The growth characteristics data of a chemically short crack were generated for a high strength steel SNCM 439. The tests were conducted with axial loading under constant stress range at cyclic frequencies of 0.1, 1.0 and 10 Hz in room air and a 1% NaCl solution. The effect of cyclic frequency on short crack growth in a corrosive environment was evaluated and the results compared to long crack growth data generated with CCT specimens. The growth rates of short cracks were accelerated markedly in the 1% NaCl solution, as compared to those of long cracks under the same frequency. Furthermore, the short crack growth rates in the 1 % NaCl solution increased with decreasing cyclic frequency. These results indicate that the cyclic frequency is concerned with the chemical driving force of a short crack in a corrosive environment.

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Fatigue behavior of plain specimens of low carbon steel subjected to small tensile prestrains is investigated through rotating bending tests, and compared with that of annealed or strain-aged specimens. It is found that 3 % prestraining causes the acceleration of slip initiation and crack initiation, and increases the growth rate of a small surface crack of less than 0.3 mm. It decreases the fatigue limit and the fatigue life but gives no effect on the propagation of a large crack under small scale yielding. On the other hand, aging increases the fatigue strength of the prestrained specimens and the stress for the slip initiation. These effects of the small prestrain are explained on the unpinning of dislocation locking due to tensile strain before the fatigue test.

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The distribution of corrosion fatigue cracks observed on the un-notched round specimen surface differs with specimen diameter, especially in the low stress amplitude region. At a constant fatigue life ratio, many long cracks are initiated on the larger specimen, 12 mm (diameter), in comparison with the smaller specimen, 6 mm (diameter). On the other hand, in the high stress amplitude region of corrosion fatigue and fatigue in laboratory air, the distribution of cracks during the fatigue process does not depend on specimen diameters. In the low stress amplitude region of corrosion fatigue, crack growth rate does not show the usual behavior of the dependence of crack length, but shows only the dependence of stress amplitude. This unusual crack growth behavior explains why the distribution of corrosion fatigue cracks in the low stress amplitude region changes with specimen diameters.

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In the present paper, the effect of an oil environment on the fatigue strength of specimens with a circumferential notch of annealed 0.34% C steel is investigated, The fatigue crack growth rates were measured under rotating bending and reversed torsion, in air and in oil. The fatigue strength is increased by rotating bending and is hardly influenced by torsion for the existence of oil. These results are explained considering the two effects on the fatigue crack growth rate : the wedging action of oil and interlocking action.

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This paper is concerned with a theoretical analysis of a zig-zag array of circular holes in an infinite solid under uniaxial tension. We define suitable unit regions, assume the stress potentials in Laurent expansions and determine the unknown coefficients from the boundary conditions of the used unit regions. Numerical results of the maximum circumferential stress and the overall longitudinal stiffness of the solid with holes are given for various values of the parameters, and they are fitted by reliable empirical formula for convenience of practical applications.

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This paper is concerned with a theoretical analysis of a zig-zag array of circular inclusions in an infinite solid under uniaxial tension. We define suitable unit regions, assume the stress potentials in Laurent expansions and determine the unknown coefficients from the boundary conditions of the used unit regions. Numerical results of the interface stresses and the overall longitudinal stiffness of the solid are given for various values of the mechanical and geometric parameters, and they are fitted by reliable polynomial formulae for convenience of practical applications.

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A generalized solution of Elliott's solution to transversely isotropic elasticity problems is proposed in Cartesian coordinates. The solution consists of five potential functions and includes some new terms corresponding to equal roots of a quadratic equation. When elastic constant of transversely isotropic solids are replaced with those of isotropic solids, the solution is exactly coincident with a solution derived from Boussinesq's solution to isotropic solids.

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In experimenting with the lateral buckling of beams, there will be no lateral deflection, including torsion, up to the critical load in an ideal case. But actually, owing to various kinds of imperfections, the beam begins so deflect laterally, including torsion, with the beginning of loading. Thus the critical load is difficult to measure directly. In this paper, a modified Southwell's method is proposed to determine the critical load from the test data on the load and the reactive torsional moment at a clamped end of the beam. Experimenting with cantilever beams by using the multi-component loadcell developed by the authors, each critical load determined by the method agrees well with the theoretical value.

