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Out-of-Plane Constraint Effect on the Fracture Toughness of Single Edge Notch Tension Specimens |
Yizhe LI, Baoming GONG(), Xiuguo LIU, Dongpo WANG, Caiyan DENG |
Tianjin Key Laboratory of Advanced Joining Technology, School of Materials Science and Engineering, Tianjin University, Tianjin 300354, China |
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Cite this article:
Yizhe LI, Baoming GONG, Xiuguo LIU, Dongpo WANG, Caiyan DENG. Out-of-Plane Constraint Effect on the Fracture Toughness of Single Edge Notch Tension Specimens. Acta Metall Sin, 2018, 54(12): 1785-1791.
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Abstract The crack-tip stress and strain fields of single edge notch tension (SENT) specimen are similar to those of the full-scale pipe containing surface cracks under longitudinal tension and/or internal pressure. It is well known that material's fracture toughness is not constant, and the specimen size has a significant influence on fracture toughness. It is thus essential to consider the transferability from fracture specimens in laboratory testing to practical structures, i.e., size effects or constraint effects. However, the specimen dimensions for SENT specimens recommended by current design procedures have not validated the out-of-plane constraint effect on the fracture toughness. In this work, the effect of specimen thickness on the crack tip opening displacement (CTOD) of SENT specimen was investigated using an API X90 grade steel. Full-field deformation measurement by digital image correlation (DIC) technique and stretching zone width (SZW) examination were performed to analyze the size effects on fracture toughness. The results show that the critical crack initiation toughness is highly sensitive to specimen thickness, and decreases significantly as specimen thickness increases until the thickness-to-width ratio (B/W) equals to 4, beyond which the effect of specimen thickness becomes relatively weak. As the specimen thickness increases, the maximum longitudinal strain and stretching zone width decrease sharply, and the location of high-strain zones changes significantly; when B/W≥3, strain is initiated from the area opposite the cracked side rather than from the crack tip, indicating a strong loss of plasticity for thicker specimens. A dimension size is recommended for the fracture toughness testing to take the out-of-plane constraint into account for SENT specimen.
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Received: 02 April 2018
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Fund: Supported by National Natural Science Foundation of China (No.51305295) and National Key Research and Development Program of China (No.2016YFC0802105) |
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