The notion of, and the progress of continuum damage mechanics along with the microscopic aspects of material damage are reviewed. Starting from a brief review of material damage and the notion of continumm damage mechanics, mechanical modelling of the damage states and the damage variables used to describe them are discussed. Then, the extension of the classical creep damage theory to the anisotropic state of creep damage and the problems of elastic-plastic damage are discussed. Besides the application of these damage theories to the damage of metals, concrete and rocks, recent works on spall damage, fatigue damage and creep-fatigue damage are reviewed. The applicability of continuum damage mechanics to the analysis of boundary value problems, and the local approach to fracture problems by means of continuum damage mechanics are also referred to.

View full abstract

This paper reviews a vibration problem relating to industrial energy equipment such as steam generators, heat exchangers. and condensers. It focuses on unstable vibrations in circular cylindrical structures immersed in two-phase cross flows, which are caused by unsteady fluid forces induced by the interaction between structural vibration and the fluid flow. Added mass and fluid damping induced by a vibrating circular cylinder in a two-phase bubble fluid are introduced, and then the effects of air bubbles on vortex-induced vibrations such as in-line and cross-flow oscillations of a single circular cylinder are reviewed experimentally. Finally, fluidelastic vibrations in a single row of cylinders as well as in cylinder arrays are discussed in relatlon to air bubble effects on instability criteria with respect to reduced velocity and mass-damping parameters.

View full abstract

This paper shows a simple method of calculating the stress intensity factor of a through crack filled with viscous lubricating oil. A center crack specimen is assumed under plane strain conditions. For the lubricating oil, it is assumed that the pressure rise due to the squeeze effect follows the Reynolds equation. The full Reynolds equation is approximated by a one-dimensional equation in the same way as is done for sliding bearings. As the crack is closing, the squeeze effect produces pressure, which tends to open the crack. This effect varies considerably with the thickness of the specimen. For a thin specimen, the squeeze effect on the stress intensity factor can be estimated by the infinitely short approximation, where the pressure distribution is assumed to be parabolic in the thickness direction. For a thick specimen, on the other hand, the infinitely long approximation is applied, where the pressure is assumed to be constant in the thickness direction.

View full abstract

The equation of motion in the radial direction for a rotating disc contains the product of the circumferential displacement and the angular acceleration of the disc. It is theorized that circumferential deformation has a considerable influence on radial displacement as the angular acceleration increases. This influence is discussed in this paper. Adopting the cyclically-varying rotation given by ω^^-(t^^-)=Ω^^-₁ sin (Ω^^-₂t^^-), Ω^^-₁, Ω^^-₂ : constants ; the displacements are computed for various values of Ω^^-₂. The maximum amplitudes, Δu^^- and Δu^^-', for the radial displacements with and without the circumferential deformation are discussed with respect to a non-dimensional quantity, ζ=Ω^^-₂/Ω^^-₁.

View full abstract

Buckling failures are often observed in tanks subjected to seismic load. In this paper, dynamic buckling is studied, using small, plastic cylindrical tanks made of polyester sheets. Static buckling tests on the fluid-filled tanks subjected to lateral load, and dynamic buckling tests under harmonic excitation using a shaking table are carried out, and the buckling modes are compared. The stress resulting from the frequency response (the circumferential wave numbers n=1 for horizontal excitation and n=0 for vertical excitation) is calculated using an axi-symmetric shell finite element program, which includes the effect of fluid structure interaction. Static buckling stress criteria are applied to the above calculations in order to predict the occurrence of buckling. The predictions are compared with the test results and they prove to be fairly satisfactory in the restricted region the natural frequency of the fundamental mode.

View full abstract

By using the resonance method with a cylindrical specimen, the anisotropic elastic constants of an axisymmetrical specimen at room temperature and the elastic constants of isotropic polycrystalline materials in a temperature range from about -190°C to about 300°C have been measured. In the former case, anisotropic elastic constants are determined in a JIS-C3604 brass (60/40) specimen which is mono-axially deformed by a compression equal to 49% of nominal strain. In the latter, the temperature dependence of isotropic elastic constants of pure aluminum is obtained and it agrees well with the converted values from existing elastic constants on a single crystal measured by the ultrasonic method over all temperature ranges.

View full abstract

Fracture toughness tests were performed on rock samples of granite, andesite, tuff and mudstone to evaluate the fracture behavior of subsurface rock materials in geothermal areas. The effects of temperature, confining pressure and water environment on rock fracture toughness were shown through experiments using pre-notched cylindrical specimens in the presence of pressurized water, ranging from 0.1 to 30 MPa at a maximum temperature of 224°C. The rock fracture toughness (K_iAE) was defined by the critical stress intensity factor of the crack tip region at the onset of the main crack propagation, which corresponded to an abrupt increase of ΣE_AEbefore the maximum differential pressure was reached. For granite, the value of K_iAE at 200°C and 20 MPa decreased down to approximately 20% of the value observed at room temperature and atmospheric pressure. However, the K_iAE value of andesite was independent of high temperature and confining pressure, provided that the test environment conditions were less than 224°C and 27.4 MPa. K_iAE values of tuff and mudstone were obtained as intermediate between the granite and andesite.

