25CrMoA抽油杆断杆原因分析

针对25CrMoA在井下服役过程中发生早期断裂问题,进行了宏观分析、化学成分分析、低倍检测和显微组织分析。检测结果表明,抽油杆断裂失效是由于热处理参数不当造成了疲劳断裂。     

60Si2Mn钢板弹簧失效分析

某厂生产的钢板弹簧在台架疲劳试验中发生早期断裂失效,为了找出其失效原因并制定防止断裂失效的预防措施,通过宏观观察、扫描电镜、金相检验等方法对断裂钢板弹簧进行了失效分析。结果表明:断裂发生在板簧紧固处附近,断口起源于板簧喷丸面;断口区域有明显的贝纹线特征,该断裂属于疲劳断裂;弹簧扁钢局部发生过热,出现组织晶粒粗大和全脱碳等异常组织。通过降低加热温度和减少在加热炉内高温段的停留时间,选择合适的加热速度,并控制炉内气氛等措施,可减少甚至避免热处理过程中局部过热造成的板簧早期断裂失效。     

55Cr3钢轿车稳定杆疲劳断裂失效分析

采用电子显微分析、金相组织分析和显微硬度分析等方法，对55Cr3钢轿车稳定杆疲劳试验过程中断裂的原因进行了分析。结果表明，发生断裂的稳定杆表面存在明显凹坑，导致其在疲劳试验过程中引起应力集中，是稳定杆发生早期疲劳断裂的主要原因。     

千吨压砖机横轴断裂原因分析

本文通过对断裂的千吨压砖机横轴进行的高低倍分析，得出该轴的断裂是由于运行过程中与其上方的制动架拉杆摩擦，使轴的表面产生了组织变化（形成马氏体组织），而造成应力集中形成疲劳源，从而使其横轴因疲劳破坏而早期失效断裂。     

接触疲劳试验数据处理方法的探讨

接触疲劳是钢轨、轧辊、轴承和齿轮等机件的接触表面,在接触压应力的反复长期作用下,机件表层附近金属塑性应变,以及伴随硬化的局部疲劳损伤积累过程,发生以麻点,浅层或深层剥落方式而导致机件的失效。钢轨的质量问题是众所关心的。钢轨在使用过程中产生各种各样的损伤,包括磨损、压溃、擦伤、腐蚀、剥离以及断裂等,影响着钢轨寿命,甚至行车安全。从国内外线路调查的资料来看,钢轨的疲劳剥离,以及因此而扩展引起的横向断裂是重要的损伤形式之一。尤其是随着铁路运输的发展,轴重加大、速度提高,通过量增加,更加剧了这一类损伤形式。     

引风机轴断裂失效分析

该引风机轴断裂性质是疲劳断裂，造成断裂的主要原因是不恰当的补焊工艺。补焊时形成的裂纹是疲劳断裂的纹源。基体钢材晶粒粗大也是造成该轴早期断裂的原因。     

铁路机车用52CrMoV4弹簧失效分析

采用化学成分、电子显微镜、金相组织和硬度等分析方法,对运行过程中发生断裂的铁路机车52CrMoV4弹簧断裂原因进行分析。结果表明,弹簧加热成型过程中局部产生过热组织,导致其淬火产生裂纹,是铁路机车用弹簧早期疲劳断裂的主要原因,提出了预防措施。     

堆取料机走行减速机故障原因分析

对斗轮堆取料机走行减速箱齿轮齿面断裂口及齿面磨损处进行宏微观分析。认为：该齿轮系是在应力集中条件产生早期疲劳断裂。造成齿轮疲劳断裂的原因主要是,热处理工艺过程中齿轮渗碳不完善,造成齿轮表面脱碳,致使材料力学性能未达到设计要求,齿轮的疲劳抗力降低,加之圆角加工较差,工作时产生应力集中,加速了齿轮的疲劳断裂。     

轧辊扁头断裂失效分析

借助于光学显微镜、扫描电镜检验设备,结合力学性能测定、化学成分分析等方法,对材质为25Cr2Ni4MoV的轧辊扁头进行了相关检验分析,找出轧辊扁头断裂失效原因。结果表明,扁头失效形式为起源于表面缺陷的高应力低周多源疲劳断裂,堆焊表面存在气孔缺陷是扁头产生台阶状的疲劳断裂的主要原因,扁头金相组织不均匀和基体强度不足是扁头发生疲劳断裂的重要影响因素。     

TRT透平机叶片断裂分析

对某厂2号TRT透平机一级动叶片中断裂叶片的化学成分、宏观断口以及金相组织进行了分析,结果表明,该叶片属于腐蚀疲劳断裂,其疲劳裂纹起源于叶片进气边边缘部位的腐蚀麻点处,腐蚀麻点是由于叶片与湿积灰中的腐蚀性介质Cl-,SO4-等发生反应造成的。     

