Journal of the Society of Materials Science, Japan
Online ISSN : 1880-7488
Print ISSN : 0514-5163
ISSN-L : 0514-5163
Volume 46 , Issue 3
Showing 1-17 articles out of 17 articles from the selected issue
  • Yoji SHIBUTANI
    1997 Volume 46 Issue 3 Pages 218-227
    Published: March 15, 1997
    Released: June 03, 2009
    JOURNALS FREE ACCESS
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  • Tomoyuki YONEDA, Moritaka HIDA, Akira SAKAKIBARA
    1997 Volume 46 Issue 3 Pages 228-231
    Published: March 15, 1997
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    Molecular dynamics simulation of Ni crystal under uniaxial elongation and compressive deformation was performed for NPH and NVE ensembles using Finnis-Sinclair and Morse potentials from the view point of deformation induced phase transformation. In the case of NPH ensemble using Morse and Finnis-Sinclair potentials, the structure breaks down immediately above the elastic limit of elongation. The fcc structure changes into the hcp structure with the deformation of simulation-cell under compressive stress. In the case of NVE ensemble using Morse and Finnis-Sinclair potentials under tensile deformation, slip deformation occurs in the plastic region, and the strain does not recover even though the stress is removed. Under the compressive stress, the structure is deformed by slip and becomes the twin like crystal structure elastically.
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  • Takayuki KITAMURA, Kisaragi YASHIRO, Masato IEHARA, Ryuichi OHTANI
    1997 Volume 46 Issue 3 Pages 232-237
    Published: March 15, 1997
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    The mechanism of cyclic deformation is investigated by means of atomic simulation using an interatomic potential in the embedded atom method (EAM). A very thin wire of niclel single, perfect crystal is subjected to cyclic straining. The yielding tension is brought about by a slip of partial dislocation from one surface side to the opposite one on (111) plane, which brings about a stacking fault there. When the tensile strain is continued to be applied, another partial dislocation goes through the plane and the combined slips of the dislocations bring about migration toward [101] direction on the slip plane. Although the stacking fault disappears by the passage of second dislocation, steps remain on the surface around the wire. In unloading process, the crystallographic slip are easy to take place on the stacking fault because the fault increases the potential energy of wire. Two types of slips, which dissolve the stacking fault, are observed during the unloading process. One is the reverse slip that dislocation moves back. The other is the slip of another partial dislocation on the plane toward [110] direction where the steps are formed on the surface though the stacking fault disappears. The latter slip, which is irreversible, forms intrusion and/or extrusion sites on the surface in cyclic straining.
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  • Ken-ichi SAITOH, Hiroshi KITAGAWA, Akihiro NAKATANI, Shigenobu OGATA
    1997 Volume 46 Issue 3 Pages 238-243
    Published: March 15, 1997
    Released: June 03, 2009
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    Atomistic simulation of coincidence grain boundary (CSL grain boundary) on tensile strength is executed. Molecular dynamics based on the effective-medium theory (EMT) for aluminum which contains no empirical parameter is applied. For two tilt axes, which are chosen to be [100] and [110], the CSL grain boundary with ∑=5-41 and ∑=3-33, respectively, are investigated. The estimated grain boundary energy and the surface energy agree well with the previous studies. For the fracture energy estimated from tensile loading simulation, Griffith's criterion for brittle fracture gives the lower limit. And for ∑=3(A) and ∑=11(A) grain boundaries, which have extraordinarily small grain boundary energy, the amount of plastic work is several times larger than that for the other grain boundaries. It is also supposed that deformation constraint influences the brittleness and ductility of bicrystal enormously. And it is demonstrated that, when brittle fracture occurs, the effect of pre-existing grain boundary energy on the fracture strength becomes prominent.
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  • Keiko NAKATANI, Hiroshi KITAGAWA, Akihiro NAKATANI
    1997 Volume 46 Issue 3 Pages 244-249
    Published: March 15, 1997
    Released: June 03, 2009
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    Loading-unloading atomic simulations of an amorphous metal which is obtained by a molecular dynamics simulation for the melting-rapid quenching process are performed in order to obtain the fundamental mechanical properties and the changes of mechanical properties and atomic structures. The metastable structures which are created by large preloading exceeding the maximum loading point are more unstable than the initial amorphous structure. The elastic moduli decrease by the large preloading. The decrease is not explained by the volume average of individual atomic elastic moduli in the inhomogeneous deformation of internal atomic structure. However, by dealing the amorphous structure as a heterogeneous elastic body and carrying out a Finite Element Analysis, the solution shows the tendency of decrease in elastic moduli. The strength, which is evaluated by yield stress as the maximum stress, also decreases by preloading and its anisotropy appears. The strength in hydrostatic compression is larger than that in tension. These changes of mechanical properties by preloading are closely related to the destruction of intrinsic clusters composed of 13 atoms, which is viewed as the number of icosahedra by Voronoi polyhedra analysis.
