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121.
本文对结构用钢Q345的低周疲劳性能进行了试验研究。试验在常温下岛津电液伺服疲劳试验机上进行,采用轴向应变控制方法,恒定应变速率为0.005s-1,应变比为-1。试验结果表明,初始阶段,Q345在高应变幅值(0.6%)循环作用下出现循环硬化效应,而在低应变幅值(0.6%)作用下出现循环软化效应;随着加载应变幅的增加,硬化和软化率呈直线上升趋势。Q345疲劳裂纹萌生阶段占其整个寿命的60%以上,其裂纹萌生寿命与应变幅存在幂函数关系。根据Coffin-Manson公式得到了Q345的应变-寿命关系公式;采用能量预测法得到了材料的塑性应变能与疲劳寿命的关系表达式。上述结果对钢结构的设计、评估具有重要的工程应用参考价值。 相似文献
122.
经典齿轮接触疲劳强度理论是基于光滑表面赫兹干接触理论,而实际齿面具有粗糙度,且啮合轮齿多数处于混合润滑状态.本文基于齿轮润滑接触分析建立了渐开线斜齿轮的接触疲劳寿命计算模型.模型由齿轮润滑接触分析模型和基于次表面应力分布的疲劳寿命模型组成.首先将斜齿圆柱齿轮一对齿的瞬时啮合等效为两反向圆锥的接触问题,建立了齿轮的有限长弹流润滑计算模型,考虑了齿轮啮合周期内瞬时载荷、接触线长、卷吸速度等因素的影响,基于统一雷诺方程方法求得啮合齿对间的润滑压力和油膜厚度分布;在此基础上,计算轮齿接触区次表面的米歇斯应力分布,根据Zaretsky接触疲劳寿命计算模型,对齿轮组的接触疲劳寿命进行模拟预测.针对不同工况参数下接触疲劳寿命计算表明:润滑油黏度、轮齿表面粗糙度等因素对齿面接触疲劳寿命均有显著的影响. 相似文献
123.
Experimental investigation of the low cycle fatigue crack propagation in PC/ABS polymer blends 总被引:1,自引:0,他引:1
Low cycle fatigue crack propagation (FCP) behavior of two PC/ABS blends with a weight ratio of PC to ABS being 80/20 and 60/40,
respectively, is investigated. Experiments are carried out by using standard compact tension (CT) specimens. The fracture
surfaces are examined with a scanning electron microscope (SEM). It is shown that the FCP resistance of PC/ABS blend with
20% ABS particles is higher than that of PC/ABS blend with 40% ABS particles. It is found that proper ABS particle content
can result in the toughening of PC/ABS blends through particle cavitation and shear yielding in matrix.
Project supported by the Excellent Young Teachers Program and the Research Foundation for Doctoral Project of the Ministry
of Education of China. 相似文献
124.
On the use of nickel foil strain gages at varying temperatures 总被引:1,自引:0,他引:1
When a strain gage made of nickel foil attached on the surface of a specimen is subjected to repeated loads, the elastic stress
is measured by observing slip-bands in the foil resulting from repeated strain. Calibration studies with rotating-bending
tests at various temperatures between room temperature and 350°C are performed on round steel bars with nickel foil. The relation
between the threshold stress for the first appearance of slip-bands and the number of stress cycles is examined at varying
temperatures, which provides the calibration values of the nickel foil tested at varying temperatures. Assuming that the first
appearance of slip-bands is based on the linear cumulative damage law, the calibration values at varying temperatures are
calculated from those established by the calibration tests at several constant temperatures. It is found that the calculated
calibration values agree well with the results obtained by the calibration tests at varying temperatures and that the calculation
applying the linear cumulative damage law is a useful method to presume the calibration values at varying temperatures without
performing the experiment. 相似文献
125.
