JSME International Journal Series A Solid Mechanics and Material Engineering
Online ISSN : 1347-5363
Print ISSN : 1344-7912
ISSN-L : 1344-7912
Volume 41 , Issue 1
Showing 1-19 articles out of 19 articles from the selected issue
  • Masatoshi SHIMODA, Hideyuki AZEGAMI, Toshiaki SAKURAI
    1998 Volume 41 Issue 1 Pages 1-9
    Published: January 15, 1998
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    This paper presents a numerical shape optimization method for continua that minimizes some maximum local measure such as stress or displacement. A method of solving such min-max problems subject to a volume constraint is proposed. This method uses the Kreisselmeier-Steinhauser function to transpose local functionals to global integral functionals so as to avoid non-differentiability. With this function, a multiple loading problem is recast as a single loading problem. The shape gradient functions used in the proposed traction method are derived theoretically using Lagrange multipliers and the material derivative method. Using the traction method, the optimum domain variation that reduces the objective functional is numerically and iteratively determined while maintaining boundary smoothness. Calculated results for two- and three-dimensional problems are presented to show the effectiveness and practical utility of the proposed method for min-max shape design problems.
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  • Takayuki KITAMURA, Yoshitaka UMENO, Ryuichi OHTANI
    1998 Volume 41 Issue 1 Pages 10-15
    Published: January 15, 1998
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    Fracture in an aluminum conductor of an LSI(large-scale integrated circuit) is often caused by stress-induced diffusion of atoms along a grain boundary, which is called"stress migration". As the conductor is subjected to tensile hydrostatic stress at a high temperature due to thermal mismatch, it is important to understand the effect of hydrostatic stress on the diffusion. However, this effect has not yet been examined since experiments under tensile hydrostatic stress are extremely difficult. In this study, the effect is investigated on the basis of a molecular dynamics simulation using the Nose-Hoover and the Parrinello-Rahman methods. The simulation enabled us to observe the motion of atoms under constant stress and temperature. The results obtained are summarized as follows. (1)The simulated coefficient of lattice diffusion under a stress-free condition agrees very well with the experimental ones. This indicates the validity of the present simulation. (2)The motion of atoms is accelerated by tensile hydrostatic stress in the region of about 5 atomic layers near the grain boundary. (3)Tensile hydrostatic stress accelerates the diffusion along the grain boundary, while compressive stress suppresses it. (4)The coefficient is proportional to exp(-(ΔE)/(k(T/Tm)))regardless of the magnitude of hydrostatic stress where T and Tm are the temperature and the melting temperature of the grain boundary under the corresponding hydrostatic stress, respectively.
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  • Yeong-Maw HWANG, Wun-Uven WU, Tsung-Rong CHEN
    1998 Volume 41 Issue 1 Pages 16-24
    Published: January 15, 1998
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    A mathematical model for analyzing the plastic deformation behavior of a sheet during a conical closed-die blow-forming is proposed. In the formulation of this mathematical model, uniform thinning in the free bulged region is considered. Using this model, the effects of various forming parameters, such as the die entry radius, friction coefficient, and inclined angle of the die, on the optimized pressurization profile, forming time and the thickness distribution of products can be discussed systematically. Furthermore, experiments using 8090 Al-Li sheets are carried out in conical closed-die superplastic blow-forming. The predicted thickness distributions of the SPFed product obtained with different friction coefficients along the die enty, sidewall and bottom are found to be closer to the experimental data than those obtained with a constant friction coefficient.
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  • Toshihiko HOSHIDE, Takashi IIZUKA
    1998 Volume 41 Issue 1 Pages 25-30
    Published: January 15, 1998
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    Alumina coating films, which were coated on borosilicate glass by a radio-frequency(RF) magnetron sputtering method, were found to be amorphous in a previous work. It was also revealed that the microhardness of sputtered alumina film was larger with increasing RF output in the processing. There was, however, no simple model to explain experimental observations appropriately. In the present paper, the dynamics of rigid spheres was adopted in modeling the formation of amorphous coating film in a sputtering process, and a simulation based on the model was carried out to investigate structural properties of coating film. The volume fraction of deposited particles in coating film was evaluated for various conditions in the simulation, and the dependence of film hardness on RF output was also discussed. The simulated results were found to represent experimental observations qualitatively.
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  • Yukuo NANZAI, Tomoaki YAMASAKI, Sin'ya YOSHIOKA
    1998 Volume 41 Issue 1 Pages 31-39
    Published: January 15, 1998
    Released: February 18, 2008
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    Polycarbonate(PC), a prominent high-performance engineering resin, wes subjected to constant rate tension and compression at temperatures below the glass transition, and its nonlinear plastic flow was analyzed as a stress-aided activation process. The analysis yielded a relation between the activation enthalpy ΔH and the activation entropy ΔS that was in good agreement with the equation between ΔH and ΔS derived from viscoelasticity data from the PC melt. This agreement proves that the structure of solid PC is changed into melt-like structures during the yielding process. The pressure activation volume Δv was always positive, regardless of the change in sign of the hydrostatic component. This was consistent with an unchangeable increase in entropy in the activated state. A possible relationship between the linear plot of ΔH to ΔS and the nonlinear viscosity in polymer melts is briefly discussed.
