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Zhang, H.*; Wu, S. C.*; Ao, N.*; Zhang, J. W.*; Li, H.*; Zhou, L.*; 徐 平光; Su, Y. H.
International Journal of Fatigue, 166, p.107296_1 - 107296_11, 2023/01
被引用回数：4 パーセンタイル：61.91(Engineering, Mechanical)Abnormal damages in railway axles can lead to a significant hazard to running safety and reliability. To this end, a surface treatment was selected to effectively inhibit fatigue crack initiation and growth. In this study, a single edge notch bending fatigue test campaign with artificial notches was conducted to elucidate the fatigue crack non-propagation behavior in railway S38C axles subjected to an induction hardening process. The fatigue cracking behavior in the gradient structure was revealed by optical microscopy, electron backscatter diffraction, and fractography. The microhardness distribution was measured using a Vickers tester. The obtained results show that the microhardness of the strengthening layer is nearly triple that of the matrix. Owing to the gradient microstructures and hardness, as well as compressive residual stress, the fatigue long crack propagates faster once it passes through the hardened zone (approximately 2.0 mm in the radial depth). Thereafter, local retarding (including deflection, branching, and blunting) of the long crack occurs because of the relatively coarse ferrite and pearlite in the transition region and matrix. Totally, this fatigue cracking resistance is reasonably believed to be due to the gradient microstructure and residual stress. These findings help to tailor a suitable detection strategy for maximum defects or cracks in railway axles.
岩本 ちひろ*; 高村 正人*; 上野 孝太*; 片岡 美波*; 栗原 諒*; 徐 平光; 大竹 淑恵*
ISIJ International, 62(5), p.1013 - 1022, 2022/05
被引用回数：2 パーセンタイル：32.54(Metallurgy & Metallurgical Engineering)Neutron diffraction is a powerful non-destructive method for evaluating the microscopic structure and internal stress of metal plates as a bulk average. Precise neutron diffraction measurements with a high intensity neutron beam have already been carried out at large-scale neutron facilities. However, it is not easy to provide users with enough experimental opportunities. We are working on upgrading the neutron diffractometer with techniques of time-of-flight to enable stress measurements at RIKEN accelerator-driven compact neutron source (RANS). To improve neutron diffraction resolution, delayed neutrons, which expand neutron beam pulse width, should be suppressed. However, it is difficult to separate the delayed neutrons experimentally. In this study, a new analysis method has been proposed to deconvolute the diffraction peak from the delayed neutron component. Moreover, a new collimator system, called decoupled collimator system, has been developed to reduce the number of delayed neutrons. The diffraction patterns from a powder sample of pure body-centered cubic iron were measured with the decoupled collimator and the diffraction peak of {211} reflection was analyzed by the new analysis method using a model function of a single exponential decay function convoluted with a Gaussian function. By this method, the decoupled collimator system has been confirmed to achieve a smaller measurement limit of lattice strain 
than a small-aperture polyethylene collimator system and a non-collimator system. The currently available was 6.7
10
, this means that the internal stress up to 130 MPa can be well evaluated for steel materials with a Young's modulus of 200 GPa at RANS.
土屋 佳則; 菊地 賢司; 皆川 宣明; 森井 幸生; 加藤 崇; 中嶋 秀夫; Refal, M.*; 斎藤 徹*; 辻 博史
Proceedings of 6th International Conference on Residual Stressess (ICRS-6), Vol.1, p.337 - 341, 2000/00
核融合炉で必要となる巨大超伝導コイルの、加工による大型導体ジャケット内部残留応力の分布状態は、超伝導生成熱処理の際に問題になる。本講演ではコイル巻き線加工を模擬したジャケット材の内部残留応力を中性子回折法により非破壊で測定し、加工による残留応力の再分配状況を観測した結果について報告する。同時に、同形状のモデルによる計算機シミュレーションを行い、加工の各段階を追って残留応力の変化を予測した結果を示す。中性子回折による実測と計算結果の整合性を各加工段階で検証することで、複雑な形状と加工履歴をもつ材料の残留応力を事前に高い信頼性をもって予測できる可能性について議論する。
林 眞琴*; 石渡 雅幸*; 皆川 宣明; 舩橋 達
材料, 44(507), p.1464 - 1469, 1995/12
中性子回折法による残留応力測定の応用として発電プラントの小口径配管に使用されているソケット継手の溶接ルート部の残留応力を中性子回折法により測定すると共に、ひずみ取り焼鈍による残留応力の緩和挙動を評価した。
Qin, T. Y.*; Zhang, H.*; Zhou, L.*; Ao, N.*; 徐 平光; Su, Y. H.; Wu, S. C.*; 菖蒲 敬久
no journal, ,
The S38C railway axles are developed for Shinkansen (Bullet Train) through high-frequency induction hardening and the residual stresses are introduced into the axle with a depth of several millimeters. Residual stresses seriously affect the fatigue mechanical strength and fatigue life of engineering structures, and the accurate determination and the optimization control of the three-dimensional (3D) residual stress distribution of high-speed railway S38C axles are increasingly necessary for improving the axle service life. Here, the residual stresses of the S38C axle samples were measured by using the RESA (residual stress analyzer) angle dispersive neutron diffractometer at JRR-3 (Japan research reactor No.3). The large axle samples were electro-discharge machined into: (a) 3 mmH3 mmA20 mmR comb-shape stress-free coupons with a comb spacing of 1 mm to relieve the transformation induced residual stresses and determine the stress-free lattice spacing, d0; (b) sectioned bar sample 120mmA15mmR 15mmH) and sectioned fan sample (91mmR158mmH15mmA) to well measure the stress distribution in limited beam time. The residual stress distribution of the large axle samples was obtained in three directions (axial(A), radial(R) and hoop(H)) from the surface to the core. Unlike previous studies that only focused on the axial residual stresses of the axle, we found that the hoop residual stresses also have considerable values, which verified the necessity of 3D residual stress testing. Subsequently, according to the residual stress field and basic mechanical properties of the S38C axle obtained by experiments, the 3D residual stress field is reconstructed in the real axle by using an iterative technique. These results are much valuable to reveal the fatigue failure behavior of high-speed railway axles after surface strengthening and to optimize the non-destructive inspection interval.
