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压力容器等大型结构的安全性与初始裂纹的位置及尺寸、材料性能参数等不确定因素有关。概率断裂力学方法将不确定性参量作为随机变量处理,可较好地减小不确定因素对结构完整性评定的影响。本文对含表面半椭圆形裂纹平板进行了拉弯组合载荷作用下的概率断裂力学分析,估算了含表面半椭圆形裂纹平板在拉弯联合加载下裂纹尖端的应力强度因子及J积分值。失效准则考虑了基于线弹性的断裂韧性KIc准则及基于弹塑性的裂纹阻力JIc准则,将裂纹深度、材料性能等参数作为随机变量,采用Monte-Carlo方法计算了不同拉弯组合载荷作用下裂纹板的失效概率,对比分析了不同失效准则及不同拉弯组合系数下裂纹板的失效概率。 相似文献
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J积分理论是表述材料在断裂过程中裂纹尖端应力场的标准方法。但是,由于尺寸效应的存在,单参数的J积分理论不适合应用于小尺寸的断裂韧性试样的裂纹扩展控制。双参数的J-Q理论可以克服单参数J理论在尺寸效应问题上的不足,使得用小尺寸样品研究材料断裂韧性在理论模型计算方面得 相似文献
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含轴向贯穿裂纹三通断裂有限元计算方法 总被引:2,自引:0,他引:2
基于有限元程序ABAQUS开展了对含轴向贯穿裂纹三通断裂有限元计算方法的研究,重点介绍了计算模型的建立、J-积分计算方法的研究.将直管的有限元计算结果与理论计算结果进行了对比,结果表明,二者基本吻合.由此表明,在应用ABAQUS程序进行计算J-积分时,所用的计算方法、参数的输入、奇异单元的选取等是正确的.因此,可按该方法和步骤应用ABAQUS程序计算含裂纹三通的J-积分. 相似文献
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根据英国结构完整性评估标准BS7910(2013),考虑焊接残余应力影响,采用失效评估图(Failure Assessment Diagram,FAD)方法对镍基合金压力容器焊接部位内表面裂纹进行安全评估。首先采用有限元分析(Finite Element Analysis,FEA)方法,对压力容器V型、X型坡口环焊缝多层多道对接焊进行数值模拟,获取焊接残余应力分布,并将V型坡口对接焊焊接残余应力曲线与BS7910(2013)标准残余应力分布进行了对比;其次,对BS7910(2013)1级-FAC曲线进行公式化简,在焊接位置考虑残余应力、应力集中、塑性失效因子三因素的影响,对轴向内部半椭圆裂纹进行了失效应力预测。结果表明:残余应力的分布直接影响计算结果,残余拉应力越大,相应失效应力越小;残余应力值和裂纹深度a保持不变,失效应力计算结果随c/a(c为裂纹半长)增大而减小;当c/a比值不变,失效应力值随着a增大而减小。本文焊接残余应力模拟即及失效应力预测方法为以后含缺陷压力容器及管道失效应力计算(寿命预测)提供一定的参考。 相似文献
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核监测用断裂韧性Charpy尺寸试样的合理设计 总被引:1,自引:1,他引:0
预制疲劳裂纹侧槽Charpy尺寸试样是一种经济、方便的评价核压力容器用钢弹塑性断裂韧性的单试样方法。本文就几种常用压力容器用钢详细研究了侧槽相对深度对断裂韧性及相应的稳定裂纹扩展量的影响,并和满足GB2038要求的大尺寸试样的试验结果进行了对比。研究结果表明,采用预制疲劳裂纹、侧槽相对深度为30%的Charpy尺寸试样及三点弯曲试验曲线上最大载荷前的能量,可以偏安全地评价裂纹开始扩展时材料的弹塑性断裂韧性,建立了核监测用断裂韧性试验Charpy尺寸试样的合理设计。此外,还研究了侧槽的拘束效应和对试样的加厚作用,对试验结果进行了理论解释。 相似文献
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《Fusion Engineering and Design》2014,89(11):2716-2725
The inherent brittleness of tungsten at low temperature and the embrittlement by neutron irradiation are its most critical weaknesses for fusion applications. In the current design of the ITER and DEMO divertor, the high heat flux loads during the operation impose a strong constraint on the structure–mechanical performance of the divertor. Thus, the combination of brittleness and the thermally induced stress fields due to the high heat flux loads raises a serious reliability issue in terms of the structural integrity of tungsten armor. In this study, quantitative estimates of the vulnerability of the tungsten monoblock armor cracking under stationary high heat flux loads are presented. A comparative fracture mechanical investigation has been carried out by means of two different types of computational approaches, namely, the extended finite element method (XFEM) and the finite element method (FEM)-based virtual crack tip extension (VCE) method. The fracture analysis indicates that the most probable pattern of crack formation is radial cracking in the tungsten armor starting from the interface to tube and the most probable site of cracking is the upper interfacial region of the tungsten armor adjacent to the top position of the copper interlayer. The strength threshold for crack initiation and the high heat flux load threshold for crack propagation are evaluated based on XFEM simulations and computations of stress intensity factors and J-integrals. 相似文献
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利用卸载柔度法参考ASTM E1820-11标准对聚变堆候选结构材料中国低活化马氏体(CLAM)钢在室温和1 50℃条件下的断裂韧性进行了测试分析,同时对断面进行了扫描电子显微镜(SEM)微观分析。结果显示,CLAM钢1/2CT样品在室温和1 50℃条件下测试的断裂韧性J_Q分别为287 kJ/m~2和256 kJ/m~2,在这两个测试温度下CLAM钢均表现出较高的断裂韧性,且随着测试温度的升高断裂韧性有所降低。断面SEM观察显示韧窝布满整个断面,裂纹稳定扩展区域为韧性断裂。 相似文献
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M. Scibetta 《Journal of Nuclear Materials》2010,406(1):113-118
Cleavage fracture of reactor pressure vessel steels in the upper ductile to brittle transition region generally occurs with prior significant ductile crack growth. For low upper shelf materials and using PreCracked Charpy v-notch (PCCv) specimens that can be obtained from conventional surveillance programs, the effect of prior crack growth could be particularly important. In practice, the shape of the Master Curve and the failure distribution could be affected by ductile crack growth. To quantify the effect in practical applications, the effect of prior ductile on cleavage is evaluated on PCCv specimen.The methodology use finite element calculations to grow a ductile crack and infer the brittle failure probability using the local approach to fracture. It is found that for very low upper shelf toughness materials, ductile crack growth enhances the failure probability, induces a steeper failure distribution and affects the shape of the Master Curve. However, for low toughness materials, the enhanced failure probability due to crack growth is compensated by loss of constraint. 相似文献
