波纹管开裂原因分析

采用扫描电镜、能谱分析等手段分析了某机电产品用不锈钢波纹管开裂的原因。结果表明:在焊接过程中波纹管的焊接接头区域发生敏化,随后酸洗造成该区域形成沿晶界腐蚀裂纹,波纹管在经过振动试验时承受径向交变载荷,在交变应力下裂纹由最初的晶界腐蚀裂纹根部开始扩展直至穿透管壁;断口表面能够发现明显的贝纹线,证明波纹管开裂是一种疲劳失效。     

热交换器不锈钢管束断裂失效分析

采用宏观分析、金相检验、断口宏观及微观分析以及能谱分析等方法,对某炼油厂裂化车间4台热交换器不锈钢管束先后发生大面积断裂的性质及原因进行了分析。结果表明:该热交换器管束断裂是由在交变载荷和腐蚀介质作用下发生的由外向内的腐蚀疲劳开裂引起的;腐蚀疲劳裂纹起始于管外壁的点蚀坑等应力集中处,促进腐蚀疲劳裂纹扩展的管束外部介质主要是Cl^-和H₂S;裂纹先以腐蚀疲劳开裂方式扩展,而后又呈典型的应力腐蚀开裂方式继续扩展,当应力腐蚀裂纹扩展达到管束断裂强度时便发生断裂。最后提出了预防管束断裂的措施及建议。     

高压油管开裂原因分析及改进建议

某柴油机高压油管在使用过程中发生开裂,对开裂油管进行了宏观分析、化学成分分析、金相检验以及断口分析,确定了油管的开裂原因。结果表明:该油管开裂主要是因为其内壁存在裂纹、毛刺等加工缺陷,在工作过程中的交变应力作用下裂纹以疲劳方式扩展并造成开裂;油管未进行调质处理以及振幅偏大,促进了疲劳裂纹的扩展。最后对高压油管提出了改进建议。     

某地铁受电弓拉杆球铰轴承失效原因

某地铁受电弓拉杆球铰轴承在运行过程中发生失效断裂.采用宏观分析、断口分析、金相检验、硬度测试及化学成分分析等方法对球铰轴承的失效原因进行了分析.结果表明:该受电弓拉杆球铰轴承的断裂模式属于高周低应力疲劳断裂.球铰轴承在服役过程中承受频繁的振动和交变载荷作用,折角处的微裂纹成为疲劳裂纹源区,裂纹在交变载荷作用下不断扩展,...     

克深2-2-12高压气井S13Cr110钢制油管开裂和泄漏原因分析

克深2-2-12高压气井S13Cr110钢制油管开裂并发生泄漏。通过宏观检查、磁粉探伤和金相检验等对油管开裂和泄漏的原因进行了分析。结果表明:开裂和泄漏的位置处于油管力学性能薄弱管段。油管开裂属于应力腐蚀开裂,裂纹产生原因与A环空腐蚀环境、油管材料特性及油管受力条件有关,导致油管产生开裂和泄漏的载荷主要与内压和热胀冷缩交变产生的弯曲载荷等有关。     

滤清器外壳开裂分析

滤清器外壳安装在汽车发动机台架上试验500 h后出现裂纹,采用宏观和微观分析、化学成分分析和金相检验等方法对开裂原因进行了分析。结果表明:滤清器外壳的外壁局部区域在拉延时产生了微裂纹,在交变应力作用下形成疲劳裂纹,并导致早期疲劳开裂。     

输油软管开裂原因

某飞机输油软管发生漏油现象,经检查为软管开裂所致.采用宏观观察、断口分析、红外光谱分析和热失重试验等方法,对软管开裂的原因进行了分析.结果表明:输油软管的开裂性质为疲劳开裂,裂纹起源于螺纹凹槽的根部;输油软管装配后产生应力老化,导致其疲劳性能下降,在振动和内部燃油压力等交变应力的作用下裂纹从凹槽根部的损伤位置起源,并最...     

