The strength of stepped-lap bonded joints with metal adherends is investigated both analytically and experimentally. The effect of the number of steps on the joint strength is discussed. The joints used in this study have adherends of carbon steel, brass and aluminum alloy and adhesive of epoxy resin. The strain and stress distributions under a tensile shear load are analyzed by applying the finite element method. The initial cracking and final fractured loads are predicted by applying the strength laws to the adherend, adhesive and their interface. The analytical results show good agreement with the experimental ones. Though the initial cracking loads are not affected by the number of steps, the final fracture strength of the joint is improved by increasing the number of steps.

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The crack velocities of compact-tension type sheet specimens having various crack-tip radii are experimentally investigated under tension using UP and PMMA plastics. The crack velocity increases rapidly to the maximum value and decreases slowly as the crack propagates in a specimen. This velocity change is approximated by the existing velocity equation for the double-cantilever-beam type specimen. The mean velocity decreases as the crack-tip radius sharpens. The density of the fracture surface marks which appeared in the fracture surface changes with respect to the relative crack length C₁/C₀, in a manner similar to the way the crack velocity changes in each specimen. Fracture strength and the fracture surface marks also decrease as the crack-tip radius sharpens, showing that the velocity and the number of marks tend to be smaller the lower the fracture strength. The relationships among fracture strength, the number of fracture surface marks and the mean velocity are discussed.

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A cutting method for ceramic plate is proposed. This method is an application of the fracture of brittle materials under bending moment. Bending moment arise from compressive lode applied to the ceramic plate put between a concave and convex spherical surface. Then the ceramic plate is cut along the notches of desired shapes on one surface. The characteristics of the cutting method are: (1) Cutting can be carried out without dust, and the cutting sections are smooth. (2) The ceramic plate can be divided into many equal parts and cut simultaneously in square and traiangylar shapes during one compression. (3) Ceramic plate can be easily cut along various shapes such a curve and a circle. (4) This method can be cut a number of plates, almost instantly.

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Sheet thickness changes occuring in a two-ply clad sheet metal composed of steel/copper during stretch air-bending are experimentally examined. The curvature of the sheet at a punch-contact region is strongly affected by stretching superposed on or applied after bending. In pure bending, thickening occurs in a clad sheet with a steel outside layer and a copper inside layer, whereas thinning is found in the sheet of reverse configuration. The sheet thickness decreases with increasing stretching force as a result of a change in the location of a neutral axis. The sheet thickness change can be predicted by numerical simulation for a given loading path of curvature and stretching force.

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Scalelike marks are usually observed in the fracture surface of a Si₃N₄ specimen tensioned to fracture at 20°C and 500°C. They are the regularly shaped marks, ellipselike and parabolalike ones along with other irregularly shaped marks. The regularly shaped marks are carefully observed and analyzed in the same manner of defining an ellipselike mark (both ends closed mark, BECM) and a parabolalike mark (one end opened mark, OEOM) observed in unsaturated polyester resins (UP) and PMMA, as reported previously. _the marks in a smooth specimen are mostly the OEOMs where the crack velocity often reached about 4500m/s at maximum and the BECMs are dominated in the fracture surface of a single edge-notched tensile specimen in which the crack velocity reached the maximum value that is less than the above. The variation of the marks and the mechanism of forming these marks seem to be the same with the cases in UP and PMMA, and they are discussed in detail from the points of fracture strength and the crack velocity change. The shapes of the marks are approximated by the equation of fracture surface marks.

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A method for dynamic strength evaluation of ceramic circular beams containing small flaws was studied. (1) With an increase in the ratio of breadth and depth, the eigenvalues increased, except for the fundamental eigenvalue. The eigenvalues decreased monotonically, with an increase in the opening angle. (2) The critical frequency range was obtained by evaluating the strength of beams on the basis of the static-fatigue limit. (3) The critical frequency range increased slightly, with an increase in the equivalent crack length. (4) For an increase in the damping ratio, the critical frequency range was constant, and then became smaller. The fundamental critical frequency range was not affected by the damping ratio.

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Physical properties (E_x, E_y, G_xy, ν_xy) are necessary for analyzing the plane problems and fracture mechanics of orthotropic material, and measurements of physical properties and stress fringe values (f_x, f_y, f_xy) for orthotropic material are needed for each photoelastic experiment on orthotropic material. Strain gages are generally used to measure the physical properties of orthotropic material, but errors due to various factors are common. Therefore, relationships between physical properties and stress fringe values are suggested in this paper. These can be utilized instead of the strain gage to measure physical properties with stress fringe values. This is confirmed by experiment in this paper. Specimens of C. D. are better than those of B. M. for measurement of the stress fringe value of an orthotropic material. Stress fringe value fxy can be obtained from equation (19) with f_x, f_y, f_θ and θ; in this case, θ is between 40°and 65°. The optimum value is θ=45°.

