Effect of specimen geometry and testing method on mixed mode I-II fracturetoughness of a limestone rock from Saudi Arabia

Citation
K. Khan et Na. Al-shayea, Effect of specimen geometry and testing method on mixed mode I-II fracturetoughness of a limestone rock from Saudi Arabia, ROCK MECH R, 33(3), 2000, pp. 179-206
Citations number
24
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Geological Petroleum & Minig Engineering
Journal title
ROCK MECHANICS AND ROCK ENGINEERING
ISSN journal
0723-2632 → ACNP
Volume
33
Issue
3
Year of publication
2000
Pages
179 - 206
Database
ISI
SICI code
0723-2632(200007/09)33:3<179:EOSGAT>2.0.ZU;2-B
Abstract
The effect of testing method and specimen geometry such as diameter, thickn ess, and crack length and type on measured fracture toughness was investiga ted using specimens collected from a limestone rock formation outcropping i n the Central Province of Saudi Arabia. Straight Edge Cracked Round Bar Ben d (SECRBB), semicircular disk specimens under three point bending, and Braz ilian disk specimens under diametrical compression were used in this invest igation. SECRBB specimens were used for the Mode-I study, and notched Brazi lian disk and semicircular specimens were used for the mixed Mode I-II stud y. The results show that specimen diameter and crack type have a substantia l influence on the measured fracture toughness; however, loading rate, crac k size, and specimen thickness seem to have a negligible effect on the frac ture toughness. Mode-I fracture toughness is significantly influenced by sp ecimen diameter and crack type, while their effects on Mode-II fracture tou ghness are generally negligible. The different specimens (SECRBB, Brazilian disk, and semicircular) can give comparable results only when the proper s pan to diameter ratio is used. The Brazilian disk with a straight notch was found to be the most convenient geometry to use for fracture toughness det ermination. A simple method of making a precise notch inside the disk is pr esented, using the combination of a drilling machine and a wire saw.