研究者詳細 - 多田　直哉

多数き裂型損傷を受けた材料の直流電位差に関する解析

その他リンク： https://jlc.jst.go.jp/DN/JALC/00049752588?from=CiNii

多田直哉, 林義仁, 北村隆行, 大谷隆一

日本機械学会論文集. A編 63 ( 614 ) 2235 - 2242 1997年10月

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

The electric field in a conductive material with multiple circular cracks is analyzed by means of the crack-flow modification method (CFMM). It is found that the increase in the potential difference of the cracked meterial normalized by the potential difference without cracks, ΔV/V₀, is in proportion to the product of the effective volumetric crack density and the mean of the cubed crack radius, n_eff[γ³]_m. This universal relationship is also valid for multiple semi-circular cracks on the surface of the material and gives the physical meaning of damage detected by the direct current electrical potential method.

DOI： 10.1299/kikaia.63.2235

キャビティ分布と各種クリープ損傷パラメータの関係についての解析的検討

その他リンク： https://jlc.jst.go.jp/DN/JALC/00049752779?from=CiNii

Relationship between creep damage parameters and distribution of creep cavities on grain boundaries 査読

N. Tada, T. Kitamura, R. Ohtani

Computer Aided Assessment and Control of Localized Damage - Proceedings of the International Conference 535 - 542 1996年

Characterization of creep-fatigue fracture of type 304 stainless steel based on initiation and growth of small cracks

T. Kitamura, R. Ohtani, N. Tada, W. Zhou

American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP 303 377 - 382 1995年

多田直哉, 北村隆行, 大谷隆一

日本機械学会論文集 A編 59 ( 565 ) 2074 - 2080 1993年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

Analytical discussion was given on the relationships between actual cavity distribution and creep damage parameters such as volume fraction of cavities, effective cross-sectional area and the 'A' parameter. The relationships between cavity distribution and these damage parameters were derived using a very simple probabilistic model where creep cavities on a grain boundary facet were initiated and grew, depending only on the macroscopic stress (or strain rate) acting on the facet. The exact relationships were represented by Eqs. (16), (20) [or (23)] and (26), respectively. These expressions take into account the effect of the size and direction of grain boundary facets. Damage evolution during creep and creep-fatigue can be calculated using these equations.

DOI： 10.1299/kikaia.59.2074

その他リンク： https://jlc.jst.go.jp/DN/JALC/00022973115?from=CiNii

内部微小欠陥分布の逆解析による推定

多田直哉, 大谷隆一, 北村隆行, 山田雅也

日本機械学会論文集 A編 59 ( 558 ) 381 - 386 1993年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

This paper deals with a method for predicting the three-dimensional distribution of internal defects from the two-dimensional observation of intercepted defects on an inspection plane by an inverse analysis. At first, the fundamental relationships between them were analytically derived on the basis of a statistical model where multiple penny-shaped cracks in an infinite body were intercepted by an inspection plane. The validity of the method was confirmed by a numerical simulation. It was, moreover, applied to small creep fatigue cracks distributing in a smooth specimen of a Type 304 stainless steel, and the volumetric density and the distribution of crack size were successfully evaluated.

DOI： 10.1299/kikaia.59.381

粒界き裂の発生と成長挙動の相違から見たクリープ疲労の破壊プロセスと寿命特性

その他リンク： https://jlc.jst.go.jp/DN/JALC/00019660639?from=CiNii

多田直哉, 北村隆行, 大谷隆一

材料 41 ( 469 ) 1545 - 1550 1992年10月

記述言語：日本語出版者・発行元：社団法人日本材料学会

Fracture process of creep fatigue in a Type 304 stainless steel at 923K can be divided into two types ; "crack initiation type" and "crack growth type". The former is characterized by multiple small cracks initiating one after another along grain boundaries on the specimen surface and coalescing each other at the late stage of failure life, when the material is subjected to relatively large strain ranges in slow tension-fast compression (so called c-p type) strain waveforms. This failure is mostly governed by crack initiation. The latter is distinctive of the initiation and growth of little coalescence, which is revealed under small strain ranges and/or in slow-slow (c-c type) or slow very slow (c-s type) strain waveforms. Therefore, the failure life is controlled by the growth rate of small cracks in this case. In this study, a numerical simulation was done based on a model of two kinds of driving forces for crack initiation and crack growth with random fracture resistance of grain boundaries, in order to distinguish between the two types of fracture process and to estimate the failure life in relation to the cracking behavior.

