This paper discusses the environmental degradation behavior of carbon-fiber-reinforced plastic (CFRP) laminated material, due to water absorption. In order that the CFRP materials can be used more effectively as structural members with higher safety and reliability for factories, it is considered indispensable to understand in detail the influence of environment factors that accelerate dynamic degradation, such as fatigue. A summary of the results is as follows. Fick's diffusion law is applicable to analysis of water desorption and absorption characteristics of the uni-directional fiber reinforced (UD) and plain woven reinforced (CL) materials. The desorption and absorption processes are diffusion-controlled processes within matrix resins, including the skin layer. The properties of the skin layer significantly influence the fatigue life of the CFRP laminates. Furthermore, the decrease of fatigue strength is caused by the lowering of molecular weight in the regions of resin close to the reinforced fibers in the skin layer, when a small amount of absorbed water and repeated stress coexist.

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This paper discusses the possibilities of improving of fatigue strength through changing the characteristics of the surface layer (skin layer) of SMC and CFRP laminated materials by ultraviolet (UV) ray irradiation under specific conditions. The experiment for surface improvement by UV ray irradiation was performed using an ultra-high-pressure ozoneless mercury lamp. For the UV ray source, a primary wavelength of 365 nm in the long-wavelength region was selected. The surface of the specimen was irradiated by a direct irradiation optical unit. The environmental fatigue tests were performed using the 4-point bending method by an electrohydraulic servo-type material testing machine. As a result, under specific UV ray irradiating conditions (wavelength, irradiation intensity and the integrated luminous energy of irradiation), UV irradiation on the surface of SMC and CFRP laminated materials was found to contribute to the retardation of water absorption and the improvement of the fatigue life.

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Rotating bending and torsional fatigue tests were carried out on the specimens of ferritic spheroidal graphite cast iron. The initiation and propagation of microcracks were investigated through the successive observations by the plastic replica method. The fatigue limits in both types of loading are determined by the limiting stress for crack propagation. That is, after 10⁷ cycles of the stresses of fatigue limit, non-propagating cracks can be observed in both types of loading. The ratio of fatigue limit τ_w/σ_w is 0.86. The microcracks appear from both graphite and microshrinkage cavity in both types of loading. However, the crack which is related to final fracture appears from a microshrinkage cavity. The crack growth rate dl/dN of small cracks is determined uniquely by σ^8.5lin rotating bending and by τ^9.0l in reversed torsion.

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Total-strain controlled low-cycle fatigue tests were carried out at room temperature on three kinds of ductile cast iron (ferritic ductile iron ; FDI, pearlite-ferritic ductile iron ; P-FDI, and pearlitic ductile iron ; PDI) of round bar-type specimens with a small drilled notch. Fatigue deformation properties such as stress amplitude, plastic strain and cyclic stress-strain curve were measured, and the relationship between the strain amplitude and the fatigue life was investigated in the three cast irons. Propagation behavior of the surface fatigue crack initiated from the small notch was observed in detail at the surface. The fracture surface, the effects of graphite distribution and base microstructure on the crack growth behavior were investigated experimentally. The surface crack propagation rate da/dN was evaluated in the J integral range ΔJ, and the results for these cast irons were compared with the results for other metals.

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To clarify the effect of flaws in coating film on fatigue strength, cantilever-type rotating bending fatigue tests were conducted in air and in saline solution (3.0%NaCl) using the specimens of 0.37% C steel with flaws in titanium nitride (TiN) thin film coated by PVD and CVD methods. Flaws in the coating film on specimen surface were introduced by the application of 1.1∼1.6% static tensile strain before the test. The obvious decrease in fatigue life of the coated specimen with flaws was observed in both environments, as compared with that of an uncoated specimen and coated one without flaws. This behavior occured markedly at the fatigue in air, that is, the decrease of fatigue life is 90∼75% in air to 70∼50% in saline solution. Though film thickness is 3∼5μm, the flaw in the film acts as a notch effect for crack initiation on substrate. Many cracks were induced in the substrate directly under a flaw and formed a large crack by coalescence at the early stage of fatigue in air. In corrosion fatigue, corrosion pits at which crack initiates occur on the substrate under a flaw at the early stage of fatigue process and the incubation period prior to formation of pits disappears.