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A time domain approach for a higher-order boundary-time element for two-dimensional elastodynamic problems is suggested. Introducing linear time elements of equally spaced intervals and boundary elements with quadratic variations of displacements and tractions over each time interval for the discretization of time and space, the boundary integral equation, when written for every boundary element, yields a system of algebraic equations for each time step. It is also formulated that singularities at the wavefront caused by the delta function can be removed by evaluating the time integration of the discretized equation analytically. Some basic numerical examples of infinite and finite region are analyzed and the results are compared with the theoretical values.

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The indirect fictitious boundary integral method attacks three-dimensional flat notch problems. In this analysis, a new idea is introduced. That is, we set up one open fictitious-boundary surface between two neighboring real-boundary surfaces and distribute the simple- and the double-layer surface densities over it. As examples, stress concentration problems of a circular bar with a flat ellipsoidal cavity or a flat semielliptic annular groove under uniform tension are treated.

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An analytical method for elastodynamic problems combined with a multiple integral transform and numerical inversion is investigated. The integral transforms are a Fourier transform in the infinite domain or finite Fourier transform (Fourier series) in the finite domain for coordinates, and a Laplace transform for time. The transformed solutions are inverted by a numerical method using the fast Fourier transform (FFT). By this method, one-dimensional and two-dimensional problems are analyzed. By comparison between the obtained results and the exact results, it is shown that highly accurate numerical results are given by the easy procedures described in the present paper.

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Cyclic stress corrosion cracking (SCC) tests of smooth specimens under combined cyclic/static tensile and torsional loads were conducted on a 4135 high-strength steel in 3.5% NaCl solution at 298 K. The stress waveform was triangular at a stress cycle frequency of 0.1 Hz. Two series of loading patterns were employed; multiaxial cyclic load tests under in-phase cyclic tension and torsion (tensile stress ratio, R_σ, of zero, and torsional stress ratio, R_τ, of zero), and multiaxial cyclic-static tests in which one of the two applied loads was cyclic and the other static, i.e., (R_σ=0, R_τ=1) or (R_τ=1, R_τ=1). The combined stress ratios of τ_max/σ<max> were selected as 0, 1/2, 1, 2, and infinity. In the case of multiaxial cyclic load tests, a cyclic SC crack normal to the maximum principal stress was initiated at the bottom of the corrosion pit. In this case, the life of cyclic SCC was dominated by the maximum principal stress, σ_{1, max}, which equaled the maximum principal stress range, _{1, max}. In the case of multiaxial cyclic-static loads a cyclic SC crack normal to the maximum tensile stress range was initiated at the bottom of the corrosion pit, provided that the static tensile load in the plane of the maximum tensile stress range was relatively small. IN this case, the life of cyclic SCC was dominated by the maximum tensile stress range, _{n, max}. In either case, the mechanical condition dominating crack initiation at the bottom of the corrosion pit was determined by the stress intensity factor range, K_1FSCC, calculated on the assumption that the spherical corrosion pit was a sharp surface crack.

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Viscoplastic behavior of Type 304 stainless steel after various types of axial cyclic prestraining is investigated theoretically. Viscoplastic behavior, including relaxation, in tensile loading and in the following compression, can be estimated with accuracy by using the viscoplastic theory based on total strain and overstress, with some modifications. The viscosity function which dominates the difference between flow stress levels depending on strain rate is influenced considerably by cyclic loading. However, the relaxation stress drop shows little change. To explain these experimental facts that cannot be explained by the customary theories, the virtual overstress which is caused by cyclic and simple preloadings is introduced. The virtual overstress is added to the customary overstress, but it has no effect on stress-strain behavior in loading under the condition dε≠0.

