, 汪奔
, WANG Ben
研究了50CrVA高强弹簧钢在不同热处理状态下(淬火+中温回火和退火)的超高周疲劳破坏行为及其裂纹萌生机理。结果表明, 50CrVA高强弹簧钢在107~109循环周次内发生疲劳破坏, 两种热处理状态的S-N曲线下降形态不同, 均未出现疲劳极限。热处理工艺改变50CrVA的微观组织, 从而影响超高周疲劳阶段(寿命>107周次)的疲劳破坏损伤机制: 经淬火+中温回火处理材料破坏多起源于内部夹杂物, 夹杂物周围存在的应力场与溶质原子发生弹性交互作用, 吸引间隙原子向其周边扩散、富集, 使间隙原子富集区材料性能下降, 导致裂纹在内部夹杂物处萌生; 退火热处理后材料微观组织对间隙原子向材料内部夹杂物扩散起到阻碍作用, 所以超高周疲劳裂纹易于在材料表面萌生。
Ultrahigh cycle fatigue behavior of 50CrVA spring steel, which was treated successively byquenched, tempered (QT) and annealed (AD) processes, was investigated by ultrasonic fatigue testingtechnique. The results showed that in ultra-long life regimes (107~109 cycles) the fatigue damage occurred, and the S-N curves displayed different forms. Different heat treatment process could induce different microstructure of the steel; there with regulate the relevant ultrahigh cycle fatigue damage mechanism. In QT state, fatigue cracks generally originated from inner oxide inclusions. It was probably due to that elastic interaction between microcrack tip stresses and interstitial atoms, which enable carbon atoms to be enriched around the particles, causing the degradation of performance of the region rich in carbon and initiation of fatigue cracks. In AD state, the enrichment of interstitial atoms was difficult due to that the special microstructure inhibited the diffusion of atoms approaching to impurity particles so that the cracks were prone to initiate from the steel surface.
转向架轴箱弹簧是动车组运行中起承载、缓冲、转向等作用的关键部件, 其材料的选用对列车的安全运行至关重要。目前, CRH380D动车组轴箱弹簧选用的材料为51CrV4弹簧钢, 该材料全部从德国进口, 国内牌号为50CrVA高强弹簧钢。列车在高速线路区段, 弹簧主要受低幅值高频次的动态荷载影响[1], 50CrVA弹簧钢的使用寿命一般在107~109周次范围内。大量研究表明[2-6]: 高强钢在1010周次范围内仍然会发生疲劳破坏。现行的相关标准并没有对高铁用材料的超高周疲劳性能提出要求, 因此研究50CrVA弹簧钢的超高周疲劳性能, 对列车构件的疲劳寿命预测、高铁用材料的国产化等都具有非常重要的意义。
学者普遍认为解释材料超高周疲劳破坏行为的关键是明确疲劳裂纹内部萌生源区中形貌粗糙区域(Granular bright facet, 以下简称GBF)的形成机理。Murakami等[7]通过二次粒子质谱(SIMS)技术观察到在夹杂物及其周围分布有H元素, 认为在材料冶炼过程中H被内部夹杂物捕获, GBF的形成是H与应力共同作用的结果。李永德等[8]在SUJ2轴承钢中充入不同浓度的H, 发现在相同荷载作用下H的浓度与GBF的尺寸呈负相关。Shiozawa等[9]研究发现在GBF区中存在着碳化物的富集, 应力集中与荷载共同作用使得材料内部夹杂物周围的碳化物颗粒发生剥离, 形成了微小的裂纹。在低应力长时间作用下微小裂纹相互合并连接, 围绕夹杂物周围扩展, 最终形成GBF粗糙的断口形貌。但是, 该理论并没有对碳化物颗粒的生成原理做出解释。鲁连涛等[10]利用电子探针(EPMA)测量了夹杂物周围碳元素发现: 碳富集范围与GBF区面积相吻合, 而无GBF区的夹杂物周围仅有少量的碳元素存在。Sakai[11]认为在循环荷载作用下, 材料内部夹杂物周围形成一层“细晶薄层”, 细晶层与材料基体晶粒之间由于应力的作用沿其交界面发生分离致使初始裂纹生成, 并在交界面中合并、扩展, 最终生成GBF。张永健等[12]通过不同的热处理方式细化了高强度钢的晶粒尺寸, 从而提高了材料的超高周疲劳性能。李永德等[13]通过对SUJ2轴承钢的研究发现GBF的尺寸与夹杂物的尺寸无关, 但在低周疲劳阶段, 疲劳寿命与夹杂物尺寸成反比例关系。
