A numerical method to analyze three-dimensional stress waves in a metal laminate is presented, when an impulsive load is applied to the laminate. The finite difference method based on integration along the bicharacteristics is used for numerical analysis of three-dimensional stress waves in the elastic/viscoplastic laminate. Numerical results show the effects of material properties of the metal laminate on the propagation of the stress waves. The propagation of the plastic front is also affected by the impulsive loading condition significantly. This method has a wide application to dynamic problems of elastic/viscoplastic laminated media.

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In this paper we propose a simple method for identification of multiple impact forces on a simply supported orthotropic laminated plate. Acceleration responses at several points in the interior of the plate are measured in order to determine locations and histories of the impact forces. The present method can identify the impact forces at any arbitrary locations of the plate with every measurement of acceleration. First, the identification algorithm is shown for single and double impact forces at arbitrary locations on the plate. Next, through the numerical examples we examine the effect of the number of measurement points on the identified results and the measurement errors are also taken into consideration in the identification. The validity of the present method is shown by comparing the present results with exact ones for locations and histories of impact forces.

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In case of three points bending of the CFRP laminate composed of orthogonal stacking (0°/90°…), where longitudinal direction is taken as 0° axis, the fracture aspects are mainly dominated with matrix cracking (transverse crack) in 90° layers, fiber breaking in 0° layers and delamination on the interfaces between 0° and 90° layers spreading toward longitudinal direction. In the present study, numerical analysis for damage propagation of CFRP laminated beam subjected to transverse load is carried out with finite element method (FEM). Stress criterion is employed for the inspection of transverse crack and fiber breaking, while energy release rate is applied to evaluate the propagation of delamination respectively. Some numerical calculations for the CFRP laminated beam demonstrate usefulness and validity of present method through the comparison with the experimental result.

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In order to determine the characteristic feature in the deformation behavior of particulatereinforced composite material, a constitutive equation that takes into account the characteristic length scale has been developed using the strain gradient theory. By means of the plane-strain finite element method with the proposed constitutive equation, a series of simulations of inhomogeneous deformation behavior of composite materials with different volume fractions of reinforcement, particle size and distribution pattern of reinforcement have been performed. As a result, it has been determined that the resistance of composite material to deformation is substantially increased with the refinement of the particle size under constant volume fraction of reinforcement. Furthermore, the regulaization of the distribution pattern which increases the value of the maximum strain gradient in the matrix contributes toward improving the resistance to deformation.

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In general, most of execution time for large scale forging simulations by rigid plastic finite element method is spent to solve linear equations called stiffness equation. For speedup of large scale forging simulations, it is necessary to solve stiffness equation at high speed. In this paper, we present the result of accelerated computation for stiffness equation by the parallelized conjugated gradient method on the distributed multiprocessor system called cluster of workstations. As a result, the cluster of workstations, which are inter connected hierarchically by high speed network, spend less communication time than the ordinary non-hierarchical cluster of workstations. By using high speed network TPDDI (Twisted Pair Distributed Data Interface) and three-class model of hierarchical cluster of workstations which has two layers of slave CPUs, we achieved 50% reduction of communication time and about fivefold speedup of execution time of the parallelized conjugated gradient method by sixteen slave CPUs.

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Ratchet is a phenomenon that local plastic strain accumulates when a highly pressurized piping system repeats yielding and unloading under cyclic loading such as bending and torsion. In this paper an elasto-plastic FE analysis program is developed for the dynamic design of piping systems in which ratchet is anticipated. For this purpose, geometrically nonlinear elasto-plastic solid elements are employed to model the part where ratchet may occur and the rest of the piping system is modeled by pipe elements. These two parts are combined each other by the penalty method. Through a numerical example it is demonstrated that ratchet is successfully simulated during the dynamic analysis of a piping system and it influences the dynamic response of the whole system.