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To investigate the fatigue behavior of bonded ceramics, joint specimens (Si₃N₄/Si₃N₄ and Al₂O₃/Al₂O₃ butt joints) were three-point-fatigue-tested under static and cyclic loading at temperatures ranging from 300 to 1038 K in air environment. Fractographic observation was also carried out using SEM after the fatigue test. Restriction of the strain in the joint layer due to the difference of Young's modulus between ceramics and metals causes triaxial tension in the tension side of the joint layer, accelerating the nucleation of microcavities. Therefore the process of strength degradation owing to fatigue is controlled by the rate of either the cavity growth or crack growth, depending on which one is dominant. At lower temperatures, fatigue process is mainly controlled by crack growth, on the other hand, cavity nucleation and its growth seem to be predominant factor in controlling the fatigue process at higher temperatures. Therefore, the triaxial tensile stress component is a more important factor in evaluating the fatigue life of joints at higher temperatures. However, a fairly good estimation of fatigue life is obtained using conventional bending stress in the present investigation. It is also found that fatigue life can be estimated using bending strength of the joints.

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Fatigue strength and the failure process of a hole-notched glass FRP under tension-torsion biaxial cyclic loading were investigated in this paper. Thin cylindrical specimens were used. Fibers of the reinforcement (plain woven glass cloth) were aligned parallel to the longitudinal and circumferential axes of the specimen. The damage state at each biaxial stress ratio (α : the ratio of normal stress to shear stress) was observed macroscopically and microscopically. The experiments reveal the following results. The fatigue damage progression is dependent on the biaxial stress ratio. When α=1/0, damage spreads radially from the hole, but only covers an area of π/4 to either side of the circumferential axis, in both directions along the circumferential axis. When α=0/1, damage progresses radially along both longitudinal and circumferential axes. We call each of these a "fatigue band". Under biaxial loading, macroscopic and microscopic damage states have both types of damage at α=1/0 and α=0/1.

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Fatigue strength and stress-strain response of plain woven glass fabric laminates subjected to combined loadings with pulasating tension and alternate torsion were investigated in this study. To distinguish the difference of fatigue failure behavior between that under pulsating torsion loading and that under alternate torsion loading, the alternate torsion test was also conducted. Fatigue strength and stress-strain response under alternate torsion loading were compared with that under pulsating torsion loading. From the experiment, it is found that the normalized fatigue strength (which is cyclic biaxial stress divided by the static strength) under pulsating tension/alternate torsion combined loading is dependent on the biaxial stress ratio. The fatigue strength under alternate torsion loading is much lower than that under pulsating torsion loading. The stress-strain response also shows nonlinear behavior more strongly than that under pulsating torsion loading.

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Effective and conventional methods for the evaluation of fatigue-crack growth resistance and the prediction of fatigue life in conventional aluminum alloys are investigated. Under a high nominal stress, the small-crack growth law is applicable and the material constants in this law are estimated through the tensile strength of the material in many aluminum alloys, similarly as in steels. Therefore, the growth resistance of fatigue cracks and the fatigue life of any aluminum alloy can be evaluated using this law and the tensile strength. The validity of these evaluation methods is confirmed based on experimental results.

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Fatigue strength, crack initiation and small crack growth behavior in two kinds of squeeze-cast aluminum alloys such as AC8A-T6 and AC4C-T6 were investigated using plain specimens subjected to rotating bending fatigue at room temperature. Fatigue resistance of these alloys was almost same as that of the wrought aluminum alloys because of fine microstructure and of decrease in defect size due to squeeze-casting. Fatigue crack initiation site was at the eutectic silicon particle on the specimen surface or at microporosity in the specimen. Crack initiation life was successfully estimated from the evaluation of initiation site by the fracture mechanics and the statistics of extrema. Small fatigue crack growth of two kinds of alloys obeys the relation proposed by H. Nishitani et al., that is d(2c)dN= C(σ_a/σ_B)ⁿ(2c), where σ_B is the ultimate tensile strength. It was pointed out that an improvement of fatigue strength in cast aluminum alloy can be expected by refining eutectic silicon rather than by increase of static strength.

