Experimental and numerical investigations on the miniaturization for fracture toughness characterization of RPV materials
(2020) SCK CEN PhD days — Location: Mol, Belgium (13.November.2020)
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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 lifetime prediction. The fracture mechanics testing, as an effective method for the evaluation of fracture properties, receives a special attention among the international community. The characterization of fracture toughness in the transition regime requires a large number of sufficiently large specimens. However, for nuclear applications, the space available for irradiation is often very limited and therefore the use of small specimens is required. 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 results. Besides its size, eight mini-CT specimens can be machined from one broken Charpy specimen which are used in the surveillance programs. However, because of the size effect of miniaturized geometry, mini-CT specimen do not fully satisfy the requirements of the ASTM E1921 for brittle fracture and ASTM E1820 for ductile fracture. More precisely, the required accuracy of the specimen dimensions is very tight, which is believed to be not necessary for the calculation of mechanical parameters such as the J-integral, stress intensity factor and crack tip opening displacement. Moreover, given the limited thickness of the mini-CT specimen, a non-uniform crack front tends to develop during fatigue precracking. As a result, due to the tight requirements of existing standards, a large number of mini-CT specimens are not considered to be valid with respect to crack front curvature, leading to an unnecessary loss of experimental resources. One of the objectives of PhD topic is to investigate the influence of non-uniform fatigue 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. Then the evaluation method of key mechanical parameters will be modified to make the standards be fulfilled for mini-CT geometry. Finally achieve the goal of having a standardization of mini-CT geometry, and validating the use of such geometry in both brittle and ductile fracture regimes relying on scientifically-based concepts of fracture mechanics.
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Li, M., & et al. (2020). Experimental and numerical investigations on the miniaturization for fracture toughness characterization of RPV materials. SCK CEN PhD days, Mol, Belgium. https://hdl.handle.net/2078.5/106355