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通过对螺栓断口形貌、硬度测试及金相组织等进行分析,表明作为重要受力螺栓,其加工形式不恰当,使螺栓表面存在环向刀痕及微小缺陷,引起应力集中是导致螺栓疲劳断裂的主要原因;另外热处理工艺不当使螺栓表层脱碳,降低抗疲劳性能也是螺栓疲劳断裂的原因之一。 相似文献
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运用扫描电镜、金相显微镜和直读光谱仪对42Cr Mo钢制U型螺栓的断裂原因进行了分析,同时,进行了拉拔模拟试验。实验表明:由于42Cr Mo钢热轧状态心部往往存在马氏体组织,在不经过退火的情况下直接酸洗后拉拔加工,心部易出现横向裂纹,后续加工时裂纹进一步扩展,易导致螺栓发生断裂。 相似文献
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采用断口宏观分析、化学成分检测、力学性能分析和金相分析等方法对行车减速机传动轴断裂样品进行伞面分析.分析结果表明:减速机材质为45钢,金相组织为铁素体+索氏体,力学性能指标符合45钢正火状态的性能,键槽端部圆弧半径太小容易引起应力集中,当运行载荷较高时,键槽根部超过了疲劳极限,引起疲劳断裂. 相似文献
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为研究不同组织对高强度抗震钢筋性能的影响,得到其微观组织变形行为的规律,针对3种不同组织特征的500MPa级高强度抗震钢筋,其组织分别为铁素体和珠光体、铁素体和珠光体以及少量贝氏体、铁素体和少量珠光体以及大量贝氏体为主,利用原位拉伸仪观察、研究多相微观组织变形行为以及多相组织协调变形机理以及断裂机制。结果表明,铁素体和珠光体为主的试验钢,铁素体和珠光体变形明显,其中铁素体优先变形,但由于贝氏体硬质相对珠光体的阻碍作用,变形不明显,随着变形量的增加,最后导致珠光体的断裂。以铁素体和珠光体以及少量贝氏体为主的试验钢,贝氏体在初期基本不变形,而后对铁素体和珠光体的变形产生阻碍运动,仅发生一定程度的改变。以铁素体和少量珠光体以及大量贝氏体为主的试验钢,变形初期以铁素体变形为主,珠光体因其含量非常低,变形不明显。随变形量的增加,贝氏体的变形越发明显,到一定程度后促使珠光体开始变形,并最后断裂。 相似文献
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运用金相观察、扫描电镜观察和能谱定量分析等实验手段,从组织状态、夹杂物、断口形貌等方面分析了22Si2MnCrNi2MoA钎杆内螺纹处断裂原因,同时对其疲劳裂纹起源和扩展进行了探讨.22Si2MnCrNi2MoA钎杆内螺纹处断裂破坏并不是由组织异常和夹杂物引起的,而是由于22Si2MnCrNi2MoA钎杆存在明显的壁厚不均,在高频应力、严重的内外耗同时存在的应力状态下持续工作,壁厚较薄处极易成为受力薄弱区,疲劳裂纹更倾向于在此处优先形成,从而致使壁厚较薄处优先断裂,最终导致钎杆断裂失效.该钎杆疲劳破坏起源于内表面,属于多源的疲劳断裂.起源区微观形貌为韧窝形貌,扩展区的微观形貌为韧窝和沿晶的混合形貌. 相似文献
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采用降低铁素体相韧性、提高铁素体相硬度及适当脆化原奥氏体晶界的方法,开发出一种新型胀断连杆用铁素体-珠光体型中碳非调质钢,从钢种设计、微观组织、力学性能及胀断特征等方面对此钢种进行了介绍。硅和磷元素的铁素体固溶强化作用及钒元素析出强化和组织细化作用,使得开发钢不仅具有较高的强度水平和屈强比,同时具有远高于传统的胀断连杆用高碳钢C70S6的优异高周疲劳性能。此外,模拟胀断试验结果表明,开发钢的断口呈典型脆性解理断裂,胀断前后的变形量很小,具有优于C70S6钢的胀断性能,可采用胀断工艺制造连杆。 相似文献
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通过对灰铸铁缸体断口处化学成分、金相组织、断裂腐蚀产物等因素进行分析,得出机体材料组织状态、螺纹加工状态不良是造成机件发生早期疲劳断裂的因素之一。而且由于结构设计原因,安装过程可能在断面局部形成较大的拉应力,也是造成机件发生早期疲劳断裂的重要因素。 相似文献
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R. M. Ramage K. V. Jata G. J. Shiflet E. A. Starke 《Metallurgical and Materials Transactions A》1987,18(7):1291-1298
The effect of phase continuity on the low cycle fatigue and fatigue crack growth behavior of a Fe-C-Mn dual-phase steel has
been investigated. Two microstructures, one consisting of continuous ferrite and the other continuous martensite, were examined.
Although there was no difference in the low cycle fatigue lives between the two microstructures, the continuous martensite
structure exhibited an extremely high fatigue threshold value of 20 MPa m1/2, compared to 16 MPa m1/2 for the continuous ferrite microstructure. A major effect of phase continuity has also been found in the crack closure levels
during fatigue crack propagation studied over three decades of crack growth rates. The continuous martensite microstructure
exhibited much higher closure levels due to the martensite constraining the plastic deformation in the ferrite and bearing
a larger portion of the applied cyclic load. This effect is similar to the extrinsic toughening phenomenon cited in the literature.
After accounting for the closure levels the intrinsic or effective fatigue crack growth rates are similar for the two microstructures.
