Composite laminated plates have been widely applied to aircraft primary structures. However, composites have remarkable mechanical anisotropy, and material design on stacking sequences is needed. In recent years genetic algorithms have been worthy of notice as solutions for combinatorial optimum problems. Some reserachers have applied the genetic algorithm for optimization of stacking sequence, but not for stacking number. Therefore, three new approaches were proposed and examined in detail in this study. A 'two species GA model' uses two species which differ in their stacking numbers. The choromosomes of meta populations have one less genes by one than the chromosomes of actual populations in this model. However, these populations are independent of each other. A 'mixed two species model' is similar to the two species GA except for crossover, and the two species exchange their genes with each other. A 'mutant model' uses only mutation. Using these three models, a bending stiffness optimization problem was examined. As a result, both the 'mixed two species model' and the 'mutant model' are applicable in the special case that there is little difference between local minimum points, such as in this problem.

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The design methodology for braided composite tube was proposed. The weaving structures such as fiber orientation angle and crimp ratio of fiber largely affect the mechanical properties of braided composites, thus the analytical model has to represent faithfully the weaving structures. Therefore the analytical procedure involved the use of models from micro model to macro model. This method was applied to estimate flexural rigidity and initial fracture stress of braided tube under bending load. The flexural rigidity decreased with increase of fiber orientation angle, which was the angle formed between the fiber bundles and the fabric axis. The flexural rigidity was enhanced by middle-end-fiber and the effect varied with the location of middle-end-fiber. The position at which initial fracture occurred was changed depending on the fiber orientation angle. In the case of small fiber orientation angle the initial fracture stress depended on the strength of the cross resin element, so that the initial fracture stress was not always enhanced by the middle-end-fiber.

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This paper presents a micromechanical study of the effective heat conduction and thermoelastic properties of a twisted-cord/rubber composite. The homogenization method is utilized to define the overall effective properties on a macro scale, based on the microscale behavior of the composite. We develop a homogenization analysis system for heat conduction and thermoelastic problems. The microscale boundary value problem, defined over a periodic unit cell of the composite, is solved using the finite-element method. After we discuss the accuracy of this system, effective orthotropic properties are computed using this system for the twisted-cord/rubber composite as a function of pitch length.

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Fracture processes in the bending of Si₃N₄-steel joints were investigated. The initiation stresses of interface fracture and cracked areas were measured by the ultrasonic method. The results obtained are as follows. (1) The increase of the ultrasonic echo height corresponds to the increase of the specimen compliance. Using the ultrasonic method, the interface fracture process can be detected. (2) The interface crack grew on the interface in a stable manner with increasing stress intensity factor, K₁. (3) At the maximum stress, the interface crack deflected to the ceramic side in an unstable manner. The criterion for the deflection is that the stress intensity factor K₁ for the interface crack taking into consideration the joining residual stress component must reach the K_IC for Si₃N₄.

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Fatigue fracture behavior was investigated for transparent PMMA, AS and PC samples with few short glass fibers fabricated by the injection molding method. Using these samples, the deformation behavior around the interior fibers was observed through an optical microscope. It was found that the fracture for PMMA and AS occurred due to crazing at the ends of the fibers, while the debonding of the fibers from the matrix induces ductile or shear cracks for PC.

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The fracture mechanism of short-fiber-reinforced Acrylonitrile Styrene composite (FRAS) is studied by means of the acoustic emission (AE) technique to examine the effects of fiber content and for comparison with short-fiber-reinforced Acrylonitrile Butagiene styrene composite (FRABS). It is found that the loads of P_b and P_C, P_b is a load which the micro-defects connect to grow the crack and P_c is a load which the crack grow the unstable fracture, increase with an increase in the fiber content, and the loads of FRAS are lower than those of FRABS due to the butadiene in the matrix resin. It is also found that a difference between the damage zone sizes and the fractographs appear at the notch tip due to the fiber content. The AE characteristics of FRABS due to the inclusion of butadiene are clarified through comparison with those of FRAS.