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  • Fumio NARITA, Yasuhide SHINDO
    1998 Volume 41 Issue 1 Pages 40-48
    Published: January 15, 1998
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    Based on the dynamic theory of linear piezoelectricity, we investigate the scattering of Love waves by a surface-breaking crack in a layered piezoelectric solid. The piezoelectric layer is perfectly bonded to a half-space of a different elastic solid and the crack is normal to the free surface. Both cases of a partially broken layer and a completely broken layer are studied. By the use of Fourier transform techniques, the mixed boundary value problem is reduced to a singular integral equation. The singular integral equation is solved numerically to determine the dynamic stress intensity factor and the dynamic energy release rate as a function of a dimensionless frequency for various ratios of crack depth to layer thickness, and the results are presented in graphical form.
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  • Kenjiro KOMAI, Kohji MINOSHIMA, Tsuyoshi MIYAWAKI
    1998 Volume 41 Issue 1 Pages 49-56
    Published: January 15, 1998
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    An atomic force microscope(AFM) equipped with a small three-point bending testing machine was used for in situ visualization of intergranular stress corrosion(SC) crack growth under a constant displacement. The tests were conducted on a high-strength 7075-T6 aluminum alloy in laboratory air. The AFM was capable of imaging the surface topography of a growing SC crack on the nanometer order. The AFM has extremely high spatial resolution, and it was capable of monitoring very slow growth of an SC crack:even when it grew on the order of 0.1 nm/s, it grew continuously when observed on the order of microns. When the crack grew along the grain boundary inclined to the tensile stress direction, not only Mode I and II, but also Mode III crack tip displacement was observed. However, the Mode I stress intensity derived from the crack tip displacement was responsible for the crack growth. The tip of an SC crack growing in laboratory air was very sharp. However, when the environment was changed to a vacuum, the crack tip became blunt, and the growth of the crack was retarded. When the environment was changed again to laboratory air, the crack growth restarted after a crack retardation period, and the tip became sharp again. We discuss the SC crack growth mechanisms based on nanoscopic in situ visualization using AFM.
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  • Yan LIU, Sumio MURAKAMI
    1998 Volume 41 Issue 1 Pages 57-65
    Published: January 15, 1998
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    After examining the ill-natured stress sensitivity of the conventional creep damage equations of Kachanov-Rabotnov, it was shown that this stress sensitivity is one of the most essential causes of damage localization and mesh-dependence in local approach of creep fracture analyses. Then, in order to avoid this difficulty, alternative constitutive and evolution equations of creep and creep-damage are proposed from the view point of micromechanics. Finally, the proposed equations of creep and creep-damage are applied to the creep crack growth analysis of a perforated plate under tension. Significant improvement in damage localization and the mesh-dependence of the numerical results are ascertained.
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  • Yajun YIN, Toshio TSUTA
    1998 Volume 41 Issue 1 Pages 66-78
    Published: January 15, 1998
    Released: February 18, 2008
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    A rigid plastic constitutive model for porous ductile materials is constructed in this paper. Because of its solid physical basis and dispensability of experimental curve-fitting parameters, Gurson-type yield function is widely applied to investigate the effects of void nucleation, growth and coalescence on the damage behaviors of porous materials. However, it is extremely difficult to use this kind of yield condition for rigid plastic analysis. To solve this problem, a few concepts, parameters and formulations such as effective stress, effective strain rate, generalized triaxiality ratio and generalized triaxiality function, are defined. With the aid of these parameters and formulas, the stress-strain rate type constitutive model on the basis of modified Gurson's yield function is established. Brief discussions are carried out to manifest the characteristics of the present model. The reasonability of the new model is demonstrated by the comparisons with the theoretical systems of conventional models.
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  • Yajun YIN, Toshio TSUTA
    1998 Volume 41 Issue 1 Pages 79-95
    Published: January 15, 1998
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    A new rigid plastic constitutive model for ductile materials with void evolution processes, which was developed on the base of the modified Gurson's yield function in previous research, is carefully investigated in this paper. In order to check the reasonability, reliability and accuracy of this model, detailed numerical calculations on the response of porous materials under uniaxial stress condition, biaxial equal stress condition and uniaxial strain condition are carried out respectively. The influence of triaxiality on the deformation behaviours and void evolution characteristics are revealed through such kind of calculations. Systematic comparisons of the calculation results based on both the present model and the conventional models show the correctness of the new constitutive theory. The advantages of the present model over other conventional models are discussed. This research displays the possibility of estabilishing the constitutive model for porous materials, such as sintered metals, on a solid theoretical basis.
