Piezoelectric effects are extensively utilized in electric ceramic devices as well as high-power ultrasonic devices. The piezoelectric components work under elastic strain and electric fields. For the reliable service lifetime predictions of the components, an electro-fracture mechanics approach has to be considered. Piezoelectric analysis of crack problems is an important, basic subject to establish the electro-fracture mechanics in future. Following the dynamic theory of linear piezoelectricity, we consider the scattering of normally incident longitudinal waves by a finite crack in an infinite orthotropic piezoelectric solid. The problem is formulated by means of integral transforms, and reduced to the solution of a Fredholm integral equation of the second kind. Numerical calculations are carried out and dynamic stress and electric field intensity factors are obtained for piezoelectric ceramics.

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Ceramic circular plates of pressureless sintered silicon carbide were impacted with steel balls, and the experimental results were compared with quasi-static theoretical analyses and dynamic fracture analyses by the FEM code, DYNA 3D. It was shown that a simplified method of quasi-static plastic analysis, proposed by the authors, considerably simulates the plastic behavior of steel balls at impact. Moreover, a numerical method of ceramic fracture analysis, also proposed by the authors, was shown to be able to represent experimental failure modes of ceramic plates.

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A combined loading technique, named the clamp method, has been developed in order to stabilize the crack growth of ceramics. In this method, compression load is applied to the ligament of the compact specimen and the stress intensity factor K is analyzed by the finite-element method. The clamp method provides a moderately increasing or decreasing K value with increasing crack length. Measurement of the crack length is performed by the surface film technique up to the growth rate of 200 m/s. In this technique, changes in crack length are monitored by a thin layer of carbon on a surface area which encompasses the region of fracture. The propagation of a crack leads to a break in the carbon film which is atomically bonded to the surface of a specimen. Crack growth behavior has been investigated under static and cyclic loads in polycrystalline magnesia. Rising fracture resistance curves which depend strongly on specimen geometry are clearly demonstrated using the surface film technique. Unstable fast fracture occurs at the same K value for different specimen geometry; however, the crack growth rate of the fast fracture also depends on specimen geometry-Based on the clamp method, stress corrosion cracking and fatigue crack growth can be tested stably under static and cyclic loads, respectively. Crack growth characteristics are discussed in terms of a toughening mechanism produced in the wake of a growing crack.

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As fracture strength of ceramics σ_f measured in bending or tension tests decreases with decrease in stress rate σ^^., σ^^. should be sufficiently high if σ_f&sirne;σ_f0 is to be realized, where σ_f0 is true fast fracture strength (inert strength) which will be obtained when unstable crack extension occurs directly from an existing crack without preceeding stable crack growth. However, magnitude of σ^^. needed to obtain σ_f&sirne;σ_f0 has not been clarified. In this paper, a general equation of σ_f as a function of σ^^. was obtained for testing in which σ^^.=const assuming that dependence of σ_f on σ^^. results from stable crack growth. Based on this equation, it was shown that σ^^. should be higher than (0.95)ⁿ⁺¹ σ^^.₀ if σ_f≥0.95σ_f0 is to be realized, where n is the exponent in da/dt=AKⁿ, and σ^^.₀ is given by Eq, in this paper. It was then pointed out that the stress rate in usual tests of ceramics is considerablly lower than this required value. It was also shown that the range of σ^^. in which the power relation σ_f∝σ^^.λ(λ>0) holds is given by σ^^.&sirne;0.1 σ^^.₀.

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The microfracture process during the bending tests of alumina ceramics was evaluated by the acoustic emission technique. Specimens with different dimensions were used for the bending tests in order to investigate the dependence of the microfracture process on the specimen size. A remarkable point in the AE generation pattern of each specimen, at which both AE events and energy increased rapidly, was observed before the final unstable fracture. It is important that the apparent stress at those points is independent of the AE threshold level and specimen size. Using the fluorescent dye penetrant method, it has been made clear that the stress corresponds to the critical stress for the main-crack formation due to the coalescence of microcracks and/or pores. Considering the micro-fracture process, statistical treatment for the strength of brittle materials has been discussed. Consequently, it was concluded that the critical stress can be the new evaluation parameter, which is equivalent to yield strength in metals, for ceramic materials.

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In this report, firstly, the new thermal stress testing machine which uses ring specimens is developed for estimating the high-temperature strength of TiC-coated type 316 stainless steel. The effects of surface roughness as well as the thermal stress and the residual stress on bond strength are investigated. Experimental and numerical results on residual stress distribution are compared mutually for confirming the reliability of the inelastic analysis of the finite-element method.

