Abstract
This paper investigates the unstable fracture toughness of specimens of different heights using the double‐K model for three‐point bending tests on notched concrete beams. It is shown that unstable fracture toughness exhibits a significant size effect. The modified maximum tangential stress (MMTS) criterion is used to explain the size effect of unstable fracture toughness. The MMTS criterion considers the higher order terms of the Williams series expansion of the stress field. The results show that the MMTS criterion can reasonably estimate unstable fracture toughness. It is recommended that the minimum height of the specimen be 200 mm when three‐point bending tests on notched beams are used to determine unstable fracture toughness.
Highlights
Fracture toughness is an important property of fracture resistance, especially for quasibrittle materials such as rock and concrete
E purpose of this paper is to study the size effect of the unstable fracture toughness Kun using the maximum tangential stress (MMTS) criterion. e P-crack mouth opening displacement (CMOD) curves required to calculate unstable fracture toughness are derived from three-point bending tests on notched beams of Hoover et al [26, 27] in 2012. ey showed that the measured unstable fracture toughness (Kun) values were significantly correlated with the specimen size. e size effect of unstable fracture toughness can be explained by the MMTS criterion
Unstable Fracture Toughness. e maximum load Pmax and critical CMODc are directly obtained from the P-CMOD curves, and the critical effective crack length ac and unstable fracture toughness Kun can be calculated according to equations (1)–(6). e results are shown in Table 3. e initial crack length of the concrete specimen will increase slightly due to the influence of the storage and handling process
Summary
Fracture toughness is an important property of fracture resistance, especially for quasibrittle materials such as rock and concrete. Aliha et al and Ayatollahi et al [7,8,9] considered that fracture toughness is affected by the size and geometry of the specimen, mainly due to the influence of high-order terms of the crack tip stress field, and the experimental results were analyzed by the modified maximum tangential stress (MMTS) criterion. E purpose of this paper is to study the size effect of the unstable fracture toughness Kun (one of the double-K parameters) using the MMTS criterion. Ey showed that the measured unstable fracture toughness (Kun) values were significantly correlated with the specimen size. E purpose of this paper is to study the size effect of the unstable fracture toughness Kun (one of the double-K parameters) using the MMTS criterion. e P-CMOD curves required to calculate unstable fracture toughness are derived from three-point bending tests on notched beams of Hoover et al [26, 27] in 2012. ey showed that the measured unstable fracture toughness (Kun) values were significantly correlated with the specimen size. e size effect of unstable fracture toughness can be explained by the MMTS criterion
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