This review addresses fracture mechanics of interfaces as related to the process of interfacial crack growth between dissimilar elastic materials. Methods of solution of interfacial crack problems are presented. The concepts of complex stress intensity factors and energy release rate are then discussed. It is suggested that energy release rate, rather than stress intensity factors, is a more appropriate parameter for characterizing the occurrence of interfacial fracture. Topics on the competition between crack penetration and deflection at an interface, delamination of laminated beams, and fracture models for fiber-reinforced composite materials relevant to the debonding of the fiber-matrix interface are reviewed with an emphasis on the energy release rate approach.

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An axisymmetric contact problem is considered to be the cause of the indentation of a penny-shaped crack by a thin disc-shaped rigid inclusion in an elastic layer. This three-part mixed boundary-value problem is reduced to a solution of infinite systems of simultaneous equations in which the crack shape function is expressed as an appropriate series. The normal contact stress between the inclusion and the crack surface, as well as the stress intensity factor, is shown in curves calculated numerically. The effects of various values of nondimensional parameters on the stress field and the stress intensity factor are studied.

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The plane elastostatic problem of a crack branching at a fiber/matrix interface in carbon fiber reinforced composites is considered using a micromechanical model. The model is a crack which originates in one half-plane and branches at a bimaterial interface of a bonded plane consisting of an isotropic and an orthotropic half-planes. The method of continuous distribution of dislocations reduces the problem to a system of a simultaneous singular integral equations of the second kind, which is solved nemerically by use of the Lobatto-Jacobi integration rule. The singular stress field at the crack tips is investigated in terms of stress intensity factors and crack opening displacements.

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The steady-state thermoelastic problem of two bonded dissimilar finite plates 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 uniform heat flow disturbed by the insulated external cracks, and the results are shown in graphs.

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Vehicle collision characteristics are among the most important performance parameters to be examined at the design stage. These characteristics are dependent on the collapse mode of the box columns making up the side members of the body. An accordion-type collapse mode in which the columns do not bend but collapse in sequence is ideal. Beads or reinforcements are often used to produce this kind of mode ;however, most of the work done on them has been of an experimental nature owing to the lack of suitable analytical methods such as finite-element models. In this study, it is shown that a mathematically improved finite-element model, which can be run on a supercomputer, makes it possible to conduct a precise crush analysis of beaded columns When the first buckling mode is applied as the initial deflection.

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This paper is concerned with the development of an effective computational procedure for noise source identification using boundary element software and one of the algorithms available for optimum problems. The noise source identification in this study is formulated as an optimum problem to determine an optimal set of parameters which define the shape and the location of the noise source by minimizing the square sum of the residuals between the computed and measured qusntities at selected points in the acoustic field. In this study, the acoustic intensity is used as measured reference data since the acoustic intensity is a vectoral value which includes information on both the intensity and the direction of sound. Use is made of the conventional computer code based on the steepest descent method for the optimum problem under consideration. The acoustic intensity is calculated by the boundary element software previously reported on by the authors. Numerical experiments are carried out for a few sample problems using the computational softwsre developed, and the usefulness of the proposed procedure is thereby demonstrated.

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A solution is presented to a doubly mixed boundary-value problem of an elastic layer on a rigid base weakened by a cylindrical hole coaxial with a circular punch. The punch problem is reduced to the infinite system of simultaneous equations in which both the normal displacement on the lower face of the layer and the contact stress under the punch are expressed as appropriate series. Numerical results are obtained for the distribution of contact stress under the punch, the normal displacement on both surfaces of the layer and the total load applied to the punch. The effect of the presence of the hole on the stress field is also discussed.

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Green's functions in a closed form are shown for axisymmetric torsional body force problems of an elastic layer on an elastic half space. A Green's function is defined as a solution to the problem of an elastic layer on an elastic half space subjected to a torsional body froce acting on a circle in the interior of the layer. As a special case for Green's function, we can obtain Green's functions for torsional body force problems of (i) an elastic half space, (ii) an elastic thick plate, and (iii) an elastic layer on a rigid foundation. A general method of solution is presented for torsional body force problems of an elastic layer on an elastic foundation. Green's functions, mentioned above, are obtained by applying the general method of solution. As an example of the application of Green's functions we consider torsion of a hemispherical rigid body embedded in an elastic layer on an elastic foundation. Numerical reqults for the problem are shown.

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An impact torsion problem for a stepped bar composed of two semi-infinite bars bonded completely at each end is investigated. A stress singularity occurs at the corner of the bar. Therefore, the stress analysis proceeds considering this stress singularity by making use of the series expansion technique, and the problem is reduced to the infinite set of systems of linear equations for each time step. The generalized stress intensity factor for the corner, which is similar to the stress intensity factor for a crack, is defined. The values of the generalized stress intensity factor, the displacement and the stresses are shown for various values of the mechanical and geometrical properties of the bars.

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The present paper proposes mixed variational theorems of classical rate-independent elastoplasticity at finite strain based on the energy equation of Toupin, which takes into account the effects of nonsymmetric stress. The proposed variational principle can easily incorporate the internal work related to angular momentum balance, which has not been treated precisely in the previous works. Attention is also focused on the consistent and rational derivations of variational theorems based on the total Lagrangian formulation in terms of the nonsymmetric first Piola-Kirchhoff stress as well as the symmetric second Piola-Kirchhoff stress. Also discussed and clarified is the explicit derivation of complementary energy for elastoplasticity in rate form to be applicable for the finite element analysis.

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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 frozen-stress models in immersion fluid by the conventional caustic technique. The cause of 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 for applying the caustic method to such a frozen-stress model are shown.