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The erosion-corrosion characteristics of carbon steel commonly used as piping material subjected to an impinging gas-liquid two-phase flow under various pH. chloride ion concentration and flow rate combinations were investigated. Environmental condition saffected not only the damage rate but also the type of damage. One of these was the enhanced general corrosion observed mainly under high chlorine ion concentration (1220ppm) and another was flow-induced pitting corrosin observed under the pH7-[C1^-] 140ppm condition. Each condition of the chemical solution had its own flow effect. For example, in the case of high chlorine ion concentration, high flow rate accelerated corrosion damage by decreasing diffusion control. On the other hand, under low chlorine ion concentration, high-speed flow decreased the corrosion rate by the action of removing nonprotective oxide layer. To indicate the condition of occurrence for enhanced corrosion damage, a two-dimensional chart which had axes of [C1^-] concentration and flow rate was constructed for each pH value.

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This study was performed to assess the validity of the R6-Rev. 3 approach to predict fracture behavior of carbon steel pipes for LWR plants. To verify the approach, a maximum load, predicted by analysis, was compared with an experimental load, obtained at JAERI. Analysis and experimentation were conducted on a STS 42 pipe (6B, sch. 80) with a circumferential through-wall crack (2θ=180°). The comparison of the results indicates that the R6-Rev. 3 approach gives conservative maximum load prediction with reasonable accuracy. In the next step, failure assessment curve (FAC) was discussed briefly, and sensitivity analysis was carried out to clarify the effects of initial crack length, pipe size, and toughness of the material on fracture load and the possibility of occurrence of net-section collapse. Although unstable fracture was predicted to occur by a mode other than net-section collapse in all analyses, fracture load was able to be evaluated by simple limit load analysis based on yield stress, so long as a proper margin was considered.

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This paper deals with a simple method of estimating the J-integral for a single-edge cracked specimen subjected to bending moment and shearing force. The J-integral of a specimen which is subjected to mixed mode I-II loading is expressed in the form of J=J_I+J_II, where J_I and J_II are the components of mode I and mode II deformation, respectively. For the single-edge cracked specimen, J₁ can be estimated from the M-θ diagram (M: bending moment, θ:crack opening angle), and J_II can be given by the sum of the elastic part and the plastic part estimated from the F-U diagram (F: shearing force, U: crack shearing displacement). Large deformation finite element analyses were carried out for four kinds of specimens under loading conditions ranging from pure mode I to pure mode II. The validity of this simple estimation method for the J-integral was examined and the deformation behavior of the crack tip under mixed mode loading was discussed based on J-integral, J, J_I, J_II.

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The present authors have proposed an electric potential CT method for measuring two- and three-dimensional cracks embedded in a body. In this method, the observed data of electric potential distributions on the surfaces of the body are computer-processed using inversion analyses to identify the location, shape and size of cracks. Numerical simulations and experiments conducted for two- and three-dimensional cracks demonstrated the usefulness of the proposed method. In the present study, the uniqueness of the inverse solution in crack identification by thee electric potential CT method is discussed. It is shown that when the plane in which the crack exists is known in advance, cracks in the plane can be uniquely identified, if the electric potential distribution for an appropriate current application is given. When the cracked plane is not known in advance, the electric potential distributions under two current-application conditions are necessary to determine a single two-dimensional crack embedded in a body. Similarly, the electric potential distributions under three current-application conditions are required to determine a single three-dimensional crack.

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A new nondestructive method using a simulated acoustic emission (AE) technique is proposed for the monitoring of crack growth and crack closure behavior. Simulated AE signals, which propagated through a crack, were detected and the waveform changes with the crack growth were examined. It became clear that the amplitudes of the first peak of the waveforms have a strong correlation with the crack length and the state of crack closure. The numerical simulation by a finite differential method showed that about ±10mm of crack length can be measured with a pair of AE transducers, and the correlation curve between crack length and amplitude of the simulated AE shows little change with the materials. These results suggest that the simulated AE technique is applicable to the evaluation of both crack propagation and crack closure behavior.

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The steady-state thermoelastic problem of two bonded dissimilar finite materials containing external interface cracks is considered. The analysis is based on the complex variable method, and the general solution which satisfies the thermal and mechanical boundary conditions on the interface is obtained. Numerical calculations are carried out for the strength of thermal stress singularities of two bonded finite rectangular plates subjected to a heat flow distubed by the insulated external cracks, and the results are shown in graphs.

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In this study, the progression of the overstress and the internal stress during an inelastic deformation of 2··1/4 Cr-1 Mo Steel at 550°C°C, is investigated. An abrupt unloading was imposed during a fully reversed push-pull loading on the tension-going stroke at various strain levels. The rate of strain in the push-pull loading ranged from 10^-3 to 10^-5/s whereas that of unloading was at 10^-3 1/s. It was observed that the overstress increased rapidly at the start of the tension going stroke and reached a steady-state value soon thereafter. The overstress appeared to be independent of the strain rate. On the other hand, the back stress increased rapidly in the early stage of loading, and continued to increase further albeit at a lower rate of increase. The drag stress in the meantime remained constant. The internal stress thus exhibited a rate-dependency. It is concluded that the overstress controls the rate-independent component of the inelastic strain while the internal stress controls the time-dependent part.