目前对GBF形成机理尚未形成共识, 但上述研究成果表明材料超高周疲劳裂纹内部萌生不是单纯的力学问题, 王弘[14]提出GBF区内H、C等元素的富集应该是一个伴随裂纹内部萌生长大的动态过程。在荷载作用下夹杂物或内部缺陷周围存在的应力场会对H、C、O等间隙原子产生吸引, 造成夹杂物及其周围非金属元素的富集, 最终形成GBF区。目前利用间隙原子扩散理论解释超高周疲劳裂纹内部萌生机制的研究还未见报道。
为了明确间隙原子扩散诱导材料超高周疲劳裂纹内部萌生的机理, 本文选用淬火+中温回火和退火两种热处理方式的50CrVA高强弹簧钢进行超高周疲劳实验。通过改变热处理工艺控制材料的显微组织, 探究间隙原子扩散对超高周疲劳性能的影响规律。
50CrVA高强弹簧钢化学成分(质量分数, %)为C 0.51, Mn 0.95, Si 0.30, Cr 1.10, V 0.13, S≤0.015, P≤0.015, Al 0.02。实验材料取自
试样总数70个, 首先加工成超声疲劳实验试样并预留热处理磨量。第一组试样40个, 以下简称QT(Quenched and tempered), 根据GB/T 1222-2007标准进行热处理, 即对棒材进行860oC/4 h的退火处理, 再进行830oC/1 h真空油冷淬火+480oC/3 h中温回火热处理。第二组试样30个, 以下简称AD(Annealed), 只进行860oC/4 h的退火处理。热处理后所有试样经纵向打磨抛光, 表面粗糙度要求到达
图1 超声疲劳实验所用样品尺寸
Fig.1 Dimensionof specimens tested by ultrasonic fatigue system (Unit: mm)
疲劳实验是在美国BRANSON 200bdc超声疲劳试验机上进行的, 加载频率为20 kHz, 荷载比
QT组试样的微观组织为典型回火屈氏体组织, 如
图2 50CrVA弹簧钢不同热处理状态下的微观组织光学显微镜照片
Fig.2 Optical microscope (OM) images of 50CrVA spring steeltreated by (a) quenched and tempered (QT) and (b) annealed (AD) process
表1 50CrVA弹簧钢热处理后样品的拉伸性能
Table 1 Mechanical properties of 50CrVA spring steel specimens after heating treatment
两种热处理状态下材料的应力-寿命(S-N)曲线如
通过扫描电镜对疲劳试样断口进行观察发现: QT状态下, 超高周疲劳阶段大部分试样疲劳断裂起源于内部夹杂物。
AD状态下疲劳裂纹全为表面或次表面萌生, 多发生于组织缺陷或材料中两相的交界处。
图4 不同热处理状态下50CrVA弹簧钢超高周疲劳断口扫描电镜观察
Fig.4
Scanning electron microscope (SEM) micrographs of fracture surface of 50CrVA spring steel tested by ultrahigh cycle fatigue after heating treatment: (a) QT,
在超高周疲劳阶段, QT状态下疲劳裂纹倾向于在试样内部非金属夹杂处萌生。从
表2 GBF区内外的碳含量对比(质量分数, %)
Table2 Carbon content of internal and external regions of GBF (%, mass fraction)
虽然退火态材料在超高周疲劳范围内发生了疲劳断裂, 但是裂纹全在表面或次表面萌生。在退火组织中存在着粗大的珠光体团, 因其是硬脆相与铁素体的机械混合, 可以被视为分布在基体中较大的组织缺陷。位错会在珠光体团内部或与铁素体的交界处形成驻留滑移带从而引发疲劳裂纹的萌生。根据杨振国等[20]给出的超高周疲劳临界夹杂物尺寸计算公式:
式中
另一方面, 经过退火处理后, 碳主要存于粗大的片层状渗碳体构成的珠光体中, 铁素体基体中平均碳含量仅占0.02%质量分数, 碳原子以间隙形式存在的可能性降低, 使得间隙原子达到能够促使微裂纹长大的富集浓度需要更长时间。退火态组织近于平衡转变产物, 与淬火态相比材料内部位错密度大幅降低, 间隙原子通过位错扩散的通道少, 也对碳原子扩散造成一定的阻碍, 导致退火态材料内部裂纹萌生长大的几率降低, 形成可扩展的内部宏观裂纹需要时间更长。所以, 超高周疲劳阶段破坏易起源于材料表面或次表面。
1. 淬火+中温回火(QT)样品的显微结构为典型的回火屈氏体组织, 碳化物尺寸约为0.5
2.两种热处理状态下的材料在109循环周次内都发生了疲劳破坏, 均未观察到疲劳极限。但疲劳损伤机制不同, 淬火+中温回火状态裂纹起源于内部夹杂物, 而退火状态裂纹起源于材料表面或次表面。
3.在裂纹内部萌生样品中观察到的碳浓度变化规律证明GBF区碳元素的富集是间隙碳原子逐步向内部夹杂物扩散造成的。间隙原子富集引起材料性能退化, 诱导超高周疲劳阶段裂纹在材料内部萌生。经退火热处理后的材料微观组织结构对间隙原子向材料内部夹杂物的扩散、富集起到阻碍作用, 使得超高周疲劳阶段内部裂纹萌生几率低于表面, 因此裂纹易于在表面和次表面萌生。
The authors have declared that no competing interests exist.