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Elastic-plastic crack tip fields can be characterised by two parameters, J and T/Q which describes crack tip constraint. This forms the foundation of a constraint based fracture mechanics in which toughness is expressed as a function of constraint in the form of a J–(T/Q) locus. The enhanced toughness associated with shallow cracks and defects can be used in a systematic manner by constraint matching, and implemented through a simple modification to a failure assessment diagram. This methodology enables the conservatism associated with the use of deeply cracked fracture toughness measurements to be relaxed. In this work these methods have been applied to a tubular welded joint. 相似文献
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Masanori Kikuchi 《Nuclear Engineering and Design》1997,174(1):646
The ductile fracture tests are carried out using compact type (CT) specimen, three point bend specimen and center cracked tension (CCT) specimens made of A533B steel and aluminum alloy with different crack lengths. The effect of the crack tip constraint on the microscopic fracture behavior is studied by the scanning electron microscope (SEM). It is shown that the apparent JIC value increases due to the decrease of the crack tip constraint. It is pointed out that the increase of the apparent JIC value is partly due to the error of the conventional equation to estimate the J value. Based on the FEM analyses, these apparent JIC values are corrected and are compared with the valid JIC values. The good co-relation between apparent JIC value and the Q factor, proposed by O'Dowd and Shih, is shown for all the specimens. The FEM analyses based on the Gurson's constitutive equation is also carried out. The effect of the constraint on the crack tip field is discussed. 相似文献
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At VTT, development work has been in progress for 15 years to develop and validate testing and analysis methods applicable for fracture resistance determination from small material samples. The VTT approach is a holistic approach by which to determine static, dynamic and crack arrest fracture toughness properties either directly or by correlations from small material samples. The development work has evolved a testing standard for fracture toughness testing in the transition region. The standard, known as the Master Curve standard is in a way “first of a kind”, since it includes guidelines on how to properly treat the test data for use in structural integrity assessment. No standard, so far, has done this. The standard is based on the VTT approach, but presently, the VTT approach goes beyond the standard. Key components in the standard are statistical expressions for describing the data scatter, and for predicting a specimens size (crack front length) effect and an expression (Master Curve) for the fracture toughness temperature dependence. The standard and the approach, it is based upon, can be considered to represent the state of the art of small specimen fracture toughness characterization. Normally, the Master Curve parameters are determined using test specimens with “straight” crack fronts and comparatively uniform stress state along the crack front. This enables the use of a single KI value and single constraint value to describe the whole specimen. For a real crack in a structure, this is usually not the case. Normally, both KI and constraint vary along the crack front and in the case of a thermal shock, even the temperature will vary along the crack front. A proper means of applying the Master Curve methodology for such cases is presented here. 相似文献
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金属材料裂纹冲击韧性评定方法研究 总被引:1,自引:0,他引:1
工程结构在复杂环境下长期服役后,裂纹的萌生和发展难以避免。对于需要承受爆炸与冲击的工程结构,需要对所用材料的裂纹冲击韧性进行评定,避免裂纹出现可能导致的冲击脆性断裂。基于Instron VHS高速材料试验机,开发了一套材料动态断裂试验装置,测量了4种具有高冲击功金属材料的裂纹冲击韧脆转变过程,并研究了影响金属材料裂纹冲击韧脆转变速率的因素。发现材料夏比冲击功并不能完全反应裂纹的冲击韧性,预制裂纹与否、试样约束方式和试样裂尖约束因子都会影响金属材料裂纹冲击试验中的韧脆转变速率。基于以上研究结果,提出了金属材料裂纹冲击韧性评定方法的基本思路。 相似文献