Fracture toughness of polycrystalline NiAl from finite-element analysis of miniaturized disk-bend test results
- Univ. of California, Los Angeles, CA (United States). Dept. of Materials Science and Engineering
The controlled-flaw method in conjunction with the miniaturized disk-bend test (MDBT) was implemented to determine the fracture toughness of polycrystalline NiAl. This procedure was previously used to measure the fracture toughness of completely brittle materials, so the present research extends the method to a material that exhibits a small amount of ductility prior to failure. The controlled-flaw method is based on the placement of a Vickers indentation in the enter of the tensile side of the disks. In the MDBT, the specimens are disks 3 mm in diameter, and in this investigation, the disks ranged from 194 to 367 {micro}m in thickness. Fracture initiated at the corners of the indentations for indentation loads exceeding 39 N. The fracture toughness was determined from an analysis of the dependence of fracture stress, {sigma}{sub f}, on indentation load. In brittle materials, {sigma}{sub f} can be calculated from the measured load at fracture, but this is not possible when the specimen deforms plastically prior to failure. The finite-element program NIKE2D was therefore used to calculate the stress during plastic deformation, using data on the tensile behavior of NiAl to model its deformation as an inelastic cylindrically symmetric plate. The fracture toughness of polycrystalline NiAl was measured as 6.41 {+-} 1.75 MPa{radical}m, which agrees well with independently measured values for similarly processed material. The relatively large uncertainty is associated with scatter in the experimentally measured yield stresses. the results of this investigation demonstrate that the controlled-flaw method can be used in conjunction with the MDBT and finite-element modeling to provide a reasonable estimate of the fracture toughness of a material with limited ductility, provided fracture initiates at the corners of the indentation.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG03-86ER45264
- OSTI ID:
- 484848
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Journal Name: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science Journal Issue: 4 Vol. 28; ISSN MMTAEB; ISSN 1073-5623
- Country of Publication:
- United States
- Language:
- English
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