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  • Hiroyuki MORI, Shuji HATTORI, Tsunenori OKADA
    1998 Volume 41 Issue 1 Pages 96-102
    Published: January 15, 1998
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    A quantitative relation(F-N curve)was obtained betweent the constant impact load due to cavitation bubble collapse and the number of cycles to the incubation period termination. The relation was derived from the linear cumulative damage law, in which all impact loads including those of very low intensity(0.3 N)are assumed to cause damage. The slope of the F-N curve corresponds well with that of the S-N curve for a smooth specimen obtained from a standard fatigue test, provided that the contact area is obtained by the Hertz theory. The incubation period can be evaluated regardless of cavitation test conditions from the cumulative cycle ratio Σ(ni/Ni), using both the number ni of impact loads and Ni from an extrapolated F-N curve(modified Miner's law)for the corresponding impact load Fi. Similarly, the F-N' curve was obtained for the steady-state period, where N' was defined as the number of cycles required to achieve a mean depth of penetration(MDP) of 1 micron. The slope of the curve coincides well with that of the S-N curve for a slightly notched specimen. The Σ(ni/N'i)has a linear relation with the MDP in the steady-state period. Since N'i is proportional to 1/F2i from the F-N' curve, the cumulative cycle ratio was reduced to Σ F2i·ni, which is consistent with the impact energy from the authors' previous report. It is concluded that the ratios Σ(ni/Ni)and Σ(ni/N'i)are suitable parameters for evaluation of the cavitation damage in the incubation and steady-state periods, respectively.
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  • Erhard KREMPL, Toshiya NAKAMURA
    1998 Volume 41 Issue 1 Pages 103-111
    Published: January 15, 1998
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    Novel and consistent relaxation behaviors have recently been found with several steels at homologous temperatures less than 0.5, on a Titanium alloy, on an Aluminum alloy and on the polymer Nylon 66 at room temperature. A strong dependence of the relaxation rate on prior loading rate was observed. At equal relaxation times the stress at the end of the relaxation period associated with fastest(slowest)prior strain rate has the smallest(largest)magnitude. It is shown that the stress rate term in the evolution law of the equilibrium(back)stress enables the viscoplasticity theory based on overstress(VBO) to naturally model this newly found relaxation behavior. If the stress rate term is absent, as is the case for other state variable theories, this relaxation behavior cannot be modeled without modifications. Analyses valid at the beginning of and during the relaxation tests and numerical experiments illustrate the properties of VBO and other"unified"state variable models at low and high homologous temperatures.
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  • Yoshio KITSUNAI, Yutaka MAEDA, Etsuji YOSHIHISA
    1998 Volume 41 Issue 1 Pages 112-120
    Published: January 15, 1998
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    A survey of the degradation in overhead travelling cranes was performed. Fatigue cracks were often detected in highly stressed regions in cranes that had been in use for fifteen years or more. Service stresses of an overhead travelling crane with a lifting capacity of 50 kN were monitored and analyzed by the rain-flow method. A fatigue test of gusset welded joints made of SM490A steel was carried out under both constant loading and program loading determined based on service stress monitoring. The fatigue life of the gusset welded joints is dominated by crack initiation rather than propagation. The crack growth rate of the welded joints under program loading is correlated with an effective stress intensity factor range, ΔKRem estimated based on linear accumulation of the stress intensity factor range which takes into account residual stress at each step in a block. The prediction of fatigue propagation life using ΔKRem agrees with the experimental result in the range of error up to 15%, when the crack length is less than 20 mm.
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  • Juhachi ODA, Shinobu SAKAI, Satoru KEMMOCHI
    1998 Volume 41 Issue 1 Pages 121-126
    Published: January 15, 1998
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    An eggshell is cracked easily by an inside load, but has strong resistance to an outside load. In this study, the structural and material composition of an eggshell(from a hen's egg)is analyzed by microscopic observation, static and dynamic penetration tests and FEM. The results obtained are as follows. (1)From microscopic observation, the eggshell is found to have a laminated structure of many material compositions. (2)The outer eggshell membrane acts as a strong adhesive agent between the inner eggshell membrane and the eggshell. (3)A cone-type punch and striker makes an initial crack easily, but subsequently large penetration energies are required. (4)The penetration energy required from outside of an eggshell is larger than from inside because it includes the energies required to break the membrane and peel it off the eggshell.