Effect of silver content on thermal fatigue life of Sn-xAg-0.5Cu flip-chip interconnects 总被引:5,自引:0,他引:5
Shinichi Terashima Yoshiharu Kariya Takuya Hosoi Masamoto Tanaka 《Journal of Electronic Materials》2003,32(12):1527-1533
The thermal fatigue properties of Sn-xAg-0.5Cu (x=1, 2, 3, and 4 in mass%) flip-chip interconnects were investigated to study
the effect of silver content on thermal fatigue endurance. The solder joints with lower silver context (x=1 and 2) had a greater
failure rate compared to those with higher silver content (x=3 and 4) in thermal fatigue testing. Cracks developed in the
solders near the solder/chip interface for all joints tested. This crack propagation may be mainly governed by the nature
of the solders themselves because the strain-concentrated area was similar for tested alloys independent of the silver content.
From the microstructural observation, the fracture was a mixed mode, transgranular and intergranular, independent of the silver
content. Higher silver content alloys (x=3 and 4) had finer Sn grains before thermal cycling according to the dispersion of
the Ag3Sn intermetallic compound, and even after the cycling, they suppressed microstructural coarsening, which degrades the fatigue
resistance. The fatigue endurance of the solder joints was strongly correlated to the silver content, and solder joints with
higher silver content had better fatigue resistance. 相似文献
126.
Low-cycle fatigue (LCF) behavior of a lead-free Sn-3.5Ag-0.5Cu solder alloy was investigated at various combinations of strain
ratio (R = −1, 0, and 0.5) and tensile hold time (0, 10, and 100 sec). Results showed that the LCF life of the given solder,
at each given combination of testing conditions, could be individually described by a Coffin-Manson relationship. An increase
of strain ratio from R=−1 to 0 and to 0.5 would cause a significant reduction of LCF life due to a mean strain effect instead
of mean stress effect. LCF life was also markedly reduced when the hold time at tensile peak strain was increased from 0 to
100 sec, as a result of additional creep damage generated during LCF loading. With consideration of the effects of strain
ratio and tensile hold time, a unified LCF lifetime model was proposed and did an excellent job in describing the LCF lives
for all given testing conditions. 相似文献
127.
A stochastic theory for the cumulative fatigue damage of structural components with random fatigue strength under random loading is proposed on the basis of Stratonovich-Khasminskii theorem. The analytical solutions for the probability densities of the cumulative fatigue damage and fatigue life and for the reliability function are given for steel and reinforced concrete components with constant fatigue strength subject to a narrow band stationary Gaussian stress process with zero mean. The results agree very well with those of digital simulation. It is noted that the theory can be applied, in principle, to both metallic and non-metallic materials, narrow band and wide band stress process, and adapted to a sequence ofn, stationary stress processes or quasi-stationary stress process. The scatter and degradation of fatigue strength and the inspection maintenance can also be incorporated into the theory. 相似文献
128.
7050航空铝合金结构材料激光冲击强化处理研究 总被引:13,自引:4,他引:9
用自行研制的激光冲击强化处理(LSP)装置对两种重要航空铝合金结构材料7050T7451,7050T7452冲击强化试验,进行了疲劳寿命对比试验。给出了反映疲劳应力水平与结构件寿命对应关系的σm-N曲线。结果表明.在67.3MPa的加载应力水平下,激光冲击处理后7050T7451结构材料的疲劳寿命提高到未经处理的435%,而7050T7452在81.4MPa的应力水平下提高到518%。并对试件进行了激光冲击处理机理的研究。结果显示试件表面具有较大的残余压应力和较高的位错密度。 相似文献
129.
130.
提出了一种评估结构疲劳可靠性的方法-风险预测方法。该方法利用结构在服股过役过程中的信息,在考虑了工程结构承采载荷的各态历经性的基础上,结合了结构元件寿命机分布形式和Miner线性累积损伤理论,以风险值来评价并监控结构元件在不同时间失效的危险性,并用算例和试验结果进行对比分析。 相似文献