Brittle Cracking of a Cylindrical Spiral Gear of Axle Gearbox

A cylindrical spiral gear of locomotive axle gearbox failed after standing in site for 10 days. The failed gear had been assembled with the spiral gear-shaft. Inspection in site found that cracking occurred on the spoke plate between the shaft bore and the oil-pressed hole. The gear teeth are required to be carburized, but the surfaces of the shaft bore and the oil-pressed hole of gear are surface-coated to prevent carburizing. The crack initiated from the surface of oil-pressed hole and propagated along the radial of the oil-pressed hole. Metallurgical examination reveals that anti-carburizing measure was not conducted on the surface of oil-pressed hole as the specification. A simplified evaluation of the maximum hoop tensile on the wall of oil-pressed hole subjected to internal pressure for swelling bore is far insufficient to lead to brittle fracture. Delayed fracture of gear, the predominance of intergranular fracture micro-mechanism, and the presence of several secondary micro-cracks in the depth of case layer on the oil-pressed hole surface are a clear indication of hydrogen embrittlement. Hydrogen absorption occurred during gas carburizing process.     

齿轮开裂失效分析

采用断口分析、化学成分分析、低倍检验、金相检验和硬度测试等方法对某批经渗碳、淬火热处理及磨齿加工后放置一段时间发生开裂的齿轮的失效原因进行分析。结果表明：齿轮渗碳层碳化物级别过高,加上淬火后齿轮齿部应力集中,磨齿时又产生磨削裂纹,齿轮在放置期间由于应力导致裂纹扩展而开裂。     

轴承齿圈开裂原因分析

使用了约4a（年）的轴承齿圈在服役过程中发生开裂。为查明其开裂的原因,通过化学成分分析、力学性能测试、宏观及微观检验对轴承齿圈进行了分析。结果表明：轴承齿圈开裂的原因是孔内壁表面腐蚀坑处产生微裂纹,加之齿圈本身强度低于技术要求值,在交变应力的作用下发生了疲劳断裂。     

Simulation of Coupled Processes of Deformation and Cracking in Elastic Brittle Materials

We propose an approximate model of combined deformation and microcracking of elastic brittle materials leading to the formation of a system of stochastically distributed shallow microcracks.     

CB30铸钢连接圈脆性开裂失效分析

对CB30铸造铁素体不锈钢连接圈内浇口产生裂纹的原因进行了分析。结果表明:该零件显微组织中存在马氏体脆性相是导致其脆性开裂的根本原因;通过改进连接圈内浇口结构以及浇铸后铸件的脱壳方式,并延长铸件的退火热处理保温时间,可以有效地避免环形类CB30铁素体不锈钢铸件的脆性开裂。     

大型调质输入轴开裂分析

某大型调质输入轴放置约9个月后开裂,采用宏观分析、化学成分分析、低倍检验、断口分析、金相检验以及力学性能测试等手段对输入轴开裂原因进行了分析。结果表明:该输入轴为在组织应力及氢析出所造成内应力共同作用下的氢致延迟开裂;输入轴原材料氢含量高、偏析严重、非金属夹杂物含量高以及锻造不充分,引起零件内部发生了氢气积聚,形成了较大的内应力,这是导致输入轴发生氢致延迟开裂的主要原因。     

Brittle fracture of a crane hook

The objective of this work is to identify the causes that led to a failure of the crane hook in service. The study of the accident includes: (1) a summary and analysis of the peculiarities inherent to the standards that determine the manufacture and use of this type of device, (2) metallographic, chemical and fractographic analyses, (3) assessment of the steel mechanical behaviour in terms of Vickers hardness profile, its tensile strength and fracture energy, and (4) simulation of the thermal history of the hook. The visual and microstructural inspections reveal some evidences that a weld bed was deposited on the hook surface. Several cracks grew from that area into the material. Fracture surface shows features typical of brittle failures (transgranular cleavage fracture). The unalloyed, low-carbon steel contains a relatively low aluminium (<0.025%) and high non-combined nitrogen (>0.0075%) content. All the gathered evidences are in agreement with a strain-aging process triggering the embrittlement of the material, with the fracture starting from a crack generated at the heat affected zone of an uncontrolled welding of the hook.     

