Study of Fatigue Strength Simulation under Corrosion Environments

本研究是发展并提出一种腐蚀环境下的模拟方法。在腐蚀环境下接受脉动载荷的构件的疲劳强度是通过计算来要求的，而不进行腐蚀疲劳试验。在研究腐蚀环境下裂纹萌生和扩展行为的基础上，提出了将静态腐蚀坑扩展速率与断裂力学方法相结合的方法。利用提出的模拟方法进行了计算。并将模拟疲劳强度与腐蚀疲劳试验结果进行了对比。验证了所提出的仿真方法的有效性。发现了腐蚀环境下脉动载荷条件下疲劳强度模拟的可能性，主要研究结果如下：1）提出了一种基于断裂力学的静态腐蚀对早期点蚀坑尺寸随时间变化而要求寿命的模拟方法提出了一种在腐蚀环境下直接绘制裂纹发生后的裂纹扩展速率图并假设裂纹发生条件的模拟方法。4）对于疲劳裂纹扩展寿命的大部分时间，裂纹深度是在厚度的一半范围内的扩展期内度过的腐蚀坑是可能的模拟与表面裂纹从一个主坑扩展，如果忽略这些动态干扰，虽然它很大程度上发生在材料表面。6）虽然它是可能的模拟方法，提出了即使在脉动载荷条件下的结果是无法确认。

This research is the development and proposed of a simulation method under a corrosion environments. The fatigue strength of the member that receives a pulsating load under corrosion environment is requested by calculation, without carrying out a corrosion fatigue test. It did on the basis of a study of crack initiation and propagation behavior under a corrosion environment.The method that combines and carries out a static corrosion pit growth rate and a fracture mecanics method was proposed. It calculated by using a simulation method that proposed. And it went a comparison between simulated fatigue strength and corrosion fatigue test results. The efficacy of the simulation method that proposed was confirmed. That the simulation of the fatigue strength in a pulsating load condition under corrosion environment is possible was found out.The main result are as follows.1) A simulation method that it requests because an early period pit size change with the time progress and request the lifetime under an optional early period pit size by static corrosion by fracture mechanics was proposed.2) A simulation method that requests a crack propagation rate diagram under corrosion environment directly after crack occurrence and supposea crack occurrence condition was proposed.3) That the fatigue strength by the simulation and corrosion fatigue test, by simulation are agreeing well to quantitative to qualitative was able to confirm.4) As for most of a spread lifetime of a fatigue crack depth is spent in a growing period to a half extent of the thickness.5) A corrosion pit is possible a simulation with surface crack spread from one main pit, if those dynamic interference are disregarded, although it greatly occurs in a material surface.6) Although it is possible a simulation by the method that proposed even in pulsating load condition under the result was not able to confirm.