Certain service loads, when applied to practical machines and structures, could be regarded as approximately deterministic. However, most of them would be, to a degree, of a random nature with complicated temporal variation. Hence, in order to assure the desired level of reliability of critical structural components under random loading, it is of crucial importance to clarify, in particular, the effect of the randomness of the applied load on the life distributions or probabilities of failure of the components, in addition to the effects of other various uncertainty factors of the components, in addition to the effects of other various uncertainty factors usually taken into account in the reliability assurance of structural components subjected to constant amplitude loadings. In this respect, in the present paper, the fundamental concept has been discussed and a state-of-the art survey has been made to ascertain the structural reliability for stationary random loads from the viewpoint of whether the effect of the applied random load on a critical structural component is cumulative or not.

View full abstract

A solution is given for three-dimensional transient thermal stresses due to a local source of heat that moves back and forth with a constant angular velocity over the surface of an infinite elastic slab. The transient temperature distribution is obtained by means of the complex Fourier and Laplace transforms, and the associated thermal stresses are obtained by making use of the thermoelastic displacement function and the Galerkin function.

View full abstract

Few investigations have been carried out on the characteristics of bolted joints with a gasket which are subjected to external bending moments. In this paper, the characteristics of the pipe flanges with a full-face metallic gasket subjected to external bending moments are examined. In the analysis, the pipe flange and the gasket are replaced with hollow cylinders. The distribution of contact stresses, the force ratio for the external bending moment (the relationship between an increment or decrement of bolt axial force and the external bending moment) and the maximum stress produced in the bolts are analyzed as axi-asymmetrical problems using a three-dimensional theory of elasticity. For verification, experiments are performed with respect to the force ratio for the external bending moment and the maximum stress in the bolts. The analytical results are in fairly good agreement with the experimental ones.

View full abstract

This paper is concerned with the stress analysis of an elliptical crack at the interface of two bonded, dissimilar elastic half spaces when the upper and lower faces of the crack are subjected to internal pressure. By using the generalized Abel transform, we reduce the problem to the Hilbert problem with infinite unknown functions. The general method used to solve the problem is shown. As a numerical example, we apply the method to a case in which the crack faces are subjected to constant pressure.

View full abstract

This paper deals with the stress concentration problem of a circular solid cylinder with the form of a specimen subjected to torsion by a pair of rigid chucks. A method of solution is developed for the problem by using Green's functions for torsional body force problems of an infinite thick plate. The method of solution is said to be a kind of body force method, charge simulation method, or indirect boundary element method with fictious boundaries. Numerical results are shown systematically for various sized of the solid cylinder. Consideration is given to the influences of the radii at the shoulder and sizes of the solid cylinder on the stress concentration factors and on the positions where the maximum stress appears. The convergency of solution by the present method is also investigated.

View full abstract

This paper demonstrates the derivation of the equations previously proposed for an 'elastic' buckle propagation in a pipeline subjected to bending under axial tension and hydrostatic side pressure. Formulation is given for a thin cylindrical shell of infinite length in such a way that bending gives rise to a geometrically large but elastic deflection so that a significant cross-sectional deformation takes place. For simplicity, a material behavior of the pipe is assumed by Hooke's law. On the basis of the three-dimensional theory of nonlinear elasticity, the derivation utilizes the asymptotic-expansion method in terms of the thickness-coordinate of the pipe, combined with a Fourier expansion in the circumferential direction and a 'long-wave approximation' in the axial direction. Derived are the nonlinear wave equations which couple the beam-flexural mode with the ring-flexural mode. A further simplification and a physical significance of the equations thus derived are discussed.

View full abstract

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

View full abstract

This paper describes the applicability of the indirect fictitious-boundary integral method to thermal elastic stress problems with simply-connected regions. As examples, a thermal contact problem of notched bar constrained by two hot rigid surfaces in contact with its both end surfaces, and a thermal stress problem of a wall having a concavity (notch) or convexity (protrusion) on one side and heated on either side are treated. As a result, the isothermal line and the thermal stresses are obtained. The influence of shape parameters on stress distributions is also shown.