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In the analysis of frictional contact problems with large deformation, use of convected coordinate system is a natural approach, by which the frame indifference of friction law can be maintained. However, in the case of finite element method, a problem arises due to the discontinuity of the local coordinates between elements when the sliding extends over the element boundary. In this work a method is proposed to solve this problem, i.e., although the formulation is essentially based on a convected coordinate system. the sliding term is re-defined as a spatial vector and is calculated using the reference configuration. Thus, the finite sliding due to large deformation can be treated regardless of the limitation of element coordinate systems. Also, the corresponding consistent tangent stiffness is derived to obtain quadratic convergence. The effectiveness of the proposed method is verified by a couple of numerical examples including an elasto-plastic frictional contact problem with large deformation.

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In this paper, the Adaptively Shifted Integration (ASI) technique with the linear Timoshenko beam element, which can be easily implemented with a minimum effort into the existing finite element codes, is applied to the debris impact analysis of framed structures in space. In this technique, the numerical integration point in an elastically deformed element is firstly placed at the optimal point for linear analysis. Then the integration point is shifted immediately after the occurrence of a fully plastic section in the element, using the previously established relations between the location of numerical integration point and that of plastic hinge, to form a plastic hinge exactly at the position of that section. The technique prouduces higher computational accuracy with fewer elements than the conventional finite element code. By expressing member fracture by a plastic hinge located at the exact position with a simultaneous release of resultant forces in the element, discontinuous problem such as this kind can be easily analysed even by the finite element code with the displacemental form. Contact between members, and the distribution of element mass before and after member fracture has occurred, are also examined. By using the algorithms described in this paper, sufficiently reliable solutions have been obtained in the debris impact analyses of a space module unit and the International Space Station, which is due to be constructed from November. 1998.

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Scatter in bolt axial stresses, when tightening a pipe flange with a number of bolts, is of critical problem. Bibel et al. recently proposed both experimental and numerical methods to give uniform bolt axial stresses at the completion of tighening operation. However, their method is not so attractive from the practical point of view because it needs preparatory experiments and it also involves some restrictions in executing numerical analysis. In this study, a numerical approach is proposed, which can efficiently evaluate the scatter in bolt axial stresses using FEM as a threedimensional elastic contact problem, and its validity is ascertained by experiment. Specifically, the scatter in bolt axial stresses generated at the completion of tightening operation is estimated, when tightening each bolt one by one with equal axial stress. In addition, it is also investigated how much initial bolt stresses are needed to achieve uniform axial bolt tension in the final state. The analytical objects are pipe flanges specified in JIS B 2238.

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The Free Mesh Method (FMM) is simple, accurate, and suitable for parallel processing. In this method, the connectivity between nodes and elements, that is essential in usual Finite Element Analysis, is not required. This paper describes a more efficient processing with local Voronoi diagram for preprocessing at the stage of creating a set of temporary local elements in the FMM. Adopting the surface patch model to describe analysis model, the present FMM was applied to three-dimensional complex shape. In the analysis of three-dimensional steady thermal conduction problems of complex geometry, the present method was shown to work in reasonable calculation time.

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It is indispensable to understand the adhesion strength between the film and the substrate for evaluating the film integrity. In case of calculating the adhesion strength numerically, ab-initio molecular dynamics based on quantum mechanics is necessary. In this paper, in order to solve fundamental process of the nucleation of the diamond based on quantum mechanics, ab-initio molecular dynamics simulation of the nucleation of the diamond on the silicon substrate is conducted. Only one carbon atom is used for the simulation because fundamental process of the nucleation is requested to be shown. Two types of the silicon substrate, one consists of perfect crystal and the other has a point defect, are used for the simulation and compared each other. Car-Parrinello method is used for ab-initio molecular dynamics calculation. The action of the carbon atom in the simulation, and the situation of the combination between atoms are shown.

