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Investigation On Near-Threshold Fatigue Crack Growth Behavior by Using Nano-and Mesoscale Simulation and Observation

利用纳米和介观尺度模拟和观测研究近阈值疲劳裂纹扩展行为

基本信息

批准号：
13450048
负责人：
KUBO Shiro
金额：
$ 9.66万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2003
项目状态：
已结题

项目摘要

In the present research, nanoscale molecular dynamics, macroscale experiment, and mesoscale observations were applied to the near-threshold fatigue crack growth behavior. The results obtained are summarized as follows.1.High temperature fatigue crack propagation experiments were conducted for SUS 304 stainless steel, in air and in vacuum. It was found that the fatigue crack growth resistance was higher in a vacuum than in air. The threshold value of fatigue crack growth attained maximum around 550℃ in a vacuum and in air. After the threshold behavior was observed in the K decreasing tests, the crack was found to grow again when the maximum K value was increased in air and in a vacuum. By repeating this process a so-called true threshold was attained. The effect of temperature on relationship between crack growth rate da/dN and Δ K was small.Fatigue crack growth experiments were made also for Ni base super alloy and aged material.Mesoscale observations were made to find relationship between slip, plastic deformation and crack growth.2.Nanoscale simulation of the near-threshold fatigue crack propagation in iron were made by using the molecular dynamics. Crack growth was observed under mode II loading as well as mode I loading. Crack growth direction under mixed mode loading agreed well with that predicted by the maximum circumferential stress criterion.Effect of tilt grain boundary and twist grain boundary on the near-threshold fatigue crack growth was examined using the molecular dynamics. While cracks sometimes grew across Σ73 and Σ99 small angle grain boundaries, the barrier was higher for, Σ9 and Σ11 largel angle grain boundaries. For the twist grain boundary perpendicular to crack plane, the grain boundary was found to impede the fatigue crack growth.

在本研究中，纳米尺度的分子动力学、宏观尺度的实验和细观尺度的观测被应用于近门槛值疲劳裂纹的扩展行为。主要研究结果如下：1.对SUS 304不锈钢在空气和真空中进行了高温疲劳裂纹扩展试验。结果表明，真空中的疲劳裂纹扩展阻力高于空气中的疲劳裂纹扩展阻力。在真空和空气中，疲劳裂纹扩展门槛值在550℃左右达到最大值。在K降低试验中观察到裂纹的门槛行为后，发现当空气和真空中的最大K值增加时，裂纹再次扩展。通过重复这一过程，达到了所谓的真正阈值。裂纹扩展速率da/dN与ΔK之间的关系受温度的影响较小。还对镍基高温合金和时效材料进行了疲劳裂纹扩展实验，并进行了细观观察，找出了滑移、塑性变形和裂纹扩展之间的关系。2.利用分子动力学方法对铁中近门槛疲劳裂纹扩展进行了纳米尺度模拟。在II型加载和I型加载下观察到裂纹扩展。复合型加载下的裂纹扩展方向与最大周向应力准则预测的裂纹扩展方向基本一致。用分子动力学方法研究了晶界倾斜和晶界扭曲对疲劳裂纹扩展的影响。裂纹有时跨越Σ73和Σ99小角度晶界扩展，但Σ9和Σ11大角度晶界的势垒较高。对于垂直于裂纹面的扭曲晶界，晶界阻碍了疲劳裂纹的扩展。