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Fracture toughness and stress-corrosion cracking (SCC) behavior of Al-Li 2090-T8 and 2091-T8 alloys containing small amounts of Zn were studied and compared with conventional high-strength alloys 7075-T6 and 2024-T3. The fracture toughness value (K_IC) and SCC extension rate (da/dt) as functions of stress intensity factor K_I were evaluated using precracked DCB specimens with S-L orientation of the extruded plate. With Zn addition of 0.7%, 2090 and 2091 alloys showed little decrease of K_IC and also superior SCC resistance as compared to conventional alloys in terms of the threshold value K_ISCC and (da/dt)_II in region II. Fract graphic and electrochemical observations suggest that SCC of these Al-Li alloys is a result of local anodic dissolution along grain boundaries.

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In this paper, we present an elastic solution for the axisymmetric torsion problem of an infinite cylinder with circular and circumferential cracks lying on the same plane. Expressing the stress component along the crack plane as an appropriate series, we reduce the problem to the solution of an infinite system of simultaneous equations. Numerical results are shown in order to discuss the effect of the two crack depths on the displacement and stress distributions at the crack tips and stress intensity factors.

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We examined the low cycle fatigue behavior under axial loading with maximum 4% constant plastic strain range, and the effect of the shapes of specimens having various dimensions of the central part on fatigue behavior was investigated. The experimental results obtained from two types of specimens were also considered from values of elastic-plastic finite element analysis from the standpoint of the small crack growth law. The main results obtained are as follows : (1) To obtain the correct fatigue life, the ratio of length vs diameter of the parallel part has only to be more than 1.5 in the cylindrical specimens. (2) The fatigue life of hourglass specimens is longer than that of cylindrical ones and the rate of increase is 50∼70% at most. The main cause of the longer life is the value of the longitudinal tensile stress around the narrowest part of hourglass specimens being smaller than that of cylindrical ones under the same plastic strain range.

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Cyclic fatigue behavior of silicon nitride was investigated at 800°C in air, and proof tests as a method of improving reliability of fatigue life were carried out at room temperature. Fatigue life distributions for σ_max=833 MPa were compared before and after proof testing on a Weibull plot. The truncated fatigue life distribution after proof testing did not coincide with the theoretical curve F_p (N_p), and some fatigue life data after proof testing were shorter than the theoretical minimum life N_pmin. F_p (N_p) and N_pmin were predicted when no slow crack growth occurred during proof testing. A statistical method was developed to predict actual truncated fatigue life distribution F_p'(N_f) and minimum life N_fmin after proof testing. The predicted curve was consistent with the experimental life data, and N_fmin≈0.27N_pmin. From the minimum life N_fmin predicted by our method, the influence of proof testing on fatigue life was estimated in terms of the degradation of truncation strength due to slow crack growth during proof testing. It was found that the truncation strength was ≈0.94σ_p, where σ_p is proof stress.

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Creep tests of a continuous fiber-reinforced metal matrix composite, SiC_CVD/Ti-15-3, were performed in the stress range of 800 to 1200 MPa at 450°C. The fibers were oriented at 0°C to the specimen axis, and the volume fraction of fibers was 35%. We measured strain and acoustic emission in the creep tests, together with observation of damage of fibers after the tests, and found the following. When stress is high, creep rupture occurs largely due to stress relaxation in the matrix in spite of the noncreeping property of fibers. Under such intermediate stress as 1000 MPa, which is lower than the creep strength based on the stress relaxation in matrix, creep rupture does take place owing to the degradation of fibers besides the stress relaxation in matrix. Under such low stress as 800 MPa, on the other hand, creep rupture hardly occurs, because the stress relaxation in matrix does not induce sufficient increase of fiber stress, and because evolution of internal damage is not significant.