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The bending strength of Si₃N₄/S45C joints with a Cu interlayer was examined. Some of the joints showed a relatively lower strength. The fracture mechanics approach was performed for the reduction of strength. The results obtained are as follows. (1) The reason why the strength decreases is the existence of the defect and the tensile residual stress near the interface at the ceramic side. The strength of the joint can be evaluated by the stress intensity factor. (2) In the case that the indentation precrack is introduced near the interface at the ceramic side, the interlayer deforms plastically and, as a result, the redistribution of residual stresses occurs and the precrack is kinked toward the interface. Thus, the indentation method is not suitable to introduce the precrack near the interface.

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In order to evaluate fracture strength for Y₂O₃-ZrO₂, 3mol% Y₂O₃-ZrO₂ (PSZ) /SUS 304 composite materials, Macor as a machinable ceramics and comercially available ceramics (SiC, Si₃N₄, PSZ, Al₂O₃), fracture toughness tests were carried out by use of RCT or bending specimens. On the other hand, the fracture strength of these materials was evaluated and inspected the correlation between fracture toughness and fracture stress of small punch (SP) or modified small punch (MSP)test data to predict the fracture toughness value by using miniaturized specimens. Characteristic of the MSP testing method is the ability to evaluate elastic modulus (Young's modulus), fracture strength, yield strength, fracture strain, and fracture energy, etc., with high accuracy and good reproducibility for brittle materials. For a series of metal/ceramics composites which from ductile to brittle, this paper clarified clear the applicable range for SP and MSP testing methods, which suggested that the simultaneous use of SP and MSP test methods can evaluate the fracture strength of metal/ceramics composites.

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Torsional and tensile tests of alumina and silicon carbide fibers from precursors were carried out. Their shear moduli, torsional strengths, Young's moduli and tensile strengths were evaluated and compared. Their shear moduli are about one half of their Young's moduli. Their fracture surfaces show the characteristic feature of isotropic brittle structure. The measured torsional strength of the alumina fiber coincides with that deduced from the tensile strength. Thus, this fiber has extremely isotropic properties of not only structure and moduli but also of strength. However, the measured torsional strength of the silicon carbide fiber is weaker than that deduced from the tensile strength. As for this reason, it is supposed that the sheath is weaker than the core and/or defects are preferentially oriented to the fiber axis.

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A tensile test was carried out on the two kinds of SiC fiber-reinforced Al alloy composite wires, SiC/pure-Al and SiC/Al-5.7 % Ni, which were quenched or annealed. The effect of the matrix hardness and microstructural change on the tensile strength and its scatter has been investigated. The results showed that the SiC/Al-5.7 % Ni composite wires maintained a higher strength than the SiC/pure-Al composite wires after the wires were quenched from a temperature up to 450°C, and it had less strength than SiC/pure-Al after being heated to a temperature over 550°C. The scatter of the strength of SiC/Al-5.7 % Ni wire increased as quenching temperature increased, but the strength of SiC/pure-Al wire had no change in scatter. The results above were explained by the matrix microstructure, and by the tensile strength of the extracted fibers.

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A basic formulation for evaluating the failure path of composite laminates is presented. The proposed formulation is based on an in-plane failure criteria and first-order reliability method (FORM). The sequential failure path of each layer of composite laminates is simulated by means of modulus degradation and safety indices under the off-axial load conditions. Numerical analyses of graphite epoxy composite laminates are performed corresponding to various lamination configurations with symmetric lamination angles subjected to off-axial in-plane strain conditions. From the simulation analysis, a typical failure path is evaluated corresponding to an in-plane strain vector. The mechanical behaviors such as decreasing modulus and increasing in-plane strain are also simulated in correspondence with each stage of sequential ply failure. The proposed simulator enables one to search the effective failure path in order to evaluate the last ply failure probability of laminates.

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This paper presents results of stress calculations of a filament wound pressure vessel by using the finite-element method and theoretical calculations based on both the netting theory and laminar theory. Composite vessels were fabricated by winding high-strength fiber-glass-impregnated-epoxy-type resin on Al alloy liners. The winding was conducted in two modes : helical winding and hoop winding. The vessel consisted, therefore, of three layers : the metallic liner layer, the helical winding layer, and the hoop winding layer. Before the service operation, vessels were subjected to autofrettage, an overpressuring treatment, in order to produce compressive residual stresses in the metallic liner and to increase the fatigue life of the liner. Analysis of cyclic deformations of the composite vessel was performed in order to simulate the loading steps after fabrication: autofrettage, service operations, and burst. The results of calculations were compared with experimental results.

