Near-threshold behaviour of shear-mode fatigue cracks in metallic materials

článek v časopise ve Web of Science, Jimp

angličtina

This review paper presents a brief state-of-the art of the research on long fatigue shearmode cracks and describes some recent results on effective crack growth thresholds and mode I branching conditions achieved by the authors for ARMCO iron, titanium with two different microstructures, nickel and stainless steel. A special technique for preparation of fatigue precracks enabled us to substantially suppress the crack closure (friction) effects at the beginning of the experiment, and the measured threshold values could be considered to be very close to the effective ones. In all investigated materials, the effective thresholds under the remote mode II loading were found to be about 1.7 times lower than those under the remote mode III loading. Effective thresholds under mode II loading of investigated materials were found to follow a simple formula assembled by the shear modulus G, the magnitude of Burgers vector b and a goniometrical function of the mean deflection angle that depends on the number of available crystallographic slip systems. These quantities determine the intrinsic material resistance to mode II crack propagation at the threshold. A simple criterion for mode I branching in terms of effective threshold values well reflects a transition from the shear-mode to the opening-mode controlled crack propagation at the threshold. The associated transition deflection angle of 40 degrees is a material independent constant.

mode II loading; mode III loading; effective threshold; mode I branching; metallic materials

POKLUDA, J.; PIPPAN, R.; VOJTEK, T.; HOHENWARTER, A.

2014

1. 3. 2014

Wiliey

Velká Británie

8756-758X

Fatigue & Fracture of Engineering Materials & Structures

37

3

Spojené království Velké Británie a Severního Irska

232

254

23