Abstract
The fracture modes, i.e., brittle and ductile, are studied comparing the criteria in macroscopic and microscopic aspects. As the macroscopic criterion, the critical stress intensity factor is used. As the microscopic criterion, the idea of fractal is applied to the profile of fracture surface. In the experiment, the three points bending fracture of a cracked specimen of mild steel is employed. The relationship between the measured macroscopic criterion and microscopic criterion is discussed.