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A method of elastic-plastic stress analysis based on a combination (FEM + BFM) of the finite element method (FEM) and body force method (BFM) is developed to solve semi-infinte plate problems. FEM + BFM has the advantages of both methods and has many possible applications. The line elements of BFM are located along the interface between the outer elastic domain and the inner elastic-plastic domains which are composed with FEM elements. Green's function for a semi-infinite plate is used for the application of the body force method. The elastic-plastic problems of a semi-infinite plate containing a semi-elliptical nothch and a semi-infinite plate under various surface loadings such as elliptical contact loading, elliptical surface traction and forced constant and linear displacements by a rigid punch are solved. Other applications are also suggested.

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One of the most powerful theory to describe finite deformations of strong-fiber reinforced rubber is the theory of continua with internal kinematical constraints of inextensibility in the preferred direction. This ideal theory was experimentally examined by three point bending test, using glass-fiber cloth and synthetic-fiber cloth laminated rubber as composite materials. For the range of low load, the ideal theory represents the deformation behavior of these materials well. For the range of high load, these materials could no longer keep the assumption of the ideal theory (inextensibility and incompressibility). The more the number of the cloth ply, the better the model holds on the deformation of these materials. Furthermore, the method of decision for S=S(γ) was suggested and it was shown that S(γ)=G(γ+εγ³) is more suitable for these materials.

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The stress intensity factor along the periphery of a chevron crack in a cylindrical three point bend specimen (CB) is evaluated by BEM for the establishment of the rock fracture toughness test using CB specimens. So far, in the test, the stress intensity factor is assumed to be constant along the front edge of the crack and is evaluated by the compliance method. It is revealed from the present analysis that the stress intensity factor takes a minimum value at the center of the front edge so that the crack growth during the fracture toughness test makes the front edge of the crack concave. It is also shown that the stress intensity factor evaluated by the compliance method is larger than that of the concave crack with a homogeneous distribution of the stress intensity factor along the front edge. This implies that the fracture toughness test leads to over estimation.

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By shifting the discrete Fourier spectrum of the image of a deformed grating, we can obtain "the complex moire pattern". Strain distribution is given as the derivative of the argument of the complex moire pattern. The analysis is completely automatized by introducing the digital image processing. All of the laborious and subjective procedures reguired in conventional analysis such as fringe sign determination, fringe ordering, and fringe interpolation are completely eliminated and objective, fast and accurate analysis can be made.

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Granite, grahite and mortar are typical brittle materials. Recently, for evaluating the strength of these materials, a study based on fracture mechanics has been suggested. In general a microcrack process zone at the rack tip of brittle materials is created, which may determine the fracture process. So using the photoelastic coating method with a PLZT (transparent dielectric ceramics) plate (100-200 μm thickness), the strain field at the crack tip was directly measured. As a result, it was found that the strain field did not show the singularity of γ^-1/2, (γ=a distance from crack tip), as the strain field of linear elastic materials. When the strain distributions are normalized by J integral and the tensile stress σ_ult, they were expressed by a form of Δε=Δε₀((J/ σ_ult)/γ)^m : thus it is found that the strain field within the process zone can be described by the J integral, where Δε and m are material constants, and m is near 1. The strain field at the crack tip of the brittle materials is proportional to approximately γ^-1. The extension of the process zone, denoted by ω, is closely related to the J integral. The relationship between ω and the J integral can be expressed as a bilinear line. It is shown that the J integral at the knee point is equal to the critical J integral, value determined by AE technique. Thus the J integral can be an important parameter to evaluate the fracture behavior of brittle materials.

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A personal-computer based software, which enables the quantitative analysis of facet sizes of cleavage failures in Sharpy impact tests by calculating three-dimensional shapes, was developed. This software is based upon a computer image processing and pattern recognition technique consisting of two parts ; one to reconstruct the three-dimensional fracture surface topography from a stereo-pair of scanning electron micrographs, and the other to determine facet boundaries from the topography. By using this software, it become possible to measure the facet sizes quickly and with sufficient precision.