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Fretting fatigue tests under two types of fretting contacts, flat/flat and flat/cylinder, were carried out in order to investigate the effect of contact pad geometry and contact pressure distribution on fretting fatigue behavior. By changing the mean contact pressure level from 30 MPa to 1.5 GPa, the effect of the mean contact pressure on fretting fatigue properties was also investigated. The main results obtained are as follows. In the case of flat/cylinder contact, the configuration of contact pad was changed by cyclic wear with repeated fretting cycles. The mean contact pressure calculated using actual contact width is useful to evaluate the fretting fatigue properties, similarly to the case of flat/flat contact. Fretting fatigue strength and fatigue life decreased with increasing mean contact pressure and attained a constant value when the mean contact pressure was higher than about 100 MPa. Frictional force is one of the dominant factors affecting fretting fatigue properties as well as stress amplitude. The proposed fretting stress amplitude which is calculated using stress amplitude and frictional force amplitude is an effective parameter to evaluate the fretting fatigue life.

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A plane bending fatigue test was conducted in air to investigate fatigue behaviors of stainless steel (SUS304) coated with alumina by the plasma-chemical vapor deposition (P-CVD) method and ion-plating, one of the physical vapor deposition (PVD) methods, respectively. Although some difference in extent existed depending upon the coating treatments, an increase in the fatigue limit of coated specimens as compared with that of the base metal was observed. Crack initiation in the coated specimen was delayed or prevented by the hard coating film on the specimen surface, because it acts as a barrier to the gliding of dislocations during fatigue, and therefore to the formation of slip bands. The fatigue strength of the coated specimen depended largely upon the suppression effect of slip deformation and the damage behavior of the coating films. In the case of the ion-plated specimen, fatigue cracks were induced at the base metal surface, where flaws in the coating film could not suppress the slip band formation.

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Rotating bending fatigue tests were carried out on plain specimens and specimens with a circumferential notch of a 5052 aluminum alloy in order to investigate the effect of tensile pre-strain on the fatigue strength. The initiation sites of slips or cracks tended to localize in grains due to the cyclic softening phenomenon by the pre-strain, though the initiation lives of both annealed and pre-strained materials were nearly equal to each other. The crack growth rates in the pre-strained material were slightly higher than those in the annealed material. Regardless of pre-strain, the crack growth rates were expressed by the small-crack growth law (dl/dN=Cσⁿ_al) in these materials.

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The aim of this study was to investigate the effects of surface modification by ion implantation and notch radius on the fatigue life, crack initiation and early crack growth behavior for pure titanium. Three-point bending fatigue tests were carried out using an electro hydraulic fatigue testing machine under a frequency of 20 Hz and a stress ratio of R=0 in laboratory air at room temperature. The fatigue specimens used were smooth and notched specimens with the notch radii of 0.1, 0.25, 1 and 2 mm. The fatigue crack initiation and the early crack growth were successively observed using an optical microscope adopting a plastic replica method. The main results obtained are summarized as follows. (1) The fatigue life of pure titanium was decreased by the ion implantation. (2) The fatigue crack initiated from the notch root irrespective of ρ, Δσ and ion implantation. (3) The early crack growth patterns were divided into two types : the first type, in which the main crack grew continuously until the final fracture, and the second type, in which the main crack initiated from the notch root and then the secondary crack appeared in front of the main crack. The second type of crack growth tended to be observed with increasing Δσ and decreasing ρ. (4) The fatigue life of the second type of crack growth was greater than that of the first type of crack growth. (5) The first and the second types of crack growth were actually controlled by the same condition of mechanics which is the σ/Δσ value of about 1.5.

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The plane elastic problem of a crack in an isotropic half plane joined to an anisotropic half plane is analyzed by the body force method. In numerical analysis, a fundamental solution for the force acting on a point in an isotropic-anisotropic two-phase medium is used. Based on numerical results, the effect of the anisotropic phase on the stress intensity factors of the crack is investigated.

