【作者】 谈建平；

【导师】 涂善东； 王国珍；

【作者基本信息】 华东理工大学 ， 动力工程及工程热物理， 2014， 博士

【摘要】 裂尖拘束状态影响蠕变裂纹扩展速率。采用深裂纹高拘束的标准试验室紧凑拉伸(CT)试样测得的蠕变裂纹扩展数据用于评价实际含裂纹结构的蠕变寿命,可能得到过于保守或非保守的评价结果。为了提高含裂纹高温构件蠕变寿命评价和预测的准确性,需要建立纳入裂尖拘束效应的评价方法,目前国内外对此的研究还十分有限。本文通过试验、数值计算和理论分析相结合,宏观与微观相结合,力学与材料相结合的方法系统研究了拘束对Cr-Mo-V钢蠕变裂纹扩展速率的影响及机理,试验室试样和实际管道蠕变裂尖拘束的表征及关联,拘束相关的Cr-Mo-V钢蠕变裂纹扩展速率方程的构建及其应用等,致力建立纳入裂尖拘束效应的蠕变寿命评价方法。论文主要工作和结论如下：1)试验测试了不同厚度CT试样在宽范围C*区间的蠕变裂纹扩展速率。发现试样厚度引起的面外拘束对蠕变裂纹扩展速率的影响与载荷水平(C*)相关,在与实际构件工作载荷相关的低C*区,蠕变裂纹扩展速率存在显著的拘束效应。通过微细观观察探明了不同C*区拘束对蠕变裂纹扩展速率影响的机理。为建立纳入拘束效应的蠕变寿命预测模型和方法提供了物理基础。21对新发展的蠕变拘束参数R进行了修正,提出了载荷无关的蠕变拘束参数R*,基于各试样及管道在不同载荷水平下拘束参数R的大量计算结果,验证了R*的载荷无关性。深入分析了参数R*的影响因素,包括试样／结构几何、裂纹尺寸、裂尖距离和蠕变时间等。提出了R*工程应用的简化定义和计算方法。为建立纳入拘束效应的含缺陷高温结构寿命评价方法提供了双参数(C*-R*蠕变断裂力学基础。3)通过三维(3-D)有限元数值计算,分析了五种不同几何和加载方式试样和高温轴向表面裂纹管道的裂尖拘束,给出了3-D裂纹构件拘束的表征方法。计算分析了试样和管道几何、裂纹尺寸、载荷水平等对裂尖拘束的影响规律,验证了3-D裂纹管道及试样拘束R*的载荷无关性。发现单边缺口拉伸试样的蠕变裂尖拘束与裂纹管道最接近,采用3-D裂纹前沿平均拘束参数R*avg分析了二者的关联性。4)基于拘束参数R*及面外拘束蠕变裂纹扩展试验,建立了Cr-Mo-V钢拘束相关的蠕变裂纹扩展速率方程,用不同加载方式试样(不同拘束)的蠕变裂纹扩展试验验证了方程的有效性和可移植性。另外,测试获得了Cr-Mo-V钢不同拘束试样的蠕变裂纹起裂时间及蠕变断裂韧性,分析了拘束对其影响的规律。基于拘束参数R*建立了Cr-Mo-V钢拘束相关的蠕变裂纹起裂时间及蠕变断裂韧性方程。更多还原

【Abstract】 Crack-tip constraint can affect creep crack growth (CCG) rate. The use of CCG data measured from standard compact tension (CT) specimens with deep crack and high constraint will produce over-conservative or non-conservative assessment results for the creep life of practical cracked structures with different constraints. In order to improve the accuracy of creep life assessment of high temperature components, there is a strong incentive to establish life assessment method incorporating crack-tip constraint effects. However, the studies in this area have been very limited. In this dissertation, with a comprehensive approach of combining testing, finite element numerical simulation and theoretical interpretation, macro and micro-analysis, and solid mechanics and materials science, the constraint effect and mechanism on CCG rate of the Cr-Mo-V steel, the characterization and correlation of creep crack-tip constraint between axially cracked pipelines and test specimens, the establishment and application of constraint-dependent CCG rate equations of the Cr-Mo-V steel were systematically studied in order to provide a theoretical basis for creep life assessment incorporating crack-tip constraint effects. The main work and conclusions are summarized as follows:1) The CCG rate in a wide range of C*was measured by using CT specimens with different thicknesses. It was found that the effect of out-of-plane constraint induced by specimen thickness on the CCG rate was related to C*levels. In the low C*region related to the service loads of practical components, constraint significantly influences CCG rate. The mechanism of the constraint effect on CCG rates was explored through micro and meco-scale observation. It provided a physical basis for creep life prediction models and methods incorporating constraint effects.2) A modification of the new developed constraint parameter R was proposed, and a load-independent creep constraint parameter R*was defined. The load independence was validated by using extensive calculation results of constraint parameter R of various specimens and pipes under different loading levels. The influence factors of the parameter R*were deeply analyzed, including specimen/structure geometry, crack size, distance from the crack tip and creep time. A simplified definition and calculation method was proposed for the engineering application of R*. It provided a creep fracture mechanics basis using two parameter (C*-R*) for creep life assessment of structures containing crack incorporating constraint effects.3) The crack-tip constraints of five kinds of specimens with various geometries and loading modes and pipes with axial surface cracks were investigated by using three-dimensional (3-D) finite element method. The characterization method of the R*was determined for3-D cracked components. The effects of geometries, crack sizes and loading levels on crack-tip constraint of specimens and pipes were analyzed. The load independence of the constraint R*was validated for3-D cracked pipes and test specimens. It is found that the single-edge notched tension specimen provides a closely matched creep crack-tip constraint with the axially cracked pipes. The correlation between them was analyzed using the average constraint R*avg over the3-D crack front.4) Based on the parameter R*and CCG rates of out-of-plane constraint experiments, the constraint-dependent CCG rate equation was obtained for the Cr-Mo-V steel. The availability and portability of the equation were validated by the CCG rates tested from specimens with various loading modes. In addition, the creep crack initiation time and creep fracture toughness were measured for the specimens with different constraints of the Cr-Mo-V steel. Based on the constraint parameter R*, the constraint-dependent creep crack initiation time and creep fracture toughness equations were established for the Cr-Mo-V steel.更多还原