View full abstract

Studies of the rheological characteristics of water-, hydrocarbon- and diester-based magnetic fluids were carried out with and without a magnetic field. Experimental studies were made by means of the concentric-cylinder-type rotating viscometer which is operated within a strong magnetic field to clarify the effects of magnetic field, temperature and shear rate on the rheological characteristics of the magnetic fluids. The magnetic fluids are Newtonian in the case of non magnetic field. In the case of applied magnetic field, the flow curve for hydrocarbon-based fluid is still Newtonian. On the other hand, the water-based and diester-based fluids show pseudoplastic behaviour. Empirical formulae are obtained on the theoretical consideration of the laminar flow between rotating concentric cylinders.

View full abstract

This paper presents a new real time method of measuring unsteady flow rate employing centerline velocity in a circular pipe. Transfer functions which relate variables in axially symmetrical laminar flow can be obtained by mathematical analysis. We applied an approximate function of transfer function between the center-line velocity and the mean flow velocity to the measurement of unsteady flow rate. An analog electronic circuit whose transfer characteristic is equivalent to the approximate transfer function can be made easily, since it is composed of a proportional element, two first order lag elements and an element based on the second order lag element. The real time measurement of unsteady flow rate can be realized with the analog electronic circuit by inputting a measured signal of the centerline velocity to it. The validity of this method is clarified experimentally by comparing it with another measuring method whose validity has already been confirmed.

View full abstract

The two-dimensional natural convection of fluid under both a magnetic and a gravitational field was modeled by conservation equations. Sample computations were carried out for the fluid in a square enclosure for Rayleigh number of from 10⁴ to 10⁶, for Hartman number of from 1 to 10³ and for Prandtl number equal to 0.054, equivalent to melted silicon. The numerical computations converged successfully and the Nusselt numbers obtained were correlated to give an empirical equation for the rate of heat transfer. The steady state solutions were graphically visualized. At Ha=10³ and Ra=10⁶, the point at which the temperature profile was almost linear, the flow was almost suppressed and elongated in a regime with high wave numbers.

View full abstract

The two-dimensional unsteady motion of a plane shear layer and its mass transfer process were numerically simulated by using the discrete vortex method, combined with the third-order upwind finite difference method. A visualized distribution of the mass concentrations showed that the occurrence of entrainment corresponded to large eddy motion. The distribution profiles of the average concentration and the fluctuation intensity showed self-similarities. The distribution profile of the average concentration had a stepwise shape, and that of the fluctuation had two peaks. The entrainment of the fluid of the high-speed side proved to be larger than that of the low-speed side.

View full abstract

This paper is an extended study of the practical combination method of dynamic loads proposed in the previous paper, in which problems of the maximum response calculation of piping systems to multiple-support excitations were discussed. In this paper, experimental and numerical investigations are carried out in order to confirm the validity and feasibility of the proposed method. Using a simple Z-beam-shaped piping model for shaking tests, the maximum response of the piping in the fundamental mode is measured, and the combination law is applied to various correlation cases among two-vibrational loads. From the experimental results, it has been made clear that the proposed method is reasonable in comparison with other combination laws, like the square root of the sum of the squares (SRSS) method.

View full abstract

This paper deals with the self-excited vibrations of a rotating Mindlin circular plate subjected to a concentrated frictional force as a function of relative slip velocity exerted on its outer circumference. From the averaging method and a direct numerical integral method, it turns out that only single modes are stable; the generating modes are fixed in space, even if the circular plate rotates. Due to this rotation, the resulting mods deviate in the rotating direction from those generated in a stationary circular plate. Furthermore, the self-excited vibration becomes unstable or the steady-state solution ceases to exist as the rotating speed is increased. The analytical results are confirmed by experiment.

View full abstract

Based on the shallow water wave theory, the basic equations to describe the nonlinear responses of sloshing are derived, and a numerical method is presented to simulate sloshing phenomena in a rectangular tank which is oscillated horizontally. As the dispersion relation of the free surface wave plays an important role in the stable calculation of resonant responses, it should thus be taken into consideration. In this study, it is implicitly replaced by the dispersion relation produced by the discretization of the basic equations. Numerical results are in good agreement with those of experiments. In cases of shallow water depths, stable progressive waves are observed both in experiments and in numerical calculations, and the various nonlinear characteristics of sloshing, such as the hardening restoring forces and the jumping phenomena in resonant responses are well-simulated by the basic equations and the calculation method presented in this paper.

View full abstract

Linear dynamic and nonlinear steady-state curving analyses have been performed to investigate the hunting and curving behaviour of cross-braced trucks. The effects of interaction between cross-braced stiffness and suspension parameters on hunting stability and curving performance have been assessed. As a result, it has been analytically confirmed that cross-bracing improves hunting stability and curving performance. Moreover, optimal suspension parameters, which provide considerable improvement in both hunting stability and curving performance, are assessed.

