Journal of the Society of Materials Science, Japan

Analysis of Stress Intensity Factors for a Three Dimensional Bent Surface Crack

Yukitaka MURAKAMI, Chu SAKAE

1992 Volume 41 Issue 467 Pages 1214-1220
Published: August 15, 1992
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.41.1214

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The analysis of stress intensity factors K_I, K_II and K_III by the body force method was developed for a three dimensional bent surface crack which consists of plural crack planes. The stress intensity factors for various types of bent rectangular cracks at the surface of a semi-infinite body were numerically calculated.
The stress intensity factor K_θ which prescribes the stress field of the tangential stress σ_θ in the polar coordinate system (r, θ) at the crack tip was analyzed. The validity of Murakami's approximate formula: K_θmax≈0.650σ₀√π√area_P (area_P: crack area projected onto the plane perpendicular to the maximum remote principal stress σ₀) proposed for an arbitrarily shaped single plane surface crack was examined for various bent surface cracks. It was confirmed that Murakami's formula can be applied to most of bent cracks without loss of accuracy except for strongly bent V-shaped and L-shaped cracks. Furthermore, if one assumes a small amount of crack growth at the tip of strongly bent V-shaped and L-shaped cracks to the direction perpendicular to σ_θmax, Murakami's formula can be applied widely without loss of accuracy.

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Study on Failure Assessment Diagram Based on the Concept of Overall Strain

Kouji MICHIBA, Takashi SHIMAKAWA

1992 Volume 41 Issue 467 Pages 1221-1226
Published: August 15, 1992
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.41.1221

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A preferable failure assessment diagram (FAD) is recommended in the latest CEGB R6 Rev. 3, depending on the categories of assessment. However, FAD defined by the applied stress/net section plastic collapse stress ratio (Lr) as the abscissa is not necessarily useful for assessing the integrity of structures suffering the strain over the full yielding, for example, in the case of high ductile structual components.
In this paper, a modified FAD for the estimation of ductile fracture behavior is proposed based on the concept of overall strain. For the purpose of confirming the validation of the proposed FAD experimentally, the FAD is compared with the reference data of fracture tests using center cracked panel specimens and compact tension specimens of 304 austenitic stainless steel at room temperature and 550°C. It is concluded that the proposed FAD can express the ductile fracture behavior in the strain region over the full yielding more reliably than the conventional R6 FAD.

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Evaluation of Cleavage Fracture Toughness by Statistical Local Fracture Criterion Approach

Tetsuya TAGAWA, Takashi MIYATA, Akio OTSUKA

1992 Volume 41 Issue 467 Pages 1227-1233
Published: August 15, 1992
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.41.1227

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Statistical behavior of the cleavage fracture for several types of steels was experimentally and analytically investigated. Two types of low alloy steels with different grain size, a conventional mild steel and a simulated HAZ of steel welds were tested. The weakest link model was introduced to describe the scatter of the cleavage fracture stress and the fracture toughness. Based on the statistical local fracture criterion approach, a correlation between the cleavage fracture toughness in the transition temperature region and the cleavage fracture stress was investigated. Theoretical consideration on the correlation was done on the basis of FEM analysis for fracture toughness specimens. The experimental results showed a good agreement with the analytical prediction of the correlation. The validity of deterministic local fracture criterion in the previous work was also confirmed by the present statistical approach.

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Evaluation of Degradation of Cr-Mo-V Casting Steel using a Miniatured Charpy Specimen

Isamu YAMAMOTO, Futoshi MAEDA, Toshiro KOBAYASHI, Masuo MORITA

1992 Volume 41 Issue 467 Pages 1234-1240
Published: August 15, 1992
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.41.1234

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There are two methods of evaluation of material degradation, that is, destructive and non-destructive. In this study, the degradation of Cr-Mo-V casting steel which has been used for about ten years as the internal casing of turbine was evaluated using a miniature Charpy impact specimen. The miniature specimen (thickness: 1.5mm, width: 1.5mm, length: 16mm) was taken from the Cr-Mo-V casting steel and the ductile-brittle transition curve was measured by the instrumented Charpy impact test. Moreover, the effects of specimen dimension on the ductile-brittle transition temperature (DBTT) and upper shelf energy and a relationship between the change of DBTT and micro-structural properties were investigated. The results of this study are summarized as follows:
(1) When the specimen dimension becomes smaller, the difference of DBTT due to the difference in degradation becomes smaller.
(2) The degradation of material can be successfully evaluated with a 1/6 size specimen.
(3) The change of DBTT can be predicted from the changes of hardness, innergranular hardness, diameter of precipitated carbide and depth of etched grain boundary groove.

