Evaluating the dynamic fracture toughness of graphite via accurate determination of the dynamic crack propagation length

• Published in: Journal of nuclear materials Vol. 543; p. 152502
• Main Authors: Yi, Yanan, Liu, Guangyan, Lin, Guang, Sun, Libin, Shi, Li, Ma, Qinwei, Ma, Shaopeng
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.01.2021; Elsevier BV
• Subjects: Brittle materials; Correlation analysis; Crack propagation; Digital image correlation (DIC); Digital imaging; Dynamic crack length; Dynamic fracture toughness; Earthquakes; Extensometers; Fracture toughness; Graphite; Heat treating; High temperature; High temperature gas cooled reactors; Impact velocity; Mathematical analysis; Nuclear engineering; Nuclear reactors; Nuclear safety; Reactors; Seismic activity; Virtual extensometer; Dynamic fracture toughness; Digital image correlation (DIC); Dynamic crack length; Graphite; Virtual extensometer
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/j.jnucmat.2020.152502

•Proposed approach to accurately measure dynamic crack propagation length of graphite.•Obtained fracture toughness via virtual extensometers and digital image correlation.•Dynamic fracture toughness increases with increase in impact velocities.•Proposed approach is simple to operate. Nuclear graphite is widely used as a moderator, reflector, and core structure material in very/high temperature gas-cooled reactors. However, because graphite may experience impacts with medium-low velocities during its transport and installation or under extreme conditions such as severe earthquakes, it is necessary to evaluate the dynamic fracture toughness of graphite to assess the safety of the reactors. The ASTM standard recommends a formula to calculate the fracture toughness; however, this formula includes the crack length parameter, which cannot be measured accurately in a dynamic process. To enable the accurate measurement of the dynamic crack propagation length of graphite and subsequently obtain the fracture toughness, a virtual extensometer method based on digital image correlation was established in this study. Three-point bending experiments were conducted using pre-cracked specimens to obtain the dynamic fracture toughness of graphite IG11 under medium-low impact velocities. The results indicated that the dynamic fracture toughness of graphite IG11 increased with the increase in the impact velocities, and its value was substantially higher than the static fracture toughness in certain cases. The proposed approach involves a simple operation, yields a high accuracy, and can enable automatic calculation. Moreover, this approach can be used to evaluate the dynamic fracture performance of other brittle or quasi-brittle materials.