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Fracture toughness tests were performed at -50°C in the ductile-brittle transition temperature region for a low-strength steel SM400C using 0.3T, 0.5T, 0.8T and 1T compact specimens. All the locations of the cleavage crack initiation sites and fibrous crack shapes were investigated in detail from the fracture surface using by a scanning electron microscope and a binocular stereoscopic microscope. The probabilistic characteristics of cleavage fracture toughness and the thickness effect of cleavage crack initiation sites were analysed systematically. All cleavage crack initiation sites were found within a certain distance from the specimen surfaces. By locating all the sites and investigating fibrous crack shapes, the plane strain regions in specimens were deduced. The criterion for obtaining plane strain at the midplane of the specimens is given by B≥0.004(K_C(J)/σ_ys)²+0.01. This criterion indicates the specimen thickness necessary for the plane strain condition to be fairly smaller than the size requirements in ASTM Standard E399.

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By using the eigenfunction-expansion method, the authors have discussed the crack tip singularities of various open cracks meeting at the interfaces of different materials for a solution to plate-bending problems. The thin plate theory (i.e., classical theory of a plate without shear deformation) was utilized for the calculation of sectional forces such as shear force and bending moment when they were provided with free boundaries at the crack interfaces. Numerical results are illustrated in this paper.

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Longitudinal tensile tests were conducted on necked-on-thickness specimens to clarify the factors affecting fracture mode transition in unidirectional CFRP. Specimens having fiber volume fraction ranging from 30% to 70% were tested in the range of environment temperature from room temperature (23°C) to -150°C, and the fracture morphologies of each specimen were examined. The results revealed that a transition of the fracture mode from interlaminar shear fracture to tensile fracture occurred when the thickness of the necked region (t), fiber volume fraction (Vf) and testing temperature decreased. This transition is due to the change in the relationship between tensile fracture load, P^*_σ, and interlaminar shear fracture load, P^*_τ. The tensile fracture mode is more likely to occur at low values of Vf, small t and low testing temperature. A three-dimensional fracture mode map showing the effects of these three factors on fracture mode is presented.

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This paper presents a numerical analysis technique for shape optimization of linear elastic structures subject to multiple loading conditions. The technique presented here is based on the traction method for determining the domain variation that reduces the objective functional. Using the speed method, a volume minimization problem is formulated in which the mean compliances associated with individual load cases act as constraints. The shape gradient function, which is equivalent to the shape sensitivity, for this problem is obtained using the Lagrange multiplier method. With the traction method, the domain variation is numerically analyzed using a commercial FEM code. A method is also proposed for finding the domain variation so as to satisfy equality and inequality constraints. The analytical results show the effectiveness and practical utility of the proposed method in solving shape optimization problems involving multiple loading conditions.

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This paper is concerned with an analytical formulation and a numerical solution of the thermal elasto/visco-plastic deformation of multi-layered moderately thick shells of revolution subjected to thermal loads due to fluid. The temperature distribution through each layer thickness is assumed to be a quadratic curve and is determined using the equations of heat conduction and heat transfer. The equations of equilibrium and the relations between the strains and displacements are derived from the Reissner-Naghdi theory. For the constitutive relations, the Perzyna equations are employed. As numerical examples, two-layered cylindrical shells composed of mild steel and titanium subjected to locally distributed thermal loads due to fluid are analyzed. The results show that the present method gives correct initial responses and that temperature distributions, stress distributions and deformations are significantly varied depending on the ratio of the thickness of the titanium layer to the shell thickness.

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Roughening of the internal contact surface of polycrystalline copper during compressive plastic deformation is studied. Rectangular split block specimens with initially flat contact surface are pressed against each other. The roughening of the internal surface as well as that of the free side surface is measured with a stylus instrument. It is found that the degree of roughening of the internal surface increases in proportion to the applied strain, but that the magnitude is about half that of the free surface. The detailed shape of the surface roughness curve of the internal surface is different from that of the free surface. From observation with a scanning electron microscope, it is seen that mountains and valleys appearing on the free surface are sharp, while those appearing on the internal contact surface are rather rounded.

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Internal residual stress of an 18.2-mm-thick eight-pass butt-welded plate joint is evaluated using the inherent strain analysis. The residual stress distribution is obtained in detail along the thickness direction from measurements using multiple strain gauges. The residual stresses agree well with the results of thermal elastic plastic analysis, as well as with values obtained by direct measurement of the specimen surface, which is not used in inherent strain analysis. These results indicate that both inherent strain analysis and thermal elastic plastic analysis are effective in evaluating internal residual stress. Therefore, each analysis method should be selected after considering the object to be evaluated and the characteristics to be analyzed.