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The fracture mechanisms and interfacial properties of single-fiber composites with different surface treatments of the fiber are examined by acoustic emission. The fracture surfaces are observed with a polarized microscope. As a result, it is confirmed that AE events are generated at every fiber breakage. It is found that the fracture mechanisms of SFC are different when the surface treatment of a fiber or a matrix resin is changed. A method to measure the mean fragment length and evaluate the interfacial shear strength of fiber/matrix is proposed using AE events which are almost equal to the number of fiber breakages. The difference in the interfacial shear strength due to the fiber surface treatment can also be identified by this method. From the observation of a fiber surface with SEM, it is also found that this difference in the interfacial shear strength depends upon the surface roughness of the fiber.

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Mixed-mode fracture of two glass ceramics with different grain sizes and soda-lime glass due to inclined knoop indentation flaws was studied in diametral compression tests. These tests were carried out under various environments of vacuum, air, and water. Mode I and mode II stress intensity factors at fracture and the directions of crack extension were analyzed. Fracture envelopes obtained from experiments under vacuum atmosphere indicated less sensitivity to mode II loading than those in existing theories, and less sensitivity to mode II loading of the glass ceramics than the soda-lime glass. It was considered that differences in the relative sensitivity to mode II of the glass ceramics and soda-lime glass are attributed to microstructure effects on shear resistance on the crack tip faces. The maximum stress theory modified by considering the shear resistance on the crack tip faces explained the experimental results well. In fracture under corrosive environments, both mode I and mode II stress intensity factors at fracture became lower in the order of vacuum, air, water, due to subcritical crack growth. However the sensitivity to mode II loading in glass ceramics was somewhat larger in a water environment than a vacuum environment due to the decrease of the shear resistance by crack tip blunting.

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A hybrid experimental-numerical investigation was undertaken to establish a crack kinking criterion and hence crack arrest at a tear strap under mixed-mode crack-tip deformation. Experimentally determined crack velocities and crack paths for 2024-T3 and 7075-T6 aluminum alloy, cruciform fracture specimens, 0.81 mm thick. with a 25.4-mm-wide and 0.81-mm-thick tear strap, were input to a dynamic finite-element program to compute the necessary fracture parameters. These results were then used to verify three-parameter crack extension and curving criteria under mixed-mode loading.

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The characteristics of mixed-mode fracture toughness in sialon were investigated by flexural tests using specimens with controlled surface flaws. The experimental results show that the obtained relationships between K_I and K_II at fractures are consistent with the theoretical ones derived through a modified energy-release-rate theory or Shetty's experimental equation. The value of mixed-mode fracture toughness increases with temperature or upon removing the tensile residual stress at crack tips, but the geometries of K_I-K_II relations at fractures do not change. While the mixed-mode fracture condition does not depend on the crack length, it does depend on the kind of materials.

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This paper deals with mixed mode fracture toughness and fracture mechanism in short-glass-fiber-reinforced polycarbonate. The fiber volume fractions of four materials fabricated by injection moulding are 0%, 10%, 20% and 30%, and short fibers in these materials were aligned mostly in the mould-fill direction. Mode I fracture toughness for a crack perpendicular to the fibers is higher than that for a crack parallel to the fibers, and the difference between the two "namely anisotropy" increases with an increase in the fiber volume fraction. The direction of crack extension and fracture toughness under mixed mode loading are affected by the anisotropy of the materials. In order to predict the fracture behavior from a mixed mode crack in anisotropic materials, a new criterion is proposed. Microdamage such as debonding of the fiber-matrix interface, fiber fracture and matrix plasticity, develops around a crack tip and acts as the toughening mechanism, especially in the case of crack extension perpendicular to the fibers. However, such a toughening mechanism does not sufficiently apply to a material with a high content of fibers in which the matrix plasticity and the microdamage are restrained in the vicinity of the crack surfaces.