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Prediction Method of Fracture Toughness K_IC Transition Curve from Charpy V-Notch Impact Test Results

Tadao IWADATE, Hiroyuki TAKEMATA

1992 Volume 41 Issue 467 Pages 1241-1247
Published: August 15, 1992
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.41.1241

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This paper presents two methods to predict the fracture toughness K_IC transition curve of low alloy steels using Charpy V-notch impact test results and tensile properties. One is the method using a single master curve of the K_IC/K_IC-US versus excess temperature relationship of each material where K_IC-US is the upper shelf fracture toughness and the excess temperature is a test temperature minus FATT. Another method is the one using a K_IC/K_IC-US versus T-T₀ master curve and the temperature shift ΔT between lower shelf fracture toughness K_IC-LS and Charpy impact transition curves, where To is the temperature showing 50 percent of K_IC-US of the material.

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Effect of Hydrogen-Charging on the Fatigue Crack Propagation Behavior of Ti-13V-11Cr-3Al Alloy

Keijiro NAKASA, Masaaki HORITA, Hiroshi SATOH

1992 Volume 41 Issue 467 Pages 1248-1254
Published: August 15, 1992
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.41.1248

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In order to investigate the influence of hydrogen on the fatigue crack propagation behavior of β-titanium alloy, two types of fatigue tests were carried out. One was the fatigue test in air on the hydrogen-precharged specimens, where the charging was carried out in H₂SO₄ aqueous solution electrolytically under the current density i_c of 1000A/m² for 260ks. Another was the fatigue test under electrolytic hydrogen-charging in H₂SO₄ aqueous solution at i_c=1000 or 3000A/m². Both test results were compared with the result obtained from the fatigue test of the non-charged specimen in air.
The fatigue crack propagation rate da/dN of the precharged specimen was much larger than the da/dN of the non-charged specimen in all the range of stress intensity factor, ΔK. The crack propagation rate da/dN under hydrogen charging was larger than the da/dN of the non-charged specimen only when ΔK was smaller than 15MPa·m^1/2, and the da/dN was much smaller than that of the precharged specimen. The fatigue fracture surface of the specimens which were hydrogen-charged by both methods revealed the cleavage fracture, which corresponded to the decrease in cohesive strength of the cleavage plane of β-phase by the dissolution of hydrogen atoms.

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Long-term Creep Crack Growth Behaviour of 316 Stainless Steel

Masaaki TABUCHI, Kiyoshi KUBO, Koichi YAGI

1992 Volume 41 Issue 467 Pages 1255-1260
Published: August 15, 1992
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.41.1255

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The long-term creep crack growth tests of more than 10000 hours were conducted using CT specimens of 316 stainless steel at 650°C and 750°C. The crack growth rates in the long-term tests were faster than those in the short-term tests at 650°C. This difference was caused by the difference in creep fracture mode. The creep crack which gave wedge-type or cavity-type intergranular fracture showed higher growth rate than that under transgranular fracture. The difference in crack growth rate between the wedge-type intergranular and transgranular fracture modes was attributed to the effect of creep ductility. The crack growth under cavity-type fracture, which was observed at higher temperatures and longer creep tests, should be investigated by taking into account the accumulated creep damage ahead of the crack tip.

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Fatigue Small Crack Growth in a Single Crystal Ni-Base Superalloy at Elevated Temperature

Masakazu OKAZAKI, Tetsuya IMAI, Takayuki SATOH, Shinichiroh NOHMI

1992 Volume 41 Issue 467 Pages 1261-1267
Published: August 15, 1992
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.41.1261

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Strain-controlled low-cycle fatigue tests were carried out on a single crystal Ni-base superalloy, CMSX-2, under a strain ratio of zero at 873K in air. The CMSX-2 showed higher fatigue strength, compared with some other kinds of polycrystalline Ni-base superalloys or with a directionally-solidified superalloy, CM247LC-DS. The fatigue small crack growth behavior was also investigated by using a replication technique. The small crack growth rate increased proportionally with increasing crack length on the macroscopic level. On the microscopic level, however, they were significantly affected by the microstructure. From the microscopic observations of the crack path, fracture surface and deformation around the crack tip, it was found that the small cracks propagated in the γ phase matrix on {100} cubic planes, accompanying with negligible deformation of γ' phases, when the crack length was short enough. As the crack became longer, on the other hand, the crack propagation planes were converted onto {111} slip planes. In this stage the crack rapidly grew by the slip plane decohesion mechanism, cutting the γ' phases. The above transition of crack propagation plane occurred when the stress intensity factor range reached a critical value. Based on the foregoing results, the differences in the small crack growth rate and the fatigue strength between CMSX-2 and CM247LC-DS were also discussed.

