Cyclic fatigue in ceramics is reviewed, focusing on recent research. Several cyclic fatigue mechanisms hereby proposed are summarized briefly in section 3. In section 4, fatigue characteristics of all available materials are explained. Alumina, silicon nitride and lead zirconate titanate (PZT)are prone to cyclic fatigue degradation, but silicon carbide, mullite, lead titanate (PT), β-alumina and glass are not. The rough fracture surface typical of intergranular fracture seems to be a key factor in judging cyclic fatigue degradation, except in the case of transformation-toughened zirconia. The cyclic fatigue mechanism based on cyclic degradation of the bridging effect is supported by substantial experimental evidence. The cyclic fatigue mechanism, which is based on the premise that the crack resistance caused by microcrack branching or crack-path deflection during tensile loading and the crack reactivation due to the asperity contacts during unloading occurs repeatedly, seems to be promising also.

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We apply the conventional consideration of an analytical method in linear thermoelastic problems to nonlinear thermoelastic problems in the second-order theory. The basic equations of nonlinear thermoelastic problems are formulated by using Adkins perturbation method. Thermoelastic potentials applying the Helmholtz theorem are also introduced for analyzing nonlinear thermoelasticity problems. Moreover, by applying these thermoelastic potentials, we propose a formulation of the analytical method to solve boundary-value problems of axisymmetrical uncoupled quasi-static thermoelasticity in finite deformations. Finally, some potentials for axisymmetrical thermoelastic problems of finite deformations are shown.

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A new theory of propagation of elastic waves in porous materials was developed for pore characterization. The idea is based on the arrival probability of a direct ray, reflecting ray, and creeping ray. The theory gives a good account of the nature of elastic waves propagated in porous solids not only qualitatively, but also quantitatively. The authors show a rather good correlation between pore characteristics (porosity and pore size) and ultrasonic characteristics (waveform and arrival time), and propose a nondestructive technique based on the presented theory for evaluating the porosity and pore size.

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Coupling effects between the temperature field and structural changes are considered in the analysis of the laser transformation hardening process. The volume fractions of the structural constituents, the latent heat during the phase transformation and structure dependence of the thermophysical properties are introduced during the iterational calculations of the steady-state temperature distribution and the structural changes. The carbon content of a steel, the mean value of the grain size of the prior austenite, and the size and the interlamellar spacing of the pearlite colony are input for the initial parameters. Finite-element calculations are carried out to obtain the temperature distribution and the structural changes in the process, and the microhardness distribution in the hardened layer. An example of the numerical computations is shown for a 0.45 %C carbon steel. The calculated results are compared with those of the experiments on the laser transformation hardening and are found to be in good agreement.

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The method of numerical analysis of the singular integral equations for crack analysis by using the method of continuously distributed dislocations model is presented. This method is based on the concept of the boundary collocation and reduces singular integral equations into linear algebraic equations. The presented method made it possible to obtain the solution of the singular integral equations in symmetrical or asymmetrical problems including two or more unknown functions. The accuracy of stress intensity factors obtained by this method was verified by comparing these values with the exact solutions or the reliable numerical solutions obtained by the other researchers.

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In an idealized 2-dimensional crack, the deformation constraint is kept constant along the crack front line. Thus, it is expected that the fracture mode is also kept constant along the crack front line. However, the deformation constraint and fracture mode generally change along the crack front line in a 3-dimensional crack, and this deformation mode change cannot be dealt with by applying conventional parameters such as K or J. The CED (crack energy density) was proposed as a parameter which has no restriction on the constitutive equation and is expected to be applicable to almost all kinds of crack problems. This paper purports to demonstrate that the deformation mode change above can be evaluated quantitatively when the CED is applied.

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With the boundary element analysis in composite materials in mind, this study describes the details of a data-base-utilizing method paying attention to the similarity of kernel functions. It is ascertained that the coefficient matrices of a region are usable for composing those of another region under the condition that the shape is similar even if the number of divisions differs. This indicates that the coefficient matrices can be composed without a numerical integration scheme so that a drastic reduction in CPU time will be expected. On the basis of the results, a new analysis system that avails itself of the data base has been constructed. The advantages of this system are verified by means of several examples.

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This paper is concerned with a method for measuring an impact load acting on a body of arbirary shape. The present method is estimation of the impact load from strain response of the body by deconvolution. The transfer function between the impact load and the strain response is estimated by dynamic calibration. It is often difficult to obtain a good estimate of the impact load since the deconvolution is mathematically ill-posed and expands noises involved in measured signals. In this paper, we compare five methods to estimate the transfer function so as to obtain a good estimate of the impact load by deconvolution. Moreover, we apply the present method to the instrumentation of a Charpy impact testing machine and demonstrate its effectiveness.

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The pressure decay process during the so-called pressure pulse test is analyzed for evaluating in situ hydraulic properties of rocks deep in the earth's crust. The present analysis takes the effects of the compliance of the tubular connecting the straddle packer to the pressurizing pump and the compliance of the well bore on the pressure decay process into account; these effects are ignored in the conventional approach. The results show that the pressure decay curve is highly dependent on the tubular compliance, and, as a result, the hydraulic properties obtained using the conventional method, which assumes that the tubular is rigid against pressure, induce large errors. Based on the analysis, a new method is proposed for evaluating in situ hydraulic properties from pressure decay curves, taking the effect of the tubular compliance into account, and the method was successfully applied to a set of experimental data of the pressure pulse test performed at a geothermal model field.