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The θ projection concept was proposed to describe a wide range of creep curve shapes, and has been mainly studied for ferritic steels in which applied stresses were kept constant until rupture. In this paper, we examined whether it could also predict creep behavior when the applied stress was changed during creep deformation. Conventional creep tests of an austenitic stainless steel were conducted at 700°C. In a series of stress-change creep tests, the initial stress of 90 MPa was loaded for a given test duration, after which the stress was increased to 140 MPa. Creep strain produced by the initial stress was determined to range from the primary to the tertiary stage of creep. Employing the θ projection concept and the strain hardening law, creep behavior after the change of the applied stress was estimated. Estimated creep curves agreed well with experiments when the creep strain due to the initial stress was within the early part of the tertiary stage.

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This paper describes a new automated system for analyzing the stress intensity factors of three-dimensional cracks. Mesh refinement is well controlled by the fuzzy knowledge processing technique, while nodes and tetrahedral elements are generated quite rapidly by the computational geometry techniques. Material properties and boundary conditions are easily attached onto a generated mesh by clicking parts of geometrical model, such as loops or edges, using a mouse, and by inputting values. For accurate analyses of the stress intensity factors, the singular elements in which mid-point nodes near the crack front are shifted to quarter-points are automatically placed along the three-dimensional crack front. The complete finite element model generated is given to one of the commercial finite-element codes, MARC, and a stress anaysis is performed. Stress intensity factors are also automatically calculated, using the displacement extrapolation method. To demonstrate the practical performance of the present system, it is applied to the analysis of surface cracks in a plate subjected to uniform tension.

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This paper describes a quantitative fractographic technique using scanning electron microscopy (SEM) and scanning probe microscopy (SPM) of scanning tunneling (STM) and atomic force microscopes (AFM). The techniques quantitatively evaluate the three-dimensional shapes of fracture surfaces. For the technique using SEM, software based on supercomputer, image processing and pattern recognition technique, is applied to a pair of stereofractographs, and a three-dimensional shape is reconstructed. The STM and AFM techniques evaluate surface topography on the nanoscopic order. From the obtained three-dimensional shapes of brittle cleavage or intergranular fracture surfaces of steels, ceramics and single crystalline silicon, surface area ratio, fracture roughness and profile roughness parameters were computed with various scanning areas and measuring units. Attention was also paid to a fractal nature of a fracture surface ; the relationships between ductility and three-dimensional parameters, and nanoscopic fracture morphology were discussed.

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The stress and displacement are analyzed at the boundaries of cavities or rigid inclusions having various diamond shapes with sharp corners under in-plane and out-of-plane loadings. The stress singularity factor around the corner point of the hole and rigid inclusion is examined. The relationship between the crack opening displacement (COD) and direction angle of the loads at infinity is discussed. The analysis is based on the complex variable method using a conformal mapping technique. Numerical results are in agreement with those of several investigators as particular cases of our solution.

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A method of elastic analysis is studied for SCF {single-wall corrugated fiberboard made of different kraftliners (KL : KL₁ and KL₂)} under uniform bending in the moment axis perpendicular to the machine direction. The numerical calculation is performed according to this analysis method. The following results are obtained. The Maximum stress σ_{k1 max} (maximum of absolute stress for KL) is on the outer surface of the thin KL (thickness T_k1 of KL₁<thickness T_k2 of KL₂), and increases with the decrease of T_k1 and the longitudinal elastic modulus for the KL₁. The maximum stress σ_{s max} for SCM (semichemical corrugating medium) is at the KL·SCM joint on the inner SCM surface of the thin KL side. Consequently, σ_{s max}decreases with the decrease of the wavelength and with the increase of the wave height and T_k2 for SCM. The change of σ_{s max} with the change of T_k1 is small in comparison to the change of σ_{k1 max} within the range of change rate 0.3 (=ΔT_k1/T_k1) for T_k1.