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Effect of Surface Grinding on Flexural Strength of Alumina

Kaname MORI, Hiromi YOSHINARI, Soji NENNO, Takeo YOKOBORI

1992 Volume 41 Issue 467 Pages 1268-1272
Published: August 15, 1992
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.41.1268

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Strength of ceramics depends on the structure that is based on the manufacturing process, the loading condition and the environment. It also depends on the size, the geometry and the mechanical working conditions of the component. In this study, the effect of surface grinding on the flexural strength of alumina is investigated. The flexural strength of alumina ground in the parallel direction to the specimen significantly increased with the size of grinding grit. On the contrary, the strength of alumina ground in the transverse direction to the specimen strongly decreased with the size of grinding grit.

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An Evaluation System for Impact Damage and Erosion of Ceramic Gas Turbine Components

Seiichi HAMADA, Tetsuo TERAMAE

1992 Volume 41 Issue 467 Pages 1273-1278
Published: August 15, 1992
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.41.1273

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A practical computing system was developed to analyze the impact damage and erosion of the ceramic gas turbine components in the gas flow mixed with solid particles. This system includes flow analysis in the blade row supplemented by boundary layer calculation, particle trajectory analysis, impact fracture and erosion analysis.
The fracture analysis impacted by solid particles is based on our proposed method which treats the damage of ceramics as the stiffness reduction. This method was implemented into a general purpose dynamic stress analysis program, DYNA3D. The validity of our proposed method was verified by the results of numerical simulation regarding the impact tests using ceramic plates and some spherical particles.
As for the erosion analysis, an empirical equation obtained from the erosion tests at elevated temperatures was implemented into the code for the analysis of blade erosion. In many advanced fuels, solid particles may be formed as by-products of combustion. Therefore the problem of solid particle erosion has great importance in industrial gas turbines viewed from the aerodynamic performance.

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Cycle and Crack Length Dependence of Crack Growth Characteristics in Silicon Nitride

Akio OTSUKA, Hiroto SUGAWARA, Sung-Keun YOO

1992 Volume 41 Issue 467 Pages 1279-1284
Published: August 15, 1992
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.41.1279

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Crack growth tests on silicon nitride have been made to clarify the crack growth characteristics under static and cyclic loading. The test results have shown that, under static loading, the crack growth rate decreases with an increase of crack extension until the crack is arrested, while under cyclic loading, the crack grows with almost constant velocity without being arrested, even in the range of K values where no growth is observed under static loading. Crack length dependence of “K-V relation” (K: stress intensity factor, V: crack velocity) and crack velocity dependence of “K-Δa relation” (Δa: crack extension) have been obtained from the crack growth data concerning the relations between crack velocity and crack extension under static loading and cyclic loading. Crack velocity is higher for smaller cracks than larger cracks at the same K values and the effect of stress cycling in accelerating crack growth is much larger at smaller K values. The effect of stress cycling is obvious in crack growth tests even in the material in which no effect of stress cycling is observed on cyclic fatigue tests on smooth specimens.

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Effects of Fiber Content and Fiber Orientation on Fatigue Strength of Short-Fiber Reinforced Plastic

Yoshiaki AKINIWA, Shoji HARADA, Yoshinori YAGYU, Masahiro NAKANO

1992 Volume 41 Issue 467 Pages 1285-1291
Published: August 15, 1992
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.41.1285

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The effects of fiber content and fiber orientation on the mechanical properties and the fatigue strength of a short-fiber reinforced plastic were investigated. Thin plates of carbon short-fiber reinforced polycarbonate were injection molded. An image processing analyzer was used to measure the fiber content and the fiber orientation. The distribution of fiber length was almost unique irrespective of the fiber content. The hardness, Young's modulus and tensile strength became higher with increasing the fiber content. Smooth specimen and center-notched plate were fatigued under cyclic tension-compression. The propagation behavior of fatigue cracks was observed together with the measurement of crack closure. The fatigue strength at finite life and the resistance of crack propagation became higher with increasing the fiber content. The relation between crack propagation rate and the effective stress intensity factor divided by the Young's modulus was almost unique, irrespective of the fiber content or fiber orientation.

