According to our experimental investigations of varying load amplitude , it was found that the phenomena of fatigue crack growth retardation occurred for pmma material following a high overload cycle exerted among the regular constant amplitude load cycles , the ratio of peak value of overload to that of the regular cycles should be over at least 1 . 35 to make the retardation taking effect . the experiment scheme for measuring the shutting - off ratio of overload ( defined as the overload ratio when da / dn < 10 - 7 / cyc . ) 本文试验分析了变幅载荷对裂纹扩展的影响，证实了有机玻璃也存在超载迟滞现象，通过金相观察分析，提出超载迟滞的过程实际上是裂纹前缘萌生新的裂纹的过程的观点，同时提出超载迟滞的合理的解析，并且给出超载迟滞比，为随机载荷下疲劳扩展模型的建立提供了一个重要的参数。
In the present thesis , researches on the micro - mechanisms and the macro - mechanical models of fcp in high ductility - , low ductility - and brittle materials , including metals , ceramics and polymers , are briefly summarized . furthermore , systematic investigation is made on the general fcp pattern , the fcp micro - mechanisms , the mechanical models and the intrinsic - and extrinsic factors affecting fcp by using the approach combining the analysis and the experiments . finally , an almost perfect formula for fcp is developed 本文系统地分析和总结了中外文献对高塑性材料、低塑性材料和脆性材料，包括金属材料、高分子材料和陶瓷材料的疲劳裂纹扩展微观机制和宏观力学模型的研究结果，进而采用理论分析与实验研究相结合的方法，从微观和宏观两个方面对疲劳裂纹扩展的一般规律、影响因素、微观机制、力学条件和宏观规律及其定量理论进行了深入的研究，给出了为实验结果所验证的接近完善的疲劳裂纹扩展表达式。
This thesis presents a new analysis and simplification to the energy principle of crack propagation by using the concept of crack - circle and strain energy principle in elastic mechanics . the analytic models of crack propagation motivity and its length measurement and angle measurement , the displacement of crack propagation motivity and the angle of crack propagation motivity , are builded 本文利用弹性力学中的应变能定理和裂纹圆模型的概念对裂纹扩展的能量机理作了新的剖析和简化，提出了裂纹扩展动力及其长度度量? ?裂纹扩展动力位移和角度度量? ?裂纹扩展动力角的解析模型和物理意义。
The forth chapter analysis the stress on the basis of reliability , the result illuminates that the stress obeys the normal disturbing and uniformity disturbing , however quantity of the stress that can affect the flaw extending is not same with the work cycle . so if we want to get the number of the stress that affects the extending life , we should use carefully the statistic tool 本文第四章经过基于可靠性理论的实测载荷谱分析，发现那些能够促使裂纹扩展的应力幅服从正态分布或均匀分布，而且其量上也有一定差异，只有经过仔细分析比较才能获得影响裂纹扩展的正确的应力幅统计数据。
With the experiment of surface crack growth of bhw - 35 weld metal , the law of the surface crack shape variation when it grows was obtained , and the law of surface crack growth rate was also gotten . these direct the evaluation of the surface crack fatigue growth life and the critical value of its length 对bhw - 35钢焊缝材料进行表面裂纹扩展试验研究，得到裂纹的扩展形貌变化规律，并对其疲劳扩展寿命进行预测研究，为汽包下降管角焊缝部位的表面裂纹扩展寿命预测提供依据，同时也确定了其表面裂纹扩展的临界值。
Triumphant good pe uses the german battenfield polyethylene tubing for the water pipe production equipment to squeeze out the production line , its unique sieves the basket type nose design , can effectively destroy the polyethylene raw material , thus guarantees the polyethylene tubing to have the performance in the use which the fine anti - slow crack growth and the anti - fast crack expands 凯佳pe给水管生产设备采用德国battenfield聚乙烯管材挤出生产线，其独特的筛篮式机头设计，能有效地破坏聚乙烯原料的记忆性，从而确保聚乙烯管材在使用中具有优良的抗慢速裂纹增长和抗快速裂纹扩展的性能。
