In this study, the effect of pre-existing corrosion pits on the fatigue behavior of 7075/T6 aluminium alloy in very long life range and in the near threshold regime was investigated by using piezoelectric accelerated fatigue test. The results indicate that the presence of pre-existing corrosion pits, produced by 1-day, 4-day, and 7-day immersion in salt water significantly reduces the fatigue life of the aluminum alloy by a factor of 10-100.

The effect of inclusions on crack initiation and propagation in gigacycle fatigue was investigated experimentally and analytically in six high strength low alloy steels. Fatigue testing was performed at very high numbers of cycles through ultrasonic fatigue tests at 20kHz. Inclusions at subsurface are common sites for fatigue crack nucleation in these alloys when cycles to failure was 107 cycles. A significant change in the slope of the S-N curve was observed accompanying the transition from surface to subsurface crack initiation. A deterministic model has been developed to predict the total fatigue life, i.e. crack initiation life and crack propagation life, from the measured inclusion sizes. The predicted fatigue strength agreed reasonably well with the experimental results. It is a tendency that smaller inclusions are associated with longer fatigue life. The results demonstrated that the portions of life attributed to subsurface crack initiation between 107 and 109 cycles are>99%. Science Ltd. All rights reserved.

复合材料贴片修补损伤金属结构件已被证明是一种可靠的低成本高效益结构补强延寿方法。对复合材料贴片修补前后的含裂纹70752T6铝合金薄板进行了拉伸和疲劳性能研究。结果表明，修补后构件的强度和疲劳寿命都明显提高，随着硼2环氧复合材料补片层的增加，修补铝合金板的疲劳扩展速率显著下降，疲劳寿命可获得10倍以上的改善。基于Rose分析解发展了一个简单的疲劳寿命预测模型，通过与试验结果比较证明了该模型的简单有效。

利用20kHz压电超声疲劳试验技术，对六种抗拉强度高于1500MPa的低合金钢进行测试。结果表明，这些材料并不存在传统规范中所谓的“疲劳极限”，它们在超过107，甚至109应力循环后仍然继续发生破坏，而且其S-N曲线表现出“阶梯”型特征。研究还发现，这些材料都存在一个分界应力幅值区间（或应力循环数区间,大约在106到107 的平台内），裂纹萌生由试件表面向其内部转换。实验证明了十亿周级超高周疲劳裂纹由试件内部萌生的机理。

结构钢作为一种用途广泛的建筑结构材料其优点十分显著，但是不容忽视的是结构钢对温度很敏感,高温很容易使其遭到破坏。近年来，关于在火（高温）环境中结构钢材性研究已取得了较大的进展，本文对基于不同材性模型的分析结果进行了比较，讨论和评述了包括火（高温）对结构钢的微观结构性能和力学性能的影响。