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Photoplasticity is a full-field technique that is based on the interpretation of optical patterns in transparent birefringent materials that are, or have been stressed beyond their elastic limit. Polycarbonate resin, a photoplastic model material has been subjected to a lot of studies. In this study, we attempted to investigate the dependence of the stress-strain curves of polycarbonate resin on temperature and tensile speed at high temperature, to find the best temperature for plastic strain freezing Further, it was considered whether the application of the theoretical equation of Ramberg-Osgood in the stress-strain curve that was obtained by photoplastic experiment is available.

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In bar rolling, it is important to analyze stress distribution to determine the roll force and controlling texture. We proposed an energy method using a finite element division and applied it to the analysis of low of a material. In this paper, we develop this method to obtain the stress distribution in bar rolling. Recently, Tomita obtained a stress distribution using a grid method so that the equilibrium condition may be satisfied approximately, whereas More evaluated the accuracy of the results obtained by rigid-plastic FEM by considering the equivalent nodal forces which are assumed to equilibrate. Therefore we combined these methods and applies them to determine the stress distribution. The following results are obtained. (i) The results are prove to be reasonable by comparing the roll force in flat rolling with a theoretical formula. (ii) In the square-diamond and round-oval pass, the roll force depends on the volume of the part which is reduced indirectly. (iii) In the square-oval pass, no part is reduced indirectly, and the roll force depends on the average value of the ratio of the projected contact length to the material thickness.

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The elastic-plastic constitutive equation with a vertex-hardening effect (MG c.e.) proposed recently by the author is applied to the analysis of deformation processes in axi-symmetric sheet metal formings, such as the in-plane bore-expansion, the bore-expansion by a rigid punch, and the pure-stretching and deep-drawing by flat-headed and hemi-spherical punches. Normal anisotropy is also considered by the use of the fourth-order yield function proposed earlier by the author, which involves the parameter X (=the ratio of the out-of-plane yield stress to the in-plane one) as well as the conventional γ-value. From the numerical results, it is emphasized that MG c.e. is very effective to predict the strain-localization and thus breakage of the sheet undergoing deformation, and that variations of the combinations of the three parameters γ, X and ρ have a strong influence on the stress-and strain-distributions and the breakage strain, where ρ is the parameter which governs the vertex-evolution rate in MG c.e..

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The present paper is concerned with thee formulation of an elaborate constitutive model of non-proportional cyclic viscoplasticity. For this purpose, we first introduced the notions of memory surfaces for the kinematic hardening variable as well as for the isotropic hardening variable. Then by examining the cross-hardening phenomena induced by the torsional cycles after tension-compression cycles, we formulated the rational parameter describing the non-proportionality of the deformation process and the relevant evolution equations. The new model is established by incorporating these notices into the viscoplastic model proposed by Chaboche et al. Comparison of the predicted results with the corresponding experimental ones shows that the proposed model can describe the cyclic hardening behavior in various proportional and non-proportional loading conditions with constant and variable amplitudes.

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The constitutive equations of laminated plates of FRM were derived. The previously proposed constitutive equations for unidirectionally fiber reinforced metals and laminate theory were used to derive the theory. The proposed theory is expected to describe the inelastic behavior of FRM and the strain rate sensitivity of stress-strain relations. The validity of the proposed constitutive equations was confirmed by comparing the calculated results with the experimental ones.

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The present study has been conducted because of the absence of previous studies on the stress and the fracture of FRP angle ply laminates with a fastened pin joint. The following became evident after examing results from 3-D FEM stress analysis and by experiments on three practical GFRP angle ply laminates. (1) The distribution of each stress component, the maximum shear stress and their concentration in each reinforced lamina which is oriented at 0°, ±45°and 90° to the tensile loading axis and in the very thin matrix layer. (2) The effect of the fastening force to the reinforced lamina and the matrix layer. (3) Posibility of estimation of the fracture strength and the mode of the fracture of the fastened pin joint laminates applying some proposed fracture criteria using stresses by FEM analysis.

