Investigation on the Influence of Highly Oriented Texture and Internal Stress on Fatigue Crack Growth

Fatigue crack propagation stage is considered to be the dominant in fatigue fracture of welded joints and some solutions regarding stress issue have been developed. It is known that fatigue crack forms slip band at crack tip and propagates by accumulation of irreversible deformation against cyclic loading. Then if angle difference between (110) plane which is the main slip plane of body centered cubic lattice and the plane of which angle is 45 ° to the crack plane with respect to crack propagation direction is maximum, suppression of fatigue crack growth is expected. And the delay of fatigue crack growth is also expected, when the compressive stress is developed in the steel plate. In the present study, fatigue crack path and fatigue crack growth rate in the test steel with highly oriented texture and internal stress distribution were investigated. The angular difference with (110) plane and crack plane got largest by accumulating the (110) plane perpendicular to the plane thickness direction and propagating the crack in the thickness direction. Fatigue crack growth rate of steel with highly oriented texture was lower than that of normalized steel, and the crack growth was remarkably suppressed when compressive stress was superimposed inside the steel plate. It is considered that crack closure effect by fracture surface contact with increase of the fracture surface ruggedness appeared, because fatigue crack branching and bending in steel with highly oriented texture were observed.