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: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=741309
• 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，如核压力容器和管道、油气管道、航空航天和海洋工业等，具有重要的现实意义。在使用寿命期间，焊缝中可能会出现缺陷，表现为表面裂纹、角裂纹和埋入裂纹。因此，为了确保这些结构的安全运行并促进其使用寿命的延长，拥有先进的工程工具来量化此类焊件缺陷的行为并提供可靠的疲劳和断裂失效安全裕度是至关重要的。在当前的工程实践中，基于断裂力学的方法已被广泛应用于缺陷焊接结构的安全评估。在断裂力学框架内，处理材料不均匀、失配和裂纹前沿约束以及考虑焊接残余应力影响的特殊技术现已得到很好的发展。然而，到目前为止，大多数开发都是针对模式I(打开模式)加载下的缺陷。工程焊接结构的使用条件复杂，通常涉及拉伸、弯曲、扭转和剪切载荷。结果表明，三维裂纹前缘的局部加载条件由三种模式组成，即模式I(张开)、模式II(面内剪切)和模式III(面外剪切)。为了正确地对这些情况进行安全评估，必须考虑混合模式的影响。目前，还没有专门的工具来正确地评估混合模式加载下的焊接件的三维缺陷。这项研究的目的是通过开发和验证先进的工程工具来填补这一知识空白，以便在复杂的混合模式使用载荷条件下可靠地评估具有各种三维缺陷的焊接结构的结构完整性。拟议的工作包括以下四个方面的进展：1)。综合考虑材料不均匀、强度失配和残余应力等不同特征的复合模条件下焊接件裂纹前沿场的表征；采用细观力学模型研究了复合型载荷下焊件裂纹的失效过程，建立了相应的断裂失效判据；对具有不同焊接特征的复合型断裂和疲劳试件进行实验测试，以校准和验证失效准则；以及4)。应用新开发的断裂失效准则对焊接结构件三维缺陷的失效评估和疲劳裂纹扩展预测。研究结果将有助于全面了解复合型载荷对焊件延性断裂和疲劳扩展行为的影响，对高性能焊接工程结构的设计和安全运行具有重要的工程意义。