Plastic-strain distribution at the root of a sharp notch

A new experimental technique employing a pattern of microhardness indentations has been developed to permit an accurate measurement of the plastic-strain distribution at the root of a mechanically introduced notch. The method allows measurements to be made to within 0.001 in. from the crack tip. The longitudinal strain distribution was determined for notched 2024-T3 aluminum-alloy specimens, and both the longitudinal and the transverse distributions were obtained for notched specimens of high-purity aluminum. The results from the experiments indicated that a relationship exists between the grain size and both the strain magnitude and distribution. The specimens having the largest grain size developed the highest strain gradients, and exhibited the greatest degree of symmetry about the center line. The symmetry of the strain distribution around the notch improved as the applied load approached that required to produce crack propagation whereas, at low loads, there was little evidence of any symmetry.