【作者】 王宁；

【导师】 涂善东；

【作者基本信息】 华东理工大学 ， 机械设计及理论， 2013， 博士

【摘要】 在电力、石化、核能及航空航天等工业领域中,广泛采用高温工艺。在高温下长期服役的结构部件中,不可避免地产生蠕变损伤。加之在制造和服役过程中常常产生夹渣、凹坑、减薄等体积型缺陷,削弱了结构的极限承载力。传统的安全评定规范不考虑结构中蠕变损伤的累积对结构极限承载力的影响,可能导致不合理的评定结果。本文针对这一问题,考虑蠕变损伤对极限载荷的影响,基于“合乎使用”的原则,通过理论计算与数值模拟相结合的方法,构建了耦合材料蠕变损伤的弹塑性本构模型,系统地研究了含体积型缺陷高温结构的极限载荷,提出了考虑结构中蠕变损伤累积的安全评定方法。论文的主要研究工作及结论如下：(1)基于幂律强化材料本构模型,推导了无缺陷厚壁及薄壁圆筒的内压极限载荷的解析解。用有限元计算了结构尺寸及材料参数对无缺陷圆筒的内压极限载荷的影响规律,并验证了解析解。(2)通过实验观察,分析了2.25Cr1Mo钢蠕变损伤的物理机制和影响因素,并将这些因素耦合到弹塑性本构方程中；构建了基于Ramberg-Osgood方程的耦合蠕变损伤的弹塑性本构模型,可以预测含蠕变损伤的高温结构的弹塑性响应,为计算含蠕变损伤高温结构的极限载荷奠定基础。(3)基于该弹塑性本构模型,运用有限元计算分析了各种形状尺寸的凹坑及局部减薄缺陷的圆筒形容器在内压或弯矩的作用下,塑性区域的扩展过程和失效模式。着重分析了缺陷尺寸和蠕变损伤累积对结构塑性极限载荷的影响规律。(4)考虑了结构中的蠕变损伤累积,建立了基于归一化的蠕变时间和归一化的缺陷尺寸为参量的安全评定方法。可以简便地进行含体积型缺陷高温结构的安全评定。更多还原

【Abstract】 High-temperature technologies are widely used in many industries, ranging from electricity generation, petrochemical, nuclear power plants to aeroengines. The high temperature components are usually designed for long term operation. Creep damages are inevitable in the service. Flaws such as inclusions, pits, thinning and other volumetric defects can occur during manufacturing process and in-service period. These defects may cause severe reduction of the limit load of structures. The existing assessment procedures do not take into account the effect of creep damage, which may lead to inaccurate assessment results. Therefore the dissertation is aimed to investigate the limit load of pressurized components with volumetric defect subjected to high temperature creep damage. An elasto-plastic constitutive model with coupled creep damage effects is proposed. The limit load of high temperature structures with volumetric defects is systematically studied using finite element method. Safety assessment approach for structures considering creep damage effect is subsequently proposed based on the principle of "fitness for service". The main research work and conclusions are summarized as follows:(1) Base on the strain strengthening constitutive model, derived are the analytic solutions for limit load of thick and thin cylinders subjected to internal pressures. By using finite element method, the analytic solutions are verified and effects of dimensions and material parameters on the limit loads are also discussed. Through experimental observation, the mechanism that creep damage degrades the limit loads of2.25CrlMo steel structure has been studied. Creep damage is subsequently coupled into the Ramberg-Osgood equation. The modified model is able to reasonablely predict the elasto-plastic response of creep-damaged materials. The obtained results could be applied to the calculation of the limit load of structures with high-temperature creep damage through finite element analysis.(2) Based on the modified model, the failure behavior and limit load of high temperature pressurized components with volumetric defects are studied, when subjected to the internal pressure or bending moment using the elastic plastic finite element method. Emphasized are the effects of defect sizes, creep damage on the limit load of structures.(3) Considering the accumulation of creep damage effect, the safety assessment procedure is amended with the introduction of normalized creep time and defect size. The proposed safety assessment procedure is able to assess the load carrying capacity of the high-temperature structures with volumetric defects.更多还原