View full abstract

An iteration method of the finite element synthesis is presented on the basis of a new notion: that the objective design is searched for in the vicinity of the initial design, while the structural response to the objective value ia approximated by the first-order Taylor series expansion of the response with respect to the design variables. A functional is composed of the squared sum of the design variables and the equality constraint conditions representing the response approach to the objective value incorporated by the Lagrange multipliers. The design variables are determined by the minimization of the functional. The numerical examples are concerned with the contour adaptation of two-dimensional elastic structures so as to decrease the concentrated stresses around the hole in a square plate under bi-axial tension and the fillet bending stress in a gear tooth.

View full abstract

The CED (crack energy density) in an arbitrary direction ε_φ, is expected to describe the fracture behaviors of a mixed mode crack. It was shown previously that ε_φ can be evaluated by a path-independent integral with sufficient accuracy for practical purpose. In this paper, as another evaluation method of ε_φ a method based on the relationship between ε_φ and load- displacement curves is discussed. The contents are as follows. 1) A relationship between initial crack lengths, load-displacement curves and ε_φ, which holds until cracks start to grow, is derived by considering the strain energies of the specimens with different initial crack lengths. A method of evaluating ε_φ from the load-displacement curves is proposed based on this relationship. 2) Based on this method, evaluation of ε_φ is attempted from load-displacement curves obtained by finite element analyses and also from experiments for specimens under tension with a crack inclined to the loading axis, and it is shown that this method is practical for evaluating ε_φ through comparison with the theoretical values and the values found by the path-independent integral.

View full abstract

Two-dimensional stress waves in an elastic circular tube are analyzed numerically when axisymmetric impacts are applied to the end face of the tubes. For the numerical analysis, a finite difference method based on integration along the bicharacteristics is employed. By obtaining the numerical results for various tube sizes, and for the impact loading condition, it is clearly demonstrated that, when the rise time of the applied impact velocity is sufficiently short, a large tensile stress arises on the boundary of the internal surface of the tube. It is also found that the maximum value of the caused tensile stress on the boundary of the internal surface becomes larger when the rise time becomes shorter, and when the ratio of the thickness of the tube to the outside diameter becomes larger than about 0.3.

View full abstract

A "complex moire pattern" is obtained by shifting the discrete Fourier spectrum of the image of a deformed grating. The strain distribution is given as the derivatives of the phases of the complex moire fringes. The analysis is completely automated by digital image processing. All of the laborious and subjective procedures required in conventional analysis, such as fringe sign determination, fringe ordering, and fringe interpolation, are completely eliminated, and objective, fast and accurate analysis is performed.

View full abstract

This paper describes the experimental results of mechanical ratcheting under biaxially varied stress conditions. The experiments were conducted by subjecting thin-walled tubular specimens of a carbon steel to a combination of a cyclic axial load and internal pressure at room temperature. The effect of the simultaneous variation of maximum effective stress, stress ratio and superposed stress with an increase in the number of cycles on the biaxial strain accumulation is discussed. The strain history dependence on the orientation of strain accumulation was observed in the ratcheting under varied superposed stress conditions. The results of numerical simulations obtained by the constitutive equation, previously presented by the author and his co-workers, agree comparatively well with the corresponding experimental results, except during rapid variation of a superposed stress.

View full abstract

Measurements of ultrasonic transverse waves were made in order to investigate the development of elastic anisotropy of a polycrystalline metal with plastic deformation. From the same bar of S18C steel, specimens were prepared so that the velocities v₁ and v₂ of two polarized transverse waves could be measured for several values of the compressive plastic strain e along the bar axis, and of the angle θ of the direction of propagation from the axis. The results show that the anisotropy of the material is composed of the initial transverse isotropy and the transverse isotropy developed in proportion to the compressive plastic strain, and that these are nearly equal in type, but opposite in sign. It is also shown that the elastic anisotropy thus determined is not coincident with that derived from the Voigt model of a polycrystalline material, but that the difference between them is of allowable degree.

View full abstract

While experimental studies to find out the correlation between the mechanical properties of materials and the damage due to cavitation by the testing method of cavitation with magnetostriction vibration (direct method) have been published, no correlation that is universally applicable has yet been found. This is principally due to the fact that the testing method has not been established or standardized to measure reproducible data, and the mechanism of damage due to cavitation has not yet been made clear. In this report, the author used the method previously reported by which reproducibility of the testing data and the method of representing the results is improved, and clarified the mechanism of damage in this testing method. Then, on the basis of the assumption made by modeling the method, the theoretically derived a semi-empirical formula with which the maximum average rate of damage can be estimated from the mechanical properties and the frequency and amplitude of the test vibration.

