利用CT试件J-A2裂纹约束和三维裂纹网格调整管道J-R韧性曲线

G. Thorwald, K. Bagnoli
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引用次数: 0

摘要

本文的目的是利用双参数断裂力学将材料的J-R阻力曲线(即韧性)从试样几何形状调整到开裂构件几何形状。由于大多数工厂设备都是在“上层货架”上设计和运行的,因此延性撕裂分析可以更真实地评估缺陷容限。在大多数情况下,撕裂曲线来源于确保高度约束的试样几何形状,例如SENB和CT,因此,考虑试样几何形状和部件几何形状之间的约束差异可能会有很大的好处。在单参数断裂力学中,单个参数K或j积分足以表征裂纹前缘应力。当观察到几何相关效应时,可以使用双参数断裂力学来改进裂纹前缘应力的表征,使用t应力、Q或A2约束参数。本研究采用A2参数。通常的J-R幂律方程有两个系数来曲线拟合材料数据(ASTM E1820)。将调整后的J-R曲线系数修改为A2约束参数的函数。测量的J-R值和计算的A2约束值通过绘制J-R测试数据与A2值的关系来关联。A2约束值是通过将HRR应力解与试件几何的裂纹前缘应力结果进行弹塑性有限元分析来计算的。利用试验数据中两个Δa裂纹扩展值处的J值求解两个J- r曲线系数。调整后的J-R系数的封闭解使用自然对数的性质。结果表明,调整后的J-R指数系数对于特定的材料和试样几何形状将是一个恒定值,从而简化了调整后的J-R曲线的应用。不同的试样几何形状可以用来验证调整后的J-R曲线。选择另一种具有不同A2约束值的试件几何形状,可以得到调整后的J-R曲线,并与实测的J-R曲线进行比较。与材料测试样品相比,组件的几何形状也期望具有不同的A2约束。这里的例子是管道的轴向表面缺陷。计算了轴向表面裂纹管的A2约束,得到了调整后的J-R曲线。调整后的J-R曲线显示,与CT测量值相比,管道的韧性有所增加。调整后的J-R曲线可用驱动力法或韧性撕裂不稳定性分析来评估缺陷稳定性。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Adjusted J-R Toughness Curve for Pipes Using J-A2 Crack Constraint of CT Specimens and 3D Crack Meshes
The objective of this paper is to use two-parameter fracture mechanics to adjust a material J-R resistance curve (i.e. toughness) from the test specimen geometry to the cracked component geometry. As most plant equipment is designed and operated on the “upper shelf”, a ductile tearing analysis may give a more realistic assessment of flaw tolerance. In most cases, tearing curves are derived from specimen geometries that ensure a high degree of constraint, e.g., SENB and CT Therefore, there can be significant benefit in accounting for constraint differences between the specimen geometry and the component geometry. In one-parameter fracture mechanics a single parameter, K or J-integral, is sufficient to characterize the crack front stresses. When geometry dependent effects are observed, two-parameter fracture mechanics can be used to improve the characterization of the crack front stress, using T-stress, Q, or A2 constraint parameter. The A2 parameter was be used in this study. The usual J-R power-law equation has two coefficients to curve-fit the material data (ASTM E1820). The adjusted J-R curve coefficients are modified to be a function of the A2 constraint parameter. The measured J-R values and computed A2 constraint values are related by plotting the J-R test data versus the A2 values. The A2 constraint values are computed by comparing the HRR stress solution to the crack front stress results of the test specimen geometry using elastic-plastic FEA. Solving for the two J-R curve coefficients uses J values at two Δa crack extension values from the test data. A closed-form solution for the adjusted J-R coefficients uses the properties of natural logarithms. The solution shows the adjusted J-R exponent coefficient will be a constant value for a particular material and test specimen geometry, which simplifies the application of the adjusted J-R curve. A different test specimen geometry can be used to validate the adjusted J-R curve. Choosing another test specimen geometry, having a different A2 constraint value, can be used to obtain the adjusted J-R curve and compare it to the measured J-R curves. The geometry of the component is also expected to have a different A2 constraint compared to the material test specimen. The example examined here is an axial surface flaw in a pipe. The A2 constraint for an axial surface cracked pipe is computed and used to obtain an adjusted J-R curve. The adjusted J-R curve shows an increase in toughness for the pipe as compared to the CT measured value. The adjusted J-R curve can be used to assess flaw stability using the driving force method or a ductile tearing instability analysis.
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