【摘要】：在電力、石化、核能及航空航天等工業(yè)領域中,廣泛采用高溫工藝。在高溫下長期服役的結構部件中,不可避免地產(chǎn)生蠕變損傷。加之在制造和服役過程中常常產(chǎn)生夾渣、凹坑、減薄等體積型缺陷,削弱了結構的極限承載力。傳統(tǒng)的安全評定規(guī)范不考慮結構中蠕變損傷的累積對結構極限承載力的影響,可能導致不合理的評定結果。本文針對這一問題,考慮蠕變損傷對極限載荷的影響,基于“合乎使用”的原則,通過理論計算與數(shù)值模擬相結合的方法,構建了耦合材料蠕變損傷的彈塑性本構模型,系統(tǒng)地研究了含體積型缺陷高溫結構的極限載荷,提出了考慮結構中蠕變損傷累積的安全評定方法。論文的主要研究工作及結論如下： (1)基于冪律強化材料本構模型,推導了無缺陷厚壁及薄壁圓筒的內壓極限載荷的解析解。用有限元計算了結構尺寸及材料參數(shù)對無缺陷圓筒的內壓極限載荷的影響規(guī)律,并驗證了解析解。 (2)通過實驗觀察,分析了2.25Cr1Mo鋼蠕變損傷的物理機制和影響因素,并將這些因素耦合到彈塑性本構方程中；構建了基于Ramberg-Osgood方程的耦合蠕變損傷的彈塑性本構模型,可以預測含蠕變損傷的高溫結構的彈塑性響應,為計算含蠕變損傷高溫結構的極限載荷奠定基礎。 (3)基于該彈塑性本構模型,運用有限元計算分析了各種形狀尺寸的凹坑及局部減薄缺陷的圓筒形容器在內壓或彎矩的作用下,塑性區(qū)域的擴展過程和失效模式。著重分析了缺陷尺寸和蠕變損傷累積對結構塑性極限載荷的影響規(guī)律。 (4)考慮了結構中的蠕變損傷累積,建立了基于歸一化的蠕變時間和歸一化的缺陷尺寸為參量的安全評定方法�？梢院啽愕剡M行含體積型缺陷高溫結構的安全評定。
[Abstract]:High-temperature technology is widely used in the fields of electric power, petrochemical, nuclear energy, aerospace and so on. Creep damage is inevitable in structural components in long service at high temperature. In addition, volume defects such as slag, pits and thinning are often produced in the process of manufacture and service, which weaken the ultimate bearing capacity of the structure. Traditional safety assessment codes do not consider the effect of creep damage accumulation on the ultimate bearing capacity of structures, which may lead to unreasonable assessment results. In this paper, considering the effect of creep damage on the limit load, an elastic-plastic constitutive model of coupled material creep damage is established by combining theoretical calculation with numerical simulation based on the principle of "fit for use". The limit loads of high-temperature structures with volumetric defects are systematically studied, and a safety assessment method considering creep damage accumulation in structures is proposed. The main research work and conclusions are as follows: (1) based on the constitutive model of power-law strengthened materials, the analytical solution of the internal pressure limit load of the thin-walled and non-defective thick wall is derived. The influence of the structure size and material parameters on the internal pressure limit load of the non-defective cylinder is calculated by finite element method, and the analytical solution is verified. (2) through experimental observation, the physical mechanism and influencing factors of creep damage of 2.25Cr1Mo steel are analyzed, and these factors are coupled to the elastoplastic constitutive equation; The elastoplastic constitutive model of coupled creep damage based on Ramberg-Osgood equation is constructed, which can predict the elastoplastic response of high temperature structures with creep damage, which lays a foundation for calculating the ultimate loads of high temperature structures with creep damage. (3) based on the elastoplastic constitutive model, the expansion process and failure mode of plastic region under the action of internal pressure or bending moment of various shapes and sizes of pits and cylindrical vessels with local thinning defects are calculated and analyzed by using the elastoplastic constitutive model. The influence of defect size and creep damage accumulation on the plastic limit load of the structure is analyzed. (4) considering creep damage accumulation in structure, a safety assessment method based on normalized creep time and normalized defect size is established. It is easy to evaluate the safety of high temperature structures with volume defects.
【學位授予單位】：華東理工大學
【學位級別】：博士
【學位授予年份】：2013
【分類號】：TB302.3;TH49

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