NEUTRON-DIFFRACTION MEASUREMENTS OF INNER LOCAL STRAIN OF FATIGUED CARBON-STEEL

The residual strain for three directions x, y, z at every I mm mesh po int on the notch root of a round fatigued steel bar with a diameter of 8 mm was detected nondestructively, using a special neutron diffracti on apparatus, residual stress analyzer (RESA) at JRR-3M, with a beam d iameter of 2 mm. The residual stress for the three directions calculat ed from the observed strain showed that the stress was tensile and lar ge near the surface of the specimen. This result is consistent with th e well-known phenomenon that the fracture starts from the surface of t he notch root. The residual stress near the center of the notch root w as also tensile in che axial direction of the round bar.