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国内目前动车组最高运行速度已达到350 km/h.在研究高速动车组轴箱弹簧载荷测试技术基础上,对某型高速动车组动力和非动力转向架轴箱弹簧力进行连续10天的线路测试,总测试里程约为11 000 km.获得轴箱弹簧力动态特性,给出典型工况下弹簧的载荷时间历程,抽样分析高速直线、曲线、道岔、进出车站、进出车库以及制动等典型运用工况下的弹簧载 荷特性,并在统计基础上给出弹簧一定运用里程下的弹簧载荷谱以确定载荷出现幅值、次数与测试里程之间关系.研究结果表明,高速动车组载荷特性与运用线路等 级密切相关,且弹簧载荷最大值一般出现在等级更差的进出车库、车站以及联络线区段,测试得到的最大轴箱弹簧动态载荷系数为0.28;频域分析结果表明,高 速线路区段弹簧力有1.1 Hz左右的稳定振动频率,即该测试线路区段存在波长为100 m左右的轨道高低不平顺激扰;另外,高速时由于车轮转动引起的弹簧低幅值动态力的主频率为一般为11 Hz.研究结果可用于指导转向架设计以及相关理论研究等.
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<p>合金材料在超高周疲劳下具有与低周和高周疲劳不同的裂纹萌生和扩展行为以及不同的 S--N曲线特征. 材料的强度、循环加载的频率、所处的环境等都显著影响超高周疲劳的特性. 本文综述了合金材料超高周疲劳行为的基本特征和影响因素的研究进展.</p>
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The effect of inclusion size on fatigue behaviour of high strength steels in the very high cycle fatigue (VHCF) regime (>10(7) - 10(9) cycles) is reviewed. Internal fatigue fractures of high strength steels in the VHCF regime initiate mostly at non-metallic inclusions. The critical inclusion size below which it is hard to initiate fatigue cracking of high strength steels in the VHCF regime is found to be about half the critical value characteristic of the high cycle fatigue (HCF) regime (about 10(5) - 10(7) cycles). A stepwise or duplex S-N curve is observed in the VHCF regime. The shape and form of the S-N curves are affected by inclusion size and other factors including surface condition, residual stress, environment and loading modes. Fatigue strength and fatigue life for high strength steels have been found to obey inverse power laws with respect to inclusion size D of the form sigma(w)proportional to D-n1 and N-f proportional to D-n2 respectively. For fatigue strength, the exponent n(1) has been reported to be similar to 0.33 in the literature for the HCF regime and, more recently, to fall in the range 0.17-0.19 for the VHCF regime. For fatigue life, the exponent n(2) is reported to be similar to 3 in the HCF regime, and in the range 4.29-8.42 in the VHCF regime. A special area was often observed inside a 'fish eye' mark in the vicinity of a non-metallic inclusion acting as the fracture origin for specimens having a long fatigue life. The major mechanisms of formation for this special area are discussed. To estimate the fatigue strength and fatigue life, it is necessary to know the size of the maximum inclusion in a tested specimen, and to be able to infer this value using data from a small volume of steel. The statistics of extreme value (SEV) method and the generalised Pareto distribution (GPD) method are introduced and compared. Finally, unresolved problems and future work required in studying the VHCF of high strength steels are briefly presented.