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Ceramic matrix composites based on silicon carbide (SiC) matrix offer high strength, toughness and oxidative stability up to 1200°C. However there are many cases in which it is difficult to evaluate stiffness and stress of SiC/SiC composites because of material's microscopic factors. Therefore, in this paper, (1) the relationship between stiffness and porosity were estimated by a Monte-Carlo simulation technique based on a finite element method. Results approximated to the equation of Wagh et al. (2) The effect of sin waved fiber was analyzed. Microscopic-scale stress distribution was investigated.

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A method was investigated for nondestructive evaluation of 2-D crack or slit depth by measurement of temperature difference between two points on the material surface in non contact. In the first, experiment was performed on the specimens of 304 stainless steel with a slit. Local temperature field around the crack or slit was formed by heating small area near the crack or slit with Nd : YAG laser beam, and temperature at a point was measured by infrared thermography. The slit depth was evaluated exactly by comparing experimental results with numerical analysis of non-steady heat conduction problem. Next similar experiment was carried out to evaluate the fatigue crack depth. However it was difficult to evaluate crack depth. because formed temperature field hardly changed either existence of the crack or not. So the effect of crack opening displacement on the temperature field was examined. It is shown that evaluating crack depth is possible by the present method, provided that load is applied to open the crack.

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It was shown that the fracture mode of a mixed-mode crack in a homogeneous ductile material changes from mode I (opening type) to mode II (shear type) or vice versa by changing the loading type in the neighborhood of a crack tip. The characteristics of this fracture mode change may depend not only on the loading type but also on the brittle/ductile property of a material. Thus, in the present study, the fracture experiments of the specimens with an inclined crack made up by using acryl resin and aluminum alloy are carried out under tensile and shear type loadings and it is confirmed that the different fracture modes can be realized between the specimens of above two materials even under the same loading type. Moreover, the CED in an arbitrary direction is evaluated through the finite element analyses corresponding to the experiments. Finally, it is shown that the observed fracture phenomena can be explained and the effects of brittle/ductile property of a material and loading type at the crack tip on fracture mode of a mixed mode crack can also be grasped in a unified way, by the fracture criteria based on the CED in an arbitrary direction.

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The effects of local damage fields on the asymptotic stress field of a Mode III crack in a nonlinear-hardening material or in a creep material are discussed. Two kinds of the damage distribution 1-D=h (0) (γ/γ_o)^m represented by a power function of radius γ from the crack-tip are postulated for the damage variable D, and the damage effects are included into the power-hardening law or the Norton creep law by means of the effective stress concept of continuum damage mechanics. For a given strain hardening exponent n of the power-hardening law or of the Norton creep law, the exponent p of the resulting asymptotic stress fields σ_ij^■γ^p is found to be governed by the exponent m of the power-law damage distribution. It is elucidated that when the exponent of damage distribution m increases, the exponent p of the stress field increase from a singular (negative) HRR exponent p=-1/(n+1) to a nonsingular (positive) value.

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The stress concentration factors for basic notch shapes in sheet specimens made of three kinds of materials with different thermoelastic constants and for cross shaped specimens which made imitation weld toe shape, and stress intensity factor ranges for CT and CCT specimens made of a mild steel plate were evaluated using a thermoelastic stress analyzer. The results were compared with finite element method or theoretical results. The stress concentration factors measured by the thermoelastic stress analyzer were slightly lower than those of the finite element method or theoretical results regardless of specimen configurations, and the error tended to increase with increasing stress concentration. The mode I stress intensity factor ranges determined by thermoelastic effect agreed with other comparable independent values in the range of error within 9% regardless of specimen type and stress ratio.

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The crossover of ropes in many layers around a drum is analyzed on differential geometry and calculus of variation with movable boundaries. As a geometrically nonlinear problem for linearly elastic ropes, the center line of ropes is modeled as a space curve which is restricted by the surface of the first-layer rope. The bending stiffness, tensile force and friction force acting on the rope and geometrical parameters of the hoisting drum are taken into account. The virtual work of the non-conservative tensile force and the bending energy of the cross-over are expressed by the first and second fundamental forms of the restrictive surface. Thereby the variational equation and boundary conditions are obtained. By the transformation of variables, the Euler equation is changed into an implicit form of the variable, and the expression of crossover is obtained. An experiment measuring the central angle of the cross-over is made to examine the result of theoretical analysis.

