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This paper presents stress-intensity factors for a wide range of quarter-elliptical corner cracks in rectangular bars. Cracked configurations were subjected to remote tension, in-plane bending, or out-of-plane bending. The ratio of crack depth to crack length ranged from 0.2 to 2; the ratio of crack depth to specimen thickness ranged from 0.2 to 0.8; and the ratio of crack length to specimen width ranged from 0.04 to 0.8. The configurations analyzed varied from a square bar to a very wide plate. These particular crack configurations were chosen to cover the range of shapes and sizes that have been observed to grow in experiments conducted on rectangular bars. The stress-intensity factors were calculated by a three-dimensional finite-element method. Finite-element models employed singularity elements along the crack front and linear-strain elements elsewhere. The models had about 7000 degrees of freedom. Stress-intensity factors were calculated using a nodal-force method.
The present results were compared with other numerical results for a quarter-circular corner crack configuration. The present results along the interior of the crack generally agreed within 3% with those from the literature. Some larger differences (3 to 13%) were observed near the intersection of the crack front and the free surfaces (in the boundary-layer region). Thus, analyses were also performed to study the effect of mesh refinement in the boundary-layer region and the influence of Poisson's ratio on the distribution of stress-intensity factors.
cracks, surface cracks, crack propagation, fracture, stress analysis, materials fatigue, stress-intensity factors, finite elements, boundary-layer region, fracture mechanics
Senior scientist, Analytical Services and Materials, Inc., Hampton, VA
Senior scientist, Materials Division, National Aeronautics and Space Administration, Langley Research Center, Hampton, VA