CAE technology has been widely applied for the crash safety design of vehicles.Nevertheless, the optimum design approach has not been completed for the crash behavior of the vehicles because of the non-linearity of the dynamic problem.The authors have proposed a Statistical Design Support System(SDSS), and brought forward that the SDSS is one of the available optimal approaches for the nonlinear and dynamic problems such as the vehicles crashing. In this study, the SDSS was applied for the multi-objective optimization design of the main reinforced members of a vehicle. The thickness of each member was chosen as the design variables, and the total weight and the deformation of the cabin as the multi-objection functions.It was shown that the SDSS could satisfactorily be used as a practical multi-objective optimization design fool for the crash safety design of vehicles, and the design cycle could be significantly cut down using SDSS.

抄録全体を表示

Elastic constants are usually obtained experimentally, since it has some problems to predict elastic constants of materials analytically from atomistic viewpoint.In the previous papers, the authors proposed a method for expressing internal forces from motions of atoms, and the conservation laws for solids are introduced microscopically.In the present paper, constitutive equations and elastic constants not only for stresses but also for higher-order stresses are derived by dividing the kinematical quantities of atoms into the macroscopic deformation and thermal motion.In the process of derivation, a concept of a hierarchical Reynolds decomposition is infroduced.It is an expansion in power series which can be divided into an average value and a deviation in each hierachy.The hierarchical deviation terms are expressed by characteristic tensors which can be called P-tensors.The P-tensors are the indexes of atomic configurations and are used effectively for the expression of the elastic constants.

抄録全体を表示

In this paper, a genetic algorithm(GA) with diploid gene encoding structure is applied to obtain the optimum layout, size, and coolant condition parameters of injection mold.Although GA is effective in searching globally the parameter space of desing variables of optimzation problems, it is costly when such a heavy computation as that by FEM or BEM is required for evaluating the fitness of each individual.In the present work, a diploid gene structure is employed as the encoding scheme for the design variables of an optimization problem for designing cooling channels running through injection molds.In order to evaluate the fitness, which is a function of temperature over the cavity surface of the mold, the boundary element method(BEM)is employed due to its easiness in remeshing the boundary corresponding to design parameters of each individual.Several numerical demonstrations show that the proposed diploid GA can give optimum values of the design variables more repidly with a smaller number of populations than the standard GA with haploidy.

抄録全体を表示

Most of the calculation time for large scale numerical simulation which uses rigid-plastic finite element method is occupied by the solver part of simultaneous linear equation called stiffness equation.We incorporated the parallelized conjugated gradient method onto our cluster of workstations to shorten the computation time of them.It is important for high speed parallel computation in our cluster system of many workstations to reduce the data communication time through TPDDI network.In this paper, we propose a new method which enables to reduce data communication time by using the skewed tree multiple data transfer through concurrent or parallel paths from plural slave processors to that of others like systolic pulsations. Then, we achieve about eightfold speedup of execution time by twenty-four slave processors.And, we infer that the method shown in this paper is also effective to elastic finite element method.

抄録全体を表示

Every beam cross-section possesses a point through which transverse forces may be applied so as to produce bending only with no torsion of the beam.This point is called the shear center. In this study, the problems of coupled shearing and torsional were analyzed by using the finite element method. Namely, the simultaneous equations with respect to the warping, shear deflection, angle of torsion and Lagrange's multipliers are derived by finite element approximation.Solving them numerically, the matrix of the shearing rigidity and torsional rigidity is obtained.This matrix indicates the coupled shearing and torsional deflection.The shear center can be obtained determining the coordinate axes so as to eliminate the nondiagonal terms.

抄録全体を表示

The homogenization method, which was proposed to evaluate accurately the microscopic stress of heterogeneous composite materials and recently has been known as the optimaization method as well, has been applied to the infinitesimal displacement problem, so far.However, this method originally dose not take account of the large deformation of the structures.Therefore, in this study, a new homogenization method considering large deformation of structures is developed.The geometrically non-linear homogenization method based on the assumption of small strain at microscopic structure is introduced.In addition, since the homogenization theory is not valid near the free boundary, the stresses there are corrected by removing the excess stresses due to the periodical constraint condition.Finally, by means of this method, the numerical examples in the large displacement problem are demonstrated to show the validity of the proposed method, and by this method applied to the sensitivity analysis, which has often been used in the optimization procedure, the optimization problem in large deformation is illustrated.