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A systematic study of the variation of elastic moduli and Poisson's ratio of sintered iron compacts of porosity (up to 0.6) has been carried out by measuring longitudinal and shear wave velocities. In this study, new equations of Young's modulus (E), shear modulus (G) and Poisson's ratio (v) as function of porosity (P) were proposed as follows ; E (P) = (-K_E·P+E₀)·(1-P) G (P) = (-K_G·P+G₀)·(1-P) v (P) =0.5 (-K_E·P+E₀)/(-K_G·P+G₀)-1 where K_E and K_G are experimental constants of Young's modulus and Shear modulus, respectively. And E₀ and G₀ are Young's modulus and shear modulus at P=0, respectively. In these equations, K_E, K_G, E₀ and G₀ at P&lnE;0.2 are different from those at P<0.2. Because the results of Poisson's ratio against porosity of sintered iron compacts show that downtrend of Poisson's ratio at P>0.2 was different from at P&lnE;0.2. The downtrend change is caused by pore connection as connecting pores increase and closed pores decrease at P&lnE;0.2. The fitting data of Poisson's ratio by these equations correspond with the measurement data by comparison with the published equations of many researchers.

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This paper analyzes the contact pressure distribution and the elastic deformation of a blanket in offset printing due to a contact force of the impression (or plate) cylinder with the blanket cylinder, considering anisotropic properties and the laminated construction of the blanket. The two dimensional elastic theory is applied to solve the contact problem of the blanket and the numerical solution provides details of the contact pressure distribution, the deformation of the blanket surface, and the contact width of the blanket with the impression (or plate) cylinder. Influences of Young's moduli and thickness of each layer of the blanket on the contact pressure distribution and the deformation of the blanket surface, are examined by the theory in detail. To prove the validity of the theory, experiments are carried out using the device developed to measure the contact pressure distribution and the deformation of the blanket. The calculated results are in good agreement with those of experiment.

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Uniaxial ratchetting characteristics of 316 FR steel at room temperature are studied experimentally. "Strain-controlled ratchetting" tests, in which maximum strain increases every cycle by prescribed amounts of strain, are done systematically in addition to conventional monotonic, cyclic, and ratchetting tests. Thus hysteresis loop closure, cyclic hardening and viscoplasticity are discussed in the context of constitutive modeling for ratchetting. The strain-controlled ratchetting tests reveal that very slight opening of hysteresis loops occurs, and that neither accumulated inelastic strain nor maximum inelastic strain induces significant isotropic hardening when strain range is relatively small. These findings allow us to conclude that uniaxial ratchetting of the material at room temperature can be brought about by slight opening of hysteresis loops as well as viscoplasticity without noticeable influence of isotropic hardening.

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The aim of this paper is to clarify the crush phenomena of a hexagonal honeycomb core of aluminum alloy under the static and dynamic loading. The peak load (buckling load), the effect of debonding of braze welding on a core and the energy absorption capacity are derived from experimental results using the ball screw type test machine and the Hoppkinson-bar method. FEM calculation is performed to investigate the effect of load condition on the crush load. The static buckling deformation occurs almost at center of the side plates, but under the dynamic load the local buckling deformation occurs on different places of side plates randomly. The energy absorption capacity is mainly dependent on the crush load after the peak load.