某型飞机襟翼导轨支架开裂原因

某型通用飞机在飞行时其左侧襟翼导轨支架发生开裂。采用宏观观察、化学成分分析、扫描电镜分析、硬度测试及有限元分析等方法研究了该支架开裂的原因。结果表明：裂纹起源于襟翼导轨支架下部拐点的尖角处，断口呈疲劳条带特征，说明该支架发生了疲劳开裂；襟翼收放产生的交变应力和高循环次数是造成支架疲劳开裂的主要原因。采用安装加强补片的方法可以提高支架应力集中区域的强度。     

某井钻杆接头断裂原因

在对某油气井的钻探过程中,钻杆接头发生断裂。采用宏观观察、化学成分分析、扫描电镜分析、力学性能测试、金相检验等方法对该钻杆接头的断裂原因进行分析。结果表明：该钻杆接头的断裂性质为疲劳断裂,钻杆钻进过程中频繁发生跳钻、憋钻现象,使其瞬时载荷较大,在钻杆大端螺纹根部萌生了疲劳裂纹,在复杂的交变载荷作用下,裂纹快速扩展,最终导致钻杆接头发生断裂。     

DN50不锈钢波纹软管开裂失效分析

通过宏观检验、扫描电镜观察以及X射线能谱分析等手段,对某304奥氏体不锈钢DN50波纹软管开裂原因进行了分析。结果表明:软管开裂是由于腐蚀疲劳所致,软管的管壁内、外表面在腐蚀介质和外界应力的综合作用下产生沿晶微裂纹和蜂窝状腐蚀形貌,并受到交变应力作用,因而发生双向多源疲劳开裂失效。     

Numerical simulation study of fatigue crack growth behavior of cracked aluminum panels repaired with a FRP composite patch using combined BEM/FEM

A combined boundary element method and finite element method (BEM/FEM) is employed to investigate the fatigue crack growth behavior of cracked aluminum panels repaired with an adhesively bonded fiber-reinforced polymer (FRP) composite patch. Numerical simulation of crack growth process of a cracked aluminum panel repaired with a FRP composite patch under uniaxial cyclic loading has been carried out. The curve of crack length on unpatched side of the cracked panel versus the number of cyclic loading is determined by the numerical simulation, and it agrees well with experimental data. Furthermore, the crack front profiles of the cracked panel during fatigue crack growth and the distributions of stress intensity factors along crack fronts are also numerically simulated.     

含裂纹平板的振动及裂纹扩展分析

针对含裂纹平板的振动与疲劳问题,研究含裂纹平板耦合动力学建模方法。首先在变形相似性原则下通过力学平衡原理推导出含裂纹项的平板振动方程,进而基于应力关系式形成裂纹项的表达式。在此基础上,利用Galerkin法将含裂纹板简化成单自由度振动系统,根据Berger经验方法产生方程的非线性项构建含裂纹板的非线性振动模型。最后通过算例探讨含裂纹板的动力学特性,协同Paris方程研究含裂纹平板动力学与裂纹扩展的耦合行为。研究结论表明,阻尼大小和激励力的变化对含裂纹板的振动特性及裂纹扩展规律具有显著影响。所提出的含裂纹平板耦合动力学建模方法,考虑了振动与裂纹扩展的耦合效应,为飞行器板结构抗振动疲劳设计提供理论依据。     

Modelling fatigue crack propagation of a cracked metallic member reinforced by composite patches

The concept of fracture for material elements at front of a crack for fatigue crack propagation was extended to the fatigue crack propagation of a cracked metallic member reinforced with a composite patch in this paper. From static mechanics and linear elastic fracture mechanics, force transfer on a cracked member through a composite patch was analyzed and a formula connecting the stress intensity factor with crack length was obtained. Thereafter, a fracture model for fatigue crack propagation of a repaired cracked metallic member was proposed. A new expression for the fatigue crack propagation rate has thus been derived. The expression was verified objectively by the test data. It is in good agreement with the test results.     

考虑裂纹表面摩擦阻尼的振动疲劳裂纹扩展分析

以含表面裂纹悬臂梁为研究对象,研究了裂纹面摩擦效应对裂纹疲劳扩展的影响。分析时,用双线性弹簧描述裂纹呼吸行为,用Galerkin方法把呼吸裂纹梁简化为单自由度系统,基于Coulomb摩擦模型和能量耗散理论推导了摩擦阻尼损耗因子,运用广义的Forman方程模拟疲劳裂纹扩展,通过振动分析与裂纹扩展计算同步进行的方法考虑振动与疲劳的耦合效应,探讨了摩擦阻尼对裂纹梁疲劳裂纹扩展寿命的影响。结论表明,摩擦阻尼损耗因子随裂纹扩展呈单调递增趋势,摩擦阻尼对振动疲劳裂纹扩展的影响不容忽视     

