【作者】 何磊；

【导师】 龙伟；

【作者基本信息】 四川大学 ， 机械工程， 2022， 硕士

【摘要】 金属压力容器作为工业生产中的基础设备,广泛应用于化工、航天、核电等各个领域。由于其内部常需储存具有易燃、易爆、剧毒、腐蚀等类型的危险介质,金属压力容器一旦发生爆炸或泄露就会引发严重的安全事故。因此,对压力容器安全性评估方法的研究一直是设备安全领域关注的重点和热点。疲劳裂纹是引发压力容器安全失效的主要原因。由于制造工艺的限制,金属压力容器的裂纹缺陷常常具有先天性与隐蔽性。在极端工作环境的持续作用下,裂纹缺陷的疲劳扩展不仅会严重消耗压力容器的使用寿命,甚至还会引发重大安全事故。传统安全评估方法对压力容器裂纹缺陷安全裕度的表征,通常都是以裂纹尖端在某一时间点的静态数据为计算依据。然而,由于忽略了缺陷在疲劳扩展过程中安全失效速率的时变性,以射线法和平行线法为代表的传统方法对压力容器安全裕度的表征方式并不准确。为此,本论文以四川大学龙伟教授提出的安全衰减路径以及路径速度积分方法为理论依据,通过力学公式推导、Abaqus裂纹实验仿真与裂纹疲劳扩展实验相结合的方式,研究了压力容器表面裂纹缺陷在疲劳断裂过程中的深长尺寸扩展规律,探索了裂纹缺陷在疲劳载荷作用下的安全衰减过程,建立了一种能够反映裂纹缺陷失效速率时变性的安全衰减速率表征模型,并据此提出了一种曲线积分形式的压力容器裂纹缺陷安全裕度表征与剩余寿命预测模型,从而实现了对裂纹缺陷安全衰减过程的准确表述。本文依托于国家自然科学基金项目《基于衰减路径速度积的压力容器缺陷安全裕度及剩余寿命研究》,主要工作内容如下:(1)建立了基于Forman公式的裂纹缺陷深长尺寸关联函数拟合方法本文在Forman疲劳扩展公式的基础上,通过力学公式推导建立了生成裂纹缺陷深长尺寸关联函数的Forman迭代拟合方法。所提Forman迭代方法构建的裂纹尺寸关联函数不仅与裂纹缺陷在稳定扩展阶段的扩展规律相吻合,而且还适用于表征裂纹缺陷在快速扩展阶段的深长尺寸扩展趋势。(2)构建了压力容器裂纹缺陷的安全衰减速率表征模型本文以安全衰减路径理论为依据,根据裂纹缺陷深长尺寸关联函数与安全衰减路径的数值对应关系,建立了裂纹尖端安全评定点沿其安全衰减路径的瞬态位移关系式,得到了一种能够反映裂纹缺陷失效速率时变性的安全衰减速率模型,从而实现了对裂纹缺陷安全衰减过程的准确表征。(3)提出了曲线积分形式的剩余寿命预测模型与安全裕度表征模型本文在安全衰减速率模型以及安全衰减路径理论的基础上,根据裂纹缺陷在安全失效过程中的一般规律,构建安全衰减路径以及安全衰减速率之间的数学关系式,得到了一种基于安全衰减速率曲线积分形式的裂纹缺陷剩余寿命预测模型;通过结合安全衰减路径理论中的-路径速度积思想,建立一种与裂纹缺陷实际失效过程相吻合的的安全裕度表征模型。(4)开发了压力容器裂纹缺陷安全失效仿真平台为了便于压力容器安全评定方法的实际工程应用,本文以《在用含缺陷压力容器安全评定(GB/T 19624 2019)》中的平面裂纹缺陷安全评定准则为基本框架,结合本文所提安全衰减速率与安全衰减路径方法,开发了一套压力容器裂纹缺陷的安全失效仿真平台。更多还原

【Abstract】 As the basic equipment in industrial production,metal pressure vessels are widely used in chemical,aerospace,nuclear power and other fields.Due to the frequent storage of dangerous media with flammable,explosive,highly toxic,corrosive and other properties inside,once the metal pressure vessel explodes or leaks,it will cause serious safety accidents.Therefore,the research on the safety assessment method of metal pressure vessels has always been the focus and hotspot in the field of equipment safety.The main reason for the safety failure of pressure vessels is fatigue cracks.Due to the limitations of the manufacturing process,the crack defects of metal pressure vessels are inherent and concealed.The fatigue expansion of crack defects under the continuous action of extreme working environment will seriously consume the service life of pressure vessels,and even lead to major safety accidents.The traditional safety assessment methods are based on the static data of the crack tip at a certain time point as the calculation basis to characterize the safety margin of the crack defect of the pressure vessel.However,since the time-varying safety failure rate of crack defects is ignored,the traditional methods represented by the ray method and the parallel line method are not accurate in representing the safety margin of pressure vessels.Therefore,based on the safe decay path and path velocity integral method proposed by Professor Long Wei of Sichuan University and combining the derivation of mechanical formula,Abaqus crack experiment simulation and crack fatigue propagation experiment,this paper studies the deep and long dimension propagation law of surface crack defect in pressure vessel during fatigue propagation.The safe decay process of crack defects under fatigue load is explored,and a safe decay rate characterization model that can reflect the time-varying failure rate of crack defects is established.In addition,to achieve an accurate representation of the safety decay process of crack defects,a curve-integral form of safety margin characterization and remaining life prediction model for pressure vessel crack defects is proposed based on the rate model.This paper relies on the National Natural Science Foundation of China project "Research on Defect Safety Margin and Remaining Life of Pressure Vessel Based on Attenuation Path Velocity Integral ".The main contents are as follows:(1)A fitting method for the correlation function of the depth and length of crack defects based on Forman’s formula is established.The deep-long size correlation function generated by this method is not only consistent with the growth law of crack defects in the stable growth stage,but also suitable for characterizing the size growth trend of crack defects in the rapid growth stage.(2)A safe decay rate characterization model for crack defects in pressure vessels is constructed.In this paper,based on the numerical correspondence between the correlation function of the depth and length of the crack defect and the safe decay path,the transient displacement relationship of the safety assessment point at the crack tip along its safe decay path is established.Through the relation,a safe decay rate model that can reflect the time-varying failure rate of crack defects is obtained,thereby realizing the accurate characterization of the safe decay process of crack defects.(3)The remaining life prediction model and safety margin characterization model in the form of curve integral are proposed.Through the general law of the crack defect in the safe failure process,this paper constructs the mathematical expression between the safe decay path and the safe decay rate,and then proposes a prediction model for the residual life of crack defects based on the curve integral of the safe decay rate.By combining the S-v path velocity integral idea in the safety decay path theory,a safety margin characterization model that is consistent with the actual failure process of cracks is established.(4)Developed a pressure vessel crack defect safety failure simulation platform.To facilitate the practical engineering application of the pressure vessel safety assessment method,this paper takes the plane crack defect safety assessment criteria in "Safety Assessment of Pressure Vessels Containing Defects in Service(GB/T 196242019)" as the basic framework,and develops a pressure vessel crack defect failure Simulation System.The system incorporates the latest methods of safe decay path theory.更多还原