Mode III and Mode I fatigue crack propagation behaviour under torsional loading

Tschegg, E. K.

doi:10.1007/bf00542053

Cited by 104 publications

(63 citation statements)

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“…Furthermore, the extent of crack tip plasticity in torsional loading, and hence the prevalence of flat mode growth, is also dependent upon the size of the cylindrical component [11,12]; small diameter shafts being more prone to flat crack growth than large shafts for the same stress, or strain, intensity factor. In these cases, a large ratio of the applied torque to the plastic collapse limit torque of the shaft, as would occur in a small diameter shaft, extends the crack tip plasticity beyond that expected for the level of strain intensity factor applied.…”

Section: Introductionmentioning

confidence: 99%

Crack paths under mixed mode loading

Yates

Zanganeh

Tomlinson

et al. 2008

Engineering Fracture Mechanics

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Section: Introductionmentioning

confidence: 99%

Crack paths under mixed mode loading

Yates

Zanganeh

Tomlinson

et al. 2008

Engineering Fracture Mechanics

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“…This transition has been taken to define a pseudo mode III threshold for macroscopically flat fatigue crack growth [3], the value of which is in general considerably higher than the fatigue threshold corresponding to factory roof cracking. Pook and Sharples [4] have suggested from consideration of a mode Ibranch at a mode III crack that the ratio of this latter mode III threshold to the mode I threshold for a given material should theoretically be 1.35.…”

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confidence: 99%

Some observations on mode III fatigue thresholds

1985

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The purpose of this note is to report some preliminary results from a study of near-threshold fatigue crack growth in a rail steel under mode III loading and, on the basis of these results, to make some general observations concerning the nature of mode III fatigue threshold. Table 1 contains the chemical composition and mechanical properties of the standard carbon rail steel used in this investigation.Edge-notched bar specimens having square cross-section were machined from the head of a heavy haul rail.Mode III fatigue tests were then conducted on these using a novel test rig developed at the University of New South Wales [i], which allows any desired combination of mode II and mode III loading conditions to be applied to the test specimen.The mode III fatigue threshold value was determined by an increasing load technique.Each specimen was tested for 4 million cycles at a given load range, with load ratio R_>0. If no evidence of fatigue cracking was found, either by the use of a specimen protection device sensitive to changes in the compliance of the specimen or by visual inspection of the notch with a monocular eyepiece, the specimen was re-tested at a higher load range.The results obtained by following this procedure are shown in Fig. I, from which a mode III fatigue threshold value for standard carbon rail steel of AKIIIt h = 18.8 ± 2.0 MPa/m is indicated.It is well established from torsion tests on cylindrical, circumferentially-notched specimens [2] that fatigue crack propagation under mode III loading generally leads to a macroscopically flat (mode III shear) fracture surface for high stress intensity ranges and short crack lengths, while a "factory roof" morphology (resulting from the growth of mode I branch cracks) develops at low stress intensity ranges.For a given applied loading, the growth rates of both types of crack diminish rather than increase with increasing crack length due to interference between the crack faces, and a transition commonly occurs from a macroscopically flat to a factory roof type of fracture surface. This transition has been taken to define a pseudo mode III threshold for macroscopically flat fatigue crack growth [3], the value of which is in general considerably higher than the fatigue threshold corresponding to factory roof cracking. Pook and Sharples [4] have suggested from consideration of a mode Ibranch at a mode III crack that the ratio of this latter mode III threshold to the mode I threshold for a given material should theoretically be 1.35. The value of AK . reported in the present note is larger by a factor of about 1.4 than ~I t~ " Table I, in e mean value of AK h for rail steel glven in t fairly good agreement with this pre~iction. 29 (1985) R45 R46 Examination of the fatigue fracture surfaces by scanning electron microscopy revealed the presence of a factory roof morphology in all cases, as expected from the considerations outlined above. However, the fracture surfaces of some specimens also exhibited a number of small, macroscopically flat regions where fatigu...

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“…In contrast, experimental studies of Mode III crack growth behavior are rare (3,(7)(8)(9)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21), …”

Section: Introductionmentioning

confidence: 99%

“…rN), the parameter (rN-r')y clearly is finite and defines the intensity of plastic shear strain in the crack plane. For cyclic loading, this gives (6): Typical crack growth data (7,8,(14)(15)(16)(17)(18)(19)(20), determined by such procedures using electrical potential methods to monitor crack extension (38) Limited data (8,13) are available on the role of mean stress, or load ratio R (i.e., ratio of minimum to maiimum load or stress).…”

Section: Crack Tip Fieldsmentioning

confidence: 99%

“…6c) are far from understood. However, the transition is promoted at lower growth rates, with increasing crack length (7,(14)(15)(16) and in larger specimen diameters (18). This can be explained qualitatively in terms of the lower "effective" tJ<III or (l~CTD)III experienced at the tip, favoring Mode I separation, as the latter two factors have been shown to enhance crack tip shielding due to sliding crack surface interference from the increased fracture surface area (7,(14)(15)(16)18).…”

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confidence: 99%

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A Comparison of Fatigue Crack Propagation in Modes I and III

Ritchie

1988

Fracture Mechanics: Eighteenth Symposium

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ABSTRACT:The propagation behavior of fatigue cracks in Mode III (anti-plane shear), measured under cyclic torsion, is described and compared with more commonly encountered behavior under Mode I (tensile opening) loads.It is shown that a unique, global characterization of Mode III growth rates, akin to the Paris 11 law 11 in Mode I, is only possible if characterizating paramaters appropriate to large-scale yielding are employed and allowance is made for crack tip shieldin9 from sliding crack surface interference (i.e., friction and abrasion) between mating fracture surfaces. Based on the crack tip stress and deformation fields for Mode III stationary cracks, the cyclic crack tip displacement, (~CTD)III' and plastic strain intensity range, ~riii, have been proposed and are found to provide an adequate description of behavior in a range of steels, provided crack surface interference is minimized. The magnitude of this interference, which is somewhat analogous to crack closure in Mode I, is further examined in the light of the complex fractography of torsional fatigue failures and the question of a 11 fatigue threshold 11 for Mode III crack growth. Finally, micro-mechanical models for cyclic crack extension in anti-plane shear are briefly described, and the contrasting behavior between Mode III and Mode I cracks subjected to simple variable amplitude spectra is examined in terms of the differing role of crack tip blunting and closure in influencing shear, as opposed to tensile opening, modes of crack growth.KEY WORDS: fatigue (materials), cracking (fracturing), crack propagation, torsion, Mode I (tensile opening), Mode III (anti-plane shear), cra.ck closure and sliding interference, fatigue thresholds, v ari ab 1 e amp 1 i tude .1

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Mode III and Mode I fatigue crack propagation behaviour under torsional loading

Cited by 104 publications

References 12 publications

Crack paths under mixed mode loading

Crack paths under mixed mode loading

Some observations on mode III fatigue thresholds

A Comparison of Fatigue Crack Propagation in Modes I and III

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