抄録全体を表示

In general, thin shaped outer housings of plastic materials, for information appliance use, often cause the cracks due to the lack of impact strength.An evaluation method of plastic material properties against impact load has been developed for molding of outer housings.The FEM analyses were carried out, based upon the damping factors obtained by this evaluation method. Analytical strains for plastic materials were compared with measured ones for drop impact experiment and the proposed method by use of damping factors is suggested to be effective and practical to optimize the material properties.

抄録全体を表示

The homogenization theory for time-dependent nonlinear composites with periodic internal distributions developed by the present authors is rebuilt by taking notice that micro-stress and micro-strain may distribute point-symmetrically in unit cells in periodic composites.It is pointed out that the field of perturbed velocity may satisfy the symmetry with respect to the cell center and facet centers of a unit cell.The symmetry is then used for imposing the boundary condition on perturbed velocity and for developing the theory in an integral form in which a half region of the unit cell is taken as the domain of analysis.As applications of the theory, elastic-viscoplastic elongation of unidirectional composites is analyzed by assuming the square and hexagonal arrays of fibers subjected to either transverse or off-axial loading.It is thus shown that the point-symmetry can be used for computing efficiently the inelastic behavior of nonlinear, periodic composites.

抄録全体を表示

An elastic-plastic stress analysis was conducted for inhomogeneous fiber-reinforced plastic (FRP)containing a mode I matrix crack by means of the finite element method.The inhomogeneous FRP was modeled as a two-dimensional laminated structure composed of elastic-perfectly plastic matrix, orthotropic elastic fiber and homogeneous FRP.The extent and the shape o the yielding zone around the crack tip for the inhomogeneous FRP were compared to those for the unreinforced matrix material.Under the same value of the matrix stress intensity factor, K_Im, the length of the plastic zone ahead of the crack tip, ω_χ/d_m, for the inhomogeneous FRP was nearly equal to that for the unreinforced matrix material in the range of K_Im≨0.7σ_Y(πd_m)¹/2, where σ_Yis the yield stress of the matrix material and d_m is the height of the matrix phase in the inhomogeneous FRP.In the range of K_Im>0.7σ_Y(πd_m)¹/2, ωχ/d_m for the inhomogeneous FRP was larger than that for the unreinforced matrix material.The plastic zone height, ω_y/d_m, is nearly identical between inhomogeneous FRP and unreinforced matrix material. A simple method is proposed to estimate the height and the length of the plastic zone in the inhomogeneous FRP from the elastic stress distrigution in the inhomogeneous FRP.

抄録全体を表示

This paper demonstrates crack reconstruction from the relative signals, which overlap with noises in eddy current testing. A method for the reconstruction from the signals, a kind of inverse problem, has been developed with fast signal predictions and the steepest descent algorithm. The signal predictions use a pre-computed unflawed database approach based on edge-based finite elements and the reciprocity theorem.This approach makes it possible that the problem domain of an electromagnetic field is reduced to a small region where a crack/cracks possibly exist.In the inspection of steam generator tubes in nuclear power plants, this test detects deposits on the surfaces of thetubes and structures to fix the tubes such as support sheets or plates, and rigs, as well as defects.The signals from the structures are thought to be noises when finding out the defects.Crack profile identification is given from the crack signals with residual noises, which remain after multi-frequency processing of the signals disturbed by the presence of copper/magnetic deposits and support plantes.

抄録全体を表示

Crack growth mechanisms considering the oxidation and mean stress effect for nickel-and cobalt-based superalloys are investigated.Crack growth tests, which employ the strain waveform to take into account compressive strain hold, were carried out.Cracks propagated at the dendrite boundary in both superalloys and crack growths were accelerated by increasing the compression hold time.Oxidation around the crack tip was detected by EPMA analysis and accelerated the fatigue crack growth.In compressive strain hold test, the increment of non-dimensional crack growth rate by oxidation was proportional to about 1/3power of the compressive hold time.Furthermore, mean stresses were increased by compressive strain hold in the nickel-based superalloy, which has a high proof strength even at high temperature.This mean sress effect for crack growth was also discussed.A crack growth model that considers effects of both oxidation at crack tip and mean stress was derived.