DOI： 10.2472/jsms.41.1545

クリープ疲労微小き裂発生・成長の数値シミュレーションによる高温構造材料の余寿命診断方法

その他リンク： https://jlc.jst.go.jp/DN/JALC/00017478090?from=CiNii

北村陸行, 多田直哉, 大谷隆一

日本機械学会論文集 A編 57 ( 540 ) 1732 - 1737 1991年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

In order to achieve the objective of securing the reliability of high-temperature components, it is necessary to establish a method for predicting the remaining life of their materials subjected to severe creep-fatigue damage. It was reported by the authors that multiple small cracks initiated along grain boundaries on the specimen surface at the very early stage of life in creep-fatigue and their growth and coalescence formed the main crack which induced the failure. Moreover, the process of small crack initiation and growth showed random behavior due to microstructural inhomogeneity. A stochastic model was proposed and the failure process was numerically simulated by means of the Monte Carlo method. This paper provides a scheme of the small-crack-simulation-method for the evaluation of remaining life of the materials in high-temperature components, which is an integration of our previous studies and is summarized in a flow chart.

DOI： 10.1299/kikaia.57.1732

直流電位差法による半だ円表面き裂形状・寸法測定のための電位解析

その他リンク： https://jlc.jst.go.jp/DN/JALC/00010853924?from=CiNii

多田直哉, 坂之上悦典, 北村隆行, 大谷隆一

日本機械学会論文集 A編 56 ( 522 ) 259 - 264 1990年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

It is necessary for determination of crack size and shape by means of D.C. potential drop technique to know electric potential distribution at the surface of cracked body beforehand. The potential distribution on a body with semi-elliptical surface-crack is investigated in this paper. The results obtained are summarized as follows. (i) Exact distribution is derived as Eqs. (1)∼(3) for semi-infinite body with a semi-elliptical surface-crack. As it requires numerial integral to evaluate the potential, a simple approximation method (Eqs. (14) and (15)) is proposed for convenience. It is confirmed by numerical analysis that the error of approximation is very small. (ii) We propose an easy method to make a cracked body with an arbitrary crack shape and size for the calibration of electric potential distribution. Plate specimens with a semi-elliptical surface-crack are made of a wood metal, and the potential distribution is examined experimentally. The values measured coincide the solution of infinite body (see (i)) except that the crack depth is nearly equal to the thickness of plate. It implies that specimen's back surface affects fairly little on the potential distribution at the front surface.

DOI： 10.1299/kikaia.56.259

ＳＵＳ３０４の結晶粒界長さおよび角度分布とそのクリープ疲労微小き裂発生・成長に及ぼす影響

その他リンク： https://jlc.jst.go.jp/DN/JALC/00000700672?from=CiNii

北村隆行, 多田直哉, 栗山義英, 大谷隆一

日本機械学会論文集 A編 56 ( 524 ) 702 - 707 1990年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

In order to elucidate the microstructural effect on initiation and growth of intergranular small cracks under creep-fatigue conditions, we discuss the randomness of grain-boundary length and inclination. This study consists of the following investigations; (1) the length and inclination of grain boundaries of a stainless steel, SUS 304, are measured by means of image analysing system; (2) a numerical generation method of polycrystal grains is developed on the basis of an isotropic grain growth model; and (3) the crack length and inclination are measured by means of an image analysing system under creep-fatigue conditions. The results obtained from each investigation are summarized as follows, respectively. (A) The grain-boundary inclination of the steel is uniformly distributed and the length between adjacent triple points has a wide scatter between 10 and 100 μm. The length and the inclination are independent of each other (B) The simulated length and inclination of grain-boundaries coincides well with the actual grains of the steel. This method is useful for the stochastic simulation of initiation and growth of microstructurally small cracks, which will be reported in the next paper. (C) Cracks preferentially initiate on the grain boundaries perpendicular to the stress axis by a span between adjacent triple points. The crack growth rate shows a little dependence on the crack tip angle.