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Effect of Fiber Orientation on the Mode I Interlaminar Fracture Behavior of CF/EPOXY Laminates

Iton CHOU, Isao KIMPARA, Kazuro KAGEYAMA, Isamu OHSAWA

1992 Volume 41 Issue 467 Pages 1292-1298
Published: August 15, 1992
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.41.1292

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The mode I delamination resistance and delamination growth behavior of CF/EPOXY laminates were investigated. DCB (Double Cantilever Beam) test was employed to study the effect of fiber orientation on the mode I interlaminar fracture behavior. Investigated in this study were the delamination growth behavior at [0/0], [30/-30], [60/-60] and [0/90] interlaminae of fabricated laminates with unidirectional prepreg as well as that at [(0/90)/(0/90)] interlamina of fabricated laminate with plain weave prepreg. The delamination resistance was estimated with the mode I energy release rate, G_I. The highest value of G_IC, G_I at crack initiation, was obtained at the [(0/90)/(0/90)] interlamina, and the lowest one was at the [0/0] interlamina. The delamination at [0/0] interlamina showed a stable fracture behavior. On the other hand, the delamination at [(0/90)/(0/90)] interlamina showed a crosslinked stable-unstable fracture behavior. The values of G_IR, G_I during crack propagation, were almost constant macroscopically in these two cases. Contrary to it, the delamination growth at [30/-30], [60/-60] and [0/90] interlaminae showed the R-curve characteristic. The values of G_IC at these interlaminae had little difference. Especially the values of G_IC at [30/-30] and [60/-60] interlaminae were almost equal to the value of G_IC at [0/0] interlamina. However, the values of G_IR at [30/-30], [60/-60] and [0/90] interlaminae had very big difference. G_IR at [60/-60] interlamina, compared with G_IR at [30/-30] interlamina, and G_IR at [0/90] interlamina, compared with G_IR at [60/-60] interlamina, got higher immediately as the crack propagation proceeded. The fracture surface observation by SEM was also conducted. Consequently the effect of fiber orientation on the mode I interlaminar fracture behavior was clarified.

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Evaluation of the Fatigue Strength of Adhesive Joints Based on Interfacial Fracture Mechanics

Ryoji YUUKI, Jin-Qiao LIU, Jin-Ouan XU, Toshiaki OHIRA, Tomoyoshi ONO

1992 Volume 41 Issue 467 Pages 1299-1304
Published: August 15, 1992
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.41.1299

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Fatigue tests of the single lap adhesive joints of thin mild steel plates were carried out and the effect of the thickness of the adhesive and plate on the fatigue strength was investigated. The boundary element two-dimensional elastostatic analysis was also carried out and the effect of the adhesive and plate thickness on the stress distribution at the interface was investigated. Moreover, to evaluate the fatigue strength of adhesive joints quantitatively, the stress intensity factors for interface cracks in the adhesive joints were analyzed by using the BEM. The extrapolation method proposed by the authors was used to determine the stress intensity factors. It was found that the stress intensity factor range ΔK_i=√ΔK²₁+ΔK²₂ can well characterize the fatigue strengthes of SLJ type adhesive joints with different adhesive and plate thicknesses. It is expected that the interfacial fracture mechanics is very useful for evaluating the fatigue strength of the adhesive joints.

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Adhesive Strength of FRP Lining on Concrete

Yoshiki URAKAMI, Kenji SEO, Fumio NOKATA, Masanori IOKA, Shojiro TAKAS ...

1992 Volume 41 Issue 467 Pages 1305-1310
Published: August 15, 1992
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.41.1305

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Recently, it has been reported that the corrosive damage of concrete structures occurs at many waste water treatment facilities. In order to prevent this problem, FRP lining is being applied on the concrete surface. In this application, the lined FRP should show a fairly high adhesive strength to the concrete surface.
Generally a Kenken-type adhesive strength tester is used to evaluate the adhesive strength between them. But it was revealed that this method could not evaluate such an adhesive strength precisely. Therefore, in this report, it has been studied to develop a new practical way to evaluate this adhesive strength.
In this new method, the real adhesive strength between lined FRP and cement mortar was measured in such a way that only a vertical peeling force was loaded to the end of the FRP. The results obtained were discussed in terms of stress intensity factor K as a fracture mechanical parameter.

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Polymers in Concrete-Recent Development-

1. Polymers in Concrete as Composite Construction Materials

K. Okada

1992 Volume 41 Issue 467 Pages 1311-1315
Published: August 15, 1992
Released on J-STAGE: June 03, 2009

DOIhttps://doi.org/10.2472/jsms.41.1311

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