展直至传动轴发生断裂。     

活塞销失效分析及工艺改进

某柴油发动机活塞销在使用中发生大批量失效事故。采用了宏、微观检验、化学成分分析、冷挤压工艺分析及现场工艺试验等检测手段对断裂的活塞销进行了分析。结果表明，活塞销断裂的主要原因是冷挤压工艺不当导致活塞销内孔表面和次层产生裂纹。提出了工艺改进意见。     

550kV断路器操作机构轴销的断裂原因分析

在断路器1 000~2 000次机械操作试验中,30CrNi3合金钢渗氮轴销发生断裂。通过化学成分分析、断口分析、低倍检验、金相检验、力学性能测试的方法,对轴销的断裂原因进行了分析。结果表明:该轴销的断裂性质为双向弯曲疲劳断裂;轴销材料渗氮层存在脉状氮化物,内部存在疏松、大尺寸夹杂物和气泡缺陷,降低了材料的力学性能;在周期性旋转弯曲力作用下,轴销表面缺陷处出现裂纹并不断扩展,最终导致轴销疲劳断裂。     

钻杆吊卡轴销断裂原因分析

采用化学成分分析、断口分析、金相检验以及力学性能测试等方法,对某钻杆吊卡轴销断裂原因进行了分析。结果表明:由于该轴销外表面存在原始淬火裂纹,加之其冲击韧度和塑性较差,从而导致其在较大的冲击载荷作用下裂纹失稳扩展而脆性断裂。     

某天然气公交车发动机主轴承盖螺栓断裂原因

某天然气公交车发动机主轴承盖螺栓发生断裂,通过宏观观察、化学成分分析、扫描电镜及能谱分析、硬度试验和金相检验等方法,分析了螺栓断裂的原因.结果表明:螺栓的失效模式为氢脆断裂;在服役过程中,螺栓在较长时间的应力作用下,其头部圆角处产生应力集中,且存在初始裂纹,螺栓、水汽和天然气中的微量氢元素向螺栓初始裂纹附近扩散、聚集,...     

Characterization and Failure Analysis of an Automotive Ball Joint

This case study describes the failure analysis of an automotive lower ball joint that fractured under normal driving conditions. Through spectroscopy, the material was determined to be SAE-AISI 5135H steel. The metallographic examination revealed a tempered martensitic structure, and hardness measurements radially across the surface of the cut ball stud suggested that the stud was through hardened. Scanning electron microscopy of the fracture surfaces indicated fatigue as the main failure mechanism. Finite element analysis was used to analyze the performance of the part under a normal loading condition. A detailed fatigue analysis to determine the effect of various loads on the life of the ball joint was completed using three methods: S-N curve approximation using hardness values, S-N approach using Basquin’s equation, and a linear elastic crack-growth model. The cause of failure was determined to be from surface cracks forming in the high stress concentration neck region where the ball and stud are joined. The presence of a small surface flaw in this region was shown to significantly reduce the fatigue life of the ball joint.     

Failure of a Fusion Welded Ball Joint as a Result of Modification in MnS Direction

A failure investigation was performed on a ball joint from an ATV front suspension system. The location of the fracture was the bearing ball/stud interface, which is a fusion-welded joint, and occurred after approximately 20 h of field-testing. The two parts are made out of carbon steel and were previously heat-treated. Many elongated MnS inclusions were found in the stud material, and these inclusions were parallel to the symmetry axis. Even though these inclusions were not significantly sized, their number was important. Macroscopic evidence showed that the joint failed in a ductile mode under centered tensile overload. Microscopic examination showed that MnS orientation changed in the fusion joint area. The inclusions had been redirected during the welding process and laid parallel to the fracture surface. This reorientation caused a significant decrease in the effective cross section of the joint and overload fracture occurred.     

Life Prediction of Ball Grid Array Soldered Joints under Thermal Cycling Loading by Fracture Mechanics Method

［1］J.J.Wang, M.F.Lu, D.Q.Zou and S.Liu: IEEE-CPMT(B), 1998, 21, 79. ［2］Y.H.Pao, E.Jih and V.Siddapureddy: J. of Electronic Packaging, 1996, 118, 235. ［3］H.U.Akay, N.H.Paydar and A.Bilgic: J. of Electronic Packaging, 1997, 119, 228. ［4］D.J.Xie, Y.C.Chan and J.K.Lai: IEEE-CPMT(B),1996, 19, 669.     