抄録全体を表示

Fatigue crack growth tests were carried out on thin plates of a Fe-3.2% Si single crystal with an appropriate orientation for striation formation.To clarify the mechanism of crack growth, behaviors of slips near a crack tip during the loading and unloaaing parts of a fatigue cycle were observed in-situ with an atomic force microscope and a scanning electron microscope and fracture surfaces were also analyzed.Following results are obtained.(a)Striations on a pair of fracture surfaces reveal peaks to valleys matching other than any kinds of symmetrical matching.(b)Profiles of striations reveal shallow ripples.(c)During loading, a pair of concentrated slips activated alternately at a crack tip lead to crack opening and thus crack advance.(d)During unloading, reverse slips which lead to crack closing are activated in a distributed manner.(e)At much higher growth rate both opening and closing processes by a number of alternating slips are observed.(f)Vacuum environment facilitates a number of alternating slips:this is one of the causes for observing no distinctive striations on fracture surfaces in vacuum.In result, a fundamental model for fatigue crack growth is proposed on the basis of observations mentioned above.

抄録全体を表示

Fatigue tests of spheroidal graphite cast iron FCD600 were carried out under cyclic compressive load using round bars with circumferential notch.Cracks were observed propagating at the notch bottom of the specimens that were not fractured after 1×10⁷ cycles under the repeated compressive load.The change of the stress intensity factor range =K accompanied by the crack propagation was studied based on fracture mechanics, considering the residual tensile stress distribution due to the plastic deformation.The applied and residual stresses were calculated by elastic-plastic finite element method.=K was compared with =K_th of short crack taking intrinsic crack length a_o into consideration, and it was considered that crack propagation is stop at the depth of =K<=K_th.The estimated value of crack propagation depth is in good agreement with the experimental value.

抄録全体を表示

Influences of residual stress and mean stress on the endurance limits of gas-carburized specimens which were post-treated with shot peening and/or chemical polishing have been examined.(1)The residual stress influence coefficient m_r (inclination in a diagram of endurance limit and residual stress)is larger in the case of as carburized and shot peened specimens which have a oxidized layer than in the case of chemical polished and shot peened plus chemical polished specimens which the oxidized layer is removed.This means the oxidized layer behaves as a defect.(2)When abovementioned m_r was compared with the mean stress influence coefficient m(inclination in a endurance limit diagram), the m_r was about a half in specimens which included shot peening in the process though both agreed in as carburized and chemical polished specimens.It is necessary to treat separately with the residual stress and the mean stress when the process especially includes shot peening.

抄録全体を表示

To investigate the "fatigue strength reduction factor"(β), data of fatigue limit which have already published are analyzed by the "modified ε₀method"which considers the high-degree term components of the stress distribution at the notch root.The relationship between tensile strength (σ_B)and material constant(ε_o)is ε_o=103·σ_B^-1.12for JSME's data and is ε_o=25.7·σ_B^-1.04 for Nishitani's data but in JSME's data the expected difference between σω₁ and σω₂is not recognized and in Nishitani's data the unexpected dependency of the notch root radius onε₀ occurs.The factors β for individual data are calculated by using the above two relationships and are compared with experimental data.The results show that β calculated by the relation of ε₀=103·σ_B^-1.12 coincides with β obtained from the JSME's proposal equation for JSME's experimental data, but is critical for Nishitani's data.On the other hand, the relationship ε₀=25.7·σ_B^-1.04 give conservative β which is convenient for structural design in both JSME's and Nishitani's data.

抄録全体を表示

Rotating bending fatigue tests were performed for a squeeze cast Al alloy using the V-grooved specimen in order to investigate the influence of microstructure on the notch sensitivity which was assessed in terms of the limiting stress for crack initiation σω₁ and that for crack propagation σω₂.Although the influence of microstructure on the notch sensitivity for σω₁ was hardly recoginized, the notch sensitivity for σω₂ was low in larger size of microstructure.The results were discussed in view point of the influence of microstructure on the crack initiation and propagation behavior.

抄録全体を表示

Rotating bending fatigue tests were carried out for a squeeze cast Al alloy in order to-investigate the influence of microstructure on the crack initiation and its growth behavior.Although the influence of microstructure on the crack initiation behavior is small, the crack growth behavior is markedly influenced by microstructure, i.e.eutectic Si particles and dendrite arm spacing.That is, the crack grows along the slip direction in the early stage of crack growth and is blocked by the eutetic Si particles. And then the crack grows in a zigzag manner reflecting the influence of microstructure.Consequently, the crack grows rapidly in the early stage of crack growth and n in the relation dl/dN-lⁿ decreases with growth of crack.