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Residual stress distributions of Si₃N₄/SUS304 joints with insert layer of copper were analyzed by a 2-dimensional thermo-elastic-plastic finite-element method (FEM). By superposition of plane-stress and plane-strain models, the analytical result showed good agreement with the measurement result of the X-ray diffraction method. It was found that residual stress was concentrated near the interface. The stress perpendicular to the interface is tensile at the ceramic side and compressive at the metal side. Stress singularities near the interface can be also studied by finite-element analysis. The result showed that the exponent of a stress singularity at an edge was smaller than that at the center of the specimen, although the intensity coefficient at the edge was larger.

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Using the micromechanics-based elastoplastic analysis method that has been formulated elsewhere, stresses to be produced at the cooling stage of hot-consolidated ceramic/metal "functionally gradient material (FGM)" plates are numerically analyzed with particular reference to composition-graded, ZrO₂-Ni particulate composite laminates formed by hot-press diffusion bonding. The effect of in-plane and out-of-plane deformation constraints upon cooling is examined for plates with different patterns of compositional grading. The outermost ceramic layer suffers a very large tensile stress (far beyond its fracture-initiation level) upon cooling irrespective of the grading patterns if and only if both of these constraints are imposed. Residual thermal stress in the ceramic layer after removal of the constraints becomes tensile or compressive, depending on the grading patterns. A beneficial effect of the compressive residual stress in cyclic heat exposure of FGM plates is demonstrated.

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Steady thermal stress analysis without heat generation can easily be solved by the boundary element method. However, for the case with heat generation, a domain integral is necessary. This paper shows that the problem of steady heat conduction with heat generation can approximately be solved without the domain integral using an improved multiple-reciprocity boundary element method. In this method, the domain integral in each step is divided into point, line and area integrals in the case of a two-dimensional body. In order to solve the problem, the contour lines of heat generation, which approximate the actual heat generation, are used.

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This paper describes the shape optimization analysis of solid structures, where the shape optimization problems of linear elastic structures are treated to improve the strength or to reduce the weight of solid structures. The shape optimization system is developed based on the growth-strain method. The growth-strain method, which modifies a shape by generating bulk strain, was previously proposed for analysis of the uniform-strength shape. The generation law of the bulk strain is given as a function of a distributed parameter to be made uniform such as von Mises stress. In this paper, improved generation laws are proposed for the volume and maximum stress constraints. The laws make the stress uniform while controlling the volume and maximum stress to target values. PID control is introduced as the control method. A simple example using a cantilever beam and examples applied to suspension arms are presented. The results show sufficient validity and practicality of this method and developed system in terms of strength improvement and weight reduction of solid structures.

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Much time is required to numerically analyze the residual stress in a thermoviscoelastic body caused by the thermoviscoelastic behavior of materials through the cooling process by molding. Using constitutive equations simplified based on the characteristic of the thermoviscoelastic behavior of material through the cooling process, two simplified and efficient numerical methods are proposed to analyze the residual stress in plastics. The first method is applicable for the evaluation of the entire thermal stress history, while the second is suitable only for residual stress calculation. The validity of these methods are clarified by numerically analyzing the residual stress in an epoxy beam which has been cooled rapidly.

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Stress dependence of anhysteretic permeability was used for nondestructive measurement of residual stress in a welded plate. Magnetic flux density in a ferromagnetic material depends on its magnetic history, which is well known as the hysteresis. If a decaying AC magnetic field is superimposed on a certain DC field, the flux density converges at the anhysteretic value, which is independent of the history. The relationship between these values and the magnetic field is called an anhysteretic curve. We measured the initial permeability of the anhysteretic curve as a function of stress for mild steel. We found that the anhysteretic permeability decreases with the stress when the specimen is magnetized parallel to the compressive stress or perpendicular to the tensile stress. The stress dependence was used for estimating residual stresses in a butt-welded plate. Anisotropy of the anhysteretic permeability was defined to be used for the evaluation of the principal stress difference. The results showed good agreement with the conventional acoustoelastic measurements and the straln gauges.

