Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : December 22, 2018 - December 24, 2018
Fatigue crack initiation occurs through dislocation structure formation around stress concentration sources near surfaces. The crack propagation is attributed to plastic deformation at the clack tips. Plastic deformation is caused by the dislocation glide under loading condition. Therefore, direct observation of the dislocation behavior under the loading condition gives important information for fatigue mechanisms. The formation of lattice defects is also key to understanding the fatigue mechanisms because dislocation glide is governed by the presence of other lattice defects: dislocations, stacking faults, grain boundaries. In addition, residual stress around the stress concentration sources has large effect on fatigue behavior. Electron channeling contrast imaging in a scanning electron microscopy is a powerful technique, which enables us to detect lattice defects and elastic strain fields in bulk specimens. A bulk austenitic steel specimen was pre-deformed up to 2% tensile strain. Then, the specimen was reloaded in the elastic regime and subsequently kept the displacement in a secondary electron microscopy. We observed the microstructure around a circular hole (a stress concentration source) during the displacement holding by electron channeling contrast imaging. In-situ electron channeling contrast observation allowed us to visualize elastic relaxation of residual stress, dislocation motions and the formation of plane defects.
