Investigations on the influence of the fatigue precrack front on the mechanical behavior of mini-CT specimen
(2019) SCK CEN PhD days — Location: Mol, Belgium (2.October.2019)
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- Abstract
- The material properties of reactor pressure vessel (RPV) are among the key points for producing reliable integrity assessment and accurate residual life prediction. The fracture mechanics testing, as an effective method for the evaluation of fracture properties, deserves a special attention among the international community. The characterization of fracture toughness in the transition regime requires a large number of thick specimens. Moreover, for nuclear applications, the space available for irradiation is often very limited requiring the use of small specimens. The miniature compact tension specimen (mini-CT), as one of the geometries that offers significant advantages, can optimize the use of available material and generate meaningful fracture toughness values. Besides its size, eight mini-CT specimens can be machined from one broken Charpy specimen that are used in the surveillance programs. However, because of the size effect of miniaturized geometry, mini-CT specimen doesn’t fully satisfy the requirements of the ASTM E1921 for brittle fracture and ASTM E1820 for ductile fracture. More precisely, the specification on the specimen dimensions relative to specimen width is too tight, which is not necessary in the calculation of mechanical parameters such as J-integral, stress intensity factor and crack tip opening displacement, etc. Moreover, given the limited thickness of the mini-CT specimen, a non-uniform crack font tends to be obtained during fatigue precracking. As a result, due to the tight requirements of existing standards, a large number of mini-CT specimens do not fulfill the standard requirements with respect to crack front curvature, leading to an unnecessary waste of experimental resources. Therefore, the main objective of the research at this stage is to investigate the influence of non-uniform precrack front on the mechanical behavior of mini-CT specimen, further to demonstrate that some of the standard requirements can be relaxed without affecting the accuracy of results. Combining the test data, a large number of finite element simulations were performed using the finite element software- ANSYS, the influence of tilted straight precrack front and curved precrack front on several mechanical parameters was analyzed. The obtained results [1] proved that the influence of non-uniform precrack front can be considered negligible, test data obtained from mini-CT specimens with invalid precrack front might still provide relevant information.
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Li, M. (2019). Investigations on the influence of the fatigue precrack front on the mechanical behavior of mini-CT specimen. SCK CEN PhD days, Mol, Belgium. https://hdl.handle.net/2078.5/106356