抄録全体を表示

The stress concentrations of plates with circular holes and notches in cosine residual stress fields were investigated by the finite element analysis.When the plate had a central circular hole, the residual stress at the bottom of the hole remained always tensile, even though the initial (no-hole)residual stresses at that point were compressive.In case of the plate with a circular hole in higher order cosine residual stress fields, the concentrated stresses at the concentrated stresses at the bottom of the hole repeatedly followed with retardation the sign of the initial residual stress.The stress concentration problems due to welding residual stresses were studied by these cosine residual stress results using the superposition principle combined with Fourier's series expansion.The results of the superposition agreed quite well with the analytical results using the original welding residual stress distribution.

抄録全体を表示

In order to characterize the "Repeating-division type"and "Island-delamination type"cracking patterns which are often observed in brittle coating on a ductile substrate under increasing biaxial tensile stress, computer simulations of the cracking processes were made for cermet or ceramic coating which was thermally sprayed on the substrate of a low carbon steel.The simulation was carried out by using Monte Carlo method and the analytical equations which express the relation among crack size, tensile stress, strain, thickness and material's constants of coating and substrate.In the simulation, many cracks which have been nucleated randomly on the coating grow to either of the above cracking patterns depending on the relative strength of coating and interface.The simulated cracking patterns agree well with those observed in bulge experiments.

抄録全体を表示

The mode III fracture toughness testing method using single axis testing machine is developed.Four point shear specimen is used with small amount of mode I loading to avoid the contact of crack surfaces.The shape of the specimen, and the amount of mode I loading are determined based on the three dimensional FEM analysis.The crack tip stress field is also obtained, and compared with the HRR(Hutchinson-Rice-Rosengren)singularity.The conventional equation to evaluate the J-integral by the load-displacement record is proposed and the accuracy of this equation is verified.Finally the mode III fracture toughness, J _IIIC, of aluminum alloy and A 533 B steel are obtained.

抄録全体を表示

The point-by-point measurement of in-plane displacement was conducted by the point-wise filtering approach of speckle photography.Young's fringes analysis is based on the 2-D fast Fouriertransform and bounded Newton-Raphson algorithm.This system can analyze many fringe patterns with high speed and accuracy.A large number of Young's fringe patterns around the crack tip were taken by a CCD camera and analyzed by the image-processing system developed in my laboratory.The displacement obtained by speckle photography is not as smooth as that obtained by the finite element analysis.Therefore, the displacement data were smoothed by 2-D fast Fourier transform and the least squares method.Then, stress-strain analysis was conducted by using those data.

抄録全体を表示

The surfaces of many industrial products, such as a holl drill, gas turbine engine and so on, are coated with diamond and ceramic material for improving the material properties.On the other hand, the surface may accumulate an oxidation layer by reaction of oxygen with inceasing time.These Common damage, in service, is "delamination".It is known that the delamiation will be caused by compressive stress in these coating layer which is generated by vibration and fatigue loading for industrial coating, and volume expansion for oxidation.The actual coating delamination process as follow had been clarified by many studies.The coating layer is buckled locally by compressive loadingand is then delaminated along the substrate.The aim of this study is to clarify the coating delamination mechanism under compressive stress by observing continuously buckling and delaminating process in the coating layer, which is modelled by engineering plastic in this study. The delamination evaluation method is proposed based on an interface mechanics, and an accuracy of the evaluation is examined using finite element analysis.Finally, the proposed evaluation are applied to the experimental results obtained by this study.

抄録全体を表示

Recently the number of gan-turbine-powered, combined-cycle plants has been increasing because of their environmental compatibility and high efficiency.Gas turbine operating conditions are severe, especially for hot gas path components.To improve the reliability and extend the life of such components, a life management system has been developed that is based on a residual life assessment method.The system makes possible integrated residual life assessment based on numerical analyses, material destructive-tests, nondestructive inspections, statistical analyses of field machine data, and use of a database.The primary damage mechanism for each component is clarified and material degradation is evaluated.For nozzles, the system describes a method of predicting the maximum surface crack growth.The validity of the methods is verified by assessment of the inspection data.This paper also describes optimization of operating cost and RAM(reliability, availability and maintainability).