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  • Katsuhiro MAEKAWA
    1997 Volume 46 Issue 3 Pages 250-255
    Published: March 15, 1997
    Released: June 03, 2009
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    The establishment of nano-scale machining technologies is required in the field of ultra-precision fabrication, in which it is vital to clarify cutting phenomena such as chip formation, cutting force, surface roughness and sub-surface damage. The present paper investigates diamond machining of a copper single crystal with atomistic defects by means of molecular dynamics simulation. Postulating the Morse potensials, the influences of initial vacancies and the duplex cutting on the cutting mechanism are analysed when a (111) plane of the crystal is orthogonally machined in a [101] direction. Existing vacancies and edge dislocations in copper result in further disorder of the atomistic structure and the increase of cutting force owing to the interaction between the defects and the dislocations propagated from the tool tip. These phenomena can be seen at a vacancy density of 0.5%. In the case of the duplex cutting of the perfect crystal, the displacement of work atoms is limited to at or just below the finished surface, which requires lower cutting force and produces more work atoms removed as a chip. These results suggest that a prerequisite for a damagefree machined surface is that the work material be as pure and perfect as possible.
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  • Chobin MAKABE, Masumi HIYANE, Hideo KANESHIRO
    1997 Volume 46 Issue 3 Pages 257-262
    Published: March 15, 1997
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    Fatigue crack propagation behavior of a center cracked plate was observed by an optical microscope in the low cycle fatigue regime. The fatigue tests were carried out under a stroke-controlled condition. The crack propagation rate da/dN was proportional to the crack length a and the crack propagation law could be expressed by da/dN=Cεαta, where C and α are constants and Δεt is the reversed nominal strain range. Also, the nominal stress at maximum load was inversely proportional to the crack length normalized by specimen width a/W. Furthermore, the crack growth behavior in the case of low cycle fatigue of the present experiment was compared to that in the case of ductile fracture of a center cracked plate. In both cases, the crack growth behavior could be correlated with the crack length and the crack opening geometry.
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  • Yoshinori EBIHARA, Toshiro MIYOSHI, Chiaki HIRAI
    1997 Volume 46 Issue 3 Pages 263-267
    Published: March 15, 1997
    Released: June 03, 2009
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    The stress intensity factor of a chevron notched bend specimen was analysed by using three dimensional BEM and the results were compared with those obtained by using Bluhm's slice model. The stress intensity factor was evaluated in two ways as a function of crack length; one is the average value of maximum stress intensity factor and minimum one at crack front, and the other is the average one obtained by energy approach. Those average stress intensity factors evaluated by BEM and slice model show good agreements. The distribution of stress intensity factor along crack front was also evaluated for several crack lengths. Four point bending test using the chevron notched Si3N4 specimens was further conducted and the fracture toughness was evaluated using the average stress intensity factor mentioned above. This fracture toughness was compared with that measured by Indentation Microfracture Method. As a result, when the chevron notched specimen fractured stably, a good agreement was shown between the measured values of fracture toughness by two methods. On the other hand, when unstable fracture occurred in the chevron notched specimen, the fracture toughness by the chevron notched specimen is more than 10% larger than that by Indentation Microfracture Method.
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  • Kazuyuki NAKASAKI, Tatsuo INOUE
    1997 Volume 46 Issue 3 Pages 268-275
    Published: March 15, 1997
    Released: June 03, 2009
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    Measurements of temperature variation and residual stress during and after laser-quenching operation are difficult due to too small area of the referred region and too short time of the operation. This motivates the importance of the numerical simulation treated in this paper. The CAE system “HEARTS” developed based on the metallo-thermo-mechanics, the validity and accuracy of which had already been confirmed elsewhere, is applied to the simulation of the quenching process of a carbon steel (S45C) by pulsed YAG laser beam in order to evaluate the coupled fields of phase transformation, temperature and stress. The results of the simulated stress distribution seem to represent the practical mode of shear stress on the quenched boundary, and the shape of the martensite transformed region is compared with the observed micrograph.