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The behavior of delamination crack growth in creep was investigated using DCB specimens of unidirectional CFRP, APC-2 (carbon fiber : AS4 and matrix : poly-ether-ether-ketone (PEEK)) at the test temperatures from 443 K (170°C) to 483 K (210°C). The creep crack grew steadily along the boundaries between the matrix and the fiber. The crack opening displacement (COD) rate measured during the crack growth test coincided with the elastic COD rate calculated from the change in elastic compliance due to the crack growth. It implied that the creep took place only in the vicinity of the crack tip and the creep zone was surrounded by te elastic stress field. Such a small scale creep (SSC)condition might be caused by the constraint of matrix deformation by the fibers, which was partly proven by the experimental observation of the crack-tip white-colored zone at the specimen side, caused by a large creep deformation. Thus, the crack growth rate was insensitive to the test temperature and correlated well with the elastic energy release rate.

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Near-net-shape fiber preforms will be the major focus of advanced composite materials which are capable of cutting processing costs and obtaining structures with better properties. Braiding is one of these technologies. We have proposed that modification of conventional braiding machines can fabricate braiding construction with various complex shapes. It is difficult to decide the initial spindle setting pattern on the track with the various complex configurations. We previously showed the mechanism simulation techniques for basic flat braiding and basic cord braiding. In this paper a new program based on simulation of the basic flat braid is developed to apply to three-dimensional configuration. Moreover, regularity of braiding construction is appraised by use of fiber crossing.

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Damage of CFRP (carbon-fiber-reinforced-plastic) laminates due to iterative impact is evaluated with the compliance responses of deflections. The instrumented drop-weight impact test system converts the strain histories in the drop weight into the impact loads and deflections according to one-dimensional wave equation. It is shown that the impact load histories of laminates include the signals having high frequencies due to generation of the damage. The compliance responses, which are considered as the rigidity of laminates, are computed from the yielded loads and the deflections. As the experimental result, it is shown that impact damage can be estimated with the compliance response. When the fiber breaks during the impact process, the rigidity of laminates reduces considerably. The reduction of the rigidity is not marked for the case of quasi-isotropic laminate or CF/PEEK.

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Residual fatigue strength for CFRP (carbon-fiber-reinforced plastic) laminates having impact damage is evaluated with the four-point bending test. A steel ball launched by an air gun collides against CFRP laminates to generate impact damage. The static and fatigue tests are performed to evaluate the residual strength of impacted laminates. After the experiments, the laminates are observed by optical and ultrasonic microscopes. As a result, the static and fatigue residual strengths are reduced compared with virgin laminates, particularly when the impacted side of the laminates is compressed. It is found that the cracks from the impact impression and the delaminations following the cracks influence the fracture of the laminates.

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The perforation fracture of CFRP (carbon-fiber-reinforced-plastic) laminates is investigated in the present paper. A steel ball launched from the air gun perforates CFRP laminates having different laminate structures. The velocities of the ball before and after impact are measured to evaluate the absorbed energy by high-speed camera. The fracture patterns of the laminates are observed by the optical microscope and the ultrasonic microscope. As results, it is found that the absorbed energy and delamination area of carbon/epoxy are less in the case of higher impact velocity. In comparison with carbon/epoxy, the cabon/PEEK laminates could absorb larger energy.

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FRP is often used in various environments where excellent corrosion resistance is requived. For composite structures such as vessels, it is very important to clarify the liquid degradation behavior. Since joints are a most important factor in composite structures, special attention must be given to their design. In this study, we investigated the hot water degradation behavior of mechanically fastened GFRP joints. Immersion tests were carried out for the double lap joint specimens with different failure modes. Tensile and bearing failure tests were performed to examine the residual tensile and bearing strengths of the joint after the immersion tests. It is cleared that immersion in hot water has a considerable effect on the bearing strength. Furthermore, the change in the failure mode according to the degradation behavior was estimated from the stress distribution of the joint calculated by FEM. The calculated results weve found to agree well with the experimental results.

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The effects of a gradient distribution of components on the deformation and fracture of functionally gradient materials (FGM) in the corundum/plaster model system were examined as a function of the volume fraction of corundum powder and the No. times of gravity (i.e., multiples of gravity). The radial crushing strength of the FGM was measured under the combined conditions for casted rings with three different volume fractions and three different No. times of gravity. The distribution patterns of stress and strain in FGM rings were analyzed by the conventional curved beam theory considering the change of elastic modulus. The brittle fracture was initiated from the inner surface of the ring on the load action line independent of the distribution of corundum powder. The variation of strength with the gradient distribution of corundum powder and with the centrifugal force was also studied.

