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

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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.