高温结构蠕变裂尖拘束效应

如何对蠕变裂纹扩展寿命进行准确预测和评价是高温结构完整性评定、寿命设计和运行维护中需要解决的核心问题.基于宏观单参数C?的蠕变断裂行为的评价方法,未有效纳入裂尖拘束效应的影响,因而其评价结果过于保守或非保守.目前国内外还未建立起有效纳入裂尖拘束效应的高温结构蠕变寿命评价的理论体系和技术方法,还没有纳入蠕变拘束效应的高温结构完整性评定规范.本文综述了作者近年来在高温蠕变断裂拘束效应方面的研究工作.主要包括:裂尖拘束对材料蠕变裂纹扩展行为的影响及机理;蠕变裂尖场和拘束参数R的定义和影响因素;载荷无关的蠕变拘束参数R? 的提出及其应用基础;承压管道表面裂纹的拘束参数R? 解及纳入裂尖拘束的蠕变寿命评价方法;试样与管道轴向裂纹蠕变裂尖拘束的关联;基于裂尖等效蠕变应变的面内与面外蠕变裂尖拘束的统一表征参数Ac的研究;材料拘束相关的蠕变裂纹扩展速率的建立;宽范围C? 区蠕变裂纹扩展速率及其拘束效应的数值预测;材料拘束对焊接接头蠕变裂纹扩展行为的影响及机理等.这些研究为建立纳入裂尖拘束效应的高温部件的蠕变裂纹扩展寿命评价方法奠定了理论和技术基础.论文对后续拟开展的工作也进行了展望.

Creep crack-tip constraint effect in high temperature structures

Accurate prediction and assessment of creep crack growth life are key problems for structural integrity assessment, life design, and service maintenance of high temperature components. The life assessment method based on a single-parameter C? in creep fracture mechanics cannot effectively incorporate crack-tip constraint effect, thus the assessment re-sult is either over-conservative or non-conservative. At present, theoretical framework and technical methodology for creep life assessment of high temperature structures have not been established, and there is yet no high temperature structure integrity assessment codes incorporating the creep constraint effect. This paper reviews our recent research work on the constraint effect in high temperature creep fracture. It includes: effect and mechanism of the crack-tip constraint on creep crack growth behavior of materials;the creep crack-tip field, and definition and influencing factors of a constraint parameter R; proposition of a load-independent creep constraint parameter R? and its applications; the creep constraint parameter R? solutions and creep life assessments incorporating the creep constraint effect for surface cracks in pressurized pipes;correlation of the creep crack-tip constraint between test specimens and axially cracked pipelines;study on a unified characterization parameter Ac of in-plane and out-of-plane creep constraints based on crack-tip equivalent creep strain;establishment of constraint-dependent creep crack growth rates of materials;numerical pre-diction of creep crack growth rate and its constraint effect in a wide range of C?; effect and mechanism of the material constraint on creep crack growth behavior in welded joints. The research work may lay foundation of theory and technology for establishing the life assessment methodology of creep crack growth incorporating the crack-tip constraint effect for high temperature structures. We also present prospects for future explorations.