The miniaturized disk bend test(MDBT) can be used to measure the fracture toughness at “infinite" crack length, K ∞, of ordered intermetallic compounds. The specimens tested are disks 3 mm in diameter and typic...The miniaturized disk bend test(MDBT) can be used to measure the fracture toughness at “infinite" crack length, K ∞, of ordered intermetallic compounds. The specimens tested are disks 3 mm in diameter and typically range in thickness from 250 to 400 μm. A Vickers indentation is impressed within ±10 μm of the center of a metallographically polished disk under a known load, F . The specimen is then subjected to biaxial loading, with the indented side in tension, and tested to failure. In completely brittle intermetallics the fracture stress, σ f, is calculated using a standard formula and measured experimentally as a function of F . When plasticity intervenes prior to fracture it is necessary to calculate the stress using finite element modeling (FEM), the FEM program NIKE2D has been used. Whether or not the specimens deform plastically, the resulting data on σ f vs F are analyzed using established equations of fracture mechanics in conjunction with an empirical rising R curve equation that characterizes the increase in fracture resistance, K R( c ), with crack length, c . Results are presented on several ordered intermetallic compounds. These include Ni 3Ge and Ti 5Si 3, which exhibit no ductility prior to fracture, and NiAl and a complex TiAl alloy, which both exhibit limited ductility before fracturing. The values of K ∞ determined with the MDBT are in very good agreement with values of K IC measured using conventional methods.展开更多
文摘The miniaturized disk bend test(MDBT) can be used to measure the fracture toughness at “infinite" crack length, K ∞, of ordered intermetallic compounds. The specimens tested are disks 3 mm in diameter and typically range in thickness from 250 to 400 μm. A Vickers indentation is impressed within ±10 μm of the center of a metallographically polished disk under a known load, F . The specimen is then subjected to biaxial loading, with the indented side in tension, and tested to failure. In completely brittle intermetallics the fracture stress, σ f, is calculated using a standard formula and measured experimentally as a function of F . When plasticity intervenes prior to fracture it is necessary to calculate the stress using finite element modeling (FEM), the FEM program NIKE2D has been used. Whether or not the specimens deform plastically, the resulting data on σ f vs F are analyzed using established equations of fracture mechanics in conjunction with an empirical rising R curve equation that characterizes the increase in fracture resistance, K R( c ), with crack length, c . Results are presented on several ordered intermetallic compounds. These include Ni 3Ge and Ti 5Si 3, which exhibit no ductility prior to fracture, and NiAl and a complex TiAl alloy, which both exhibit limited ductility before fracturing. The values of K ∞ determined with the MDBT are in very good agreement with values of K IC measured using conventional methods.
