Detection and Evaluation of Infinitesimal Fatigue Crack in the Welded Joints
Detection and Evaluation of Infinitesimal Fatigue Crack in the Welded Joints
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焊接接头无限小疲劳裂纹的检测与评价
DOI：
10.2534/jjasnaoe1968.2002.507
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
K. Horikoshi
中科院分区：
文献类型：
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作者：
J. Katsuta;K. Kawano;Takuya Yoshida;K. Horikoshi
发现长度超过几百毫米的疲劳裂纹，并在维修时进行修复，现在通过目视检查执行。这些疲劳裂纹是在局部腐蚀、漏水和异常振动等次要现象中检测到的。然而，疲劳裂纹的存在无法直接检测，本文提出了一种从微裂纹的早期阶段检测疲劳裂纹的方法，即目前的视觉维修判断没有疲劳损伤。根据裂纹检测结果和有限元分析估计裂纹尺寸。根据裂纹尺寸的大小，考虑了断裂可能性的判断以及剩余强度和剩余疲劳寿命的估算方法。结果表明：1）应变降低率（裂纹萌生后的应变与无损伤时的应变之比）可作为监测参数; 2）从无损伤时起监测应变降低率，可检测出微小裂纹阶段及其以后的疲劳裂纹; 3）在循环载荷变化的情况下，可通过应变集中降低率检测出裂纹。
Fatigue cracks of more than several hundred millimeters in length are found and repaired upon maintenance, which is now executed by visual check. These fatigue cracks are detected in and through a secondary phenomenon, as local corrosion, water leakage, and abnormal vibration. The presence of fatigue cracks, however, cannot be directly detected.This paper proposes a method to detect fatigue cracks from the early phase of infinitesimal fatigue cracks, in which present visual maintenance judges that there is no fatigue damage. A crack size is estimated according to results of crack detection and by FEA. The judgment of fracture possibility and the method to estimate residual strength and remaining fatigue life are considered in accordance with the crack size. The results obtained from this study are as follows:1) Lowering rate of strain, calculated as the ratio of strain after crack initiation to strain at the time of no damage, is proposed as a monitoring parameter.2) Monitoring lowering rate of strain from the time of no damage allows a fatigue crack in and after the phase of the infinitesimal crack to be detected.3) In cases of the changes in cyclic loading, cracks can be detected by lowering rate of strain concentration.