【作者】 柳晖；

【导师】 轩福贞；

【作者基本信息】 华东理工大学 ， 化工过程机械， 2012， 博士

【摘要】 蠕变是高温结构破坏的主要形式之一,是高温强度设计中的一个核心问题,相关研究人们已开展了半个多世纪。但由于蠕变断裂失效的时间相关性、蠕变断裂失效微观和宏观机理的多样性、以及蠕变拘束效应的复杂性,对如何利用短时而有限的蠕变试验数据,描述与时间、温度和应力等有关的蠕变问题,仍是一个富有挑战性的工程难题,迄今还没有得到很好地解决。本文以汽轮机转子用材料25Cr2NiMolV铁素体耐热钢作为研究对象,着重探讨了如何利用量纲分析的方法,去研究蠕变裂纹扩展的规律、蠕变试样的相似准则,以及利用能量方法研究蠕变断裂寿命的预测问题。本文研究的主要内容和结论如下：(1)运用量纲分析方法及相似性的原理,研究得到蠕变裂纹扩展速率da/dt与c*、应力强度K、净积面应力σnet、裂纹张开位移速率dδ/dt和参量Q*之间的关系模型。并且证明了模型中的有关参数不是材料的常数,而是与尺寸特征有关的参数。(2)利用量纲分析方法推导出蠕变试样的相似准则,建立了单轴拉伸蠕变试样的尺度关系,在无量纲载荷和无量纲应力与无量纲直径之间得到了一系列关系式和关联曲线。这一结果对于蠕变力学和断裂力学的深入发展都是有帮助的。(3)从反映物系运动的能量守恒定律出发,采用蠕变损伤力学的方法,推导出在等温条件下蠕变预测的新模型,即单位体积外载荷所作的机械功Wc与时间t幂函数之积为常数。该模型与2.25Cr-1Mo、1Cr-.0.5Mo、18Cr-12Ni-Mo和1Cr-1Mo-0.25V钢在不同温度下的试验数据具有较好的吻合性。为由短期试验数据外推长期蠕变寿命提供一种基于能量守恒定律的蠕变寿命预测新模型。(4)推导出基于耗散功率的蠕变寿命新的参数预测方法(LHP),与传统的Larson-Miller方法(LMP)相比,通过对2.25Cr1.0Mo钢和TiAl合金钢试验数据的拟合、分析,表明该方法不但能够对试验数据内的蠕变数据进行很好地拟合,同时可以准确把握持久曲线、断裂寿命曲线的变化趋势,从而提高了长期蠕变持久强度和断裂寿命的预测精度。更多还原

【Abstract】 Creep fracture is one of main reasons for high temperature structures damage. As a key and basic problem in the field of strength design for high temperature structures, the creep crack behavior has been investigated for more than half a century. However, it remains very challenging to reasonably describe the creep crack behavior in terms of time, temperature and stress given limited testing time and data. The difficulties mainly root in the varieties of micro-mechanism and time-dependent characteristic for the creep crack failure as well as the complexity for the creep crack constraint.High chromium ferritic steel 25Cr2NiMol V is the material developed for the steam turbine rotor of ultra super-critical power stations. In this thesis, the steel is selected to investigate its creep properties, crack behavior and failure mechanism by the experiment. By using dimensional analysis technique and energy methods, creep crack regulations, similarity of uniaxial tension creep specimens and prediction method of creep crack life are put forth effort to study. All research work and results for the thesis are generalized as follows:(1) Dimensional analysis and self-similar principles have been applied in the study of crack behavior of materials under creep loading conditions. The correlations between creep crack growth grate da/dt and C*, stress tension factor K, net section stressσnet, crack open displacement rate dd/dt and Q* have been established. Parameters in the above correlations were proved not to correspond to material characteristics based on the concept of incomplete similarity. On the contrary, they are dependent on dimensional characteristics.(2) The similarity rules and scaling relationships of the loads, the stress and the life of uniaxial tension specimens are derived by using dimensional analysis. The relationship curves have been gained between the dimensionless forces, stresses and specimens diameters. Thus, the results of the paper contributes researches of creep mechanics and fracture mechanics. (3) A new model for life estimation of creep derived from the law of energy conservation principle was proposed with damage mechanics. By mathematical technique, the expressions of the model is transformed into a simple function, which can describe between Wc the mechanic work per unit by applied loads and time t power function that it accumulates for the constant at uniform temperature. To check the validity of the new model proposed in this paper, the published data of 2.25Cr-1Mo, 1Cr-0.5Mo,18Cr-12Ni-Mo and 1Cr-1Mo-0.25V steels have been studied and analyzed. A well agreement is noted between the model and the results. A new model for life estimation of creep was developed for long term creep life from short experimental data based on energy process.(4) A new model for creep life prediction is proposed based on power processes. The dissipated power of applied loads is used to describe creep processes. Based on comparisons with the published data for 2.25Cr1.0Mo steel and TiAl-base intermetallics, the model of the relationship between stress and time to rupture is a better representation of the creep process compared with the Larson-Miller method, represents the published data well and produces extreme extrapolation results that behave as would be expected. the model developed in the present study more accurately predicts creep life.更多还原