Review and evaluation of the double-torsion technique for fracture toughness and fatigue testing of brittle materials

Measurement of dynamic fracture toughness by double torsion testing

“…The critical stress intensity factors were found to be independent of the crack length when the crack length was less than 0.6L. The crack length at which the critical stress intensity factors began to decrease from a constant value was a little shorter than the crack lengths measured in other results of the static tests (Tait, et al, 1987). In this study, the initial crack length, a, of the specimens in the experiment were determined to be 10 mm.…”

“…(1) is independent of the initial crack length, a. The width W, height d, and length of the specimen L in the experiment was set to 35 mm, 5 mm, and 70 mm, respectively, so that the aspect ratio of the rectangular specimen, W/L, would be 0.5, in accordance with one of the previous studies (Tait, et al, 1987). The depth dw and width Wg of the central channel were 2.5 mm and 4 mm, respectively, and Wa = Wm.…”

“…Several testing methods for measuring fracture toughness have been suggested, improved, and standardized over the years, such as compact tension, double-edge notched tension, single-edge notched bending. The double torsion test (Trantina, 1977), (Fuller, 1979), (Pletka, et al, 1979), (Tait, et al, 1987), (Shyam and Tadaharu ADACHI*, Zoltan MAJOR**, Kenji FUJII***, Kohei MIKUMA****, Markus Karamoy UMBOH*****, Kyohei TAKEO****** and Yosuke ISHII******* Lara-Curzio, 2006), (Becker, et al, 2011) is one of the most useful testing methods for studying rate dependencies of the fracture toughness of brittle materials. Because the double torsion test is based on a four-point bending test of a precracked specimen, fracture behavior can be measured independently of length of crack in the specimen as it propagates in a uniform tensile stress field.…”

Fracture Toughness of Thin Plates by the Double-Torsion Test Method

“…Once precracked, the specimens were unloaded for crack length measurement and then failed at a stroke rate of 2 mm/minute. Specimen width to depth of 6 < W/d < 15, length to width of L/W > 2, and crack length of W < a < L-W have been recommended 3,5 . where…”

“…Three objectives were sought in this work: (1) to determine the effect of section thickness on the measured fracture toughness using the DT test specimen; (2) to compare the DT test to accurate, well documented standardized test techniques such as the SEPB (single-edgedprecracked-beam), CN (chevron-notch) and SCF (surface crack in flexure); and (3) lay the foundation for an ASTM standard on the DT test specimen. Because so much controversy exists regarding the DT specimen 5 , a direct experimental approach was taken by using model materials: silicon carbide, alumina, and soda-lime silicate glass. Alpha silicon carbide is stiff, has consistent fracture toughness with little R-curve behavior, and is very insensitive to stress corrosion.…”