Fractographic analysis of fatigue crack initiation and propagation in CP titanium with a bimodal harmonic structure

Nukui, Yuhei; Kubozono, Hiroki; Kikuchi, Shoichi; Nakai, Yoshikazu; Ueno, Akira; Kawabata, Mie; Ameyama, Kei

doi:10.1016/j.msea.2018.01.054

Cited by 32 publications

(19 citation statements)

References 32 publications

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“…Hardness value of the MM series is higher than that of the untreated series (125.2±3.6 HV). The sintered materials were sliced into disks approximately 1.5 mm thick and machined into a blunt-notched specimen for four-point bending fatigue tests [26,27]. After machining, the specimen surface was polished with emery paper (#240 to #4000) to a thickness of 1 mm and polished in a SiO 2 suspension to obtain a mirror finish.…”

Section: Materials and Specimensmentioning

confidence: 99%

“…Fatigue tests were interrupted after a certain number of cycles, and acetyl cellulose films were placed on the specimen surface using the replica method to examine fatigue crack initiation and propagation. Once the crack length was measured using optical microscopy, the stress intensity range, K, was calculated [27,28,32]; the aspect ratio, c/a, for small cracks was estimated as follows:…”

Section: Testingmentioning

confidence: 99%

“…Our research group has designed a harmonic structure using powder metallurgy to sinter mechanically milled stainless steel powders [18][19][20][21][22][23], which improve both their strength and ductility by suppressing necking during tensile deformation [20]. In particular, we have focused on the fatigue properties under fourpoint bending [24][25][26][27] and near-threshold fatigue propagation of long cracks [28][29][30] in titanium-based materials with a bimodal harmonic structure. To achieve sufficient performance with the newly developed harmonic structured stainless steels, their fatigue properties and fatigue crack propagation behavior need to be examined.…”

Section: Introductionmentioning

confidence: 99%

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Evaluation of Fatigue Properties under Four-point Bending and Fatigue Crack Propagation in Austenitic Stainless Steel with a Bimodal Harmonic Structure

Kikuchi

Nakatsuka

Nakai

et al. 2019

Frattura Ed Integrità Strutturale

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Austenitic stainless steel (JIS-SUS304L) with a bimodal harmonic structure, which is defined as a coarse-grained structure surrounded by a network of fine grains, was fabricated using powder metallurgy to improve both the strength and ductility. Four-point bending fatigue tests and Kdecreasing tests were conducted in air at room temperature under a stress ratio R of 0.1 to investigate fatigue crack propagation in SUS304L. The fatigue limit of this harmonic-structured material is higher than that of the material with a homogeneous coarse-grained structure. This is attributable to the formation of fine grains by mechanical milling and to the suppression of pore formation. In contrast, the threshold stress intensity range, Kth, for the harmonicstructured material is lower than that for the homogeneous coarse-grained material, while the crack growth rates, da/dN, are higher at comparable K. These results can be attributed to a reduction in the effective threshold stress intensity range, K eff,th , due to the presence of fine grains in the harmonic structure.

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Section: Materials and Specimensmentioning

confidence: 99%

Section: Testingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Evaluation of Fatigue Properties under Four-point Bending and Fatigue Crack Propagation in Austenitic Stainless Steel with a Bimodal Harmonic Structure

Kikuchi

Nakatsuka

Nakai

et al. 2019

Frattura Ed Integrità Strutturale

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“…[11][12][13] However, unlike the cases of steels and aluminium alloys, striation characteristics of titanium and titanium alloys have not been examined in detail. In order to use as structural application, in addition to tensile properties characterization, the fatigue behaviour of titanium is required to be investigated.…”

Section: Introductionmentioning

confidence: 99%

“…Accordingly, fatigue behaviour and properties of titanium and its alloys have been investigated with respect to mechanical 9,10 and metallurgical approaches. [11][12][13] However, unlike the cases of steels and aluminium alloys, striation characteristics of titanium and titanium alloys have not been examined in detail. In particular, striation features associated with small crack growth are yet to be investigated.…”

Section: Introductionmentioning

confidence: 99%

Minimum fatigue striation spacing and its stress amplitude dependence in a commercially pure titanium

Ahmed

Islam

Yin

et al. 2019

Fatigue Fract Eng Mat Struct

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We report the fatigue striation spacing of commercially pure titanium with respect to stress amplitude. Rotating bending fatigue tests were performed at 150, 175, 200 and 227 MPa in which samples did not fail at 150 MPa. No fatigue striation up to a certain crack length is observed for the studied conditions. For each condition, a minimum striation spacing value is found that decreases from 0.45 to 0.36 to 0.24 μm with increasing stress from 175 to 200 to 227 MPa, respectively. The minimum striation spacing remains constant up to a certain crack length for each condition. Thereafter, it starts increasing with crack length. It is quite understandable that the constant striation spacing over a certain crack length may not represent the macroscopic fatigue crack growth rate. The fatigue crack growth mechanism during the constant striation spacing region has been discussed in detail. K E Y W O R D Scommercially pure titanium, fractrography, metal fatigue, fatigue striation

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Evaluation of Deformation and Fracture Behavior in 304L Austenitic Steel Harmonic Structures through Nanoindentation

Paul

Ameyama

Ota-Kawabata

et al. 2022

steel research int.

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Investigating the mechanical properties of harmonic structures during various stages of deformation, particularly after fracture, is critical. Herein, nanoindentation is used to evaluate the local deformation and fracture behavior of SUS304L steel harmonic structures. Electron backscattering diffraction is employed to observe the strain distribution in the fracture‐deformed samples, where high kernel average misorientation is evident near the shell–core boundary region. Comparison of the deformed sample reveals that the nanohardness of the shell and core regions significantly increases after deformation. This phenomenon indicates the capability of strain hardening. Furthermore, plastic inhomogeneity is observed before the fracture occurs. Strain‐induced α′‐martensite is observed in the fractured area, especially in the core region near the shell–core boundary, because of the high strain. High nanohardness is evident due to the high dislocation density and formation of strain‐induced α′‐martensite. The resulting high stress concentration can lead to void formation and crack initiation originating from the region near the shell–core boundary.

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Fractographic analysis of fatigue crack initiation and propagation in CP titanium with a bimodal harmonic structure

Cited by 32 publications

References 32 publications

Evaluation of Fatigue Properties under Four-point Bending and Fatigue Crack Propagation in Austenitic Stainless Steel with a Bimodal Harmonic Structure

Evaluation of Fatigue Properties under Four-point Bending and Fatigue Crack Propagation in Austenitic Stainless Steel with a Bimodal Harmonic Structure

Minimum fatigue striation spacing and its stress amplitude dependence in a commercially pure titanium

Evaluation of Deformation and Fracture Behavior in 304L Austenitic Steel Harmonic Structures through Nanoindentation

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