Some experimental results on behavior of fatigue crack propagation in grain oriented silicon iron thin plates
- Under various directions of loading and starting notches in air -
Kikukawa Makoto; Sugeta Atsushi; Misawa Toshiaki
Abstract:In order to investigate Mode II and III besides Mode I fatigue crack propagation in grain oriented silicon iron thin plates with coarse grains, some experiments were carried out, selecting favorable directions of loading and starting notches for these modes. Mode II crack growth was expected by loading parallel to rolling direction of specimens with starting notches along a preferential slip direction, however, Mode II crack growth along this direction could not continue beyond about one mm in any case and the crack suddenly bent 110 degree to conjugate preferential slip direction. Striation-like patterns with a few mm spacing, which corresponded to crack growth during hundreds cycles, were observed in these fractographs. These results suggest existence of some substructures caused by cycling slips on one direction during hundreds cycles which may arrest continuous crack growth on one plane. The tensile test loaded perpendicular to rolling direction showed enough out of plane shear deformation and fracture ductility. Mode III crack growth was expected by loading perpendicular to rolling direction of specimens, but Mode I crack growth with brittle striation occurred and any shear lips could not be observed. Key Words:fatigue crack propagation, mode I, II and III, grain oriented silicon iron, fractograph