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The numerical methods which have been proposed by the present authors for Lamb waves in an anisotropic laminated plate and its transient responses are expanded for the wave propagation analysis of functionally gradient material (FGM) plates. The material properties of the plate change gradually in the thickness direction, and are anisotropic in the plane of the plate. The plate is divided into N plate elements. In the element, we assume that the material properties change linearly in the thickness direction, and that the displacement field is expressed by second-order polynomials. The principle of virtual work is used to develop approximate dynamic equilibrium equations. The dispersion relation and the mode shape of the Lamb waves are obtained by using the free boundary conditions. The energy velocities of the Lamb waves are formulated with the aid of the Rayleigh quotient. The method of Fourier transforms in conjunction with the modal analysis is used to determine the response of displacements. The formulation of the theory is described in this paper.

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The numerical mathods present in the previous paper for the wave propagation analysis of anisotropic functionally gradient material (FGM) plates are applicated to a SiC-C plate, which is a kind of functionally gradient material plate. The frequency spectum, energy velocities, and the mode shapes of the Lamb waves in the SiC-C plate are obtained. The transient responses of the SiC-C plate excited by time-step impact loads time-pulse ones are computed. The results obtained for the SiC-C plate and for an isotropic homogeneous C monolith plate are compared. It is found that the displacements are much more concentrated on the softer surface of the SiC-C plate than on the surfaces of the homogeneous C monolith plate, and that the displacement responses cooresponding to the surface waves of the SiC-C plate are larger than those of the C monolith plate.

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Two-dimensional stress waves in a circular tube made of functionally gradient materials are analyzed numerically, when an axisymmetric impulsive load is applied to the outer surface of the tube. For the numerical analysis of the dynamic problem of the circular tube with nonhomogeneous material properties, the extended finite difference method based on integration along bicharacteristics is employed. By obtaining the numerical results for the cases of various patterns of the distributions of materials, it is demonstrated that the effect of the distribution of materials on the propagation of stress waves appears clearly. By changing the pattern of the distribution of materials suitably, it is also found that the maximum value of the caused tensile stress decreases, so that the possibility of the occurrence of impact fracture also decreases.

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In order to reduce the residual stresses and the residual deformation caused by the sintering process, the compositional profiles of the Functionally Gradient Material(FGM) of ceramics and metal were analysed by FEM. Based on the results, the optimum material design of FGM for the heat loading was performed. The results obtained are as follows. (1)Due to the difference of the contraction along the interface, the deformation occuers along the free edge (x direction) near the interface. This deformation corresponds to the residual stresses along the free edge near the interface. The residual deformation and the residual stress can be reduced by the following methods. i) Increase of the division numbers of interlayers. ii) Taking the aspect ratio of the particles as one. iii) Introduction of the voids in the ceramics. (3)The thermal stress can be reduced by controlling the distribution of the residual stresses by the following methods. iv)Decrease of the gradient of the compositional profiles in the ceramic side.

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A functionally gradient material which decreases thermal stresses has been developed for structural components and/or mechanical elements in fields such as nuclear, aircraft and space engineering fields. Steady-state thermal stresses in a plate made of the functionally gradient material with temperature-dependent material properties are discussed. The main theme of this subject is how to distribute the components of the materials in the functionally gradient material to decrease thermal stress. The plate of an optimally functionally gradient material was determined to decrease the steady thermal stresses.

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The plane strain and generalized plane stress problems of two materially dissimilar isotropic homogeneous wedges bonded together on a common edge are treated within the context of classical elastostatics. Stress and strain singularities at the intersection of the surfaces and the interface of the two materials are investigated using a characteristic equation deduced in terms of the familiar Airy stress function. It is found that free-edge stress singularities disappear for certain combinations of wedge angles of a pair of materials, even for a so-called bad pair, which has stress singularities when bonded at right angles to the surfaces. Expressions of geometrical conditions of the wedge having no free-edge stress singularities are given in terms of the Dunders composite parameters α and β. To demonstrate the validity of the expressions, numerical calculations are made. The conditions of no free-edge stress singularities are shown graphically. The proposed expressions can be used for designing the optimum shape of composite materials.

