摘 要 核电一回路蒸汽发生器传热管是一种典型的薄壁管结构。薄壁管在冷弯曲成型过程中容易产生截面椭圆度变形、外壁减薄，内壁褶皱等缺陷，而薄壁管弯曲残余应力更是影响核电一回路管路材料应力腐蚀开裂的重要因素之一。研究表明，充压冷弯可以有效解决薄壁管弯曲过程中的许多工艺问题。 本文利用理论分析和数值模拟相结合的办法，建立了一种针对薄壁管冷弯成型的充压弯曲模型，研究了内压对薄壁管弯曲成型过程以及冷弯残余应力对裂纹尖端力学场的影响规律，完成的主要研究工作有： （1）利用ABAQUS软件建立了管内充压弯曲成型的有限元分析模型，通过给管内施加不同内压，计算得出了内压对薄壁管成型后的椭圆度以及壁厚变化的影响规律； （2）对蒸汽发生器传热管充压冷弯过程中弯头区域应力应变变化规律进行了计算和分析，得出了弯曲角度对弯管力学性能的影响以及弯曲过程中中性层的变化规律； （3）计算并分析得出了蒸汽发生器传热管弯曲成型，以及充压冷弯工艺成型下的弯管残余应力场分布规律和特征； （4）建立了含有表面半椭圆型裂纹的有限元子模型，分析得出了不同裂纹深度及不同弯曲角度下弯管残余应力对核电蒸发器传热管裂纹尖端力学场的影响规律。 本文研究成果为加压薄壁管弯曲工艺以及弯管残余应力对蒸发器传热管裂纹扩展状况分析提供了一定的参考依据。

ABSTRACT The pipe in nuclear power steam generator is a typical thin-walled pipe structure. The thin-walled pipe would have an elliptical deformation in cross-section, wall thinning, and inner surface defects in cold bending process. And the cold bending residual stress in the thin-walled pipe is an important factor influencing the stress corrosion cracking of the nuclear primary piping materials. Studies have shown that inner-pressurized could solve many technical problems in the cold bending process of the thin-walled pipe. An inner-pressurized cold bending model of thin-walled pipe is established, and the inner-pressurized bending process of the thin-walled pipe and the effect of the cold bending residual stress on the mechanical field at the crack tip are researched combined by the theoretical analysis and the numerical simulation in this thesis. The main researches are performed in this thesis are as follows: (1) A bending model of the inner-pressurized pipe is constructed by using ABAQUS, and the effect of oval degrees and wall thickness changes of the thin-walled pipe are obtained through imposing different pressure to the pipe; (2) The characteristic of stress-strain variation of the steam generator pipe bending by the inner-pressurized is analyzed, and the effect of bending angle on the bending mechanical properties and the changes in the bending process of neutral layer are researched; (3) The characteristics of the inner-pressurized bending process of the thin-walled pipe are analyzed, and the cold bending residual stress feature and distribution low of the steam generator pipe are researched; (4) The effect of residual stress at the crack tip is analyzed under different crack depth and bending angle based on the cold bending process of thin-walled pipe with a surface half-ellipse crack.