菖蒲 敬久
no journal, ,
加工された構造材料内部には様々な残留応力が発生している。本講演では材料に対する高い透過力を持つ中性子を活かした応力測定技術に関して紹介する。
岩本 ちひろ*; 高村 正人*; 栗原 諒*; 徐 平光; 鈴木 康介*; 高橋 進*; 山本 和喜; 菖蒲 敬久; 大竹 淑恵*
no journal, ,
中性子回折による応力測定には、回折線ピークの微小なシフトを測定するために高い回折線測定分解能が必要である。大型施設では、回折線測定分解能向上のためにチョッパー機構やポイズンモデレータなどの短パルス化デバイス導入が一般的である。しかしながら、これらのデバイスは、ビーム強度を低下させ、かつ追加遮蔽導入によるシステムの大型化にもつながる。そのため中性子ビーム強度の低い小型中性子源の現場導入を前提とした開発には不向きである。本研究では、中性子線源より下流側で中性子ビームの長パルス化を引き起こす"遅延中性子"に着目し、中性子ビーム強度と回折線測定分解能の間のトレードオフの関係を打開するための2つの開発を行なった。ひとつは、遅延中性子の発生を防ぐ非結合型コリメータシステムの開発、もうひとつは遅延中性子による長パルス化の影響を分離できる新しい回折線フィッティング関数を導入した解析法である。理化学研究所の小型加速器中性子源RANSのビームラインにおいて、これらの手法を取り入れてBCC鉄粉回折線を測定し、改善前のセットアップ時における回折線分布と比較した結果を図2に示す。(211)格子面からの回折ピークに対して、検出された回折中性子収量が非結合型コリメータシステムを使用することで2倍増加させながら、ひずみ分解能6.810を達成した。これはヤング率が約200GPaの鉄鋼材料の応力を130MPaまで測定可能であることを示している。また、S45C試料に応力を付加させた既知応力サンプルからの回折中性子トライアル測定を行った。その結果500MPa
200MPaの圧縮応力を格子ひずみから同定することに成功した。
Qin, T. Y.*; Hu, F. F.*; 徐 平光; Zhang, H.*; Zhou, L.*; Ao, N.*; Su, Y. H.; 菖蒲 敬久; Wu, S. C.*
no journal, ,
Gradient compressive residual stress with a depth of several millimeters exists in railway S38C hollow axles subject to surface induction hardening, which is a challenging problem for structural integrity assessment. To address this, the axial, hoop, and radial residual stress values inside the axles are measured by neutron diffraction technology. By integrating the limited neutron diffraction data, an innovative nodal stress based coordinate assignment (INSCA) approach was then proposed, to numerically reconstruct the global initial residual stress field in three dimensions for S38C axles. The comparison between simulations and experiments clearly show that approximately 515 MPa (axial), 710 MPa (hoop), and 43 MPa (radial) compressive residual stresses were retained underneath the induction hardened martensite layer, which also validates the newly-developed INSCA method. By including the measured axial- and hoop-direction residual stresses, the crack propagation behavior of railway S38C axles were investigated, in terms of fracture mechanics. It was clearly shown that the presence of compressive residual stress leads to a lower driving force of crack propagation, in terms of stress intensity factor range (
). Such smaller also indicates that this compressive residual stress can effectively prolong the service lifetime of high-speed railway axles subjected to induction hardening treatment.
徐 平光; 岩本 ちひろ*; 山本 和喜; 諸岡 聡; 高村 正人*; Wu, S.*; 大竹 淑恵*; 菖蒲 敬久
no journal, ,
Considering the large potential applications of neutron diffraction techniques, close cooperation has been carried out to realize the rapid development of various neutron instruments, involving in the steady-state reactor neutron source at Japan Research Reactor No.3 (JRR-3), the large spallation neutron source at J-PARC, the compact neutron source at RANS. Based on the experience of developing the TAKUMI time-of-flight texture measurement technique at J-PARC neutron facility, the high stereographic angle resolution has been utilized to the panel division of the RANS neutron position-sensitive detector to realize the bulk texture evaluation of IF steel using a compact neutron source. Furthermore, the angle dispersive neutron diffractograms from all sample orientations during the RESA neutron diffraction experiment at JRR-3 neutron facility have been employed to carry out the Rietveld texture analysis simultaneously and to realize the reliable texture evaluations of complex crystal structure materials. Nondestructive stress measurement contributes significantly to the design and manufacture of mechanical structures aimed at high performance, high reliability, and long life, and improves the reliability and structure integrity of a wide range of machinery and structures, including machine gears, high-speed train axles, automobile and rocket engines, infrastructure structures, and welded structures simulating power plants, etc. Our recent neutron transport simulation about RANS has already reproduced the measured compact neutron diffractograms of BCC Fe powder at various stereographic orientations, suggesting the future simulation work will be highly valuable to optimize the related technical conditions of RANS neutron instruments for compact stress measurements.
