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Study of a Crack-Tip Region Under Small-Scale Yielding Conditions
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CaretThe computer-assisted moire technique was used to measure displacements and strains in the neighborhood of a crack tip. An aluminum 6061-T6 compact tension specimen was utilized to perform the measurements. The u (parallel to the crack direction) and v displacement fields (perpendicular to the crack direction) were determined, as well as the corresponding strains. Tension and fracture tests were performed to obtain the properties of the material. The stress-strain curve was fitted with a Ramberg-Osgood type of constitutive law. The stresses were computed from the strains using a two-dimensional generalization of the Ramberg-Osgood constitutive equation. The J-integral was computed along several paths. Good agreement was found between the KI computed from the J-integral with the KI obtained from the application of the ASTM Test Method for Plane-Strain Fracture Toughness of Metallic Materials (E 399-83) standard polynomial. The HRR solution was compared to the experimental results. Some important conclusions can be obtained: 1. In small-scale yielding, the HRR field can only be observed very close to the crack tip. 2. The region dominated by the HRR field is only a few crystalline grains in size. 3. The HRR field models the radial stresses very poorly but gives a good estimate of the tangential stresses. 4. The experimental results support the view point that in small-scale yielding, the J-dominance is independent of the validity of the HRR solution.
linear fracture mechanics, small-scale yielding, J, -integral, HRR stress field, plastic zone, plastic radius, crack opening, fracture mechanics, fatigue (materials)
Professor and director, Experimental Mechanics of Materials Laboratory, Illinois Institute of Technology, Chicago, IL
Assistant professor, University Federal de Santa Catarina,
Research assistant, Illinois Institute of Technology, Chicago, IL