A transferability approach for reducing excessive conservatism in fracture assessments
A transferability approach for reducing excessive conservatism in fracture assessments
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DOI：
10.1016/j.engfracmech.2016.11.011
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发表时间：
2017-04
影响因子：
5.4
通讯作者：
N. Larrosa;R. Ainsworth
中科院分区：
文献类型：
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作者：
N. Larrosa;R. Ainsworth
在结构完整性评估中，不确定性和保守性的一个来源是所使用的断裂韧性（Kmat）值。对于保守的结果，K值通常来自深裂纹试样，如标准紧凑拉伸试样，C（T）。高约束条件附近的裂纹尖端的保证，这对应于下限韧性值独立于试样的尺寸和几何形状。然而，在单边缺口拉伸，SE（T），试样和管道，例如，是已知的，是不太严重的比那些在一个深刻的尖锐裂纹的尖端，导致增加的能力，以维持负载和更高的韧性。当评估非尖锐缺陷（例如，坑、沟、凹痕）。约束损失或缺口效应在三轴应力场中产生松弛，而在深度尖锐裂纹试样中存在严重的应力场。因此，需要一种方法来提供一个简单的程序来评估使用更高断裂韧性以减少过度保守性的适用性。本研究使用双参数断裂力学方法（J-Q）来量化组件（例如，具有表面裂纹的管道）和断裂试样（即，单边拉伸[SE（T）]、标准紧凑拉伸[C（T）]和缺口紧凑拉伸[C（T）ρ]试样）中的约束水平。结构抵抗断裂的能力由具有类似J-Q响应的试样的断裂韧性给出。通过虚拟试验框架构建的撕裂阻力曲线（J-R曲线）获得了不同试样的断裂韧度值。所提出的工程方法被用作一个平台，通过使用一个韧性断裂模型，通知一个经典的断裂力学方法（J-Q），结合更基本的理解的驱动力和作用的几何形状和加载条件进行更准确的断裂评估。
A source of uncertainty and conservatism in structural integrity assessments is the value of fracture toughness (Kmat) that is used. For conservative results, the value ofKmatis commonly derived from deeply cracked specimens, such as standard compact tension specimens, C(T). High constraint conditions near the crack tip are ensured and this corresponds to lower-bound toughness values independent of specimen size and geometry. However, the local stress fields in single edge notched tension, SE(T), specimens and pipes, for example, are known to be less severe than those at the tip of a deep sharp crack, resulting in an increased capacity to sustain load and higher toughness. Similar behaviour is expected when assessing non-sharp defects (e.g., pits, gouges, dents). The constraint loss or the notch effect produce a relaxation in the triaxial stress field in comparison to the severe stress fields present at deeply sharp cracked specimens. A methodology providing a simple procedure to evaluate the suitability of the use of a higher fracture toughness to reduce excessive conservatism is then required. This study uses a two-parameter fracture mechanics approach (J-Q) to quantify the level of constraint in a component (e.g. a pipe with a surface crack) and in fracture test specimens, i.e. single edge tension [SE(T]), standard compact tension [C(T)] and notched compact tension [C(T)ρ] specimens. The ability of the structure to resist fracture is given by the fracture toughness of the test specimen with a similarJ-Qresponse. Fracture toughness values for different specimens have been obtained from tearing resistance curves (J-R curves) constructed by means of a virtual testing framework. The proposed engineering approach is used as a platform to perform more accurate fracture assessments by the use of a ductile fracture model that informs a classical fracture mechanics approach (J-Q) by incorporating more fundamental understanding of the driving forces and the role of the geometry and loading conditions.