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Over the last decade, it has been shown for a number of metals that failure occurs even beyond the classical fatigue limit. High frequency testing techniques make it possible to conduct fatigue tests up to 10(9) or even 10(11) cycles for various alloys, ranging from aluminium to high strength steels. As a consequence, the characterisation of fatigue life and damage mechanisms at N> 10(7) cycles [very high cycle fatigue (VHCF)] has become a major research issue. Fatigue life in this regime is dominated by crack initiation. With the overall strain being in the purely elastic range, microstructural features acting as stress raisers lead to localised and inhomogeneously distributed irreversible deformation. Hence, microstructural discontinuities become the leading features controlling fatigue life at very high numbers of cycles. The present survey will focus on dislocation arrangement, grain orientation, grain size and surface roughening and their implications on the VHCF behaviour for selected virtually defect free metals, thus providing a sound basis for a detailed understanding of the relevant deformation and damage evolution mechanisms. It will also focus on the VHCF behaviour of materials representing a 'transition' between non-defect related damage evolution and defect based crack initiation, thus pointing out the complexity of damage evolution in the VHCF range. In this context, the term defect is limited to hard non-metallic inclusions, which can be found, among others, in high strength steels as well as pores in casting materials, both dominating the VHCF behaviour of these material types. In contrast, second phases, precipitates or intermetallic particles are considered as irregularities of the microstructure and will not be classified as defects. The current review will show that a true understanding of the VHCF behaviour requires a careful differential analysis of the possible microstructural features leading to localised plastic deformation and that not only crack initiation, but also crack growth behaviour analysis is essential to gain a sound basis for a reliable fatigue life prediction.
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ABSTRACT The crack propagation law was derived from the S–N data in the very high cycle fatigue of a bearing steel. The propagation rate, d/d(m/cycle), of surface cracks was estimated to be a power function of the stress intensity range, Δ(MPa√m) with the coefficient 65=655.8765×6510and the exponent 65=654.78. The threshold stress intensity range was 2.665MPa√m. The crack propagation from internal inclusions was divided into Stages I02and II. For Stage I, the coefficient of the power law was 65=653.4465×6510and the exponent 65=6514.2. The transition from Stage I02to II took place at Δ65=654.065MPa√m. For Stage II, the coefficient was 65=652.0865×6510and the exponent 65=654.78. The specimen size and loading mode did not influence the surface fatigue life, while the internal fatigue life was shortened in larger specimens and under tension–compression loading. For ground specimens, the surface fatigue life was raised by the compressive residual stress, while reduced by the surface roughness introduced by grinding. For shot-peened specimens, fatigue fracture did not take place from the surface because of a high surface compressive residual stress. The internal fatigue life was reduced by the tensile residual stress existing in the interior of the specimens.
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[本文引用:1]
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[本文引用:1]
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采用了两种不同的充氢方法(浸泡充氢和高压气相热充氢)研究了氢对断口上颗粒状亮区(Granular Bright Facet/GBF)尺寸的影响.研究表明,浸泡充氢并没有改变“GBF”的颗粒状特征,高压气相热充氢使得“GBF”的颗粒状特征变浅甚至消失.不论哪种充氢方法,充氢均使得“GBF”在较低的外加载荷下出现,且与充氢前相比“GBF”尺寸明显增加.电化学充氢没有改变疲劳寿命与(SGBF)1/2/(Sinc)1/2之间的关系,但是高压气相热充氢后疲劳寿命与(SGBF)1/2/(Sinc)1/2之间的关系有显著变化.
