Three-Dimensional Mixed-Mode Fracture Mechanics Methodologies for Structural Integrity Assessments of Welded Structures

用于焊接结构结构完整性评估的三维混合模式断裂力学方法

• 批准号: RGPIN-2020-06550
• 负责人: Wang, Xin
• 金额: $ 1.97万
• 依托单位: Carleton University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=759531
• 关键词: Three; Dimensional; Mixed; Mode; Fracture

Safe operation of high-performance welded engineering structures, such as those in nuclear pressure vessel and piping, gas/oil pipelines, aerospace and offshore industries, is of significant practical importance. During the service life span, flaws can occur in the welds and are in the form of surface, corner and embedded cracks. Therefore, to ensure safety operation and to facilitate the life extensions of these structures, it is critically important to have advanced engineering tools to quantify the behaviors of such weldment flaws and to provide reliable estimates of the safety margins against fatigue and fracture failures. In current engineering practice, fracture mechanics based methodologies have been widely used for the safety assessment of defective welded structures. Within the fracture mechanics framework, special techniques for treating the material inhomogeneity, mismatch and crack front constraint, and for accounting for the effects of welding residual stresses, have now been well developed. However, most developments thus far are for flaws under mode I (opening mode) loading. The service conditions of engineering welded structures are complex, generally involving tension, bending, torsion and shear loading. As a result, the local loading conditions around 3D crack fronts consist of all three modes, i.e., mode I (opening), mode II (in-plane shear) and mode III (out-of-plane shear). To properly carry out the safety assessment for these cases, mixed-mode effects must be considered. Presently, specific tools are not available to properly carry out assessment of 3D flaws in weldments under mixed-mode loading. The objective of the proposed research is to fill this knowledge gap by developing and validating advanced engineering tools for the reliable assessment of structural integrity of welded structures with various 3D defects under complex mixed-mode service loading conditions. The proposed work includes advances in the following four areas: 1). characterization of crack front fields in weldments under mixed-mode conditions incorporating the effects of different features including material inhomogeneity, strength mismatch and residual stress; 2). study of failure processes of cracks in weldment using micromechanics-based models under mixed mode loadings to establish corresponding fracture failure criteria; 3). experimental testing of mixed-mode fracture and fatigue specimens with different weldment features to calibrate and validate the failure criteria; and 4). failure assessment and fatigue crack growth prediction of 3D defects in welded structural components by applying the newly developed fracture failure criteria. The outcome of the proposed research will provide comprehensive understanding of mixed-mode loading on ductile fracture and fatigue propagation behavior of weldments, and be of significant engineering importance to the design, safe operation of high-performance welded engineering structures.

高性能焊接工程结构的安全运行，例如核压容器和管道，天然气/石油管道，航空航天和近海行业的安全运行，具有重要的实际意义。在使用寿命范围内，焊缝可能会出现缺陷，并以表面，角和嵌入式裂缝的形式出现。因此，为了确保安全操作并促进这些结构的寿命延长，拥有先进的工程工具以量化此类焊接缺陷的行为并提供可靠的估计疲劳和断裂故障的安全余量，这一点至关重要。在当前的工程实践中，基于断裂力学的方法已被广泛用于有缺陷的焊接结构的安全评估。在断裂力学框架内，现在已经开发出了很好的发展，用于治疗材料不均匀性，不匹配和裂纹前部约束的特殊技术，并考虑焊接残留应力的影响。但是，到目前为止，大多数发展是在模式I（打开模式）加载下的缺陷。工程焊接结构的服务条件很复杂，通常涉及张力，弯曲，扭转和剪切负荷。结果，局部加载条件围绕3D裂纹正面，包括所有三种模式，即模式I（开放），模式II（面内剪切）和模式III（平面外剪切）。为了适当地对这些情况进行安全评估，必须考虑混合模式效应。目前，没有特定的工具可以正确地对混合模式加载下的焊接中的3D缺陷进行评估。拟议研究的目的是通过开发和验证高级工程工具来填补这一知识差距，以可靠地评估具有复杂混合模式服务加载条件下各种3D缺陷的焊接结构的结构完整性。拟议的工作包括以下四个领域的进步：1）。在混合模式条件下焊接中裂纹前场的表征，结合了不同特征的影响，包括材料不均匀性，强度不匹配和残留应力； 2）。在混合模式载荷下使用基于微力学的模型来建立相应的断裂故障标准，研究焊接中裂纹的故障过程； 3）。具有不同焊接特征的混合模式断裂和疲劳样本的实验测试，以校准和验证失败标准；和4）。通过应用新开发的断裂故障标准，焊接结构组件中3D缺陷的失败评估和疲劳裂纹生长预测。拟议研究的结果将为焊接的延性裂缝和疲劳繁殖行为提供全面的理解，并且对设计，高性能焊接工程结构的安全运行至关重要。