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  • Yasuo OCHI, Kohji HARAGUCHI, Akira ISHII, Shigemi SASAKI
    1997 Volume 46 Issue 3 Pages 276-281
    Published: March 15, 1997
    Released: June 03, 2009
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    Four-point bending tests were conducted on smooth and Vickers indentation notched specimens of Al2O3 and Si3N4 ceramics at room and elevated temperatures. The effects of surface polishing and grinding on the flexural strength of the smooth specimens of Al2O3 ceramics were studied at room temperature at first. And the detailed observation of fracture surface of the smooth specimens by a scanning electron microscope was carried out in order to specify the defect morphology as the fracture site and to study the relation between defect size and flexural strength at room and elevated temperatures. The fracture toughness evaluation by the indentation strength (IS) method was also studied on two kinds of ceramics at room and elevated temperatures for the Vickers indentation notched specimens under different load conditions. Then, by introducing the assumed equivalent crack length, the general evaluation of the relation between strength and crack size (defect size) for the smooth and notched specimens of two kind of ceramics were tried at room and elevated temperatures under the conditions of this study.
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  • Hiroshi HOHJO, Hirotaka SHIBATA, Nobuo KAMIYA, Akio OTSUKA, Takashi MI ...
    1997 Volume 46 Issue 3 Pages 282-287
    Published: March 15, 1997
    Released: June 03, 2009
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    Static fatigue crack growth tests of several silicon nitride ceramics with various microstructures were carried out by a constant moment method. Correlations between the static fatigue crack growth behavior and microstructures, such as the size and distribution of grains and the fraction of rod-like grains, were investigated.
    The experimental results showed the following tendency. The larger average grain size, the higher fatigue crack growth resistance. The more uniform distribution of grain size, the higher gradient of fatigue crack growth resistance curve for crack length ranging to about 5mm. And the fraction of rod-like grains was not so correlative to crack growth resistance.
    Furthermore, a grain bridging model which may explain the influence of microstructure on fatigue crack growth behavior was proposed. In this model, the bridging force reducing effective stress intensity is described as a function of crack opening displacement and size and interval of bridging grains. The simulation showed that the more uniform distribution of grain size, the higher fatigue crack growth resistance. Also, the larger average grain size and the more fraction of rod-like grains, the higher fatigue crack growth resistance. These results were conformed qualitatively by the experimental results.
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  • Toshinori YOKOMAKU, Masao KINEFUCHI, Susumu TERADA, Hideki SUGIMURA, Y ...
    1997 Volume 46 Issue 3 Pages 288-294
    Published: March 15, 1997
    Released: June 03, 2009
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    Low-cycle-fatigue tests under creep- and ratcheting-conditions were conducted at 800 and 900°C on a heat-resisting cast alloy, HP-Nb. The fatigue life in the cp-test (slow-fast test) at 800°C was shorter than at 900°C, which was attributed to the lower creep ductility at 800°C. By adding tensile ratcheting-strain to each cp-strain cycle, the tensile peak stress increased, which led to life reduction. The life reduction by adding ratcheting-strain was remarkable in the small strain range region and especially at 800°C. The strain range partitioning method proposed by Manson et al. was appropriate for the creep-fatigue life prediction of this material. In the case of creep plus ratcheting-condition, a reasonable and conservative life prediction was obtained by combining the strain range partitioning and the ductility exhaustion as follows; [{nf·∑(1/Nij)}α]β+∑(δ/εc)=1, where nf and Nij are the number of cycles to failure and the partitioned life respectively, δ is the racheting strain, εc is the creep ductility and α and β are material constants. The severe life reduction in racheting-condition at 800°C was thought to be caused by accelerated grain-boundary void formation with an increase in tensile peak stress.
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  • Katsuhiko SASAKI
    1997 Volume 46 Issue 3 Pages 295-301
    Published: March 15, 1997
    Released: June 03, 2009
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    In this paper, both the AE (Acoustic Emission) measurement and the microscopic observation of CFRP[±45°]4 subjected to cyclic tension-compression loading with a constant strain amplitude under a constant strain rate are conducted to verify the method to predict fatigue failure of CFRP, which was previously proposed by the present author from the microscopic change of the specimen. The method is based on the number of cycles to fatigue failure defined by using the relationship between the inelastic strain energy per cycle and cycle of loading. As a result, it is found that the relationship between the damage variable observed microscopically and cycle of loading is correlative with the relationship between the accumulated AE event count and cycle of loading. Moreover, it is also found that the number of cycles to fatigue failure determined by the proposed definition is coincide with the unique number of cycles observed from the relationship between the accumulated AE event count and cycle of loading. Thus, the method is considered verified from the microscopic structural change of CFRP[±45°]4.