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Abstract The mechanism of subsurface crack initiation and propagation in high strength steel in a very high-cycle fatigue region was studied by a computational simulation using a fracture surface topographic analysis (FRASTA) method for specimens of a high carbon chromium bearing steel with data obtained from rotary bending fatigue testing in air. Distinctive features of the fracture surface formed in the vicinity of a non-metallic inclusion at the fracture origin inside the fish-eye zone, the GBF area, was observed in detail using a scanning probe microscope and a three-dimensional SEM for comparing the microstructures of the materials. The GBF area, in which a rich carbon distribution was detected by electron probe microanalysis, revealed a rough granular morphology compared with the area inside the fish eye. It was clearly simulated by the FRASTA method in which during the fatigue process multiple microcracks are initiated dispersively by decohesion of spherical carbide from the matrix around a non-metallic inclusion, and coalesce with each other into the GBF area. In the study, the mechanism for the formation of the GBF area was proposed as the 鈥榙ispersive decohesion of spherical carbide鈥 model.
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为了研究高速工具钢超长寿命S-N曲线特征和内部裂纹萌生行为,使用沙漏形状试样在室温空气环境下进行旋转弯曲的疲劳试验。结果表明,材料的S-N曲线均由表面裂纹萌生型和内部裂纹萌生型组成。表面裂纹萌生型的S-N曲线位于高应力幅短寿命区,内部裂纹萌生型的S-N曲线位于低应力幅长寿命区。前者的S-N曲线向后者的转移几乎是连续的,回火温度对疲劳强度和寿命没有明显的影响。分别使用扫描电子显微镜、扫描探针显微镜和电子探针X射线微区分析仪对内部裂纹萌生位置和材料组织进行对比观察,在萌生内部裂纹的夹杂物周围存在一个颗粒区域,该区域内凸起的颗粒是组织中的球形碳化物。颗粒区是在内部裂纹扩展的应力强度因子门槛值范围以下形成的,对超长寿命疲劳起着重要的作用。
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ABSTRACT In recent years, mechanical structures such as railway wheels, rails, offshore structures, bridges, engine components, load bearing parts of automobiles, etc. have to endure for a long term up to 108-1010 loading cycles in order to save resources and to reduce the cost together with the environmental load to the globe. Thus, the fatigue behavior of structural materials in the very high cycle regime of 108-1010 cycles has become an important subject of the research. In this paper, a review of the current studies in this area performed by many researchers is described in order to provide a certain milestone in the history of the research on fatigue behavior of the metallic materials in the very high cycle regime.