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The stress singularities at the tip of an open crack (including a slit crack), lying arbitrarily inclined to the interface of two different materials, are examined. Using the eigenfunction-expansion method, the crack tip stress singularities for various crack and material combinations are computed for plane problems as well as for antiplane problems. The results show that the present analysis makes possible a highly accurate and efficient numerical solution of fracture mechanics problems.

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This paper deals with the effects of crystalline lattice rotation on multiaxial creep of a nickelbase directionally solidified alloy. Combined tension-torsion creep tests of directionally solidified IN738LC at 850°C are first discussed to find features which become noticeable with the advance of creep deformation. The results of the tests are then analyzed on the basis of the crystallographic slip theory of finite deformation. We thus show that the crystalline lattice rotation explains the experimental features ; it is mostly responsible for the change of the non-coaxiality between creep rate and stress in combined tension-torsion creep, and partly for the earlier appearance of tertiary creep under combined tension-torsion than under pure tension or torsion.

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An experiment with cyclic loading and unloading and an experiment with heating and cooling under the constant stress of TiNi shape memory alloys were carried out. The starting condition and the completing one of the martensitic transformation and the reverse transformation, the cyclic behavior of recovery strain and the conditions for application of recovery deformation were discussed. The results are summarized as follows. During the thermomechanical cycles, the yield stresses of the martensitic transformation and the reverse one decrease, but the transformation temperatures increase. The starting condition and the completing one of both transformations under the cyclic deformation are described by the behavior of the transformation lines in the stresstemperature plane. During the thermal cycles under constant stress, the recovery strain may appear or diminish depending on the relation among the initial strain, the heating temperature and the cooling temperature, thus showing complex cyclic deformation behavior. The cyclic recovery strain is represented by the relation among the heating temperature, the cooling temperature, the transformation lines and the transformation strain. It is important for the shape memory alloy elements to determine the conditions for application based on the cyclic characteristics of the transformation stress, the transformation strain and the transformation temperature.

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In this paper, the numerical analyzing method for multiple laminated structures, which are composed of some plates and some layers bonding them, is proposed. The finite element method is applied in the technique by using the special connective element for the adhesion part and the normal two-dimensional element for the plate part. As numerical examples, two-and three-laminar-structure models are analyzed. The results coincide with the values evaluated using the three-dimensional finite element method (3DFEM). Moreover, the calculation time and the memory capacity of the computer are largely decreased compared with the case of 3DFEK.

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The behavior of bending-twist elastic coupling of a composite pipe which has structurally unsymmetric laminated construction is studied. The deformation of a canti-levered pipe is analyzed using the laminate plate theory and Castigliano's theorem. The analytical results show good agreement with the calculated results by using the finite-element method and the experiments. It is found that either pure bending loading or pure twist loading causes both bending and twist deformation. The concept of the elastic principal axis is introduced to consider the bending-twist coupling. The axis is found to be different from the geometric principal axis, and any loading along the elastic principal axis does not cause twist at the loading position.

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A method for the measurement of slow crack growth in an optical glass fiber, the dimension of which is 125μm in diameter, was developed. The precracked fiber specimen was used for the measurement under a tensile test with constant load in atmospheric air. The fiber specimen was subject several times to unloading and slight vibration in the transverse direction during the test. By the unloading and vibration, the front shape of a growing crack was clearly recorded on the delayed fractured surface. The changing front shape in the growth of the crack was measured by the observation of the fractured surface. Based on the obtained results, the crack growth law of the optical glass fiber was evaluated. The validity of the results was discussed.

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A molecular dynamic (MD) approach to interface crack problems is proposed. A 2-body interatomic potential which provides a linear elastic character to the solidis is used for both the bonded materials and the interface. It enables direct comparison of the molecular dynamic analysis with the continuum model. The critical state of the interface crack propagation is analyzed on the 2D dissimilar solid made up of closed-packed atoms. The elastic local displacement field at the interface crack-tip which is characterized by the stress intensity factors is used as the boundary condition for the MD-analysis. The analysis shows that the critical stress intensity factor fluctuates with a period of the lattice constant. In case of the weak interface where an interface failure occurs, the critical stress intensity factor is in good agreement with the value obtained by the interface fracture energy. However, under shear loading conditions, dislocations and other defects are introduced into the interface region, and critical stress intensity factor differs from the data of the fracture energy.

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A three-point tensile test method was proposed to evaluate effectivly Young's moduli of thin films. Young's modulus of aluminum foil was first evaluated by using the proposed three-point tensile test, and then the three-point bending test was carried out by using a specimen of a laminal construction of aluminum foil and sheet glass. By comparing these experimental results, the effectiveness of the three-point tensile test was comfirmed.

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