抄録全体を表示

This paper deals with interaction problems of elliptical and ellipsoidal inclusions under bending using singular integral equations of the body force method.These problems are formulated as a system of singular integral equations with Cauchy-type or logarithmic-type singularities, where unknown functions are densities of body forces distributed in the χ, y and r, θ, z directions in infinite bodies having the same elastic constants as those of the matrix and inclusions.In order to satisfy the boundary conditions along the elliptical and the ellipsoidal boundaries, the unknown functions are approximated by a linear combination of fundamental density functions and polynominals.The present method is found to yield the exact solutions for an elliptical and spherical inclusion under bending.Also, the present method yields rapidly converging numerical results for interface stresses in the interaction of inclusions.

抄録全体を表示

This paper describes an analytical formulation and a numerical solution of the elastic dynamic problems of porous shells of revolution saturated in viscous fluid.The equations of motion and the relations between the strains and displacements are derived by extending the Sanders elastic theory.As the constitutive relations, the consolidation theory of Biot for models of fluid-solid mixtures is employed.The fluid flow equations and deformation equations of shells are numerically solved using the finite difference method.As a numerical example, the simply supported cylindrical shell under sudden internal pressure rise is analyzed, and the varitions of pore pressure, displacements and internal forces with time are discussed.

抄録全体を表示

In order to study dynamic mechanical properties of the ceramics Si₃N₄, SiC and TiB₂, plate impact experiments with PVDF(Poly Vinylidene Di Fluoride)stress gauges were conducted using a shock gun system. From the experiments, we obtained the Hugoniot curves and the Hugoniot elastic limits of the ceramics.

抄録全体を表示

This paper proposes a new joining method of n-type thermoelectric element(Bi₂Te₂.85Se₀.15).The paper says that the bonding strength can be enhanced by coating Sn/Mo layer on the thermoelectric element.In case that a diffusion barrier material is coated directly on the thermoelectric element, the bonding strength is very weak.However, it shows high bonding strength when Sn alloy layer is formed.Additionally, the result of the reliable test clarified that Sn alloy layer does not adversely affect the performance of thermoelectric element.The reliable test conducted includes heat cycle test, heating test and cooling performance test.These results show the Sn/Mo layer coating method is very effective in joining electrode to thermoelectric element.

抄録全体を表示

It is an interesting but complicated problem to understand the relationship between the local mechanical property of bone and its structure.An ultra-microindenter was utilized for the evaluation of the local mechanical properties of rabbit and rat bone tissues.The tangents of the loading curve and the unloading curve, A and D, were adopted as the parameters for the hardness and elasticity of the bone tissue respectively. An anisotropy due to the orientation of collagen fibers between sagital and transverse planes of rabbit tibia was observed under the loading condition of 19.6mN.When the indentation load was lower, the fragile properties of the hydroxyapatite could be evaluated.This indenter was further used for the rat caudal vertebrae during mechanical adaptation in order to investigate in-plane distribution of the local mechanical property.The decrease of A and the increase of 1/D observed near the periosteum in the cortex indicated that the immature bone was formed and mineralized progressively. Additionally, higher A and lower 1/D in the subchondral bone of the loaded rat suggested that the subchondral bone stiffened to adapt to the mechanical stimulation.

抄録全体を表示

This paper is concerned with the formulation of a mathematical model to describe mechanical bone remodeling process.Firstly, mechanical stimulus is defined as a function of the rate-of-deformation power per unit mass.Physiological signal transmission processes of remodeling from the mechanical stimulus to change of bone density are described by n+1 sequential evolution equations with n+1 macroscopic internal state variables.The evolution equations are established on the basis of the experimental results in a literature.The value of the internal variable in the last step specifies the balance level of bone density, which is the target of the current bone density.The comparison of the predicted results with the corresponding experimental ones shows that this model can quantitatively describe a time-dependent process of bone remodeling.

抄録全体を表示

The structure of engineering ethics was analyzed and it was divided into five categories.The first category is "ethics for human beings".The second is "profound understanding on purpose of engineering".The third category is "ethics for specialists".The forth is "ethical basis on culture and organization".And the fifth category is "One's own ethics and standard of one's action".Although engineering ethics is based on ethics for human beings, it is not universal because it is strongly affected by history, religion, Western or Eastern civilization and other factors.The defintion of engineering purpose is thought to be indispensable for considering the ethics, but it is still unsettled and engineers have not been able to reach a consensus.Engineers find it difficult to set their own ethics and the standard of their action under their circumstances.As the results of the engineer's efforts cannot be refused by society even if it is ill-suited for it, the engineer must seriously consider the ethics.

抄録全体を表示