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  • Masashi NAKAMURA, Hideto SUZUKI, Tadao HARAGUCHI, Yutaka WATANABE
    1998 Volume 41 Issue 1 Pages 127-133
    Published: January 15, 1998
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    In this paper, the influence of environmental temperature on fatigue reliability for advanced carbon-fiber-reinforced-thermal-plastic PEEK was examined. Attention was focused on the mechanism of growth from mesocracks to macrocracks at elevated temperature. The main results were as follows, (1)The fatigue life at elevated temperature was arranged by the fatigue strength of CF15 and gf30 materials decreased with increasing environmental temperature. Further, the strength of CF15 material was superior to that of gf30 material. (2)The influence of stress and environmental temperature was represented by the Nf -1/T diagram and S-T(C+log tr)diagram. Therefore, it was suggested that high-cycle fatigue life could be estimated from these parameters. (3)From the results of fractography using SEM, the fracture surface of CF15 material was ductile, on the other hand, that of gf30 material was brittle. (4)It was appeared that the temperature rise in the fatigue damage zone was closely related to the mesocrack formation process. (5)It was thought that the difference of mesocrack formation between CF15 material and gf30 material was reflected in the difference of the activation energy.
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  • Koji SHIMIZU, Masahiro SUETSUGU, Tadashi NAKAMURA, Susumu TAKAHASHI
    1998 Volume 41 Issue 1 Pages 134-141
    Published: January 15, 1998
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    The caustic pattern which is formed by a concentrated load P acting on a half-plane of an optically anisotropic material is theoretically considered, and the method of determining the value of P by caustics for birefringent as well as optically inert materials is shown. The effect of initial curve γ0 on the evaluation of P is experimentally studied. It is shown that the value of P determined from the caustic pattern is influenced by the radius of γ0 when the dimension of γ0 is less than half the thickness of the specimen. The reason for this phenomenon is discussed from two points of view, namely, the existence of three-dimensional stress and the effect of load distributed by the shape of the loading pin. Moreover, a technique for measuring the optical constants in caustics is proposed. These constants can be easily determined from the caustic pattern obtained by the concentrated load, and the validity of the technique is experimentally ascertained for several polymers such as Plexiglas, epoxy resin and polycarbonate. The absolute photoelastic coefficients and the photoelastic sensitivity of these materials are also obtained by this method.
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  • Takanori SASAKI, Hideki SEKINE, Hisao FUKUNAGA
    1998 Volume 41 Issue 1 Pages 142-148
    Published: January 15, 1998
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    Using piezoelectric actuators which have the capability to induce various amounts of strain upon activation, it is possible to reduce stress concentrations under varying external load conditions by distributing them in high stress regions in advance. In this paper, we verify experimentally the relaxation of stress concentrations in an adaptive plate with a circular hole using piezoelectric actuators. The adaptive plate is a simple actuator/substrate system in which the substrate is an acrylic acid resin plate with a circular hole and actuators are PZT piezoelectric ceramics bonded to the plate surfaces around the hole. The optimal voltage calculated to minimize maximum stresses in the substrate subjected to uniaxial tensile load was applied to each piezoelectric actuator. The experimental results of circumferential stress distributions on the circular hole boundary were compared with the numerical ones. Both results appeared in agreement and the relaxation of stress concentrations in the adaptive plate was verified.
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  • Tatsuro NAKAI, Junnichi MOTEGI, Toshiya NAKAMURA, Yasuhide ASADA
    1998 Volume 41 Issue 1 Pages 149-155
    Published: January 15, 1998
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    Creep-fatigue tests were conducted using 316FR stainless steel at 650°C in air under a variety of strain time programs including symmetric continuous, unsymmetric continuous and strain hold cycles. By comparison of the results with the test data obtained in vacuum, it was found that the life reduction which occurred for a slow tension-fast compression strain wave and the tensile strain holding wave was smaller in air than in vacuum, and that the symmetric continuous cycle gave the largest life reduction from the data obtained in vacuum. Following the creep-fatigue tests, failure surfaces were investigated by SEM. When time/rate-dependent life reduction occur red, the fracture mode in vacuum was intergranular, but in air, striations were observed and intergranular fracture was rarely observed.
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  • Koji SHIMIZU, Masahiro SUETSUGU, Takeshi SENOO, Susumu TAKAHASHI
    1998 Volume 41 Issue 1 Pages 156-162
    Published: January 15, 1998
    Released: February 18, 2008
    JOURNALS FREE ACCESS
    A new technique is proposed for evaluating the optical constants of caustics under dynamic loading. In this technique, the optical constants are determined from the caustic pattern under a concentrated load and the dynamic value of the concentrated load, which is obtained using strain gages bonded to the surface of the falling weight. The optical constants of caustics c0 for several polymers are accurately evaluated from the caustic pattern formed by a concentrated load acting on a half-plane, and the dependence of c0 on the loading rate is determined. The results show that the value of c0 decreases considerably with increasing loading rate in Plexiglas and Araldite D containing 30% softening material. On the other hand, the values for polycarbonate, Araldite B and Araldite D not containing softening material decrease slightly with increasing loading rate.
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