Anisotropy of Crack Propagation and Fracture Surface in Fatigue of Rolled Steel

Examinations Based on CT Specimens

Abstract

Pulsating tensile fatigue tests were carried out, using the CT specimens cut out from a rolled steel having remarkable laminated structures, in three different directions. The crack growth rate in each directional specimen was measured and the fracture surface was observed by a scanning electron microscope.
The main results obtained are as follows:
(1) An anisotropy of crack propagation was observed in a severely laminated structure, even in the case that inclusions hardly contributed to crack propagation.
(2) The resistance for fatigue crack propagation was smallest in the specimen (SL specimen) whose cracks propagated along the laminated structure, and it was largest in the specimen (LS specimen) whose cracks propagated by cutting the laminated structure alternately.
(3) The existence of the anisotropy of crack propagation was confirmed also by the observation of fracture surface. That is, in the specimen (LS specimen) whose resistance for fatigue crack propagation was largest, the secondary cracks originating from the laminated structure were observed frequently at right angle to the direction of crack propagation.