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The results of numerical calibration of a standard short-rod rock specimen with a chevron crack used in the ISRM suggested method are reported, where the boundary element method was used to compute compliance, the stress intensity factor based on the compliance and the distribution of the local stress intensity factor along the crack front edge for various crack depths. The local stress intensity factor is never uniform for a straight front edge of the crack. The change of the shape of the front edge during the fracture toughness test was computed for two cases. In the first case, crack growth resistance is independent of crack growth and, in the second case, crack growth resistance increases with crack growth. Based on the results of the calibration, the validity of the ISRM suggested method for the measurement of rock fracture toughness is discussed.

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The Japan Atomic Energy Research Institute has long been carrying out high-temperature gas-cooled nuclear reactor (HTGR) development, including constructing the High Temperature Engineering Test Reactor (HTTR) . Statistical properties of the uniaxial tensile, bending and compressive strengths of a fine-grained isotropic IG-110 graphite for the HTTR core components have been assessed. The assessment based on the data sources compiled from seven mechanical testing programs leads to the following conclusions. The mean tensile strengths for both axial and radial orientations change within ±7% among seven lots. The anisotropy of tensile strength is practically negligible. Combined data sets for tensile, bending and compressive strengths, each consisting of more than 350 measurements, can reasonably be represented on the whole by normal distributions. A Weibull distribution is not justifiable for any data set. Taking into account the statistical bases established, some requirements are presented for defining specified minimum ultimate tensile and compressive strengths (design minimum strengths) in conjunction with material acceptance tests.

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Plastic strain distributions at the net section of notched bars subjected to large deformation are obtained using the Vickers microhardness test and the numerical calculation proposed. Each notched bar is loaded up to 0.7 P_max (P_max: maximum tensile load), 0.8 P_max, 0.9 P_max, 0.95 P_max, P_max, 0.98 P_max beyond P_max and 0.95 P_max beyond P_max. Strains at a point are calculated by making an assumed curve of radial displacement touch the real curve of radial displacement distribution at that point. The distributions of the equivalent and axial plastic strains are concave at all load levels tested. The equivalent plastic strain is only slightly greater than the axial plastic strain, even at the notch root where the difference between these two strains is the largest. The magnitude of the axial plastic strain at the notch root at P_max is about twice as large as that of the axial plastic strain at P_max of the unnotched specimen.

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The crack propagation rate of a mode I surface crack in a plate, the crack tip opening stresses or displacements under various biaxial stress ratios by the simultaneous action of plane bending and cyclic torsion are examined. The aspect ratio of a crack is not affected by the biaxial stress ratio, but the relationship between the propagation rate da/dN and the stress intensity factor range ΔK or the effective stress intensity factor range ΔK_eff depends on the biaxial stress ratio. This is mainly due to the differences of both CTOD and the scale of the slipped region at the crack tip caused by the difference of the biaxial stress ratio.

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Thermal shock behavior of cermets and cemented carbides was studied in detail by using unnotched smooth bar specimens. Thermal shock was applied to the specimens by plunging them into a water bath at 290 K. After thermal shock experiments, bending strength, micro-Vickers hardness and fracture toughness of the specimens were investigated. As a result, two different types of thermal shock behavior were observed between cermets and cemented carbides. This difference indicates that microcracks occur more easily in cemented carbides than in cermets during thermal shock experiments.

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The response of a transversely isotropic half-space and a plate with its symmetry axis parallel to the surface, subjected to a transient surface point load at an arbitrary angle is determined. The problem is formulated in terms of an integral transform method in the frequency domain. To obtain the near-field solution, double infinite integrals involved in the inverse transform are evaluated by extending the Clenshaw-Curtis quadrature scheme to two dimensions. Approximate far-field solutions are obtained by evaluating the double integrals using the residue theorem and the stationary phase method. As a companion problem, the response of a finite simply supported plate subjected to d dynamic surface load in also obtained using classical plate theory (CPT) with appropriate modifications to include the transverse shear effect (TSE)and rotatory inertia. The numerical results obtained by the different approaches are compared.

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Mechanical properties such as load distribution and stress concentration in the threaded regions of an eyebolt and an eyenut are analyzed using the finite element method (FEM) which deals with elastic contact problems, where the "regularization method" is incorporated into stiffness matrices to avoid the singularities involved. Unlike a conventional bolt-nut connection, both external and internal threads in eyebolt and eyenut connections are in tension. Accordingly, it is considered that they might exhibit different mechanical properties. A single eyebolt or eyenut model is treated, and the external force is applied as gravity force corresponding to the allowable load specified in JIS so that the effects of the block shape can be examined by changing its height and diameter. Thus, the influences of the friction on the pressure flank, material properties and nominal diameter of threads upon the load distribution and stress concentration are evaluated for both an eyebolt and an eyenut. Furthermore, an elementary calculation method for load distribution is presented and compared with FEM.

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