Vol. 4 No. 1 CONTENTS

Special issue on Fatigue of Materials
Regular Articles

Special issue on Fatigue of Materials (Vol.4 No.1)

Review Paper (Vol.4 No.1)

THE GROWTH OF SHORT FAIGUE CRACKS:A REVIEW

Arthur J.McEVILY

3

General Papers (Vol.4 No.1)

EVALUATION OF FATIGUE STRENGTH OF WC CERMET- AND 13Cr STEEL-SPRAYED MATERIALS

Takeshi OGAWA, Keiro TOKAJI, Toshikatsu EJIMA, Yoshifumi KOBAYASHI and Yoshio HARADA

12

INITIATION AND GROWTH OF SMALL FATIGUE CRACK IN TiAl INTERMETALLICS AT ELEVATED AND ROOM TEMPERATURE

Yoshiharu MUTOH, Tomoaki MORIYA, Shijie ZHU and Youji MIZUHARA

19

ROLE OF GRAIN BRIDGING DEGRADATION OF SMALL CRACK ON CRACK PROPAGATION BEHAVIOR IN POLYCRYSTALINE ALUMINA UNDER CYCLIC LOAD

Akira UENO and Hidehiro KISHIMOTO

26

FATIGUE CRACK GROWTH ANISOTROPY IN ANNEALED AND PRE-STRAINED COMMERCIALLY PURE TITANIUMS

Kazuhiro KUSUKAWA and Ken-ichi TAKAO

33


Regular Articles (Vol.4 No.1)

General Papers (Vol.4 No.1)

EVALUATION OF MECHANICAL AND THERMAL PROPERTIES OF CUBIC BORON NITRIDE BY AB-INITIO CALCULATION

Yoshitada ISONO, Hirokazu KISHIMOTO and Takeshi TANAKA

39

MOLECULAR DYNAMICS SIMULATION OF HEAT CONDUCION AND THERMAL STRESS IN RELATION WITH CONTINUUM MECHANICS

Takuya UEHARA and Tatsuo INOUE

45

COMPARIS0N OF INVARIANT IMBEDDING AND LAYER-PEELING METHODS IN INVERSE PROBLEM

Tomas NOVOTNY, Eiji MATSUMOTO and Thshinobu SHIBATA

53

BIOMIMETIC COATING OF BONE-LIKE APATITE ON GLASS BEADS

Akiyoshi OSAKA, shinji TAKEMOTO, Satoshi HAYAKAWA and Chikara OHTSUKI

60

ESTIMATION OF CORROSION RESISTANCE OF ZN-0〜30% Al HOT-DIP COATINGS ON STEEL

Yoshihiko TAKANO, Koshi TAKADA, Takashi HATANO, Tetsuya NAKADA and Tatsumi IZEKI

64

Short comunication (Vol.4 No.1)

NEW ADHERENCE-PROOFING METHOD OF FRESH CONCRETE IN MIXER AND AGITATOR TRUCK

Norio SAKAMOTO, Tohru SAKAMOTO, Naoki KATO and Kiyoshi KATO

71


Vol.4 No.1 ABSTRACT


THE GROWTH OF SHORT FAIGUE CRACKS:A REVIEW

Arthur J.McEVILY

Abstract:The behavior of short fatigue cracks differs from that of long cracks because of greater sensitivity to the microstructure, a greater size of the plastic zone relative to crack length, and a lesser extent of crack closure. Advances have been made in the understanding of the fatigue crack growth process of short cracks, and this understanding has been employed in the development of analytical treatments of short fatigue crack growth.The present paper reviews this progress and also discusses the relevance of short fatigue crack behavior to technologically significant areas.

Key Words:Short fatigue cracks, Fatigue crack growth, Microstructure, Crack growth models, Scatter


EVALUATION OF FATIGUE STRENGTH OF WC CERMET- AND 13Cr STEEL-SPRAYED MATERIALS

Takeshi OGAWA, Keiro TOKAJI, Toshikatsu EJIMA, Yoshifumi KOBAYASHI and Yoshio HARADA

Abstract:>Rotating bending fatigue tests have been conducted at a room temperature in laboratory air using specimens of medium carbon steel(S45C), low alloy steel(SCM435) and titanium alloy(Ti-eAl-4V) with high velocity oxy-fuel(HVOF) sprayed coating of a cermet(Wc-12%Co) and S45C with wire flame spraying(WFS) sprayed coating of a 13Cr steel(SUS420J2), and the fatigue strength and fracture mechanisms were studied. The fatigue strength evaluated by nominal stress was strongly influenced by substrate materials and the thickness of sprayed coatings. Detailed observation of crack initiation on the coating surface and fracture surface revealed that in the WC cermet sprayed materia1s, small defects initiated at WC grainboundaries coalesced and then the crack grew rapidly in the coating, and while in the 13Cr steel-sprayed material, many microcracks were initiated from defects on the coating and coalesced to be a main crack. Cracks were initiated in the substrate due to the stress concentration of the crack in the coating, which was modeled by finite element analysis. The fatigue strength of the sprayed materials was dominated by that of the spayed coating. Thus, the fatigue strength could be evaluated uniquely in terms of the true stress on the coating surface.