View full abstract

A highly accurate acoustical holography is proposed, in which noise is measured on a hemispherical surface surrounding the noise source, and noise sources are reconstructed by a new reconstruction equation. It has been verified that this method has a resolution as high as a half-wavelength in the lateral direction and one wavelength in the range direction, and gives shift-invariant reconstructed images. This is confirmed by an experiment using a point-sound source. However, since actual noise sources have various forms and characteristics, this method cannot be applied to all noise sources. Therefore, for practical applications, it is necessary to apply holograms of various forms, such as of plane and hemicylindrical surfaces. Accordingly, the reconstruction equation for these holograms which gives highly accurate results has been derived by transforming the coordinates of the reconstruction equation for the hemispherical surface hologram. Finally, examples of the detection of noise sources with machines are shown.

View full abstract

A design method of a model reference adaptive control system based on exact model matching techniques is presented in this paper. The adavantages of this method compared with previous design methods are the following : (1) The concept of positive realness is not needed. (2) The introduction of an augmented error signal is not needed. (3) The design method can bee applied irrespective of the relative degree of the plant to be controlled. Therefore, the principle of the adaptive control is very simple. The proof of the stability is original and independent of any other proofs hitherto presented.

View full abstract

In this paper, a new scheme is presented for solving the Reynolds equation for gas lubrication in a high Λ region by the direct numerical solution method. This scheme derives from the concept that Poiseuille flow has an elliptical property and Couette flow has a parabolic one. This scheme has the following advantages : (1) High stability in a high Λ region ; (2) High precision in the case of coarse meshes ; (3) Simple algebraical expression ; (4) The required quantity of computer memory and cpu time is less than that required by other schemes ; (5) There is no waving of pressure results, which is often seen in conventional finite element methods.

View full abstract

From the point of view that scoring is a kind of transition process from a fairly lubricated condition to catastrophic adhesion, changes in tribological parameters such as the friction coefficient, the surface temperature, and the state of oil film formation, at every load step, were reinvestigated from previous test results of scoring conducted with a step-load condition using a two-disk machine. The relation between the surface temperature T and the coefficient of friction f varied with the conditions of asperity interaction, which were controlled by the direction of lay, the roughness heights, and the running-in process. The improvement of conformity between the microgeometries of the two surfaces made the T-f relation similar to that of smooth surfaces. The change of friction coefficient corresponded to the state of oil film formation. In the case of a hunting drive ratio of 1.95, when the T-f relation showed thermally unstable changes, that is, a simultaneous increase in the surface temperature and the friction coefficient just before the end of the load step, scoring did not always occur. Sometimes the scoring limits were higher than when using an integral drive ratio of 2, though no significant difference was observed in their T-f relations .These facts suggest that there is a difference in the probability of transition to scoring by the drive ratio.

View full abstract

The present paper deals with an analysis of the kinematics and geometry of the tooth engagement of a wave gear drive comprising a non-deformable rigid gear and a flexible gear in wave-like motion, such as a circular spline and a flexspline in the harmonic drive. The analysis is carried out in a plane mechanism . From the analysis of the motion of the rigid gear and the flexible gear, the shapes of the rolling contact plates which move together with each tooth are determined, assuming that the tooth of the flexible gear is rigid, although the tooth grooves is flexible, and that the pitch of the teeth on the unstretchable neutral line of the flexible gear is constant. Then the tooth profiles of both gears are determined, according to the theory of gear mechanism that the common tooth normal at the meshing point passes through the momentary contact point of the rolling contact plates. As an example, a theoretical new tooth profile of a flexible gear meshing with an involute profile internal rigid gear is obtained.

View full abstract

An algorithm for the accurate evaluation of a cutting area considering the tool tip radius and the multiple regenerative effect was proposed. This made it possible to follow the time historical behaviour of the cutting area during self-excited vibration. The cutting area which was accurately evaluated showed good agreement with the cutting force. The ratio of the cutting area to that for stationary cutting reaches about 3 at the maximum. The ratio was sbout 4 for cases where the tool tip radius and the multiple regenerative effect were neglected. These evaluations were kept constant even though the amplitude of the vibration was varied. The behaviour of the number of multiple regenarations during the vibration was also obtained. It is related to the amplitude. it was shown that the number was 4 or 4 while the amplitude was kept constant. however, it reached 12 when the vibration was disturbed by varying the rotational speed. The correlation of the cutting area with the cutting force was evaluated by adopting a factor to minimize the square root of the sum of the squares of the difference for both quantities.

View full abstract

The slider's three dimensional displacements due to contact deformation at sliding joints are analyzed. The sliding joints are represented by non-linear spring elements which are distributed evenly on the sliding face, and the kinematic model of the slider, including the sliding contacts, is introduced. By using this model, the slider's three-dimensional displacements caused by external forces can be analyzed. It is shown that the analysis can well explain the experimental results which were made through the model of an existing machining center's table. Secondly, the analyzed slider's displacements are converted to the machining error components, and the effect of contact deformation is evaluated. the component which most significantly affects the machining accuracy is regarded, and the corresponding slideway is redesigned to increase its contact stiffness. By repeating this process, the optimal slideway specification can be determined.

View full abstract