View full abstract

The contact-pressure distribution in upsetting is estimated by measuring the elastic-strain distribution in the loading platen. The strains in the platen are measured by pipe-type strain gages, and are converted into contact pressure by a finite-element analysis. Compensation for the strains due to the friction on the contact surface is possible to some extent. The estimated pressure distributions almost agreed with those measured by the pressure-pin method. The pressure was distributed uniformly over the contact surface in the well-lubricated specimens regardless of the diameter-to height ratio of the specimen, d₀/h₀. Friction hills were observed in the unlubricated specimens with d₀/h₀=4 and 2. A concave pressure distribution was obtained for the specimen with d₀/h₀=1, where the pressure increased from the center to the periphery of the contact surface. The present method can be applied to measure die-pressure distributions in practical metalworking processes.

View full abstract

Crack propagation behavior has been observed in A7003- T6 aluminum alloy under low cyclic loading with hold time over the frequency range 4×10^-31 Hz in 3.0% saline solution. From the experimental results, the effect of cyclic frequency on crack propagation rates was found to be exemplified by two different regimes. One has a positive dependency on the frequency below a critical frequency, f_crit, at which point maximum environmental attack occurs in terms of da/dN, and the other is negative above f_crit. The behavior of crack propagation below f_crit was explained by the concept of stress assisted dissolution which tends to inhibit mechanical failure by crack blunting and microbranching. The number and depth of secondary cracks occurring under the fracture surface were measured by metallographic examination, and the actual crack tip stress intensity factor was estimated.

View full abstract

In order to accurately estimate the reliability of the service life of a pressure-proof connector made of polycrystalline alumina, static and cyclic fatigue of polycrystalline alumina and its brazing part were examined. Static and cyclic fatigue tests and static bending tests under 4-point bending loads were carried out using three types of specimens: A; plates, B;plates with a center hole, and C; plates with a center hole brazed to a Cu pin with Ag-Cu alloy. Fatigue failures of both the A- and B-type specimens were basically controlled by the static fatigue stress-corrosion cracking, but in addition, the effect of cyclic stress on their failures could be recognized from estimating the time to failure under cyclic stress based on the data from static fatigue tests. On the other hand, fatigue failures of the C-type specimens were mainly controlled by cyclic fatigue, such as metal fatigue. This is because the main mechanism of fatigue in the C-type specimens is the initiation of a fatigue crack in the brazing alloy.

View full abstract

An investigation of the effect of water absorption on the mechanical properties and fatigue strength of ±45° angle-ply carbon/epoxy composites, i.e., 130°C-cure-type composites T-1/347 and 180°C-cure-type MM-1/982X, has been carried out. In both composites, water absorption lowers the strength of the interface, resulting in a decrease in a tensile strength, an elongation a the break, and fatigue strength. In a higher stress region in laboratory air, cyclic loads make the temperature of a T-1/347 composite so high that plastic deformation of the matrix is enhanced and the fatigue life is shortened. In water, however, the cooling effects of water circulation around specimens become predominant, and hence the fatigue life increases in a high-stress region. We also point out the usefulness of scanning acoustic microscope in the examination of the internal damage of the composites.

View full abstract

Fine ceramics offer excellent strength and durability characteristics at elevated temperatures, however brittle materials exhibit catastrophic failure without any plastic deformation. In consideration of these characteristics, we discussed the structural design concepts which must be established to assure the best use of ceramics for high-temperature machines requiring high reliability. Based on the ceramic-oriented structural design concepts, a ceramic/metal hybrid structure of the 1st stage ceramic stator vanes in industrial gas turbines was developed. In this hybrid stator vane, components exposed to high temperature and a corrosive environment were made of ceramics. Metal was used as the strength member. Moreover, a thermal shock testing method for ceramic to evaluate thermal shock resistance, which is an extremely important factor in ceramic component use was proposed.

View full abstract