Torsional Fatigue of a Medium Carbon Steel Containing an Initial Small Surface Crack Introduced by Tension–compression Fatigue: Crack Branching, Non‐propagation and Fatigue Limit

Abstract

In order to examine the threshold condition for the fatigue limit of materials containing a small crack under cyclic torsion, reversed torsional fatigue tests were carried out on 0.47% C steel specimens containing an initial small crack. Initial small semi‐elliptical cracks ranging from 200 to 1000 μm in length were introduced by the preliminary tension–compression fatigue tests using specimens containing holes of 40 μm diameter. The threshold condition for the fatigue limit of the specimens containing artificial small defects under rotating bending and cyclic torsion are also reviewed. Crack growth behaviour from an initial crack was investigated. The torsional fatigue limit for a semi‐elliptical small crack is determined by the threshold condition for non‐propagation of Mode I branched cracks. The torsional fatigue limit of specimens containing an initial small crack can be successfully predicted by the extended application of the √area parameter model in combination with the σθmax criterion.

Fatigue life improvement of 12Cr1МoV steel by irradiation with Zr+ ion beam

“…Fourthly, presence of softened (according to data of nanoindentation) modified subsurface layer along with new phases formed hinders formation of strain induced relief and by doing so, delays nucleation and propagation of fatigue crack both under cyclic tension and alternating bending. A similar effect was previously observed in medium carbon steel under torsional fatigue [30].…”

Fatigue crack path and threshold in Mode II and Mode III loadings

“…This result is similar to those reported in Ref. [9]. It must be noted that the discussion on the branching angle at the crack tip under Mode II loading is not so simple because of the problem of the corner point singularity of 3D crack [13].…”

Branch crack development from the flank of a fatigue crack propagating in mode II

“…1). A recent paper by Murakami and Takahashi 8 reports a similar observation on a medium carbon steel (see Fig. 4 of Ref [8]).…”