Determination of Required Quality and Quality Control by Ultrasonic Testing of Welded.joints for Steel Bridges

本文的主要研究内容如下：1）通过疲劳试验研究了含各种埋置缺陷的对接焊接接头的疲劳性能，发现疲劳强度与缺陷类型有关。2）根据疲劳试验和无损检测的现状，提出了缺陷的允许尺寸，板厚的六分之一。3）对现有的自动超声检测系统进行了循环试验，可以清楚地看出40mm或更薄钢板中的焊接缺陷可以通过所有测试系统检测，但某些系统无法检测到100 mm板中的那些。通过实验和有限元法波传播模拟，证明了钢板厚度方向各向异性的存在，并明确了各向异性对钢板厚度方向的影响5）通过实验和有限元法波传播模拟，证明了钢板在厚度方向上存在各向异性，它会影响超声检测中缺陷位置的确定。6）为了更准确地定量评价超声检测中的缺陷，提出了一种串联阵列换能器，并证明了其适用性。7）断裂韧性是影响焊接接头质量的重要因素之一，母材夏比冲击试验表明，当钢板经历塑性应变历史时，断裂韧性会发生劣化，但其破坏程度与塑性应变或缺口的方向无关。

The summary of this study is as follows.1) The fatigue performance of butt welded joints containing various embedded defects was investigated by tatigue tests and it became clear that the fatigue strength depends on the type of defects.2) Based on the fatigue tests and the present level of non-destructive testing, as the allowable defect size, one sixth of plate thickness was suggested.3) The round robin test of existing automatic ultrasonic testing systems was carried out and as a result, it was made to be clear that welded defects in 40mm or thinner steel plates can be detected by all the tested systems, but that those in 100mm plates cannot be detected by some systems.4) The existence of anisotoropy in thickness direction of steel plates was shown and it was made to be clear by experiments and wave propagation simulation by finite element method that it can affect the determination of the location of defects in ultrasonic testing.5) The existence of anisotoropy in thickness direction of steel plates was shown and it was made to be clear by experiments and wave propagation simulation by finite element method that it can affect the determination of the location of defects in ultrasonic testing.6) For the purpose of more accurate quantitative evaluation in ultrasonic testing, tandem array transducer was proposed and the applicability was shown. And it was shown that by utilizing the transducer, the difference between fatigue cracks and weld defects can be recognized by evaluating the characteristic of fatigue crack closure.7) As for fracture toughness, which is one of the most important factor for the quality of welded joints, it was shown by Charpy Impact Testing for base metal that in case that steel plates experience the plastic strain history, it can be deteriorated, but the extent of the deterioration doesn't depend on the direction of plastic strain or notch.