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The strength and mechanical properties of giant magnetostrictive materials fabricated by powder metallurgy and Bridgman method were investigated. The effect of the shape and volume of test pieces on compressive strength and compressive fatigue properties were examined for the powder metallurgy specimens. Test results showed : (1) The compressive strength of the powder metallurgy material specimens (PM) was about 2/3 of the Bridgman material specimens (BM), while the strength scatter of PM was smaller than BM. (2) The radial compressive strength was about 1/20 of the compressive strength, and both kinds of specimens showed brittle fracture features. (3) Specimens of both materials showed nonlinear stress-strain curves, and the modulus of elasticity rapidly increased with increasing stress in the low stress region. (4) The compressive strength of PM was influenced by the shape of specimens : the compressive strength of prism type specimens was lower than that of rod type specimens. However, the strength was not influenced by the volume of specimens. (5) There was an apparent fatigue limit at about 60% of the compressive strength for PM.

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It has been commonly accepted that effective proof testing demands rapid loading-unloading to prevent strength degradation, and that the truncated strength depends upon the rate of unloading. The interpretation of the characteristics in the proof test of ceramic materials seems to be derived from the work by Fuller et al who analyzed the problem by adopting the fracture criterion 「K₁&gne;K_1C ; K₁ ; the stress intensity, K_1C ; the critical fracture toughness」. In the present work, an analytical method is newly presented to characterize proof testing of a large population of ceramic samples. By analyzing the loading & unloading rate effect on the residual strength after proof testing, the accepted interpretation in proof testing has been rechecked ; it has become clear that the rapid unloading as well as rapid loading does not bring any improvement in residual strength distributions after proof test, but the average strength of survived samples rather decreases by the rapid loading and unloading. The obtained results are diametrically opposite to the ones which have been accepted as the common sense in proof testings.

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By assuming that the crack velocity a can be expressed as a power function of the stress intensity factor K₁, a&vprop;Kⁿ₁, the degradation of strength during proof test of ceramic material was analyzed, and Weibull distributions both for residual strength S_r and fracture strength σ_F after proof testing were analytically formulated. The analyzed results show that Weibull curve for the S_r value has a slope of about n-2 at low fracture probability levels (n ; proof test condition), and also show that the corresponding Weibull curve for the σ_F has a slope of about (n-2)·{(N-1)/(N-2)} (N ; fracture test condition).

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Effects of the temperature-dependence of matrix and fiber-matrix interface properties on the offaxis fatigue behavior of unidirectional T 800 H/Epoxy composite have been studied. Tensiontension fatigue tests were performed for seven kinds of plain coupon specimens with different fiber orientation angles at room temperature (RT) and 100°C. Using a non-dimensional effective stress defind on the basis of the classical static failure theories together with a formulation based on the continuum damage mechanics, a fatigue failure criterion was developed. The off-axis fatigue strengths at RT and 100°C decreased as the off-axial angle increased, and they were reduced significantly as the test temperature became higher. Almost linear S-N relationships were obtained in the whole range of fatigue loading up to 10⁶ cycles, irrespective of off-axis angles and test temperarures. Normalizing the maximum fatigue stress with the static strength at test temperature, the off-axis fatigue data eventually fell on a single S-N relationship which showed no apparent dependence on temperarure. This characteristic was described well by the non-dimensional effective stress which may be interpreted as a theoretical strength ratio. It was also verified that the fatigue damage mechanics model proposed can describe the observed off-axis S-N relationships and it has a potential capability in more practical fatigue failure analyses for multidirectional laminates.

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Fatigue behavior of unidirectional fiber-metal laminates GLARE 2 has been studied under various off-axis loading conditions. Tension-tension fatigue tests were performed for nine kinds of plain coupon specimens with different off-axis angles at room temperature. A non-dimensional effective stress implied by the classical static failure theories was applied as a fatigue strength parameter to the off-axis fatigue. Using the non-dimensional effective stress, a fatigue damage mechanics model was developed. Applicabilities of the classical composite fatigue failure models were evaluated on the basis of the observed off-axis S-N relationships. Off-axis fatigue stengths decreased significantly as the off-axial angles increased. Irrespective of the off-axis angles, almost linear S-N relationships were observed in the intermediate range of fatigue, and they were followed by apparent fatigue limits. The non-dimensional effective stress was found to be very useful to unify the off-axis fatigue data. The characteristics of the observed off-axis S-N relationships were described by the classical fatigue failure models. The predictive capability of the proposed fatigue damage mechanics model was almost comparable, which verified a potential applicability to fatigue life analyses for multidirectional laminates.

