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中进行10000 h的热暴露处理,随后再加工上述的表面和贯穿型直线缺口. A,B两组光滑试样的S-N高周疲劳(HCF)强度测试实验是在PLG-100型微机控制高频疲劳试验机上采用四点弯曲模式完成.室温条件下,采用应力比R=0.1(),试验频率f=100 Hz左右,逐个测定每一样品在交变疲劳应力下的最大断裂应力()和相应的疲劳失效周次(N).当样品在经历107周次仍然不断裂时,把这时的最大应力定义为...4所示.长时间的高温热暴露导致光滑样品的疲劳极限有少量的增加(11%).如前面所述,虽然热暴露导致合金显微组织出现脆化,组织脆化会使得疲劳样品的最大受力面上形成微裂纹的趋势增加;但长期热暴露也会给样品带来一种类似回火的稳态效应.样品内部应力集中的释放,组织中偏聚的缓解,缺陷的钝化均有益于提高材料抵抗微裂纹萌生的抗力,这属于一种良性效应.S-N光滑疲劳样品在10000 h的热暴露中承受着这两个相反效......
数 Table 1 Main parameters of vehicle-track coupled model 表2 扣件主要参数 Table 2 Main parameters of rail fastener 2.3.1 S-N曲线的选取 扣件弹条采用60Si2Mn弹簧钢制成,其95%存活率时的σ-N曲线公式为[20]  ...冰, 彭佳纯. 寿命服从对数正态分布,有置信度时概率疲劳S-N曲线的合理重构[J]. 应用数学和力学, 2007, 28(4): 413-418. ZHAO Yongxiang, YANG Bing, PENG Jiachun. Rebuilding of the probabilistic S-N curves under fatigue life following lognormal......
images and corresponding SAED patterns of 7020 aluminum alloys in different aging conditions 2.3 疲劳强度 图2所示为不同时效状态下的S-N曲线(其中N为循环次数(用来表征疲劳寿命),S为加载应力).N的拟合公式[17]为 (1) 式中:A,B和E为拟合系数.将3种时效状态下合金的循环次数分别按式(1)进行拟合. 图2 不同时效状态下合金的S-N曲线 Fig. 2 S-N curves of the alloys in different ageing conditions 欠时效状态:  ......
,机械抛光后进行电解抛光,电解抛光液为10%高氯酸+90%乙醇混合溶液,实验电压20 V. 按国标GB/T 228.1在MTS Landmark拉伸机上进行室温拉伸性能测试,试样平行区标距长40 mm,拉伸速率2 mm/min,不同合金分别取3个平行试样.疲劳S-N曲线测试采用SDS100型电液伺服疲劳试验机,按照国标GB/T 3075进行,沿挤压方向取样,试样厚度10 mm,测试时应力比R...压型材疲劳S-N曲线,S为加载应力,N为疲劳循环次数.疲劳循环数据拟合时采用式(1)[26]进行: (1) 式中:A,B,E为待定常数.将3种不同......
surfaces and then prepared by twin-jet polishing method. 3 Results and discussion 3.1 Stress-fatigue life curve S-N results of fatigue testing for DD6 alloys with 0.1%Hf and 0.34%Hf are shown in Fig.1. The arrows indicate that the specimens are not failure during fatigue tests. Fatigue strength at the 107th cycle is usually defined as the fatigue limit. As can be seen from Fig.1, S-N curves show......
unmodified eutectic Si particles, with needle-like morphology, characteristic of alloy without process of modifications Si and refinement of grain. Fig. 6 Stress vs cycle to failure (S-N) curves as function... with the studied variables, was used. Although typical fatigue limits can be easily seen for iron or titanium- based alloys, in S-N curves of aluminum-based alloys it is not common to reach a plateau......
direction and at 3 points (with equal intervals of 12.5 mm) in the transverse direction. The force of the indenter during the microhardness test was 2 N for a duration of 10 s. For each position... at 45° (relative to the loading direction), indicating a brittle behavior of the materials. 3.5 High cycle fatigue Figure 9 illustrates the obtained S-N fatigue curves for AZ31B and AZ31B/1.5vol.%Al2O3......
(S-N curve) approach; 2) the strain-based approach;3) the fracture mechanics approach. 2.2 Stress-based approach (S-N curve) A typical S-N curve of metallic materials is shown in Figure 1(a). Around.... Estimation of S-N curves is illustrated in Figure 1(b): Ne is specified, 106 cycles for steels for instance, above which the S-N curve is horizontal; fatigue limit stress of unnotched material, σer......
或材料强化和劣化的分界点所对应的荷载循环比值.当构件经历第一级荷载循环比低于临界值的疲劳荷载作用时,构件处于强化阶段,其强度将有所提高.本文引用文献[7]中低-高两级变幅疲劳荷载作用下,临界值. 通过文献[2]得到的埋置于混凝土中的预应力钢绞线的S-N方程来近似估算预应力筋的疲劳寿命: (4) 式中:s为外加应力幅值. 将预应力钢筋在第一级荷载作用下应力幅值s=2.18 MPa代入式(4),可得...(1) 式中:Kn和K0分别为疲劳重复荷载作用n次后预应力筋的刚度与初始状态下预应力筋的刚度. MINER准则将疲劳损伤D定义为使用应力作用下循环次数n与该应力作用下材料疲劳寿命Nf之比: (2) 并且认为在多级不同应力幅疲劳荷载作用下,发生疲劳破坏时, (3) 式中:ni为第i级应力水平下的的循环次数;Nf, i为第i级应力水平下的疲劳寿命. MINER准则有以下几个局限性[20]:1) 在任......
,m=3.国际焊接学会将2×106 次应力循环数下特定的疲劳强度定为疲劳级别FAT,因此,图9中曲线是国际焊接学会推荐的FAT75的疲劳设计曲线[13,15]. 图9 闪光对焊焊接接头疲劳试验数据和S-N曲线(R=0.2) Fig.9 Fatigue test data and S-N curve for flash butt welds (R=0.2) 按表5和图9结果...芯部则经历不完全奥氏体化后的再结晶,母材芯部组织为F+P+B,表层组织为S,表层硬度HV5高于芯部硬度30 HV5,其组织和硬度变化较大;焊接接头的抗拉断负荷从焊缝到混晶区逐渐减小,焊缝和热影响粗晶区的抗拉断负荷比母材的高;采用国际焊接学会推荐的FAT75疲劳设计曲线对钢筋焊接接头疲劳强度设计是安全的. 关键词:HRB500E抗震钢筋;焊接性能;焊接接头;疲劳强度 中图分类号:TF762 ......