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The characteristic X-ray method is one of the most effective nondestructive measurement methods for residual stress. However, the classical sin²ψ method of the characteristic X-ray is difficult to use for measuring the three-dimensional stress distribution and the steep gradient of residual stress which occurs along the depth direction in a subsurface layer of the material after cold rolling and grinding. On the other hand, the possible use of polychromatic mixed X-rays of different wavelengths has been proposed for another type of residual stress measurement. This paper presents a new polychromatic X-ray method for stress measurement. Since the relationship between the diffracted beam peak of the polychromatic X-ray and the strain along the depth direction was confirmed by many tests of steel plates, the steep gradient along the depth direction of the residual stress in the subsurface layer could be estimated by means of formulas derived from this relation.

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Frequency dependence of magnetoacoustic interaction was experimentally investigated for JIS-SS400 low-carbon steel. Velocity of an elastic wave which propagates in a ferromagnetic material slightly varies when an external magnetic field is applied. This is called the magnetoacoustic interaction. This occurs because the elastic properties depend on the magnetic domain structure, which is affected by both the external magnetic field and the stress. Consequently, the magnetoacoustic interaction is dependent on the stress, and it can be applied to nondestructive stress measurements. In this study, the magnetically induced change in the longitudinal wave velocity is measured under various stress levels. The frequency dependence is explained qualitatively in terms of the domain wall motion and the rotational vibration of the domain magnetization. Effects of texture and annealing are also investigated. Discussion is presented on the applicability to the nondestructive residual stress measurement.

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In this paper the optimum position and size of an auxiliary hole are considered in order to minimize the stress concentration due to notches and holes in plates under tension. To solve these problems, the body force method is applied. Then, the problems are formulated as a system of singular integral equations with Cauchy-type singularities, where the densities of body forces distributed in the x- and y-directions are unknown functions. In order to satisfy the boundary conditions along the auxiliary hole and the notch, eight kinds of fundamental density functions proposed in our previous paper are used ; then the body force densities are approximated by a linear combination of the fundamental density functions and polynomials. To obtain the optimum conditions, the direct search method proposed by Hooke-Jeeves is employed. The results show that the position and size of the auxiliary hole are determined efficiently with high accuracy.

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The stress development mechanism during local thermal oxidation of silicon substrates is discussed based on the predicted results using a two-dimensional thermal oxidation simulation program, OXSIM 2 D, which the authors developed. Predicted stress changes during the oxidation agree well with the measured data obtained by means of microscopic Raman spectroscopy. There are three main factors which have important roles in stress development in the newly grown oxide film and the substrate. They are the volume expansion of the oxide film, the viscosity of the oxide film, and the bending of the silicon nitride film which is used for the oxidation barrier. These factors give rise to the complicated stress distribution and the stress change near the edge of the nitride film during thermal oxidation.

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Computer simulations of the dynamics of screw dislocations are performed, using the model in which screw dislocations are piled up against a hard thin layer after their slip movement in a region possessing the distribution of friction stress. The calculation of stress field in the compound layer is performed for various values of slip length and thickness of a thin surface layer in order to discuss the effect of these factors on the fatigue strength of nitrided titanium. The results show that the well-known Hall-Petch-type relation between the fatigue strength and the grain size can be predicted for nitrided titanium through analysis of the proposed model. And the results exhibit that further consideration concerning the role of crack initiation resistance of the compound layer is essential for a better understanding of the influence of the thickness of the surface-hardened layer on the fatigue strength of nitrided titanium.

