Constraint effects observed in crack initiation stretch
- Georgia Inst. of Tech., Atlanta, GA (United States). G.W. Woodruff School of Mechanical Engineering
The current paper characterizes constraint in fracture: J-modified resistance (Jr) curves were developed for two tough structural materials, 6061-T651 (aluminum) and IN718-STA1 (nickel-base superalloy). A wide variety of configurations was tested to consider load configurations from bending to tension including three specimen types (compact tension, center-crack tension, and single-edge notched tension), and a range of ligament lengths and thicknesses, as well as side-grooved and smooth-sided ligaments. The Jr curves exhibited an inflection point after some crack extension, and the data were excluded beyond the inflection. Qualified Jr curves for the two materials showed similar behavior, but R-curves were identical for equal ligament length-to-thickness ratio (RL), for the aluminum alloy, with increasing slope for increasing RL, while for the nickel, the resistance curves aligned for equal ligament thickness, B, and the slope increased for decreasing B. Displacements at the original crack tip (CToD) were recorded throughout the test for several specimens. CToD-versus-crack extension curves were developed, and data were excluded beyond the inflection point (as with the Jr curves). The data collapsed into two distinct curves, thought to represent the surface, plane stress effect and the central, plane strain effect. This was observed for both materials. A technique called profiling is presented for the aluminum alloy only, where the crack face displacements are recorded at the final point of the test as a function of the position throughout the crack cavity, along with an effort to extract the observations in a usable form. Displacements were consistent throughout the cross-section at and behind the original crack tip. In the region where the crack grew, this displacement was developed by a combination of stretch and crack growth. The stretch required to initiate crack extension was a function of the depth beneath the surface into the cross-section.
- OSTI ID:
- 597678
- Report Number(s):
- CONF-9406335-; TRN: IM9812%%129
- Resource Relation:
- Conference: 26. national symposium on fracture mechanics, Idaho Falls, ID (United States), 28-30 Jun 1994; Other Information: PBD: 1995; Related Information: Is Part Of Fracture mechanics: 26. volume; Reuter, W.G. [ed.] [Lockheed Martin Idaho Technologies, Idaho Falls, ID (United States)]; Underwood, J.H. [ed.] [Army Armament Research and Development Center, Watervliet, NY (United States)]; Newman, J.C. Jr. [ed.] [National Aeronautics and Space Administration, Hampton, VA (United States). Langley Research Center]; PB: 853 p.; ASTM special technical publication 1256
- Country of Publication:
- United States
- Language:
- English
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