Key Words:Sprayed materials, Fatigue strength, Fracture mechanics, Crack initiation, WC cermet, 13Cr Steel


INITIATION AND GROWTH OF SMALL FATIGUE CRACK IN TiAl INTERMETALLICS AT ELEVATED AND ROOM TEMPERATURE

Yoshiharu MUTOH, Tomoaki MORIYA, Shijie ZHU and Youji MIZUHARA

Abstract:The initiation and growth of small fatigue crack in a gamma titanium aluminides(TiAl) have been investigated by scanning electron microscope (SEM) in situ observation vacuum at 750 deg and room temperature. The initiation of crack occurs transgranulary at room temperature, but both transgranulary and intergranulary at 750 deg. Small cracks grow at stress intensity factor lower than the threshold value for long crack growth. The fatigue life at 750 deg is shorter then that at room temperature. When stress is modified by Young's modulus, fatigue limit at 750 deg is the same as that at room temperature. However, fatigue lives at high stresses showed difference between room and elevated temperatures.

Key Words:Fatigue crack initiation, Small crack growth, Fatigue life, Intermetallic, TiAl, Duplex microstructure


ROLE OF GRAIN BRIDGING DEGRADATION OF SMALL CRACK ON CRACK PROPAGATION BEHAVIOR IN POLYCRYSTALINE ALUMINA UNDER CYCLIC LOAD

Akira UENO and Hidehiro KISHIMOTO

Abstract:In order to investigate the effects of grain bridging degradation on the cyclic fatigue in polycrysta11ine alumina. Crack propagation tests were carried out under cyclic load and static load. Two kinds of small semi-elliptical surface crack were introduced by Knoop indenter. Polishing the surface layer, the residual stress around the Knoop indentation was complete1y removed. The cyclic loading accelerates crack propagation in sma11 crack as the same as in long crack. On the other hand, measuring and analyzing the crack opening displacement (COD) of 350 mm crack, we determined the net stress intensity factor KItip. Under the cyclic load, the reduction o for bridging force resulted in an increase in KItip which, in turn, accelerated the crack propagation rate. Furthermore, it is found that bridging degradation mechanism under cyclic loading dose occur, but that this mechanism is not sufficient to completely account for "fatigue crack growth in ceramics".

Key Words:Alumina, Small crack, Crack propagation, Fatigue mechanism, Bridging degradation, Cyclic load


FATIGUE CRACK GROWTH ANISOTROPY IN ANNEALED AND PRE-STRAINED COMMERCIALLY PURE TITANIUMS

Kazuhiro KUSUKAWA and Ken-ichi TAKAO

Abstract:Fatigue crack growth tests were carried out on commercially pure titanium sheets with a drilled hole and a center notch, in order to clarify anisotropy of fatigue crack growth and the influences of pre-straining on the anisotropy. The crack growth resistance in rolling direction was higher than that in a direction transverse to the rolling direction for surface cracks longer than 2.5 mm initiated at a drilled hole, and for cracks initiated at a center notch at DK higher than 10 Mpam1/2, in contrast to the growth behavior of various steels. Fractography observations showed that the anisotropy became remarkable after transition from cleavage-like facet dominant fracture surface to ductile appearance dominant one. The transition occurred when reversed plastic zone size at the crack tip was comparable to the grain size or the metal during crack growth. Pre-Straining had only a little effect on the crack growth anisotropy.

Key Words:Fatigue, Crack growth, Small fatigue crack, Anisotropy, Pre-straining, Pure titanium


EVALUATION OF MECHANICAL AND THERMAL PROPERTIES OF CUBIC BORON NITRIDE BY AB-INITIO CALCULATION

Yoshitada ISONO, Hirokazu KISHIMOTO and Takeshi TANAKA

Abstract:This paper describes the mechanical and the thermal properties of a cubic boron nitride (cBN) by molecular orbital molecular dynamics simulations. The interatomic potential of cBN used for the molecular dynamics simulation was proposed by an ab-initio the molecular orbital calculation for a cBN cluster. The elastic stiffness and the bulk modulus of cBN were found to be close to those of diamond by the molecular simulation. The bulk modulus of cBN in the simulation agreed with that in experiment. The equilibrium molecular dynamics simulation estimated the effect of temperature on the thermal conductivity and coefficient of thermal expansion of cBN. The thermal conductivity of cBN drastically decreased with increasing temperature above 150 K. The coefficient of thermal expansion of cBN was independent of temperature at 50 K - 900 K, but that of cBN increased above 900 K with increasing temperature.