Interaction between a cracked hole and a line crack under uniform heat flux

This article deals with the interaction between a cracked hole and a line crack under uniform heat flux. Using the principle of superposition, the original problem is converted into three particular cracked hole problems: the first one is the problem of the hole with an edge crack under uniform heat flux, the second and third ones are the problems of the hole under distributed temperature and edge dislocations, respectively, along the line crack surface. Singular integral equations satisfying adiabatic and traction free conditions on the crack surface are obtained for the solution of the second and third problems. The solution of the first problem, as well as the fundamental solutions of the second and third, is obtained by the complex variable method along with the rational mapping function approach. Stress intensity factors (SIFs) at all three crack tips are calculated. Interestingly, the results show that the interaction between the cracked hole and the line crack under uniform heat flux can lead to the vanishing of the SIFs at the hole edge crack tip. The fact has never been seen for the case of a cracked hole and a line crack under remote uniform tension.     

The wave propagation and vibrational energy flow characteristics of a plate with a part-through surface crack

In the view of structure-borne sound, vibrational wave and energy flow characteristics of infinite thin plate of finite width with a part-through surface crack are investigated. The case of an all-over part-through crack parallel to the finite side of the plate is considered. The crack is modeled as a line spring and the flexibility of the spring is deduced from the relationship between the strain energy and stress intensity factor in fracture mechanics. The responses of both intact plate and cracked plate under the excitation of harmonic force are reduced with wave propagation approach, then the input energy flow and transmitted energy flow of intact and cracked plates are calculated. The results show that the vibrational energy flow of cracked plate is highly related to the depth and location of the part-through crack. The location and the depth of the crack can be identified by the contour lines of normalized input energy flow with different driving frequencies. The research provides theoretical basis for the crack detection by measuring the vibrational energy flow in cracked plate structures.     

含表面裂纹板的振动功率流特性研究

从结构噪声的观点研究了在简谐力作用下含有表面裂纹板的振动功率流特性。由于裂纹的存在,导致了板在裂纹两边转角的不连续性,运用断裂力学的理论得到裂纹导致的附加转角。利用力作用处以及裂纹处的连续性条件推导出了含裂纹板中的弯曲波运动并得到输入功率流以及传播功率流。通过对完善板与裂纹板的输入功率流与传递功率流的对比,表明板中裂纹的存在改变了板原有的振动功率流特性,裂纹的特性参数可以通过板的输入功率流和传播功率流来反映。通过构造裂纹板的输入功率流的等值线图给出了识别板中的裂纹的方法。     

直斜裂纹转轴的时变刚度特性研究*

本文采用有限元方法建立了裂纹转子系统的动力学方程,利用应变能释放率方法得到了裂纹单元的刚度矩阵,采用应力强度因子为零法模拟裂纹的呼吸效应,详细研究了不同深度的直裂纹和45°斜裂纹转子,在一个稳态旋转周期内,裂纹开闭规律以及转轴刚度时变特性。研究表明裂纹深度的增大使裂纹转轴的刚度变化增大,直裂纹与斜裂纹转轴的刚度变化特性具有明显差异,斜裂纹引起更多与更强的耦合振动,使转子的动力学性能更复杂。     

基于响应的梁损伤识别

采用扭转弹簧模拟悬臂梁的损伤，导出了损伤梁位移模态和转角模态的近似公式，获得了损伤梁在单点激励下，零初始条件的位移和转角响应。发现损伤梁的转角响应在损伤处发生阶跃变化，而损伤梁的转角响应对位置的一阶偏导数在损伤处有脉冲两数型突变的特点，从而提出了基于损伤梁转角响应的损伤判据函数。通过对损伤梁和损伤桁架结构的数值模拟，表明提出的判据函数不仅可以利用简谐激励下的响应识别梁的损伤，电可以利用冲击激励下的响应识别桁架的损伤。实验结果表明利用所提出的判据函数，可以同时判别损伤的位置和损伤的程度。     

Stress intensity factors for cracked rectangular cross-section thin-walled tubes

For cracked structural rectangular thin-walled tubes, an exact and very simple method to determine the stress intensity factors has been proposed based on a new concept of crack surface widening energy release rate. Unlike the classical crack extension energy release rate, the crack surface widening energy release rate can be expressed by the G^*-integral and elementary strength theory of materials for slender cracked structures. From present discussions, a series of new and exact solutions of stress intensity factors are derived for cracked rectangular and square tubes. The present method can also be applied to cracked polygon thin-walled tubes.