Effect of pre-strain on fatigue crack growth behavior for commercial pure titanium at ambient temperature

Multiaxial low cycle fatigue tests under non‐proportional stress (NPSS) controlled mode were performed on commercial pure titanium (CP‐Ti). Strain responses of axial and torsional channels under highly applied stress amplitudes show an initial hardening phenomenon. Non‐proportional hardening coefficient of CP‐Ti is independent of the controlled mode. The critical plane of CP‐Ti under NPSS controlled mode is aligned with the maximum principal stress plane proved by optical microscopy observation. Optimized FSM model and KBM‐PM model with mean axial and torsional strain are established. These models are further integrated into equations related to multiaxial stress ratio with high accuracy of life prediction for CP‐Ti under NPSS controlled mode.

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“…The values of v e and v p are 0.34 and 0.5, respectively. 46 The values of n t are listed in Table 3.…”

Section: Fatemi-socie Model With Axial/ Torsional Mean Strainmentioning

confidence: 99%

Multiaxial low cycle fatigue behavior and life prediction of CP‐Ti under non‐proportional stress‐controlled mode

Zhou

Chang

et al. 2022

Fatigue Fract Eng Mat Struct

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“…Various investigations examined the microstructural evolution and deformation mechanism with pre-strain history at low rate loading [24][25][26]. A number of studies assessed the effect of plastic pre-strain on high cycle fatigue and fatigue crack growth behaviour [27,28]. The results suggest that plastic pre-strain enhances fatigue life and delays the crack growth rate.…”

Section: Accepted Manuscript N O T C O P Y E D I T E Dmentioning

confidence: 99%

Influence of Strain History on Dynamic Strain Localization and Stress State During High-Rate Tensile Loading of Titanium Alloys: Experiments, Modeling, and Analytical Methods

Gour

Thomson

Ramakrishnan

et al. 2022

Journal of Applied Mechanics

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The determination of the mechanical response of engineering materials subjected to high loading rates plays an important role in determining their performance and application. The high strain rate tensile response of metals is usually investigated by means of the Split Hokinson Tension Bar (SHTB) apparatus. The interpretation of the obtained results is, however, subjected to analogous stress and strain uniformity challenges present during quasi static tensile experiments. Beyond the onset of necking, strains cease to be uniform along the gauge length and localise around the necking zone. Consequently, the nominal strain rate underestimates the effective strain rate experienced by the material. The analysis of the effective strain rate and stress state beyond the onset of necking has received considerable attention in literature. Several research efforts have focused on the optimization of the geometry of specimens to be employed for the characterization of the dynamic tensile response using the SHTB. The present work investigates, systematically, the effects of strain history and adiabatic heating on the stress state during dynamic loading. A series of monotonic and various strain history experiments were conducted and analysed. The diameter evolution, effective strain rate and temperature histories were measured for all conducted experiments. Numerical simulations were carried out to examine the stress state during strain localisation and to accurately reproduce engineering and local thermos-mechanical variables. The effectiveness of existing post-necking corrections for high-rate experiments is assessed. A modified post-necking correlation taking into account the effects of adiabatically induced thermal softening is proposed.

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“…Atanasovska et al carried out finite element analysis of corrosion fatigue crack and turbine shaft damage based on actual turbine shaft failure cases and proposed a new method to calculate the stress concentration coefficient [8]. Li et al studied the effects of pre-strain on fatigue crack growth rate, strain energy, crack tip plastic zone size, and fatigue fracture mechanism of commercial titanium alloy (CP-Ti) under a wide range of load amplitude and load ratio, and analyzed how pre-strain affects fatigue crack growth and thus the entire fatigue life [9]. Sola et al combined the critical plane fatigue theory and URM standard to preliminarily estimate the damage and fatigue life of a crankshaft with increasing power [10].…”

Section: Introductionmentioning

confidence: 99%

Impact Analysis of Initial Cracks’ Angle on Fatigue Failure of Flange Shafts

Cui

et al. 2022

Coatings

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A fatigue test on the failure mode of flange shafts was conducted. The propagation characteristics of the initial crack at the junction between the shaft and the flange as well as its angle effect were studied. This study developed an analysis program of fatigue crack propagation, based on the APDL (ANSYS Parametric Design Language). It obtained the effective angle interval within which the initial crack is able to propagate. The fitting calculation formula was derived and the results showed that: (1) The initial crack at the junction between the shaft and the flange would propagate in the radial and axial directions; the unstable crack propagation would cause an abrupt fracture of the cross-section, failing connection; and the angle of initial crack was uncertain. (2) The crack followed the I-II-III mixed mode, which was dominated by mode I. An initial crack with a larger angle showed more noticeable II-III characteristics; KII and KIII affected the crack’s propagation angle in the radial and axial directions and they also affected the structure’s surface direction. (3) The deepest point A of the crack was located at the junction between the shaft and the flange. Its crack propagation can be divided into three stages: rapid growth (stage 1), steady decline (stage 2, buffer stage), and instability (stage 3). The initial crack angle not only affected the propagation rate at stage 1 but also influenced the fatigue life distribution of the structure during propagation. The larger the initial crack angle was, the smaller the proportion of buffer stage in the total fatigue life would be. Moreover, the propagation of crack with a larger initial angle reached instability faster after stage 1, which would cause an abrupt fracture of the cross-section. This was unfavorable for deciding the crack detection time or carrying out maintenance and reinforcement. (4) The crack propagation at the junction between the shaft and the flange was determined by the size relation between ΔKI and ΔKth, instead of the effective stress intensity factor. The effective stress intensity factor can partly reflect the law of crack propagation, but cannot serve as the only criterion for crack propagation; it must be combined with the effective angle interval, which was negatively correlated with the crack’s shape ratio, to determine whether the crack would propagate.

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Effect of pre-strain on fatigue crack growth behavior for commercial pure titanium at ambient temperature

Cited by 39 publications

References 40 publications

Multiaxial low cycle fatigue behavior and life prediction of CP‐Ti under non‐proportional stress‐controlled mode

Multiaxial low cycle fatigue behavior and life prediction of CP‐Ti under non‐proportional stress‐controlled mode

Influence of Strain History on Dynamic Strain Localization and Stress State During High-Rate Tensile Loading of Titanium Alloys: Experiments, Modeling, and Analytical Methods

Impact Analysis of Initial Cracks’ Angle on Fatigue Failure of Flange Shafts

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