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The compression strength and the shear elastic modulus of an aramid honeycomb core have been studied theoretically and experimentally. Equations have been proposed for calculation of these characteristics based on the longitudinal and shear elastic moduli of the paper material composing the core and the detailed geometry of the honeycomb shape. The effects of single and double wall thickness of the materials are taken into account in the equation. The predicted mechanical properties showed good agreement with the test results although a difficulty was found in the determination of the shear elastic modulus of the paper material. It also became clear that the aramid papers used showed considerable anisotropy which seemed to strongly influence the shear property of the core.

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The laminated rubber bearing consisting of rubber and steel plates has been widely used in base structures to absorb earthquake vibration. The function of this bearing is to support all the weight of the structure and protect the structures from shear vibration by earthquake. Due to the nearly incompressible property of hyperelasticity, the displacement-based finite-element solutions cause large errors in pressure solutions. In order to overcome this shortcoming, a mixed method has been proposed, where pressure and displacement fields are developed as independent unknown variables. Finite-element solutions depend upon shape function and the numerical integration technique ; however, the suitable numerical condition for a laminated rubber bearing has not been fully discussed. The present paper will show the mixed finite-element formulation in rate type for hyperelasticity, and show numerical examples of the laminated rubber bearing system in shear deformation to clarify the advantage of the analysis method and the fundamental feature of mechanical response.

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A self-adaptive method for the determination of element degree was developed for boundary element analysis of two-dimensional elastic problems. This method is based on acquiring the desired accuracy for each boundary element. From the numerical experiments, the relationship ξ=k(1/P)^β was deduced, where ξ is the ratio of the integral of the squared error to the integral of the squared exact value, Ρ is the element degree and β is the proportional constant. Applying this relationship to the two results for different element degrees, the element degree for the third analysis is decided. A computer program using this self-adaptive element degree determination method was developed and applied to several two dimensional elastic problems of various shapes. The usefulness of this method was illustrated by these application results.

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This paper presents the formulation of a boundary element analysis method for handling contact problems, and the technique for high-speed contact analysis using a supercomputer. This formulation is based on the idea of joint blocks for joining adjacent blocks, and it indicates contact states. Contact analysis for obtaining contact states requires an iterative process. This process is normally very time-consuming. We introduce a new, faster technique for carrying out this process. The required supercomputer CPU time for this process is examined. The iteration time with the new technique is about one-tenth that of the conventional process.

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By a new numerical approach using the indirect fictitious-boundary integral method with the time-dependent fundamental solution, analysis of the elastodynamic contact problem is performed. First, to verify the propriety of this method, the well-known case of an infinite medium having a spherical cavity subjected to impulsive pressure over its inner surface is analyzed, and it is confirmed that the present results agree well with the well-known analytical solutions. Next, more complex problem of a sphere impulsively compressed by two rigid flat surfaces is treated, and the stresses and displacements are accurately analyzed. In conclusion, the applicability of the present method to the elastodynamic contact problem is verified.

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Shear band is considered as localized necking where multi-solutions can exist on the necking plane constructing the boundary between the shear band and its outside. Therefore, shear band is substantially identical with localized necking. The necking plane is the plane with a discontinuous velocity gradient. On the other hand, characteristic planes are planes over which solutions cannot be extended without additional information, because some of the derivatives on these planes cannot be determined by their governing equations alone. Characteristic planes have the properties necessary for the necking plane, and they can have no other modes but those of two kinds under plane strain rate. Furthermore it is proven that the equilibrium condition on the discontinuous plane cannot provide useful information for determining deformation at the onset of shear band, when the relative rotation brought by the occurrence of multi-solutions is taken into account between the regions separated by the discontinuous plane. Thus, the rotation between the regions must be left out of consideration to obtain the condition by which the onset of shear band can be predicted.

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The present paper deals with the effective slenderness ratio of long columns having different cross sections. First the slenderness ratio defined in current standards is discussed to clarify the difficulties which arise when the ratio is applied to columns having different cross sections. Secondly, a new effective slenderness ratio is proposed for columns having different cross sections. Finally, the proposed effective slenderness ratio is applied to a two-cylinder column having piece wise constant cross sections and a cylindrical column having linearly varying diameter.