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We investigate the shear deformation of bicrystalline aluminum using a molecular dynamics simulation. The computational cell contains a [001](310)Σ=5 tilt grain boundary. In simulations, we use a Morse potential. The simulations show that when the strain rate is small, and when the temperature is high, the strain rate is proportional to the shear force and the Boltzmann factor. The activation energy for the deformation agrees well with the activation energy for grain-boundary sliding and migration induced by thermal activation. This means that diffusions of the same type occur in both cases. However, this type of diffusion does not seem to occur when the temperature is low. When the strain rate is sufficiently large, yielding is observed in the grain. The critical shear force becomes smaller as the temperature is raised.

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A numerical method for analysis of three-dimensional stress waves in an elastic/viscoplastic thick plate is presented, when an oblique impact is applied to the surface of the thick plate at various impact angles. For the numerical analysis, the finite difference method based on integration along bicharacteristics is employed. By obtaining the numerical results for various cases of loading conditions, the effect of the impact angle on impact fracture is examined. It is also demonstrated that dynamic behavior of the plate due to oblique impact can be examined in detail by this method.

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Ultrahigh-molecular-weight polyethylene (UHMWPE), used in artificial knee joints, is subjected to cyclic contact deformation in gait movement. In this paper, to consider the wear mechanism of the UHMWPE, the cyclic deformation of the UHMWPE is analyzed using the constitutive equation for cyclic plasticity. As a result, it is clarified that the direction of friction affects the wear mechanism of the UHMWPE. In the case of unidirectional friction, the wear particles are generated at the surface of the UHMWPE due to the accumulation of stress and strain, while in the case of reciprocating friction, these are generated under the surface due to plastic fatigue. Therefore, the life of the UHMWPE under unidirectional friction should be shorter than that under reciprocating friction.

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In the present study, impact damage in CFRP laminates under high temperature is considered through experimentation. For carbon fiber/epoxy (type A) and carbon fiber/PEEK (type P) laminates having the stacking sequence [0°/90°]_SYM, the impact damage is generated under environments from room temperature to 150°C, by the collision of a steel ball launched from an air gun. The total area of delamination is proportional to impact energy for both laminates. When the environmental temperatures are higher, critical energies of generating delaminations are larger for type A specimens and constant for type P specimens, though energies of developing delaminations are constant up to the glass transition temperature for type A specimens, and lower for type P specimens. Residual strengths of impacted specimens are estimated by static three-point bending test. It is shown that the residual strengths are reduced with decreasing total area of delamination.

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The progress of damage in perforation impact of plain woven carbon/epoxy laminates was studied using an instrumented falling weight impact testing machine. The thermal deply technique was applied to investigate the three-dimensional distribution of damage such as fiber breakage and delamination at various impact energy levels. The damage process was divided into three different stages according to the growth of main cracks with fiber breakage. In the first stage, surface cracks grew. The second stage was characterized by the propagation of through-thickness cracks. In the last stage, bending fractures of petal shape occurred. In the first and second stages, the absorbed impact energy was found to be a linear function of both the main crack area and the total delamination area. Thus, the contribution of fiber breakage and delamination was determined. The contribution of delamination was unexpectedly large.

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In the present paper we examine optimal laminate configurations to maximize combined buckling loads for symmetrically laminated plates with bending-twisting coupling. Various loading cases are discussed in this paper, that is, compressive, shear, and the combined loads. First, the buckling characteristics under combined loading are clarified with use of the lamination parameters. Next, optimal laminate configurations to maximize the combined buckling loads are obtained using a mathematical programming method where lamination parameters are adopted as intermediate design variables.

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Since unidirectional composite lamina has stiffness anisotrophy, it is well known that stress concentration around a hole can be avoided through optimum design Little researche on optimizing laminated composite structures, however, has been conducted though several studies have developed optimum design of laminated composite plates. In this study, an object-oriented finite-element analysis method was developed to make prototype systems for optimizing the laminated composite structures and it was applied to the problem of decreasing stress energy concentration. Two types of were applied to open hole and bolted joint structures. As a resul, the systems were proven to be excellent.