大型客机用300M钢疲劳破坏行为

 结合显微组织观察和力学性能测试,对国产大型客机用300M钢应力比[R＝－1]的轴向光滑疲劳性能进行了研究,分析了大型客机用300M钢的高周轴向疲劳断口形貌及起裂原因,重点研究了非金属夹杂物裂纹源的特性。结果表明,国产大型客机用300M钢冶炼纯净度较高,最终热处理后具有良好的综合力学性能,其应力集中系数[Kt＝1,]应力比[R＝－1]的高周轴向疲劳极限[σ－1]为907 MPa;通过断口SEM观察发现非金属夹杂物引起的应力集中是导致高周轴向疲劳开裂的主要原因,该类起裂源为复杂氧化物和硫化钙的复合非金属夹杂物,尺寸在5.5～20.5 μm之间,主要成分为铝、钙、硅、氧和硫等。     

Fatigue crack formation and propagation behavior of 30Cr3WVE bearing steel

The fatigue characteristics of a high cleanliness bearing steel(30Cr3WVE)produced by double vacuum melting and the effect of non- metallic inclusions on fatigue properties were studied by mechanical analysis and SEM analysis of microstructure and fatigue fracture morphology.The results show that the 30Cr3WVE bearing steel achieves excellent mechanical properties after being quenched at 870?? and tempered at 550??, and its ultimate rotating bending fatigue strength reaches 732MPa.Through observing SEM results of fatigue fracture,the fatigue crack originates from the surface defects and internalnon- metallic inclusions. Surface defects are caused by the abscission of non- metallic inclusions and machining marks. The internal non- metallic inclusions are mainly oxides of Al, Mg, Si and Ca. The influence of inclusions on the ultimate bending fatigue strength of 30Cr3WVE bearing steel is closely related to its size and distance to the surface. The model of influence of the size and distribution of inclusions on the rotating bending fatigue strength of 30Cr3WVE bearing steel is constructed. The rotational bending fatigue strength of the steel can be improved remarkably by controlling the size and quantity of inclusions.     

热风循环风机轴断裂失效分析

为了研究热风循环风机轴失效形式、影响因素和预防措施,改善相关金属零部件质量,提高设备安全性和可靠性。针对某铝合金热处理设备中的热风循环风机轴断裂失效问题,采用化学成分分析、力学性能测试、金相检验、SEM检验、有限元法等技术手段,分析了风机轴断裂失效的原因,并提出了针对性的预防与改进措施。结果表明,热风循环风机轴的断裂形式为低名义应力和轻微应力集中情况下的旋转弯曲疲劳断裂,维修时的焊接加工缺陷以及轴肩附近直径的阶梯变化,造成了不同程度的应力集中,降低了材料的疲劳寿命,最终导致了轴断裂失效。     

二联齿轮断齿分析

通过化学分析、力学性能测试、金相和断口分析,对二联齿轮失效原因进行综合分析。结果表明,主要是由于加工质量较差、原材料不合格和热处理不当等引起的疲劳断裂。     

32Cr3MoVE轴承钢旋弯疲劳特性及裂纹萌生扩展行为

摘要：采用光滑漏斗状试样对32Cr3MoVE轴承钢进行旋转弯曲疲劳测试，研究了32Cr3MoVE轴承钢旋转弯曲疲劳性能及裂纹萌生扩展行为。采用升降法测得其疲劳极限为860MPa，疲劳断口SEM观察并统计破断试样结果表明：疲劳破坏68.7%是由于非金属夹杂起裂，18.8%由表面加工缺陷起裂，125%为表面粗糙度起裂。当加载应力低于980MPa时，疲劳断裂主要是由于内部非金属夹杂引起的，高于980MPa时，疲劳断裂主要是由于表面粗糙度引起的。表面加工缺陷和表面粗糙度引起的最大应力强度因子分别为3.05和2.97MPa·m1/2，容易引发疲劳裂纹。非金属夹杂物尺寸在5.30～5.90μm范围内，局部应力从859.35MPa升至977.75MPa时，疲劳寿命从1.96×105降低到1.58×105；非金属夹杂物局部应力在840～900MPa范围内，夹杂物尺寸从2.28μm升至5.83μm时，疲劳寿命从1.10×106降低到1.96×105。     

Study of Damage and Fracture Toughness Due to Influence of Creep and Fatigue of Commercially Pure Copper by Monotonic and Cyclic Indentation

Fracture toughness is the ability of a component containing a flow to resist fracture. In the current study, the Ball indentation (BI) test technique, which is well acknowledged as an alternative approach to evaluate mechanical properties of materials due to its semi-nondestructive, fast, and high accurate qualities is used to estimate damage and the fracture toughness for copper samples subjected to varying levels of creep and fatigue. The indentation fracture toughness shows the degradation of Cu samples when they are subjected to different creep conditions. Axial fatigue cycling increases the strength at the mid-gauge section compared to other regions of the samples due to initial strain hardening. The advancement of indentation depth with indentation fatigue cycles experiences transient stage, i.e., jump in indentation depth has been observed, which may be an indication of failure and followed by a steady state with almost constant depth propagation with indentation cycles.     