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<p>研究了不同热处理制度下得到的3种具有不同晶粒尺寸的42CrMoVNb高强度钢的超高周疲劳性能. 结果表明, 超高周疲劳强度和疲劳强度比并不随晶粒尺寸的减小而单调提高, 中等晶粒尺寸的试样具有最高的疲劳强度和疲劳强度比. SEM断口观察表明, 绝大部分试样的疲劳裂纹起源于夹杂物. 随着疲劳断口裂纹源夹杂物处应力强度因子幅Δ<em>K</em><sub>inc</sub>的减小, 疲劳寿命<em>N</em><sub>f</sub>增加; 而在夹杂物周围的粗糙粒状区域(GBF)的应力强度因子幅Δ<em>K</em><sub>GBF</sub>并不随<em>N</em><sub>f</sub>变化而变化, 基本为一常数, 且粗晶粒试样的Δ<em>K</em><sub>GBF</sub>高于细晶粒试样. 这表明, 细化晶粒对高强度钢的超高周疲劳性能有着复杂的影响,存在一个合理的细化晶粒范围.</p>
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[本文引用:1]
利用超声疲劳低-高应力两步变幅加载技术研究了JIS SUJ2高强轴承钢疲劳断口上GBF(granular bright facet)内裂纹萌生与扩展规律。结果表明,随外加应力幅增加GBF尺寸减小,固定应力幅下的GBF尺寸为恒定值,与夹杂物尺寸无关;且在固定应力幅下,N f∝A槡inc-8,疲劳寿命N f随着夹杂物尺寸的增加而降低。研究表明,GBF形成于疲劳初期(在105周次左右,相应于小于1%的总寿命),随循环周次的增加,GBF尺寸基本不增加,直至接近最终疲劳寿命时(超过90%总寿命)GBF裂纹快速扩展直到最终尺寸。
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[本文引用:1]
在现代工业机械设备中，许多零部件在低应力超长寿命条件下工作，服役期内需要承受循环载荷的作用达到10~9～10~(10)循环周次。目前通用的疲劳强度设计规范和寿命预测模型一般都建立在10~7(或10~8)循环周次以下的疲劳试验数据基础上。为提高超长寿命条件下工作的零部件强度设计的可靠性和精确性，保障结构运行的安全，有关材料在10~7循环周次以上的疲劳性能和疲劳破坏行为的研究已引起工程界的高度重视。 用现有的常规疲劳试验方法完成10~7～10~(10)超高周次范围内疲劳试验要耗费大量的时间和费用，为此，本文对一种加速疲劳试验技术(超声疲劳试验技术)进行了开发研究，在对称拉压超声疲劳试验装置基础上，开发研制了非对称拉压超声疲劳试验装置和三点弯曲超声疲劳试验装置，分析了影响超声疲劳试验过程和试验精度的因素，这些研究成果对超声疲劳试验技术的推广应用和试验的标准化、规范化工作具有指导意义。在超声疲劳试验技术研究和开发的基础上，本文采用超声疲劳试验方法，结合扫描电镜断口微观分析，对40Cr钢和50车轴钢光滑试样和缺口试样在超高周疲劳范围内的疲劳性能和疲劳断裂机制进行了研究，获得了以下研究成果： 对40Cr钢和50车轴钢光滑试样和缺口试样在10~5～10~(10)循环周次范围内的S-N曲线测定结果显示，调质热处理的40Cr钢在10~5～10~(10)循环周次范围内的S-N曲线呈现“连续下降型”特征，在10~7循环周次附近不存在传统概念上的水平平台，在超过10~7循环周次后，试样仍然发生疲劳断裂。正火热处理的50车轴钢在10~5～10~(10)循环周次范围内的S-N曲线呈现“阶梯下降型”特征，S-N曲线在10~6～10~8周次范围内出现一段水平平台，超过10~8循环周次，S-N曲线第二次下降，表明在平台对应的应力幅以下超高周疲劳范围内，50钢试样仍然会发生疲劳断裂。试样断口显微分析显示，在10~7周次以下的疲劳断裂，疲劳裂纹在试样表面萌生；而在10~7以上超高周范围内的疲劳断裂，疲劳裂纹主要在试样内部或次表面材料夹杂处萌生。表明40Cr钢和50车轴钢的疲劳断裂存在疲劳裂纹表面萌生和疲劳裂纹内部萌生两种机制，分别对应不同的S-N曲线，通过两种机制对应的S-N曲线在试验研究范围内的位置关系可以描述材料的S-N曲线的形状特征，本文将这种描述方法称为“双曲线模型”。 对缺口试样疲劳性能的研究结果显示，在10~5～10~(10)循环周次范围内， 第日页 西南交通大学博士研究生学位论文 缺口应力集中对40Cr钢和50钢疲劳性能的影响呈现“阶段性特征”，疲 劳缺口系数随疲劳循环周次的变化在107循环周次附近存在一个临界循环 周次Nc(或临界范围)，对应一个最大的疲劳缺口系数;当疲劳循环断裂 周次玛Nc时，疲劳缺口系数随循环周次的增加呈上升趋势;当汉户Nc时， 疲劳缺口系数随循环周次的增加呈下降趋势。分析表明缺口应力集中对疲 劳性能的影响呈现出的这种“阶段性特征”与两种疲劳裂纹萌生机制的转 换有关。 通过对超声疲劳试验结果与常规旋转弯曲疲劳试验结果的比较分析显 示，超声疲劳载荷频率对40Cr钢和50钢的疲劳性能存在影响，超声高频 载荷使材料疲劳性能提高。分析结果显示，可以用一个加载频率修正系数 来修正超声高频疲劳试验结果与常规疲劳试验结果之间的差异，且加载频 率修正系数可通过不同应变速率下的材料断裂强度的比值来近似确定。 综合试验研究结果，本文认为疲劳裂纹内部萌生过程是裂纹形核和核 心长大成宏观概念上的可扩展裂纹的过程。其中疲劳裂纹内部萌生的核心 是材料中的第二相粒子、夹杂物或微空洞，称为微裂纹;而微裂纹的长大 是材料中间歇原子或空位等点缺陷在微裂纹尖端富集沉淀的过程，微裂纹 的长大速率受到点缺陷富集扩散速率和疲劳载荷的双重影响。本文将这种 描述疲劳裂纹内部萌生过程的微观模型称为“点缺陷沉淀”机理。并根据 该微观机理建立了疲劳裂纹内部萌生寿命的表达式，分析了影响疲劳裂纹 内部萌生寿命的因素，提出了提高疲劳裂纹内部萌生寿命的途径。 关键词:40Cr钢，50车轴钢，超声疲劳试验，S一N曲线，缺口应力集中， 疲劳性能，疲劳断裂，疲劳裂纹萌生，裂纹萌生微观机理，载荷 频率的影响
DOI:10.7666/d.y683623