基于连续球压痕法的45钢强度与韧性测试研究

为研究在役设备的材料强度与韧性测试评价问题,针对工程中常用材料45钢,采用连续球压痕方法,获取了材料的屈服强度、抗拉强度与断裂韧性,通过与常规力学性能试验结果比较,对该方法的可靠性进行了验证。通过研究球压头下压产生的塑性功,与冲击启裂能及断裂韧性之间的关联关系,建立基于仪器化球压痕测试技术的冲击韧性估算评估方法。试验结果表明,利用连续球压痕方法获取的屈服强度、抗拉强度与实际结果的偏差均小于10%,断裂韧性值与试验结果的偏差为12.3%,计算结果在试验值偏差数据范围内。利用连续球压痕技术,建立的断裂韧性与冲击韧性之间的关联公式,所预测的冲击韧性结果与仪器化冲击试验值具有较好的一致性,为在役设备材料的韧性快速评价提供了有效的测试方法。     

Strength recovery of machined Al2O3/SiC composite ceramics by crack healing

Alumina is used in various fields as a machine component. However, it has a low fracture toughness, which is a weakness. Thus, countless cracks may be initiated randomly by machining, and these cracks decrease the component's mechanical properties and reliability. To overcome this problem, a crack‐healing ability could be a very useful technology. In this study, Al₂O₃/SiC composite was sintered. This alumina exhibits excellent crack‐healing ability. Small specimens for a bending test were made from the Al₂O₃/SiC. A semicircular groove was machined using a diamond ball‐drill. The machining reduced the local fracture stress from approximately 820–300 MPa. The machined specimens were crack‐healed under various conditions. The fracture stress of these specimens after crack healing was evaluated systematically from room temperature (RT) to 1573 K. It was found that the local fracture stress of the machined specimen recovered almost completely after crack healing. Therefore, it was concluded that crack healing could be an effective method for improving the structural integrity of machined alumina and reducing machining costs.     

Some observations on the path stability in fracture propagation for biaxially stressed plates

The path stability problem for fracture starting from a straight crack in a biaxially stressed plate is investigated. The analysis is performed by employing a simple equivalent crack in order to obtain an approximate evaluation of the Stress Intensity Factors of the S-shaped crack which may be generated by the fracture propagation. It is shown that crack propagation deviates from the original direction when the applied stress parallel to the crack plane becomes higher than that perpendicular to it. The trend of the fracture trajectories and their sensitivity to small deviations caused by irregularities have also been determined for various values of the stress biaxiality ratio. Some comparisons with previous analyses are made.     

Effect of adhesive fillet geometry on bond strength between microelectronic components and composite circuit boards

Printed circuit boards (PCBs) assembled with ball grid array (BGA) microelectronics packages were tested in a double cantilever beam (DCB) configuration. The results were compared for a filled and an unfilled underfill epoxy adhesive as well as a cyanoacrylate adhesive. The original fillet, formed in the underfilling process, was modified to create fillets of different sizes. Regardless of the underfill thermal and mechanical properties as well as its curing profile, the crack initiation load and the failure mode were solely a function of the size of the underfill fillet, and the failure always initiated within the PCB. Moreover, the strength of the underfilled solder joints was increased significantly (approximately 100%) by the presence of a relatively large fillet. This effect of the underfill fillet on the crack path and the fracture load was then examined in terms of differences in the stress states using a finite element model.     

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.     

Fracture analysis for ceramic ball in backflow valve

Ceramic balls have been used as components of devices, such as those found in high‐pressure pumps for automobiles and industrial machines. In the backflow valve, for example, a ceramic ball is in contact with a conical surface. Fractures of ceramic balls are extremely rare. It is important to investigate the cause of these rare fractures to guarantee higher reliability in the backflow valve. In this paper, the fracture mechanism and strength are discussed for an equivalent normal stress σ_eq beneath the contact region and the maximum principal stress σ_p near the contact boundary using stress intensity from fracture mechanics. The fracture surface of the ceramic ball was formed perpendicular to load direction. We assumed that fracture origins (defect/crack) existed on lines through three high stresses that analysed by finite element method. Actual fracture of a ceramic ball was found to be caused by the equivalent normal stress beneath contact region and not to be caused by the Hertz principal stress. Stress intensity factor (SIF) was clarified to depend on pressure, taper angle, CrN‐coating thickness and the friction factor of the inside of the valve hole. A pre‐existing defect size involved in failure was estimated by the SIF using three‐dimensional elliptic defects and equivalent normal stress. Therefore, the actual fracture of a ceramic ball, which rarely occurs, could be evaluated by considering three‐dimensional elliptic defects and the Weibull distribution of defects.     

Near the static fatigue limit in glass

Fracture surfaces formed near the crack growth threshold in soda-lime-silicate glass are examined by atomic force microscopy. Cracks held below the apparent crack growth threshold for 16 h alter their mode of growth. The fracture plane changes from a flat surface to one that exhibits substantial out of plane growth. The direction of crack growth changes from 3° to 5° to the original growth direction. However, the change in growth direction is not uniform along the crack front; some portions of the front propagate at +3° to +5°, while adjacent portions propagating at –3° to –5° to the original growth direction. Thus, the crack is no longer flat, but becomes wavy after the 16 h hold period. This out of plane growth may be partially explained in terms of a crack growth model developed by Chuang and Fuller, which predicts an enhancement in the corrosion rate on the flank of a crack at stresses below the stress corrosion threshold. Alternatively, the unevenness of the crack plane after the hold period may be a consequence of a modification of the fracture toughness of the glass as a consequence of leaching.