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  • Takayuki KUSAKA, Tomoaki KUROKAWA, Masaki HOJO, Shojiro OCHIAI
    1997 Volume 46 Issue 3 Pages 302-308
    Published: March 15, 1997
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    The application limit of the estimation method for mode II interlaminar fracture toughness of composite materials under impact loading, which had been proposed by the authors, was determined by transient finite element analyses varying the dimensions of specimen and profile of incident stress wave. The error in estimating mode II dynamic energy release rate tends to decrease as the maximum acceleration at the central loading point decreases. The error can be reduced remarkably by calculating the energy release rate from the surface strain of specimen. The application limit of the proposed method was evaluated to be 4-400sec-1 in shear strain rate for the specimens of 1-5mm in thickness and 60mm in bending span, assuming the critical energy release rate (fracture toughness) to be 1500J/m2 and the allowable error to be 10%. This limit is much higher than those of the conventional methods (e.g. servohydraulic testing instrument, drop weight impact test, split Hopkinson system using step incident stress wave).
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  • Tohru MORII, Nobuo IKUTA, Hiroyuki HAMADA
    1997 Volume 46 Issue 3 Pages 309-314
    Published: March 15, 1997
    Released: June 03, 2009
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    This study deals with the effects of water immersion on the mechanical properties of glass fabric/epoxy laminates with different silane treatments. Both γ-aminopropyltrimethoxysilane (amino silane) and γ-methacryloxypropyltrimethoxysilane (methacryl silane) were used as silane coupling agents. The laminates were immersed in distilled water at 80°C, and the weight change and the tensile and impact properties were measured. The weight loss occurred for the methacryl silane treated laminate, and as a result, the debonding at the interface with water penetration occurred. On the other hand, the amino silane treated laminate kept good bonding at the fiber/matrix interface even after longer immersion. The mechanical properties were affected by only the degradation of the matrix in the amino silane treated laminate, while they were affected by the degradation of both the matrix and the interface in the methacryl silane treated laminate. The degradation of the interface induced the change of fracture behavior due to water immersion, and as a result, the strength reduction process changed due to the degradation of the interface.
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  • Masahiko KATO, Keijiro NAKASA, Fumiaki EGAWA, Masanobu KAMATA, Nobuhik ...
    1997 Volume 46 Issue 3 Pages 315-321
    Published: March 15, 1997
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    Tungsten-carbide cermet was coated on the smooth tensile specimens of annealed tool steel (JIS: SKD6) by high-velocity flame spraying. After the specimens were heat-cycled between high temperatures and room temperature, the tensile tests of the specimens were carried out to examine the change of interfacial energy by heat cycles, where the load was applied parallel to the film. For the specimen which is not heat-cycled, the film is divided by parallel and straight cracks repeatedly with an increase in load, and the film delamination occurs after the division is completed. For the heat-cycled specimens, three types of delamination patterns are observed: (1) The film is delaminated almost in the same way as the non heat-cycled specimen, but the cracks are curved, (2) the small blocks of film are delaminated after the division finishes, and (3) the film is heavily damaged by oxidization and the delamination occures in the film without the division. When the heating temperature T is 773K or 873K and the holding time at the temperature is short, the interfacial energy 2γ12 increases to reach a maximum with an increase in heat cycles and decreases with further heat cycles. When T are 973K and 1073K, 2γ12 decreases with small increase in heat cycles. The change in interfacial energy with heat cycles can be explained both by the strengthening due to the diffusion of Fe and Cr atoms to film and by the accumulation of fatigue damage due to the difference in thermal expansion coefficient between film and substrate. The crack interval just before delamination changes depending on the heating temperature and heat cycles, the decrease in which corresponds to the decrease in critical tensile strength of film and/or the increase in critical shear strength of interface.
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  • Shinya MOTOGI, Hiroyuki KAWADA
    1997 Volume 46 Issue 3 Pages 322-328
    Published: March 15, 1997
    Released: June 03, 2009
    JOURNALS FREE ACCESS
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