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Li, S.; 山口 義仁; 勝山 仁哉; Li, Y.; Deng, D.*
Proceedings of ASME 2023 Pressure Vessels and Piping Conference (PVP 2023) (Internet), 7 Pages, 2023/07
In this work, a framework was proposed on the comprehensive assessment of hardness and welding residual stress in Type 316 austenitic stainless steel welded joints. Firstly, an 8-pass butt-welded joint made of Type 316 stainless steel was fabricated. Finite element analysis of the welded joint was performed to investigate hardness and welding residual stress distributions. The grain growth model was developed for the hardness prediction. The Chaboche combined isotropic-kinematic strain hardening model and time-temperature dependent annealing model were adopted. The relationships between the Vickers hardness and the uniaxial plastic strain as well as grain size were collected from published literatures. The simulation results of the grain size and accumulated equivalent plastic strain were used for the hardness prediction of the welded joint. The predicted hardness was compared with the experimental data of hardness mapping. The distribution of welding residual stress on the outer surface of the welded pipe was measured by using the X-ray diffraction method and strain gauge method, respectively. The predicted welding residual stresses were compared with the measurements. The results obtained showed that the developed numerical approach can predict the hardness and welding residual stress of Type 316 stainless steel welded joints with satisfactory accuracy. The effects of structural constraint and heat input on the hardness and welding residual stress will be investigated as further works, as described in the proposed framework.
林 真琴*; 菖蒲 敬久
Residual Stress, p.100 - 132, 2021/00
構造材料は使用中に疲労破壊したり、応力腐食割れを発生することがある。その原因の1つに構造材料の製造過程における熱処理や加工により発生する残留応力がある。その残留応力を測定する手法にはさまざまなものがある。本書では実験室X線や放射光X線、中性子に始まり、超音波や磁気的な手法による測定技術を紹介する。加えて、各種材料における加工や溶接による残留応力の測定例、実機における測定例、残留応力の静的および繰返し荷重による変化挙動、さらにはその変化挙動に基づく疲労余寿命の評価手法などを概説する。
生島 一樹*; 木谷 悠二*; 柴原 正和*; 西川 聡*; 古川 敬*; 秋田 貢一; 鈴木 裕士; 諸岡 聡
溶接学会論文集(インターネット), 35(2), p.75s - 79s, 2017/06
In this research, to investigate the effect of shot peening on operation, an analysis method to predict the behavior of stress distribution on shot peening was proposed. In the proposed system, the load distribution on the collision of shots was modeled, and it was integrated with the dynamic analysis method based on the Idealized explicit FEM (IEFEM). The thermal elastic plastic analysis method using IEFEM was applied to the analysis of residual stress distribution of multi-pass welded pipe joint. The computed residual stress distribution was compared with the measured residual stress distribution using X-ray diffraction (XRD). As a result, it was shown that the both welding residual stress distribution agree well with each other. Considering the computed welding residual stress distribution, the modification of stress distribution due to shot peening was predicted by the proposed analysis system.
鈴木 裕士; Holden, T. M.*; 盛合 敦; 皆川 宣明*; 森井 幸生
材料, 54(7), p.685 - 691, 2005/07
本研究では、高張力鋼の一つであるNi-Cr鋼を用いて製作したX開先突合せ溶接試験片の残留応力分布を中性子回折法により測定し、残留応力発生メカニズムを検討した。始めに、無ひずみ状態における格子定数を測定するために、溶接試験片から幾つかの小片試料を切り出した。小片試料を用いて格子定数を測定した結果、溶接過程において生じたマルテンサイト変態などの相変態が影響して、溶接部近傍で格子定数の増加が認められた。次に、
Fe110, Fe200, Fe211の三種類の回折により溶接試験片の残留応力分布を測定した。塑性ひずみの影響が無いために、それぞれの回折により評価した残留応力分布はほとんど同様な傾向を示していた。また、溶接部近傍における残留応力はNi-Cr鋼の降伏強さの半分程度の引張残留応力であった。高張力鋼では軟鋼と比べて相変態による膨張量が大きいこと、また、引張残留応力がかなり低い温度となってから発生し始めるために、残留応力が降伏応力に至らなかったと考えられる。したがって、高張力鋼の中性子応力評価では、塑性ひずみの発生を考慮する必要の無いことを確認した。
鈴木 裕士; 盛合 敦; 皆川 宣明*; 森井 幸生
材料, 54(3), p.339 - 345, 2005/03
中性子応力測定の従来法では、格子ひずみを計算するために、無ひずみ状態の格子定数を正確に把握する必要がある。著者らは、粉末や焼なまし試料などの標準試料を用いて測定した格子定数を用いることなく、三軸残留応力を評価できる中性子応力測定法を開発した。本研究では、この提案した方法を用いて溶接材の残留応力分布を測定した。まず始めに、溶接材料から切り出した小片試料を用いて、溶接材料の格子定数分布を測定した。その結果、HAZ部(熱影響部)に生じたマルテンサイト変態のために、溶接部近傍において格子定数が大きくなる傾向が確認された。提案した方法により評価した格子定数分布もまた、溶接部近傍において大きくなる傾向を示し、また、格子定数の絶対値は、小片試料のそれとほとんど同じであった。したがって、格子定数の分布が存在するような材料であっても、提案した方法を用いることで、格子定数を推定できると考えられる。従来法及び提案した方法により残留応力分布を評価した。その結果、提案した方法により決定した残留応力分布は、従来法により求めた残留応力分布とほとんど同じであった。したがって、提案した方法は、複雑な残留応力状態を有する材料においても、残留応力分布を正確に決定できると考えられる。
Li, S.; 山口 義仁; 勝山 仁哉; Sun, W.*; Deng, D.*; Li, Y.
no journal, ,
Many flaws due to stress corrosion cracking (SCC) have been reported in the heat affected zone of austenitic stainless steel welded joints in nuclear power plants. High tensile residual stresses and hardness induced by the welding process may affect the initiation and propagation of SCC. During the welding thermal cycles, the accumulated strain hardening can be reduced or eliminated below the melting point due to the dynamic recovery, recrystallization, and grain growth of the material, which is known as the annealing effect. Different annealing models were proposed including the single-stage and two-stage annealing models, which are temperature dependent models to eliminate the accumulated strain hardening in one or two steps, and dynamic annealing models, in which the time-temperature dependent annealing effect can be considered. In this study, numerical investigations were carried out to evaluate the effect of different annealing models on the distributions of welding residual stress and accumulated plastic strain. Two butt-welded joints of Type 316 stainless steel were fabricated. The welding residual stresses of the two welded joints were measured using the neutron diffraction method and sectioning method, respectively. Two-dimensional finite element analysis was performed based on Abaqus platform. Chaboche combined isotropic-kinematic strain hardening model was used. The simulation results of welding residual stresses were compared with measurements. The results obtained have shown that the annealing effect can significantly influence the formation of the accumulated plastic strain and residual stresses in Type 316 stainless steel welded joints. The residual stresses will be overestimated if the annealing effect is neglected, or a relatively high value of the annealing temperature is used. The annealing model plays a major role in determining the magnitude of the accumulated plastic strain in the welding simulation.