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A new analysis method for nonlinear inverse problems was developed. This method consists of the following procedures. 1. The singular value decomposition of the coefficient matrix is performed, and then the rank is appropriately reduced. 2. A set of solutions is represented by Moore Penrose's solution and null space. 3. The solution is obtained by fuzzy reasoning using the set of solutions and a priori information which are expressed as fuzzy membership functions. Since the solution is identified by taking into account a priori information, the iteration converges quickly and stably, and oscillatory solutions can be avoided. Example problems were solved by this method in order to demonstrate its accuracy and applicability.

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The strain and stress behavior in a coil spring of a Ti-Ni SMA were investigated over a wide range of elongation, for the case of zero axial twist because of the simple calculation of shear and normal strain with the geometrical condition only. The basic σ-ε and τ-γ relations of the SMA material were obtained from the results of a tensile test and torsional test carried out under several constant temperatures, using a φ1 wire specimen. The strain criteria for start and finish of transformation under the combined strain were expressed by a strain circle and a modified strain circle, respectively, in each temperature. The simulation for load-elongation behavior of the SMA coil spring based on the basic stress-strain curves and the strain criteria under the combined strain showed a good correlation with experimental results.

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An ultrasonic technique was developed to study the characteristic abrasion pattern on a rubber surface under stick slip motion and to demonstrate the precisely contact pressure measurement at the end of contact. Experiments were conducted using short cylindrical rubber specimens pressed onto the rotating acril disk. It was observed that the abrasion pattern was significantly dependent on the variation in contact pressure. In addition, the experimental results showed that the formation of abrasion pattern on the middle area of contact was stimulated by the stick slip motion.

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Problems on robust structures are classified and examined from the point of view to obtain more suitable structures in the upper design process. The design method proposed by one of the authors in a previous report can be utilized for the design of robust structures in a narrow sense ; however it is also pointed out that much attention must be paid to the selection of reference functions for the design of robust structures in the broad sense. In this paper, we initially treat the static problems where an elastic strain energy is chosen as a typical reference function for static problems of robust structures in the broad sense, and two kinds of peformance indexes are discussed. One of them consists of the elastic strain energy and the other consists of the sensitivity of the strain energy to design parameters. Robust structures are designed by minimizing the value of the performance index. Here, general characteristics of these performance indexes are focused on and discussed using numerical examples. It is clarified that the robust structure for static problems in the broad sense can be effectively designed using these performance indexes for most cases, but there are cases where these performance indexes could not be always applied. Therefore, a different kind of performance index for robust structures in a broad sense must be developed in future studies.

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Recently, adaptive structures have been the focus of much attention because they change their shapes or characteristics to the optimum according to the mission or the design requirements. As a basic study on such adaptive structures, this paper attempts to control the deflection curve of a beam to the desired one using actuators. We obtain, by symbolic manipulation, the optimum solution for the moments which are applied to each part of a divided cantilever beam in order to obtain the desired deflection curve. The theoretical result is compared with the experimental one where the beam is deformed by the actuators using shape memory alloy wires.

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Scoliosis is a spinal deformity that is defined as a pathological frontal curvature with decrease of the physiological sagittal curvature, and must be evaluated three-dimensionally. We present a morphologic curve to express the three-dimensional configuration of a scoliotic spine from two plane radiograms, and evaluate spinal curvature three-dimensionally. The morphologic curve can be formulated from two plane curves approximating the frontal and sagittal arrangements of the centers of vertebral bodies. Furthermore, the Cobb angle, which is widely used in orthopaedics, can be calculated three-dimensionally as the maximum angle between two tangent vectors of the morphologic curve. In 45 spines with idiopathic scoliosis, the configurations of spines were extremely well approximated by the morphologic curves. Three-dimensional Cobb angle was significantly larger than frontal Cobb angle. Since the three-dimensional Cobb angle includes the sagittal and frontal curvatures, it can be used for three-dimensional evaluation of the scoliotic spine.

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