Near-threshold propagation of mode II and mode III fatigue cracks in ferrite and austenite

Propagation of Long Fatigue Cracks under Remote Modes II and III in Ferritic-Pearlitic Steel

“…[6,7], this unpleasant situation was improved by obtaining experimental data on ∆K IIeff,th and ∆K IIIeff,th for several single-phase materials see Table I. The data for ∆K IIeff,th were well reproduced by the following simple formula:…”

“…Three dierent specimens were used: (i) the compact-tension shear specimens (CTS) with the dimensions of 68 × 42 mm 2 and the thickness of 4 mm for pure mode II loading, (ii) the cylindrical bar with a circumferential notch with the outer diameter of 25 mm, the inner diameter of 12 mm and the length of 100 mm loaded in torsion to generate a pure mode III loading and (iii) the same cylindrical bar installed into a special device transforming tensile forces into a pure shear loading of the circular notch which resulted in a combination of loading modes II, III and II + III. A more detailed description of the specimens can be found in [6]. Precracks were made at the notch roots of the specimens in cyclic compression to suppress the friction induced crack closure eects at the beginning of the shear-mode experiments.…”

A practical expression for evaluating the small shear-mode fatigue crack threshold in bearing steel

“…When performing a fracture mechanics-based evaluation, the fracture process must be addressed as a small crack problem [1][2][3][24][25][26][27][28][29][30][31][32]. However, although significant progress has occurred over the last two decades [4][5][6][7][8][9][10][11][12][13][14][15][16][17], the shear-mode growth behavior of a crack in hard steel is still not fully understood, especially for small cracks. Recently, under these circumstances, Matsunaga et al [1,2] performed torsional fatigue tests with static compression to measure the ranges of the threshold stress intensity factor (SIF), DK IIth and DK IIIth , for the shearmode growth of small surface cracks between approximately 0.01 and 1 mm in length in a bearing steel.…”

On the connection between mode II and mode III effective thresholds in metals

“…The cylindrical specimens had a circumferential notch with the outer diameter D = 25 mm and the inner diameter d = 12 mm. A detailed description of the experimental arrangement can be found in [10]. The precracks were generated at the notch root by cyclic compressive loading [22 -24] which resulted in an open precrack and avoided closure effects such as friction and contact of the fracture surfaces.…”

“…Consequently, the shear-mode cracks usually rather quickly become opening-mode cracks and the investigation of shear-mode crack-growth mechanisms and the related intrinsic resistance is very difficult. However, one can still experimentally uncover the crack growth mechanisms and the intrinsic resistance (effective thresholds) for D loading modes II and III by minimizing the extrinsic resistance by the preparation of fatigue precracks using cyclic compressive loading and subsequent annealing [10]. Such experiments revealed two basic types of closure-free propagation of mode II and mode III cracks in metallic materials [3].…”