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Study on the safety design of welded structure with respect to unstable fracture

焊接结构不稳定断裂安全设计研究

基本信息

批准号：
61302050
负责人：
MACHIDA Susumu
金额：
$ 8.19万
依托单位：
University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Co-operative Research (A)
财政年份：
1986
资助国家：
日本
起止时间：
1986 至 1988
项目状态：
已结题

项目摘要

The final purpose of this study is to establish the design philosophy of welded structures to prevent unstable fructure. The following basic experimental studies are carried out.1) Unstable dectile fracture based on CTOA R-curve in investigated. The experimental results show that CTOA-based instability criterion can predict instability point favorably.2) Statistical investigation on the significance of defects in offshore structures is carried out. Fracture probability for a specific structural member is calculated and the influence of the variations in the parameter ( e.g. datectability of defect, fatigue crack growth rate, scatter of the toughness etc.) is also examined. It is found that the most significant parameter is the retectability of defect.3) Fatigue Strength of the weldment of offshore structure is experimentally analyzed using T-joint type bending specimens. The effect of thickness can be described using elastic stress concentration factor at weld teo.4) Fatigue crack propagation tests under wide band random loading are carried out and the relationship between fatigue behaviors under randam loading and constant amplitude loading is discussed. The significance of crack closure for understanding crack growth under variable amplitude loading is emphasized and an estimating method for fatigue crack behavior under randam loading is proposed.5) The effect of strain rate on fracture toughness of sttuctural stainless steel is experimentally investigated. The material tested is 20 mm thick SUS304 steel and the tests are carried out at liguid Helium temperature (4K). It is found that the effect of strain rate is significant and the effect of martensitic transformation is also important.

本研究的最终目的是建立防止结构不稳定的焊接结构的设计理念。开展了以下基础性实验研究：1)研究了基于CTOA R曲线的不稳定断口。实验结果表明，基于CTOA的失稳判据能够较好地预测结构的失稳点。2)对海洋结构物缺陷的重要性进行了统计研究。计算了特定结构构件的断裂概率，以及参数变化(如缺陷的可测性、疲劳裂纹扩展速率、韧性离散性等)的影响。也进行了检验。3)采用T型节点弯曲试件对海洋结构焊接件的疲劳强度进行了试验分析。4)进行了宽带随机载荷下的疲劳裂纹扩展试验，讨论了随机载荷和恒幅载荷下疲劳行为的关系。强调了裂纹闭合对了解变幅载荷下裂纹扩展的重要意义，并提出了随机载荷下疲劳裂纹行为的估算方法。5)实验研究了应变速率对结构不锈钢断裂韧性的影响。试验材料为20 mm厚的SUS304钢，在液氦温度(4K)下进行试验。结果表明，应变速率的影响是显著的，马氏体相变的影响也很重要。