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In this study the auther carried out low cycle fatigue tests at room temperature in use of the flake graphite cast iron (FC-P) and the spheroidal graphite cast iron (FCD-P) of pearlite matrix structure, and then proceeded to estimate the fatigue life of the said two kinds of cast irons. Fatigue life prediction was made for each one of the testing materials in different graphite shapes by the Manson's universal slope method. As a result, the estimated life of FC-P was nearly as long as the life obtained from the experiment, but that of FCD-P was about 20% shorter than the one obtained from the experiment. Hence, the author introduced the modified universal slope method based on the plastic strain component under the Manson-Coffin rule obtained from the experiment, and applied it to the both testing materials. In this way, it became possible for the low cycle fatigue life of the two kinds of cast irons to be guided collectively by one formula.

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It is very important to evaluate damage levels of structures for prediction of fatigue fracture. Purpose of this study is to develop a methodology for evaluating fatigue damage and conditions by a nondestructive inspection technique. Low cycle fatigue tests were conducted for carbon steel specimens (0.15 and 0.45 wt.% carbon) under various fatigue conditions. During the tests, magnetic properties and a magnetomechanical acoustic emission were measured at predetermined number of cycles. The test results exhibited 480 pattern sets which describe the relationship between the measured parameters and the fatigue information such as the damage level (Cycle ratio N/N_f), the stress amplitude (σ_a) ann the stress ratio (R). A nondestructive evaluation system consisting of measuring and a neural network was proposed. The effectiveness of this system was demonstrated by comparing results of the neural network with experimental data obtained from the fatigue tests.

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Rotating bending fatigue tests were carried out for nickel-base superalloy Inconel 718 in air at room temperature and the elevated temperatures of 300°C, 500°C and 600°C using the 60 degree V-grooved specimen in order to investigate the influence of temperature on the notch sensitivity of the alloy. The notch sensitivity was assessed in terms of the limiting stress for crack initiation σ_w1 and that for crack growth σ_w2, based on the Linear Notch Mechanics (LNM). It was found that the fatigue limits σ_w1, σ_w2 of notched specimen can be evaluated by LMN at each temperature. Although the notch sensitivity of Inconel 718 to the two fatigue limits is relatively low considering its high static strength at all the temperatures, especially to the fatigue limit for crack growth, it becomes more sensitive at the elevated temperatures than at room temperature. The results were discussed with the effect of temperature on the arresting behavior of fatigue crack growth.

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This paper presents an easy determination method for the dynamic constitutive equations of materials with strain-rate sensitivity. The proposed method will easily determine a simple constitutive equation from the results of ordinary impact tests. Previously, the determination of dynamic constitutive equations is usually attempted from a metallographical or physical standpoint. Such attempts often need detailed consideration, and most of the derived equations become complex. Furthermore, the estimation of the involved unknown parameters in the equations is also difficult. If simple dynamic constitutive equations can be determined without especially physical considerations, the simulation for mechanical deformations caused by impact will become easy. Thus, this paper tries to determine dynamic constitutive equations as polynomials which can describe various curves and be easily treated. Polynomials approximate given data more precisely with increase in the number of the involved parameters. However, as the number of parameters increases, the calculation of the equations become more difficult. Furthermore, it is not necessarily appropriate that the equation fits measured data considerably precisely, because the measured data usually contain some errors. Therefore this paper proposes the determination method for dynamic constitutive equations based on an information criterion 'AIC'. The information criterion will evaluate the appropriateness of approximate equations and reveal the required minimum number of the parameters to be used. The proposed method demonstrates that 'AIC' will easily determine appropriate dynamic constitutive equations.

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