Abstract
Stable crack growth under mode I and mixed-mode loading of two fine grained advanced graphites, SNG742 and T220, has been studied within small (18 mm diameter) specimens of the diametral compression disc geometry to investigate the criterion for crack propagation. Cracks were propagated from a central notch, inclined at 0° or 30° to the loading axis, as the tests were observed in situ by X-ray computed microtomography. The three-dimensional (3D) displacement fields were measured by digital volume correlation. The crack shape, tip location and crack opening displacements were determined by 3D phase congruency edge detection of full field displacements. Linear elastic 3D finite element simulations calculated the J-integral and mode I, mode II and mode III stress intensity factors (SIFs) acting on the crack tip, using the full field displacements as boundary conditions. For SNG742 and T220 specimens with notch angle of 0°, nearly pure mode I crack propagation was obtained. For specimens loaded with the 30° notch angle, the SIFs changed from mixed mode I/II towards pure mode I as the crack propagated. The mode II SIF was less than 20% of the mode I SIF, and as the crack extended over a distance ∼3 mm, the critical mode I SIF (fracture toughness) was insensitive to the mode II SIF, with SNG742 graphite having higher fracture toughness than T220 graphite.
Original language | English |
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Pages (from-to) | 356-367 |
Number of pages | 12 |
Journal | Carbon |
Volume | 193 |
Early online date | 24 Mar 2022 |
DOIs | |
Publication status | Published - 30 Jun 2022 |
Bibliographical note
Funding Information:This work is supported by National Science and Technology Major Project ( J2019-IV-0003-0070 ). The facilities and software used for used for the X-ray tomography and digital volume correlation analysis were supported by EPSRC Grant EP/M02833X/1 “University of Oxford: experimental equipment upgrade”. X.C. Jin gratefully acknowledges the support of the National Natural Science Foundation of China ( 12102320 ) and China Postdoctoral Science Foundation ( 2021M692571 ). The graphite test specimens were kindly provided by Sinosteel.
Publisher Copyright:
© 2022 Elsevier Ltd
Keywords
- Diametral compression
- Fracture toughness
- Graphite
- Mixed mode
- Stress intensity factor
- X-ray computed tomography
ASJC Scopus subject areas
- General Chemistry
- General Materials Science