裂尖动态张口位移及裂纹扩展寿命的工程化评估方法研究

Crack tip opening displacement (CTOD) is one of the most important parameters to evaluate the fatigue crack growth behavior, ultimate bearing capacity and security of the hull structure. However, it is quite difficult to obtain the dynamic crack tip opening displacement (DCTOD), and the crack growth life in the large scale yielding condition can not be predicted by the current fatigue crack growth models. The project aims to establish the mathematical model between DCTOD and maximum crack opening displacement (MCOD), and to propose a new crack growth model related to MCOD on the basis of DCTOD. Based on the CTOD-MCOD model under static tensile loads proposed in the previous work, the influence of loading rate is analyzed and the suitability of CTOD-MCOD model is studied under the monotonic loading. On the basis, the internal relation between DCTOD and MCOD during the unloading process is analyzed, and the effect of loading sequence is considered. The mathematical model between DCTOD and MCOD is proposed under variable amplitude cyclic loads, which is called “DCTOD-MCOD model” for short. Then, according to the crack closure theory the influence of retardation effect is analyzed, and the suitability of the DCTOD-MCOD model is then verified under random loads. Finally, the relationship between opening stress and CTOD is studied, and the crack growth model related to MCOD model is established. Meanwhile, the proposed crack growth model is verified by the experiment to realize the prediction of the crack growth life for the material with high toughness.

裂纹尖端张口位移（CTOD）是评价船体结构疲劳裂纹扩展行为以及极限承载能力和安全性的最主要参量之一。然而裂纹尖端动态张口位移（DCTOD）难以时时获得，已有的裂纹扩展模型无法预测大范围屈服下裂纹扩展寿命。本课题旨在建立含穿透型裂纹损伤船体板在随机载荷下DCTOD与裂纹最大张口位移（MCOD）之间的数学模型及以DCTOD为出发点建立与MCOD相关的裂纹扩展模型。基于申请者前期工作提出的静态载荷下CTOD-MCOD模型，分析加载速率的影响，研究单调加载时该模型的适应性。在此基础上，分析卸载过程中DCTOD与MCOD的内在联系，考虑加载顺序的影响，提出变幅循环载荷下DCTOD与MCOD之间的数学模型。再根据裂纹闭合理论，分析迟滞效应的影响，研究随机载荷下该模型的适用性。最后考虑张开应力与CTOD的内在联系，提出与MCOD相关的工程化裂纹扩展模型，通过实验验证，实现高韧性材料裂纹扩展寿命的预测。

船舶等大型结构在焊接过程中不可避免的产生裂纹损伤，掌握与结构剩余强度直接相关的裂纹尖端张口位移（CTOD）以及裂纹扩展规律是保证船体结构安全运行的前提条件。然而裂纹尖端动态张口位移（DCTOD）难以时时获得，已有的裂纹扩展模型无法预测大范围屈服下裂纹扩展寿命。基于此，本项目以含穿透型裂纹损伤船体板为研究对象，研究了反向卸载时CTOD的变化规律，提出了等幅拉伸循环载荷下与裂纹最大张口位移（MCOD）相关的DCTOD数学模型；研究了压应力的影响、分析了超载迟滞现象，建立了变幅循环载荷下DCTOD数学模型；考虑了裂纹闭合效应的影响，研究了张开应力与MCOD的对应关系，提出了以MCOD为基础的裂纹扩展新模型。.基于第一和第二个研究内容，建立了常幅拉伸循环载荷下基于MCOD变化量计算裂尖张口位移的简便方法，提出了变幅循环载荷下与MCOD相关的DCTOD估算方法。这些方法不仅弥补了无法直接估算CTOD的空白，而且消除了裂纹长度、模型边界效应、材料屈服极限、外加载荷大小、横向应力、应力比及材料硬化指数等因素的影响，具有较广的适用范围。这些方法的建立为适用于大范围屈服的裂纹扩展模型的提出奠定基础。对于这一方面的研究已在《Ocean Engineering》国际期刊上发表SCI论文1篇，将投稿SCI论文1篇。并参加国际会议1次，国内会议2次，发表2篇会议论文。指导硕士生4名，已完成硕士论文2篇。.基于第三个研究内容，建立了与MCOD相关的张开应力估算模型，提出了考虑闭合效应的以MCOD变化量为基础的裂纹扩展新模型。该模型具有较广的使用范围，适用于不同裂纹尺寸、不同载荷水平、各种应力比的任意金属材料的有限平板模型。同时研究了单次、多次连续超载的影响，提出了最佳迟滞效果的实施方案。对于这一方面的研究已在《Ocean Engineering》、《Fatigue & Fracture of Engineering Materials & Structures》国际期刊上共发表SCI论文2篇，国内EI期刊1篇。并参加国际会议1次、国内会议1次，发表2篇会议论文。指导硕士生3名，已完成硕士论文2篇。