These intrinsic thresholds are predicted by employing experimentally obtained low cycle fatigue parameters and the ferrite
grain size. 相似文献
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摘要:通过对锻态HPD-1双相不锈钢进行不同温度的固溶处理,获得两相(α、γ)比例呈梯度变化的疲劳试样,在室温环境下测试对应相比例试样的疲劳断裂次数,获得相比例对疲劳性能的影响规律并进行微观分析。结果表明,在梯度范围内,随着α/γ比例提高,疲劳性能持续增强。对疲劳试样进行SEM、EDS与TEM分析得知,塑性变形主要发生在奥氏体内,位错以平面滑移型为主在奥氏体中大量增殖发展并在相界处塞积,铁素体内基本无位错发展,微裂纹形核于奥氏体区域并沿相界向外拓展,导致疲劳断裂。 相似文献
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For the study of the DP980 steel high cycle fatigue property, high fatigue tests of DP980 steel and DP980 steel laser welded joints were carried out with fatigue testing machine, the Basquin equation was concluded. Microstructures and fractures were analyzed by optical microscope and scanning electron microscope. The results show that DP980 steel laser welding joints have the weld concavity at the welding root and top, the quality of welded joints is medium. The fatigue limit of DP980 steel is 341MPa, the fatigue limit of DP980 steel laser welded joint is 148MPa, the fatigue limit decreases by 50% compared with the fatigue limit of the base metal. For DP980 steel, the crystal boundary of the ferrite/martensite is the main location of micro cracks initiation, the fatigue fracture of DP980 steel is the quasi cleavage fracture. For DP980 steel laser welding joints, the fatigue cracks initiation is located in the weld concavity, not in the heat affected zone, the fatigue fracture is cleavage fracture. DP980 steel and DP980 steel laser welding joints crack propagation is characterized by the obviously fatigue striations coupled with secondary cracks. 相似文献
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摘要:为了研究DP980钢的高周疲劳性能,采用疲劳试验机对DP980钢和DP980钢激光焊接接头进行高周疲劳试验,得到Basquin方程,并利用光学金相显微镜和扫描电镜进行组织和断口分析。结果表明:DP980钢激光焊接接头的焊缝根部和顶部出现形状凹陷,焊接接头的质量为中等。DP980钢疲劳极限为341MPa,DP980钢激光焊接接头的疲劳极限为148MPa,激光焊接接头的疲劳极限较母材的疲劳极限降低约50%。对于DP980钢而言,铁素体/马氏体晶界是裂纹萌生的主要位置,疲劳断口为准解理断口。对于DP980钢激光焊接接头而言,疲劳裂纹源位于焊缝凹陷处,而非热影响区及母材,疲劳断口为解理断口。DP980钢和DP980钢激光焊接接头的疲劳裂纹扩展区均有明显的疲劳条带,并伴随有二次裂纹。 相似文献
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Use of the nanoindentation technique for studying microstructure/crack interactions in the fatigue of 4340 steel 总被引:2,自引:0,他引:2
Fan Yang Ashok Saxena Laura Riester 《Metallurgical and Materials Transactions A》1998,29(12):3029-3036
The objectives of this research are to study the influence of microstructure on the fatigue crack growth behavior in 4340
steel and to explore the application of the nanoindentation technique for determining the plastic deformation zone at a fatigue
crack tip. Two heat treatment conditions were chosen for the steel: annealed and quenched plus tempered. The annealed steel
consists of coarse pearlite and proeutectoid ferrite, while the quenched and tempered steel consists of fine tempered martensite.
Fatigue crack propagation tests were conducted on disklike compact (DCT) specimens. Subsequently, the nanoindentation technique
was applied to quantitatively determine the plastic deformation zone at fatigue crack tips. The plastic deformation zone size
determined by the nanoindentation test seems larger than the cyclic deformation zone calculated using the fracture mechanics
equation, which involves many assumptions. The fatigue crack growth test results show that the annealed steel has a higher
resistance to crack growth than the quenched and tempered steel. The fatigue crack in the annealed steel tends to grow along
pearlite domain boundaries, or the cementite/ferrite interfaces within a pearlite domain. In contrast, the fatigue crack in
the quenched and tempered steel tends to traverse the fine martensite laths. Consequently, the actual crack path in the annealed
steel is rougher than in the quenched and tempered steel and more secondary cracks are observed in the annealed steel. 相似文献
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The fatigue and fracture resistance of a TiAl alloy, Ti-47Al-2Nb-2Cr, with 0.2 at. pct boron addition was studied by performing
tensile, fracture toughness, and fatigue crack growth tests. The material was heat treated to exhibit a fine-grained, fully
lamellar microstructure with approximately 150-μm grain size and 1-μm lamellae spacing. Conventional tensile tests were conducted as a function of temperature to define the brittle-to-ductile
transition temperature (BDTT), while fracture and fatigue tests were performed at 25 °C and 815 °C. Fracture toughness tests
were performed inside a scanning electron microscope (SEM) equipped with a high-temperature loading stage, as well as using
ASTM standard techniques. Fatigue crack growth of large and small cracks was studied in air using conventional methods and
by testing inside the SEM. Fatigue and fracture mechanisms in the fine-grained, fully lamellar microstructure were identified
and correlated with the corresponding properties. The results showed that the lamellar TiAl alloy exhibited moderate fracture
toughness and fatigue crack growth resistance, despite low tensile ductility. The sources of ductility, fracture toughness,
and fatigue resistance were identified and related to pertinent microstructural variables. 相似文献