Fatigue crack initiation behaviour of notched 34CrNiMo6 steel bars under proportional bending-torsion loading

Branco, R.; Berto, Filippo; Kotousov, Andrei; Antunes, F.V.

doi:10.1016/j.ijfatigue.2019.105268

Cited by 38 publications

(13 citation statements)

References 32 publications

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“…These geometrical details when subjected to cyclic loading are susceptible to fatigue crack initiation which can culminate in fatigue failure. Fracture mechanics and fractography are two branches of modern engineering currently used to investigate the mechanical behaviour of structural elements during and after fatigue failure, respectively (Zeravcic et al 2006;Macek et al 2017Macek et al , 2020bBranco et al 2020;Kowal and Szala 2020). One of the methods of fracture-surface topography analysis is FRASTA, developed by SRI International (Kobayashi and Shockey 2010) and further improved by (Cao et al 2014;Martelo et al 2019).…”

Section: Introductionmentioning

confidence: 99%

Fracture surface formation of notched 2017A-T4 aluminium alloy under bending fatigue

Macek

2021

Int J Fract

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The effect of cyclic loading on facture surface topology in notched components made by aluminium alloys is not completely clear. Fractography and fracture mechanics can help to understand this interdependency. This paper aims to study the distribution of the fracture surface roughness of notched 2017A-T4 aluminium alloy after bending fatigue using an optical focus-variation surface measurement technique by applying the fracture zone concept. The effects of stress level at the notch root and the load ratio on fatigue crack growth and fracture surfaces are analysed. Profile and areal surface parameters of four fracture surface regions were investigated at incremental crack lengths of the specimens. Studies have confirmed that the surface areas associated with the main stages of fatigue phenomenon (i.e. crack initiation, crack propagation, and final rupture) have significant differences in roughness which can be explained by the different loading scenarios. Overall, fatigue fracture surfaces have smallest roughness values at the crack initiation stage and a gradual increase during the fatigue crack growth stage.

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Section: Introductionmentioning

confidence: 99%

Fracture surface formation of notched 2017A-T4 aluminium alloy under bending fatigue

Macek

2021

Int J Fract

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“…The bending–torsion fatigue testing program, originally performed in a previous study, has been conducted in a 100 kN DARTEC servo-hydraulic machine (Dartec Ltd., Bournemouth, UK) connected to a custom-made gripping system [ 44 ]. The specimens, whose geometry is presented in Figure 1 , were prepared in a high-precision computer numerical control turning center from extruded 20 mm-diameter round bars and were tested under in-phase constant-amplitude for pulsating loading conditions ( R = 0).…”

Section: Methodsmentioning

confidence: 99%

“…The two constants are evaluated under the same stress ratio (R = 0, in this case) of the multiaxially loaded geometry. The values obtained in this research, originally calculated in a previous study [ 44 ], are listed in Table 3 .…”

Section: Methodsmentioning

confidence: 99%

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Fracture Surface Behavior of 34CrNiMo6 High-Strength Steel Bars with Blind Holes under Bending-Torsion Fatigue

2021

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The present study evaluates the fracture surface response of fatigued 34CrNiMo6 steel bars with transverse blind holes subjected to bending with torsion loading. The analysis of the geometric product specification was performed by means of height parameters Sx, functional volume parameters Vx, and fractal dimension Df. Surface topography measurements were carried out using an optical profilometer with focus variation technology. The experimental results show that the doubling the bending to torsion moment ratio B/T from B/T = 1 to B/T = 2, maintaining the same normal stress amplitude, greatly reduces both Sa, Vv as well as the fractal dimension Df of the analyzed specimen fractures by 32.1%, 29.8%, and 16.0%, respectively. However, as expected, a two-fold increase in the B/T ratio, maintaining the same normal stress amplitude, resulted in a larger number of cycles to fatigue crack initiation, Ni, which can be explained by the lower shear stress level. These experiments prove that parameters Sx, Vx, Df are smaller for larger Ni values, which is an important finding. In addition, it was found a high consistency of surface topography measurements for the two sides of the broken specimens. The proposed methodology is both reliable and applicable for other engineering applications involving different geometries and loading conditions.

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“…Fatigue failure often occurs at the local stress concentration area, 3,4 which will accelerate crack initiation and propagation, thereby reducing the fatigue life of the component. For those reasons, the study of fatigue strength of notched components has increasingly attracted many scholars' attention 5–7 . Besides, the presence of stress concentration induces multiaxial stress field at the notch root and results in a more complex stress–strain response and different stress–strain distributions 8–10 .…”

Section: Introductionmentioning

confidence: 99%

Multiaxial fatigue life prediction method of notched specimens considering stress gradient effect

Liu

Ran

Xie

et al. 2021

Fatigue Fract Eng Mat Struct

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This paper investigates the effect of stress gradient on the fatigue life of U‐notched specimens under multiaxial proportional loading by studying the shear stress gradient and normal stress gradient on the crack initiation plane separately. First, based on the energy method and critical plane method, an energy‐critical plane method for determining the direction of crack initiation is proposed. Second, with the help of the concept of stress field intensity, the shear stress gradient and normal stress gradient on the critical plane are studied. Finally, a multiaxial fatigue life prediction model is established by combining the equivalent stress field intensity, composed of the shear stress field intensity and normal stress field intensity, with the Manson–Coffin equation. Theoretical analysis is verified by the experiments of Q345 steel notched specimens, and the results show that the predicted accuracy of the proposed method is not conservative and is superior to the local stress–strain method.

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Fatigue crack initiation behaviour of notched 34CrNiMo6 steel bars under proportional bending-torsion loading

Cited by 38 publications

References 32 publications

Fracture surface formation of notched 2017A-T4 aluminium alloy under bending fatigue

Fracture surface formation of notched 2017A-T4 aluminium alloy under bending fatigue

Fracture Surface Behavior of 34CrNiMo6 High-Strength Steel Bars with Blind Holes under Bending-Torsion Fatigue

Multiaxial fatigue life prediction method of notched specimens considering stress gradient effect

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