【作者】 董硕；

【导师】 喻健良；

【作者基本信息】 大连理工大学 ， 化工过程机械， 2010， 硕士

【摘要】 接管焊缝处容易出现裂纹,这对压力容器及管道安全运行带来巨大的隐患,定量研究裂纹应力强度因子和结构极限载荷对缺陷结构安全评定具有重要的意义。应力强度因子反映裂纹尖端附近区域应力场强度,是接管在相贯线焊缝处裂纹的安全评定中的关键物理量。极限载荷分析相对于常规分析更能反映出接管受力状态的本质,在缺陷接管的安全评定和强度设计中是重要的物理量。运用断裂力学理论,采用三维线弹性有限元分析方法,研究内压和弯矩下含肩部穿透裂纹接管的应力强度因子；运用弹塑性力学理论,采用三维弹塑性有限元方法,对此结构塑性极限载荷进行了计算和分析。提出了两个载荷下含缺陷结构的安全评定方法。主要研究内容及结论如下：(1)建立了轴向穿透裂纹管道有限元模型,并验证了模型求解应力强度因子和极限载荷的正确性。建立了含肩部穿透裂纹接管有限元模型,通过ANSYS提供的参数化编程语言(APDL)建立了参数化模型、加载和后处理宏程序。(2)通过第一型应力强度因子、内压下极限载荷p和弯矩下极限载荷m来衡量接管的安全水平。确定了接管无量纲化参数裂纹长度a,接管管径比do／di,容器管径比Do／Di和接管与容器径比di／Di。(3)仅受内压下,在不同的结构尺寸下,应力强度因子KIP与内压P都呈线性关系。裂纹长度越大,KIP越大,极限内压p越小。接管和容器的壁厚增加,KIP减少,p增大。当接管和容器的管径比都大于1.1时,继续增大厚度,KIP减少不明显。容器开孔越大,KIP越大,p越小。在容器和接管管径比大于1.1时给出KIP的拟合式,在管径比小于1.1时给出KIP、p与a、d0/di、D0/Di和di／Di的关系表,并给出内压下接管安全评定步骤。(4)仅受弯矩下,在不同的结构尺寸下,应力强度因子KIM与弯矩M都呈线性关系。裂纹长度越大,KIM越大,极限弯矩m越小。接管和容器的壁厚增加,KIM减少,m增大。当接管和容器的管径比都大于1.1时,继续增大厚度,KIM减少不明显。容器开孔越大,KIM越小,m越大。在容器和接管管径比大于1.1时给出KIM的拟合式,在管径比小于1.1时给出KIM、m与a.d0/dt.D0/Di和di／Di关系表,并给出弯矩下接管安全评定步骤。(5)在受内压和弯矩的联合作用下,裂纹应力强度因子为仅受内压下应力强度因子与仅受弯矩下应力强度因子线性加和,KIS=P.KIP+M-KIM。接管极限内压与极限弯矩的关系符合线性方程,mB.P+pA·M-mB·pA=0。提出在联合作用下含肩部穿透裂纹接管安全评定的所用参数断裂比Kr=KIS/Kp+ρ,载荷比并给出内压和弯矩下接管安全评定步骤。更多还原

【Abstract】 Cracks that tend to appear in weld joint between vessel and nozzle are bearing enormous risk to nozzle safety, thus quantitative investigations into stress intensity factor and limit load are of great significance to the safety rating of pressure vessel containing defects. Stress intensity factor, reflecting the stress field intensity near the tip zone of the crack, is one of the key parameters in the safety rating of weld joint cracks. And the limit load is another important parameter, the analysis of which can reveal a more authentic state of stress than conventional analysis.Based upon the theory of fracture mechanics,3D linear elastic FEA is adopted to study the stress intensity factor of nozzles with through-wall crack at the shoulder under the conditions of various internal pressure and moment. In the application of the elastic-plastic mechanics theory,3D elastic-plastic FEA is used to calculate and analyse the limit plastic load of the same structure. It is proposed the safety assessment method for vessels containing defects under two loads.The main contents and the corresponding conclusions are as follows:(1) The finite element model of piping containing axial wall-though crack is estabished then validated by calculating the stress intensity factor and limit load. APDL provided by ANSYS is applied to establish the parameterization model, loading and post-processing macro-programs, composing the finite element model of nozzle with through-wall crack at the shoulder.(2) KI (the type I stress intensity factor),p (limit load under pressure) and m (limit load under moment) are applied to rate the nozzle safety. Dimensionless numbers such as crack length a, diameter ratio of nozzle do/di, diameter ratio of vessel Do/Di and diameter ratio of nozzle and vessel di/Di are determined.(3) When subjected to internal pressure solely, KIP is proportional to P in conditions of different structure sizes. Longer crack, bigger hole and thinner wall make a larger KIp and a smaller p. When both do/di and Do/Di are larger than 1.1, KIP decreases unobviously with the increase of the thickness of nozzle and the thickness of vessel. The fitting equation is obtained when both do/di and Do/Di is larger than 1.1. The relationship table of KI, p, a, do/di, Do/Di and di/Di are presented when diameter ratio of vessel and diameter ratio of nozzle is smaller than 1.1, and safety assessment is made under internal pressure. (4) When subjected to internal pressure solely, KIM is proportional to M in conditions of different structure sizes. Longer crack, smaller hole and thinner wall make a larger KIM and a smaller m. When both do/di and Do/Di are larger than 1.1, KIM decreases unobviously with the increase of the thickness of nozzle and the thickness of vessel. The fitting equation is obtained when both do/di and Do/Di is larger than 1.1. The relationship table of KIM, m, a, do/di Do/Di and di/Di are presented when diameter ratio of vessel and diameter ratio of nozzle is smaller than 1.1, and safety assessment is made under moment.(5) When subjected to the combination of internal pressure and moment, stress intensity factor is simply the summation of the stress intensity factors that are subjected to internal pressure and moment respectively, KIS= P·KIP+M·KIM. The relation between limit pressure and limit moment fits the linearity equation, mB·P+pA·M-mB·pA= 0. And the fracture ratio and load ratio used to safety assessment under internal pressure and moment are given, which are And safety assessment is made under internal pressure and moment.更多还原