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Physical properties (E_x, E_y, G_xy, V_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) of orthotropic material are needed for each photoelastic experiment on orthotropic material. Strain gauges 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 gauge to measure physical properties with stress fringe values. This is confirmed by experimentation in this study. Spemimens of CD are better those of BM for measurement of the stress fringe value of an orthotropic material. The stress fringe value f_xy can be obtained from Eq. (19) with f_x, f_y, f_θ and θ; in this case, θis between 40°and 65°. The optimum value is θ=45°.

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Fundamental characteristics of slip initiation and surface roughening phenomena in aluminum foil during the fatigue process are investigated under constant amplitude stressing. Applicability of the foil to the fatigue gauge that utilizes these phenomena to detect fatigue damage is discussed. It is found that the slip initiation phenomena in aluminum foil are easily observed by an optical microscope and that the effects of temperature and cyclic speed on the slip initiation are quite small. Accordingly, aluminum foil can be used as the fatigue gauge that utilizes the slip initiation phenomena. It is also found that evolution of surface roughness caused by the slip deformation is dependent on cyclic stress and the number of cycles. Therefore, this phenomenon also enables use of the foil as the fatigue gauge that makes use of surface roughness. Measuring accuracy of stress by this foil is about 5MPa, and in-process measurements of cyclic strains or fatigue damage can be practicable provided that noncontact surface roughness measurement is adopted.

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A series of thermal transient fatigue tests on five SUS304 stainless steel straight pipe models with circumferential weld joints and a nozzle model were performed to study the general behavior of crack initiation and growth including crack locations, directions and densities under respective loading conditions. The crack initiation sequence at different parts of models corresponded well with the result of analytical prediction using the finite element method. The potential margin on the allowable number of thermal transient cycles according to the ASME CODE CASE N-47 and the Elevated Temperature Structural Design Guide developed by the Power Reactor and Nuclear Fuel Development Corporation was evaluated, and the result showed a considerable safety margin compared with the data on initiation of cracks of 1 mm in depth at all parts of pipe models including circumferential weldings, notches, and other structural discontinuities.

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The influences of crack length on the crack growth in stress-corrosion-cracking (SCC) of 523 K-tempered, high-strength steel, SCM435H (σ_B=1770MPa) immersed in a 3.5%NaC1 solution were investigated under dynamic loading conditions; static SCC under a sustained load, dynamic SCC under a sustained load with high frequency vibratory stresses superimposed, and cyclic SCC under low-frequency variation. Threshold values of static and dynamic SCC of short cracks, whose crack length from notch root, l, ranged from l.52mm to 2.81mm, were smaller than those of long cracks (l= 6.86 - 9.78mm). Dissolution of the fracture surface was more prevalent in short cracks than in long cracks, and a decrease in threshold values of short cracks is considered to be caused by increased hydrogen uptake at the crack tip associated with the accelerated dissolution of fracture surfaces compared to long cracks. Crack growth rates of short cracks (l ≲ 6.5mm) at the plateau region were also accelerated compared to those of long cracks (l > 6.5mm). Static SCC crack growth rates of long cracks were accelerated and the threshold value was lowered by deaeration of the solution. However, the deaeration had no influence on the crack growth rates of static SCC of short cracks. In the case of cyclic SCC at R =0.1, no influence of crack length (l > 1.18mm) on crack growth rates was observed. But at R=0.5, track growth rates of short cracks were accelerated compared to those of long cracks.

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The corrosion fatigue (CF) behavior, under a constant deflection bending condition with a pulsating tension stress form, of anodized 2024-T3 aluminum alloy in 3.5% NaC1 solution was studied in parallel with that of unanodized alloy. Similarities and differences in the corrosion potential (E_corr) variations during the CF process were found between them. These behaviors presumably can be explained by the`cracking of anodic film' and the theory of`imperfect recovery of surface film'. It is suggested that the E_corr monitoring technique can be useful for determining the remaining CF life of existing structural parts made of this alloy or other Al alloys regardless of whether or not the alloy was anodized. Furthermore, the T3 temper provides a microstructure which may retard main crack formation and penetration in the CF process of anodized alloy ; this partly lessens the negative effect of the readily crackable anodic film.

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A method for the dynamic strength evaluation of ceramic beams containing small flaws was studied, and the following were observed: (1) With an increase in the taper ratio, the eigenvalue of the first order decreases, while the eigenvalues of the second, third and fourth orders increase. With an increase in the opening angle, the eigenvalue decreases monotonically. (2) The critical frequency range is obtained by evaluating the beam strength on the basis of the static fatigue limit. (3) The critical frequency range increases gradually with an increase in the equivalent crack length. (4) With an increase in the damping ratio, the critical frequency range of each order is nearly constant, and then decreases until it disappears. The critical frequency range of lower order is less affected by the damping ratio.

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A test system for precisely evaluating the tensile strength of ceramics at elevated temperatures was newly developed. Four-point bending and tensile tests were performed on sintered silicon nitride ceramics in the temperature range from room temperature to 1300°C. The track of a ductile fracture was observed on the fractured surfaces of the tensile specimens tested at temperatures above 11OO°C, suggesting the occurrence of plastic deformation. The fracture stress of bending specimens was about 1.18-1.43 times as large as that of tensile specimens. The test temperature dependency, however, was very similar in both the fracture stresses throughout the entire test temperature range. The fracture toughnesses from tensile and bending specimens were almost the same in the test temperature range from R.T. to about 800°C. The fracture toughness obtained from the chevron-notch-type specimen was almost coincident with that from the Knoop-indented specimen in the temperature range from R.T. to 900°C. There was, however, some difference at temperatures above this, suggesting the occurrence of adhesion at the crack tip in the Knoop-indented specimen.

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