Effects of high temperature fatigue on microstructure and mechanical properties of a nickel-base precipitation hardened alloy

Effects of high temperature strain controlled push-pull fatigue on the microstructure and mechanical properties of a nickel-base precipitation hardened alloy were studied. The fatigue deformation alone at 700 °C did not impair the mechanical properties of this alloy; however, a hold period ranging from one minute to one hour at tension-peak decreased the tensile ductility and the fracture toughness significantly. This was mainly attributed to grain boundary cavitation. Continuous fatigue resulted in dislocation bands, whereas hold-time fatigue caused a coherency loss iny’ precipitates. Implications of these microstructural changes for the residual mechanical properties are discussed. Formerly with the Brookhaven National Laboratory, Upton, NY 11973. Formerly with the Brookhaven National Laboratory.     

Processing properties relationships of Ti-10V-2Fe-3Al

Beta alloys, such as Ti-10V-2Fe-3Al, can be processed and heat treated to provide a wide range in mechanical and fracture properties. A systematic study of the effect of processing and heat treatment variations on the properties combinations achievable was undertaken. The ductility and fracture toughness can be very significantly influenced by processing and heat treatment variations. The ductility increases and the toughness decreases as the morphology of the primary alpha changes from acicular to equiaxed. This morphology change was caused by alterations in forging procedures. Reducing the strength increases both fracture toughness and ductility. Microstructure has only a minor influence on fatigue performance in the high strength (about 1310 MPa UTS) condition. The micro-structure does, however, have a significant effect on fatigue behavior in a low strength, about 1034 MPa UTS, condition. More lamellar alpha results in improved notched fatigue performance, while a more equiaxed alpha improves smooth fatigue performance. These changes in properties are rationalized in terms of microstructure.     

Cyclic Void Growth Model to Assess Ductile Fracture Initiation in Structural Steels due to Ultra Low Cycle Fatigue

A new model is proposed to simulate ductile fracture initiation due to large amplitude cyclic straining in structural steels, which is often the governing limit state in steel structures subjected to earthquakes. Termed the cyclic void growth model (CVGM), the proposed technique is an extension to previously published models that simulate ductile fracture caused by void growth and coalescence under monotonic loading. The CVGM aims to capture ultra low cycle fatigue (ductile fracture) behavior, which is characterized by a few (generally, less than 20) reverse loading cycles to large inelastic strain amplitudes (several times the yield strain). The underlying mechanisms of low-cycle fracture involve cyclic void growth, collapse, and distortion, which are distinct from those associated with more conventional fatigue. The CVGM represents these underlying fracture mechanisms through plastic strain and stress triaxiality histories that can be modeled at the material continuum level by finite-element analyses. Development and validation of the CVGM is substantiated by about 100 notched bar tests, with accompanying finite-element analyses, metallurgical tests, and fractographic examinations of seven varieties of structural steels.     

Mechanisms in fatigue strength improvement of thermomechanically manufactured automotive suspension springs

In a previous work, application of thermomechanical treatment (TMT) to suspension spring samples led to high increases in fatigue strength (up to 40 %). For the purpose of a better comprehension of these results, further investigations were carried out with major attention to the mechanical properties of quenched and tempered steel 50CrV4 and a Nb-microalloyed variant of this steel, respectively. First, the samples were ground prior to presetting, stress peening and subsequent dynamic testing. This was done to work out the influence of the surface state on the benefits of TMT. An extended program of materials testing was carried out with particular attention on the crack initiation and growth features of thermomechanically treated steel compared to conventional heat treatment (CHT). One of the results was that grinding of the spring surface causes further improvement of fatigue strength. On the other hand, the advantages of TMT compared to CHT are reduced as a result of surface grinding. The reason for this result is an overproportional increase in fatigue strength of CHT specimens due to grinding. An explanation imaginable for both the improvements caused by TMT and the reduction of these improvements after grinding could be the change in fracture mechanical properties. In particular TMT causes a significantly retarded crack initiation in the finite life range and an increased permissible stress intensity without crack formation.