Key Words:Cubic boron nitride, Ab-initio calculation, Molecular dynamics, Elastic stiffness, Bulk modulus, Thermal conductivity, Coefficient of thermal expansion


MOLECULAR DYNAMICS SIMULATION OF HEAT CONDUCION AND THERMAL STRESS IN RELATION WITH CONTINUUM MECHANICS

Takuya UEHARA and Tatsuo INOUE

Abstract:Heat conduction phenomena and induced thermal stresses are simulated from a microscopic viewpoint by using a molecular dynamics method. Three dimensional rectangular parallelepiped model composed of 2000 atoms surrounded by periodic boundary is imposed for the simulations. Thermo-physical properties such as melting temperature, specific heat, heat conductivity and latent heat are evaluated at the first step to obtain the fundamental data for the following heat conduction simulation. The central part of the model is heated for two cases with and without melting and the variation of temperature potential energy and thermal stresses are simulated. These simulations are carried out with two different potential functions, Lennard-Jones and Morse type, in order to clarify the effects of the interatomic potential, which follows to qualitatively demonstrate similar tendency in spite of remarkable quantitative differences. Then the variation of temperature is compared with the numerical solution of macroscopic heat conduction equation. It is clarified that the results show good agreement with each other if they are plotted against non-dimensional time, or Fourier number. Stresses calculated by molecular dynamics method are a1so compared with macroscopic thermal stresses.

Key Words:Molecular dynamics, Materio-thermo-mechanics, Heat conduction, Fourier's law, Melting, Thermal stress, Fourier number


COMPARIS0N OF INVARIANT IMBEDDING AND LAYER-PEELING METHODS IN INVERSE PROBLEM

Tomas NOVOTNY, Eiji MATSUMOTO and Thshinobu SHIBATA

Abstract:This paper examines an implementation of a layer-peeling method to inverse scattering problems in the time domain, which is applied here to the case of one-dimensional lossless discontinuous medium. The method is based on the fast Schur recursion applied directly to the discrete problem. The method is tested on several numerical examples in order to compare its performance to the standard invariant imbedding algorithm. The reconstructions of media from both synthetic data and measured data are presented. The layer-peeling method is shown to be considerably faster than the invariant imbedding method without the loss of precision.

Key Words:Nondestructive material testing, Multi-layered material, Inverse problem, Acoustics, Invariant imbeddibg algorithm, Layer-peeling algorithm


BIOMIMETIC COATING OF BONE-LIKE APATITE ON GLASS BEADS

Akiyoshi OSAKA, shinji TAKEMOTO, Satoshi HAYAKAWA and Chikara OHTSUKI

Abstract:Soda lime glass beads were chemically treated by either an aqueous solution of NaOH (3mol/l) or a hydrogen peroxide solution (30vol%) containing TaCl5 in 5x10-3mol/l or by both of them. The treated samples were soaked up to 14 days in a simulated body fluid (SBF): Na+142.0, K+5.0, Ca2+, Mg2+1.5, Cl-147.8, HCO3-4.2, HPO42-1.0, SO42-0.5 (in 10-3mol/l), or in another solution 1.5 times as concentrated as SBF (1.5SBF). The SBFs were kept at 36.5℃ and at 7.25 in pH. Apatite was deposited on samples treated with the NaOH solution, the SBFs solution, and both of them before soaking in l.5SBF. Ta(V) ions were present on not only the samples treated with the H2O2/Ta solution but those treated with both NaOH and the H2O2/Ta solutions. It was concluded that Ta(V) ions on the surface layer had ability of inducing apatite deposition, and the ability was enhanced by the coexistence with silanol groups.

Key Words:Apatite, Coating, Glass, Biomimitric process, Chemical treatment, Hydrogen perooxide, Tantalum chloride, X-ray photoelectron apectroscopy, Surface microstructure


ESTIMATION OF CORROSION RESISTANCE OF ZN-0〜30% Al HOT-DIP COATINGS ON STEEL

Yoshihiko TAKANO, Koshi TAKADA, Takashi HATANO, Tetsuya NAKADA and Tatsumi IZEKI

Abstract:A recently developed Zn-Al hot-dip coating on steel has a higher corrosion resistance than that of the Zn hot-dip coating. For estimating the corrosion rate for the hot-dip coating on steel, the polarization resistance (Rp) was measured using a coulostatic method. The cross-section of the Zn-Al hot-dip coating was analyzed by X-ray and EPMA. The results showed a tendency in which the Al concentration increased from the surface of the coating toward the base steel side. Based on the Rp values of five kinds of Zn-Al coatings hot-dip coated in a bath with 5, 10, 15, 20 and 30% Al, the coating obtained in the 15% Al bath showed the highest Rp value. In other words, this indicated that the corrosion resistance of the coating from the 15% Al bath was superior. Electrochemical impedance spectroscopy (EIS) with a frequency response analyzer (FRA) was used to obtain further information about the interface of the Zn-Al hot-dip coating and a 5% NaCl aqueous solution of pH 8. The measurement results showed two capacitive semicircles on the high-frequency side and a diffusion curve on the low-frequency side, which are considered to be formed by a typical Randles-tytpe equivalent circuit. This results the fact that the corrosion reaction is rate limited by both the charge and materials transfer processes.

Key Words:Zn-Al hot-dip coating, Corrosion reistance, Salt-spray tests, Measurement of polarization resistance