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The mechanical behaviour of polymers is viscoelastic and time dependent. Polymers are often inhomogeneous, and hence it may be important to study the deformation behavior of inhomogeneous viscoelastic materials. A simple plane model of inhomogeneous materials is employed where two kinds of rectangular regions having a different modulus of viscoelasticity in the Maxwell model are assumed to be located regularly. This model is analysed numerically by means of the finite element method under plane stress condition. The applied stress is simple tension. The numerical results are compared with the analytical result obtained for the simple parallel or series Maxwell model. The effect of the aspect ratio of the inhomogeneous regions on the deformation behaviour is clarified.

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A constitutive law for elastic-plastic materials is presented on the assumption that deviatoric stress increments affect plastic strain increments. By the use of weighing parameters, the law is expressed as an averaging rule of the usual plastic potential law (or flow rule) and a rule that permits plastic strain increments to depend only on stress increments. The developed law permits the existence of a vertex on the yield surface. The law, however, can be written formally in the same equation as the usual flow rule : this implies that the developed law is applicable to such a solution scheme as the Finite Element Method.

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The accuracy of the finite element calculation of the J^^^-integral, which represents the dynamic energy release rate for propagating cracks, is studied. The main error is found to be caused by the calculation of the singular area integral. In order to reduce the error, a new method for evaluating the singular area integral. In order to reduce the error, a new method for evaluating the singular area integral is developed. In this method, the integrand in the singular area integral is developed. In this method, the integrand in the singular area integral is approximated by a certain function which is transformable into a line integral. The line integral is then evaluated analytically. The usefulness of the present method is demonstrated by an elastodynamic example.

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A boundary element method (BEM) for elastic contact problems is developed using the penalty function method. The contact conditions of slip, stick and opening states on the contact area are included in the virtual work function and a system integral equation of boundary values is formulated without an increase of the unknown parameter by introducing the penalty coefficients. A BEM based on this formulation is applied to typical two-dimensional contact problems such as those of a block-plate and a disk-plate. The numerical results agree well with the analytical solutions.

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This paper presents an efficient calculation method which eliminates the LDU decomposition process of the stiffness matrix in numerical solutions of the finite element method (FEM). This method is applicable to an in-plane elastic analysis of plane bent and/or curved beams composed of variable cross sections. The FEM using this method decreases CPU time and memory capacity in comparison with the conventional FEM using the LDU process. In addition, this method makes the FEM algorithm simple, and gives more accurate results, Moreover, approximate elements are developed to extend the applicability of this method to beams and/or frame strucutures with various supported conditions. Therefore, this method is effective for microcomputer aided FEM.

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This paper presents an efficient calculation method which eliminates the LDU decomposition process of the stiffness matrix in numerical solutions of the finite element method (FEM). This method is applicable to an elastic analysis of multi-branched variable cross sectional beams available as reinforced members. The FEM using this method decreases CPU time and memory capacity in comparison with conventional FEM using the LDU process. In addition, the use of this method makes the FEM algorithm simple, and gives more accurate results. Moreover, another efficient method using both this method and an influence function method is presented for an analysis of reinforced beams. The analysis of the reinforced beam requires the calculation of the connective forces and/or moments acting on each connecting node between the original beam and reinforcing members. Therefore, these methods are effective for microcomputer aided FEM.

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This paper presents an efficient calculation method composed of the two following methods : (1) the substructuring method and (2) the method eliminating the LDU decomposition process of the stiffness matrix of the substructures, in numerical solutions of the finite element method (FEM). The substructuring method contributes to the decrease of the input/output data and memory capacity to be used. The method eliminating the LDU process decreases both the CPU time and memory capacity in the numerical solution. This method composed of these methods is applicable to an elastic analysis of bent, curved and/or multi-branched beams, frame structures, etc. The FEM using this method decreases the CPU time and memory capacity in comparison with the conventional FEM using the LDU process. In addition, the use of the method makes the FEM algorithm simple, and gives more accurate results. Therefore, ther method is effective for microcomputer-aided FEM.

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