A Study on Quantitative Estimation Method for Fatigue Crack Propagation Behavior by Image Analysis

本文提出了一种利用图像分析来估计疲劳裂纹扩展行为的简单方法，并对其适用性和局限性进行了实验研究。本文的主要研究成果如下：1.在十字形焊接接头和腹板焊接接头上，利用数字显微镜进行了裂纹张开宽度的测量实验，并估算了裂纹的I型应力强度因子。试验结果表明，应力强度因子大于10 Mpa/“m的应力强度因子可以有足够的精度用于工程应用。为了将该方法推广到实际桥梁构件中，用数码显微镜和数码摄像机记录了循环荷载作用下的裂缝张开行为，并进行了估算。在所记录的数字电影数据上。当频率小于5赫兹时，可以准确地测量出裂纹张开宽度。将所提出的方法应用于钢桥构件的实际疲劳裂纹。裂缝显示出开启/关闭行为的线索，车辆通过，但。提出了从连续测量的裂纹张开行为中获取应力强度因子直方图和超概率的方法。

In this study, a simple method to estimate fatigue crack propagation behavior by image analysis was proposed, and its applicability and limitations were experimentally investigated. Main results of this study is as follows, 1. On cruciform welded joints and web gusset, welded joints, experiments to measure the opening width offatigue crack by using a digital microscope, and estimate Mode I stress intensity factor for the crack were carried out. The test results showed that the stress intensity factor more than 10 Mpa/"m could be estimated with enough accuracy for engineering use.2. In order to extend the applicability of the proposed method to real bridge structural members, crack opening behavior under cyclic loaded condition was recorded by a digital microscope and a digital video camera, and the proposed estimation was carried out. On the recorded digital movie data. When the frequency is less than 5Hz, crack opening width could be measured accurately.3. The proposed method was applied to a real fatigue crack in steel bridge members. The crack showed opening/closing behavior clue to the passage of the vehicle, but. Their frequency was about Ihz, which is within the applicable condition of the proposed method.4.The method to obtain the histograms of stress intensity factor and excessive probability was proposed from the continuously measured crack opening behavior.