两级交变载荷下船体节点疲劳损伤规律研究

The fatigue damage mechanism of joints of ship hull structure under two-stage repeated loading is complex and uncertain. The main purpose of this project is to establish a fatigue damage model for ship joints under two-stage repeated loading. First of all, based on the characteristics of structure and suffered loads of River-Sea-Going ship, taken the different notched specimens as the research objects, a series of fatigue experiments will be conducted under two-stage repeated loading, including different loading amplitudes and loading processes, to obtain the reasonable description parameters of fatigue damage, as well as establish different fatigue damage models. Secondly, according to the experimental results and numerical calculation, the comparative analyses will be made on the fatigue damage evolution law between the notched specimens and ship joints under two-stage repeated loading. Focusing on the fatigue damage relationship between the notched specimens and typical ship joints to establish the fatigue damage criterion for ship joints. Finally, model tests of typical ship joints will be carried out to further reveal the mechanism of fatigue damage development and its influence factors of the ship joints under two-stage repeated loading. Through the fatigue tests of ship joints to verify the reliability and applicability of the established fatigue damage criteria. The research conclusions can provide significant theoretical guidance and scientific basis for establishing the fatigue assessment method for River-Sea-Going ship.

两级交变载荷下船体节点疲劳损伤机理具有复杂、不确定的特点，本项目主要目的在于构建两级交变载荷下船体节点疲劳损伤模型。首先根据江海直达船船体节点结构特征和载荷特点，以不同的切口件为研究对象，开展不同载荷幅值和加载历程的两级交变载荷块作用下切口件疲劳试验研究，以确定合理的两级交变载荷下疲劳损伤的表征参量，建立表达形式不同的疲劳损伤模型。其次，基于试验结果和数值计算进行两级交变载荷下切口件和船体典型节点疲劳损伤演化规律的对比分析，研究切口件和船体典型节点疲劳损伤之间的关系建立两级交变载荷下船体节点疲劳损伤准则。最后，开展典型船体节点的模型试验，进一步揭示两级交变载荷下船体节点疲劳损伤演化机理及影响因素，通过船体节点两级交变载荷疲劳试验验证建立的疲劳损伤准则的正确性和适用范围。研究成果能为江海直达船典型节点疲劳评估方法的建立提供重要的理论基础和科学依据。

两级交变载荷作用下的船体节点疲劳损伤机理复杂，并且受不同载荷之间的交互作用影响。本项目针对江海直达船交替航行于江段和海段的航线特点，开展了不同载荷幅值比和载荷历程比的两级交变载荷作用下典型切口件疲劳性能的理论分析和试验研究，结果表明两级交变载荷下疲劳累积损伤除了小、大载荷损伤外，载荷间交互作用影响不能忽略。随着小大载荷历程比的增加，载荷交互作用首先表现为损伤效应，当超过某一历程比后，又表现为强化效应，且存在最大的损伤效应历程比。通过断口分析发现低于疲劳极限的小载荷的引入有促进裂纹形核的作用，同时裂纹尖端材料的X射线衍射结果表明，随着历程比的增加，材料晶面半宽值先增加后减小，即材料先产生了加工硬化后产生了加工软化，小-大载荷的交互作用使材料本身性能（强度和韧性）发生了改变，进而影响切口试件的疲劳性能。基于研究分析结果，提出了一种新的非线性累积损伤理论方法，在原有规范校核方法的基础上，引入载荷交互作用因子 用以考虑小-大载荷间交互作用。. 针对实际船体节点和切口试件的差异性，进一步开展了两级交变载荷下船体典型节点疲劳损伤机理研究，构建了切口件和船体典型节点疲劳损伤之间的关系，结果表明船体纵骨穿舱节点与切口试件载荷交互作用强化效应区变化规律相一致。通过开展两级交变载荷下纵骨穿舱节点疲劳裂纹扩展特性研究，结合试验与数值仿真结果，确定了特定大小载荷历程比、载荷幅值比下考虑小载荷影响的应力强度因子无量纲修正系数。. 在上述研究基础上，针对江海直达船特定航线载荷特征以及船型结构特点，建立了江海两级交变载荷下船体节点疲劳损伤准则，提出了宽扁肥大型江海直达船疲劳损伤精细化评估方法，可为江海直达船向大型化和轻量化方向发展提供基础支撑和技术支持。