Brittle fracture of a steam line

Translated from Fiziko-Khimicheskaya Meckhanika Materialov, No. 6, pp. 102–103, November–December, 1989.     

Brittle fracture of a rod under a longitudinal impact

In this paper a model of a rigid-fractured body is introduced. It is applied to the rod of variable cross-section area and of limited length striking a rigid wall. A simple approximate solution of the problem of brittle fracture of such a rod is given here. The limit stress on the fracture front is supposed to be a function of the impact velocity. Some examples are considered in Section 3.     

脆性材料的超精加工--脆性材料的钻石切削综述

在脆性材料的超精加工中，一个十分重要的现象是材料由脆性状态向可延展性状态的转变．为了成功地时脆性材料进行钻石切削加工以获得镜面表面，两种状态转变点的确定十分关键．本文阐述研究这一转变的实验技术，并讨论表面生成的机理．发现在脆性材料的钻石切削中，刀具磨损是一个严重后果．建议今后的研究应集中在这一领域．     

变速箱双联齿和512齿轮失效分析

某型号变速箱在台架试验过程中,双联齿和与之啮合的512齿轮均发生失效事件。采用断口分析、金相检验、硬度测试以及化学成分分析等方法对失效件进行了检验。结果表明:由于双联齿和512齿轮的齿面存在严重的异常接触,加之双联齿的有效硬化层深度和心部硬度均低于技术要求,从而导致在台架试验过程中双联齿表面发生严重的接触疲劳剥落,与之啮合的512齿轮发生弯曲疲劳断齿。     

Brittle fracture initiation from a blunting crack

Brittle fracture initiation under increasing load occurs from a blunting crack. The present paper proposes as a criterion for the transition from blunting to fast crack growth that the available elastic energy divided by a volume which depends on the fracture mechanism and the crack tip opening displacement reaches a critical value. This criterion is shown to be applicable for initiation from initially sharp cracks, initially rounded notches and from ductile growing cracks. The model allows a quantitative discussion on the size, temperature and notch root radius requirements for fracture mechanics testing.     

圆柱直齿轮冷精锻模拟及试验研究

针对大模数圆柱直齿轮冷锻的困难性,提出了开放式分流和齿顶分流等2种分流工艺.结合浮动凹模技术,通过数值模拟与物理试验相结合,对2种工艺进行了分析研究,并与一般轴向分流工艺方案进行了对比.结果表明:这2种工艺方案能大大地降低载荷及单位压强,提高充填性能.锻件只需车削外圆或端面即可得到合格零件,不影响齿面纤维分布.     

重载汽车主减速器盆形齿轮的致裂因素

重载汽车主减速器盆形齿轮通常都采用大模数齿轮,经渗碳淬火处理。由于齿轮毛坯经锻轧而成,齿轮在锻轧后的热处理、渗碳前的预热处理工艺和渗碳工艺参数以及淬火处理,对齿轮的成分、组织及应力都会产生重大影响。本文在对磨削加工时齿轮凹齿面出现的裂纹进行分析,通过不同工艺参数热处理后齿轮的金相组织检验,讨论了大模数重载汽车盆形齿轮热处理致裂的原因,并提出了预防措施和方法。     

Brittle failure susceptibility of metal of a large structure

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 2, pp. 74–79, March–April, 1990.     

Brittle Fracture of a Lifting Stud During Assembly Operations

A lifting stud from a stator frame broke during assembly operations. The part was hot rolled from a 50 W grade low-carbon steel (according to the Canadian standard CSA G40.21-04), which is the equivalent of AISI 1022 grade. Complete metallurgical characterization of the material showed that the chemical and mechanical requirements of the aforementioned standard were met. Moreover, the tensile testing showed that the material had good ductility. Fractographic investigation, both at the macroscale and microscale levels, indicated that the lifting stud failed under bending overload, in a brittle mode. It was found that brittle behavior of the ductile material was caused by the sudden application of the load combined with triaxial stresses promoted by the threaded geometry.     

Milling-Related Brittle Fracture Mechanisms of a SiCp/Al Composite

Strength of Materials - SiCp/Al composites were machined with carbide cutting tools, the surface morphology of the materials was examined with SEM and EDXS. The SiCp removal in the aluminum matrix...