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Nonlinear analyses of cable network structures using Newton's iteration often encounter difficulties in solving for a singular stiffness matrix stemming from the tension-stabilizing nature and slackening of cables. This paper presents a solution method, called null space projection, to traverse such a singular linear system in Newton's iteration. In the method, the current unbalance of internal and external forces is projected on the null space of the stiffness matrix and the contributions of null space basis for the variable updating are derived such that the total potential energy is reduced. Numerical example shows that the method successfully traverses singular systems in Newton's iteration process and consequently gives the equilibrium state of the structure.

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Coupling finite and boundary element method (combination method) was applied to axisymmetric problems using vector potentials which were convenient for the analysis of magnetic fields caused by current from inductors, solenoidal coil magnets and fusion reactors. Both closed-and open- space axisymmetric problems were considered to examine the validity of the combination method compared with theoretical and finite-element solutions. It was found that in an open-space domain, the results showed excellent agreement between combination and theoretical solutions, and in a closed domain, the combination and finite-element methods yield equivalent solutions, although the entire matrix of the former was by far smaller. In order to show the accuracy and applicability of the numerical approach, we also examined the magnetic forces around a solenoidal coil magnet. The analyzed solutions were in good agreement with the experimental data obtained using the cantilever beam theory.

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Birefringent acoustoelastic stress measurement has been performed on JIS-60 rail samples on the basis of the combination of noncontacting electromagnetic acoustic transducer (EMAT) and the superheterodyne phase-sensitive detector. Slight change of ultrasonic velocities with stresses can be detected using the resonance method for thin samples or using the phase-detection method in case of long propagation paths. Relative accuracy on the order of 10^-6 is easily available with both approaches. Applied compressive stress up to 76 MPa (about 60 tons), which well exceeds the buckling load of long rails, is measured using the shear waves propagating normal to the stress axis at three portions of the rail (top-to-bottom, head, and web). The evaluated stress coincides with the stress calculated from the load and the cross-sectional area within a few MPa. Discussions on the effects of liftoff and residual stresses are provided.

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The contact pressure measurement in jointed plates is investigated by means of an improved ultrasonic technique. At first, the relations between the contact pressure and the bottom echo height measured using a normal probe, when the boundary echo height is kept constant, are obtained by compressing calibration blocks under various surface roughnesses. Next, two rectangular plates and two disks with a circular hole are compressed under locally uniform pressure, and the bottom echo height, when the boundary echo height is kept constant, is measured using the normal probe. From the relations between the calibrated and measured curves, the contact pressure distribution in the jointed plates is quantitatively obtained. The experimental results agree fairly well with the analytical ones. Thus, the proposed ultrasonic method is useful for the measurement of contact pressure.

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Design method of topology and boundary shape of multiconnected plane structure, generated corresponding to arbitrary load conditions, is developed to lighten the weight of the structure. For creation of topology and boundary shape of a minimal weight structure, the layout of hollow spaces in the interior of the structure must be optimized. In the method, the structure divided into discrete square elements is analyzed by a finite-element method and the elements are detached and attached on the structure according to the sensitive function calculated by the difference of total strain energy in the structure. The topology and the boundary shape are modified by the successive approximation in steepest descent of the sensitive function. Numerical results demonstrate that the method can produce the topology and the boundary shape of the multiconnected structure as a frame. By the structural shape optimization for minimal weight, the computed final structures are modified to the construction of bars under nearly uniaxial tension. The structural shapes of well-approximated minimal weights are obtained under many load conditions.

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Cavitation erosion was studied for welding deposit metal and base metal in the area near the interface. The base metal was austenitic stainless steel and the deposit metals were five alloys : three nickel-base alloys, an iron-base alloy and a cobalt-base alloy. The erosion of welding deposit metal near the interface occurs similarly to that of the deposit metal itself. However, the erosion of the base metal is accelerated due to the softening in the heat-affected zone during the welding processing. Moreover, the selection of high erosion-resistance deposit metals is hazardous to the base metal near the interface, because the cavitation bubbles flow on the surface from the deposit metal to the roughened base metal.

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