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Strain gauges made of nickel foil are used for measuring the elastic surface stress of a specimen subjected to repeated loads. The nickel foil, about 10μm thick, is composed of crystal grains of 30μm in mean diameter. The foil is stuck on the surface of the specimen, and the elastic stress is measured by observing slip-bands in the crystal grains resulting from repeated strains. The calibration curves of the foil, i.e., the relations between the proper stress at which slip-bands begin to appear and the number of stress cycles are obtained by rotating-bending tests of (0.14)×10⁶ cycles and at several test temperatures up to 350°C. The relation between the appearance of slip-bands and the magnitude of cyclic stress is also investigated. Applying the methods using the proper stress and the proper number of cycles which are derived from the calibration curves of the foil gauge, the peak stresses in grooved shafts under bending are measured.

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It is very important to measure the absolute photoelastic coefficients in photoelasticity and the optical constants in the method of caustics when using these methods, and there are various techniques for obtaining these values. However, these techniques are not simple to employ. We applied the principle of caustics to the determination of optical constants. The fundamental idea of this technique is to utilize the deviation of light due to the stress gradient. The principle of this method is very easily explained from the standpoint of the method of caustics. Some practical techniques for obtaining optical constants were examined by means of a pure bending system and a laser beam. The optical constants of some materials are shown in the case of room temperature and also in the frozen-stress state for an epoxy resin plate.

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The caustic method is a very powerful technique for measuring the value of the stress-intensity factor. The caustic pattern, however, cannot be obtained in the frozen-stress models in the immersion fluid by the conventional caustics technique. The reason for this phenomenon is studied by using the individual values of the optical constants. It is shown that the optical constants of the frozen-stress model, which determine the shape of the caustic pattern, have very different aspects from those at room temperature. The caustic pattern in the frozen-stress model is theoretically calculated by using those optical constants and it is also confirmed experimentally. Some practical techniques to apply the caustic method to such a frozen-stress model are shown.

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A concept of higher stage polar materials, proposed in the previous report, has extended the usual micropolar theory to the n-stage. It is necessary to construct a generalized continuum mechanics for the higher-stage micropolar materials on the basis of this concept. In the present paper, the kinematics for micropolar materials of stage-2 is discussed as preliminary to this. In order to express the complicated geometric mechanism due to the multimicrostructure of higher stage polar materials, the strain gradient theory is introduced into micropolar theory. The results obtained here are summarized as follows. Micropolar materials of stage-2 have not only the degrees of freedom of displacement and microrotation, which are assigned to the usual micropolar materials of stage-1, but also one of microtorsional rotation. Additionally, transport theorem for each stage is derived.

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Mechanical balance laws for micropolar materials stage-2 are discussed on the basis of results of the previous report. The balance equations for mass, force and moment in stage-2 are derived by averaging the balance laws of stage-zero up to stage-2. It is indicated that one more balance law has to be considered, which is those of second-order moment, in order to let the balance equation system be a complete set. The missing equation is gives as the average of the balance equation for the above second-order moment of stage-zero. The authors define a new internal force characterizing the materials of stage-2 and name it "bicouple stress". This is a second order moment due to the geometric mechanism of multimicrostructures of higher-stage micropolar materials. Furthermore, it is discussed that the bicouple stress extends the concept of bimoment in the theory of thin-walled structures to three-dimensional ones.

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The author reports the application of the large deflection of annular plates with various loads and boundary conditions using the nonlinear programming theory. This method is based on the optimization technique derived from the total potential energy. Four numerical examples are presented in the case that the outer boundary is clamped, and that the ring load at the inner edge of transverse uniform load is subjected to the plates. The numerical calculation is executed for the dimensionless load ratio P/P₀, where the basic load P₀ is defined as the one which yields the same maximum deflection that equals the thickness of the plate by the elastic small deformation theory. It is concluded that the distributions of the out-of-plane displacement under the same boundary conditions for the typical load ratios show analogous behavior, and that the distributions of in-plane bending stress show the same tendencies, while distributions of bending stress differed when the load condition is changed.

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