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The surfaces of commercially pure polycrystalline copper specimens subjected to interrupted 20 kHz fatigue tests in the very high cycle fatigue regime were investigated. The stress amplitude needed to form the early slip markings was found twice lower than the stress amplitude required to fracture which confirmed the results obtained by Stanzl-Tschegg et al. (2007). Three types of slip markings were classified according to their morphology and their location in the polycrystalline material. They are compared to slip markings observed during fatigue tests at frequencies lower than 100 Hz and numbers of cycles lower than 10(7). For 20 kHz fatigue tests, stress amplitudes ranging from 45 MPa to 65 MPa produce straight and long early persistent slip markings located along twin boundaries. Stress amplitudes lower than 45 MPa produce clusters of fine early persistent slip markings mainly located at triple junctions. (C) 2014 Elsevier Ltd. All rights reserved.
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[本文引用:1]
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@article{144592, author = {De, Amar and VANDEPUTTE, S and De Cooman, Bruno}, issn = {1359-6462}, journal = {SCRIPTA MATERIALIA}, language = {eng}, number = {4}, pages = {695--700}, title = {Kinetics of low temperature precipitation in a ULC-bake hardening steel.}, volume = {44}, year = {2001}, }
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[本文引用:0]
研究了JIS-SUJ2轴承钢的超高周疲劳行为及高压气相热充氢对疲劳性能的影响.结果表 明,高压气相热充氢后疲劳性能明显降低,裂纹源周围“GBF”区的颗粒状特征变浅甚至消失.断口上裂纹源处缺陷尺寸及分布对疲劳寿命没有影响,疲劳寿命随 着“GBF”与夹杂物尺寸比的增加而增加.充氢前后裂纹源边缘的应力强度因子范围均近似正比于裂纹尺寸的1/3次方,“GBF”裂纹扩展的门槛值正比于 “GBF”尺寸的1/6次方.高压气相热充氢明显提高了氢致附加应力强度因子,估算的“GBF”裂纹尺寸的极限值与实验值能够较好地吻合.
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Fatigue tests of a high carbon chromium steel were performed using rotating bending and ultrasonic axial cycling. Fatigue crack initiated at specimen interior for very-high-cycle fatigue (VHCF) with fish-eye pattern embracing fine-granular-area (FGA) originated from inclusion. The fatigue life from FGA to fish-eye and from fish-eye to the critical crack size was respectively calculated, so as to estimate the fatigue life contributed by FGA. The crack extension rate within FGA was also estimated. Our results demonstrated that the formation of FGA is responsible for a majority part of total fatigue life. (C) 2013 Elsevier Ltd. All rights reserved.
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[本文引用:1]
依据Murakami的"夹杂物等效投影面积模型"估算了在高周 疲劳条件下一定硬度(或强度)高强钢的"临界夹杂物尺寸".估算结果表明,随着钢硬度(或强度)的增加,"临界夹杂物尺寸"逐渐减小;"临界夹杂物尺寸" 也受构件表面机加工粗糙度的影响,表面越光洁,这个尺寸也越小.从本文几种钢的实验数据以及其它已发表的数据都可以间接证明,估算的临界尺寸是合理的.
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