DOI： 10.1299/kikaia.56.702

クリープ・疲労条件下の微小き裂発生・成長に及ぼす圧縮ひずみ速度の影響

その他リンク： https://jlc.jst.go.jp/DN/JALC/00002568416?from=CiNii

北村隆行, 多田直哉, 阿部宗昭, 弓田正人, 大谷隆一

日本機械学会論文集 A編 56 ( 523 ) 575 - 581 1990年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

In order to clarify the effect of the compressive strain rate on initiation and growth of small cracks under creep-fatigue condition, the following tests were conducted using smooth specimens of Type 304 stainless steel at 650°C in air, (i) slow-tension and fast-compression (c-p type fatigue), (ii) slow-tension and slow-compression (c-c type fatigue), and (iii) slow-tension and very-slow-compression (c-s type fatigue). The results obtained are summarized as follows. (1) Multiple small cracks initiated and grew at random along grain boundaries being nearly perpendicular to the stress axis at each specimen surface. (2) The compression-going strain rate affected the crack initiation life and the crack density. The c-p type fatigue brought about the shortest initiation life and the highest crack density, and the c-s type fatigue did the longest and the lowest. (3) The crack growth rate was not influenced by the compression-going strain rate but was primarily governed by the tension-going strain rate. (4) The difference of life between c-p type and c-s type fatigue was caused by the difference of crack initiation life and crack coalescence. The highest crack density in the c-p type fatigue made the crack coalesce easily to bring about a long crack.

DOI： 10.1299/kikaia.56.575

粒界破壊抵抗分布モデルによるクリープ疲労微小き裂の発生と初期伝ぱのシミュレーション

その他リンク： https://jlc.jst.go.jp/DN/JALC/00001677843?from=CiNii

Numerical simulation of initiation and early propagation of creep-fatigue small cracks based on a model of random fracture resistance of grain boundaries

R. Ohtani, T. Kitamura, N. Tada

American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP 163 123 - 127 1989年

大谷隆一, 北村隆行, 村山英明, 多田直哉

日本機械学会論文集 A編 54 ( 503 ) 1312 - 1316 1988年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

A stochastic model and a method of simulation of the initiation and the early propagation of creep-fatigue small cracks along grain boundaries were proposed. In the model, grain boundaries between two adjacent triple points were projected and linked on a straight line perpendicular to the applied stress axis, and their length was given as random variables of a normal distribution. The grain boundaries had their own fracture resistances, the magnitudes of which were given as uniform random numbers. The fracture resistance of each grain boundary decreased by a constant magnitude corresponding to the driving force of one fatigue cycle. When the resistance become zero or a negative value, the grain boundary was assumed to fracture and to yield an intergranular facet of small crack. Based on this model, a numerical calculation was done for a smooth specimen of 304 stainless steel subjected to the slow-fast strain cycle of 1%-total strain range at 923K in a vacuum. The result of simulation on crack density, cumulative probability of crack length, and crack propagation rates coincided with the experimental results.

DOI： 10.1299/kikaia.54.1312

その他リンク： https://jlc.jst.go.jp/DN/JALC/00220856098?from=CiNii

変動温度下の高温疲労き裂伝ぱ

大谷隆一, 北村隆行, 多田直哉

日本機械学会論文集 A編 53 ( 490 ) 1030 - 1036 1987年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

In order to investigate crack propagation behavior of thermal fatigue on the basis of non-linear fracture mechanics, crack propagation tests were conducted for isothermal fatigue at several temperatures and for cyclic temperature fatigue. The results obtained were summarized as follows. (1) The fracture mechanics laws in isothermal fatigue dl/dN-ΔJ_f and dl/dN-ΔJ_c relations where dl/dN was crack propagation rate, ΔJ_f was fatigue J-integral range and was ΔJ_c was creep J-integral range) showed little dependence on temperature. (2) A simple evaluation method of the values of ΔJ_f and ΔJ_c in thermal fatigue was proposed. (3) Crack propagation under cyclic temperature could be divided into two types which were cycle-dependent and time-dependent. dl/dN had good correlations with ΔJ_f and ΔJ_c for each type, respectively. (4) The transient condition between two types was given by a function of ΔJ_f and ΔJ_c. (5) The same fracture mechanics laws were obtained in isothermal and cyclic temperature fatigue.

DOI： 10.1299/kikaia.53.1030