The education of mechanical engineers must be viewed from several perspectives : the contextual basis in which engineering is practiced ; the curricular framework, its foundations and educational outcomes; and the developmental path for engineering education in the next century. The basis of the current educational paradigm is examined and its suitability for the next century is critically discussed in light of the demands that will be placed on mechanical engineers over the next generation. Several features of the education of mechanical engineers are discussed to suggest options that both Japan and the United States may exercise. Possibilities for international collaboration in undergraduate and graduate education, precompetitive R&D, and technology transfer are suggested.

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Elastic and elastic-plastic analyses of a crack in a particulate-dispersed functionally graded material (FGM) have been carried out using a newly developed finite element method based on Tohgo-Chou-Weng's (1994, 1996) constitutive relation for particulate-reinforced composites. By setting the mechanical properties of particles and a matrix and their content graded in the thickness direction, FGMs and non-FGM are designed. From comparison of the numerical results for the FGMs and non-FGM, the influence of the gradient of the mechanical properties on a stress intensity factor and the crack tip field is discussed. The following conclusions are derived: (1) The stress intensity factor of a crack under constant boundary conditions is considerably affected by the gradient of the mechanical properties. (2) The elastic and plastic stress singular fields around a crack tip in a FGM are basically described by the fracture mechanics parameters (K_I and J_I) as well as in a non-FGM, using the mechanical properties of the material at the crack tip. (3) The size of the singular field decreases with an increase in the gradient of the mechanical properties. This means that the applicability of fracture mechanics, such as the small-scale-yielding condition and the validity of the J-integral, is affected by the gradient.

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In our previous papers, we showed that the ring crack initiation strength (microfracture strength) of gas-pressure-sintered silicon nitride, evaluated by the sphere indentation method, is not related to the conventional flexural strength of the same material, using the concept of effective area based on the Weibull distribution function. In the present study, to clarify the reason for this, a model for initiation of a ring crack emanating from a surface microcrack was introduced. Using this model, the microfracture strength was discussed from the viewpoint of fracture mechanics. The dependence of the ring crack initiation load on the indenter radius was also examined. As a result, the essential difference between the microfracture and flexural strengths was well interpreted using this model.

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Based on the internal variable theory of thermodynamics, a continuum interface constitutive model relating interface traction with interface separation was developed. An interface damage variable was introduced, and an evaluation equation was derived to characterize the degradation of interfacial rigidity with interface debonding. The present constitutive model was applied to fiber pullout from the matrix, and bridging matrix cracking of composites. Relatively simple closed form formulas were obtained for shear stress distribution along the interface, pulling stress of fiber from the matrix, and stress intensity factor of the small matrix crack tip with fiber bridging. The effects of interface parameters involved in the evaluation equation on interface shear stress distribution, and pulling stress of fiber were also discussed.

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A constitutive model to describe a coupling between deformation and damage due to creep of polycrystalline metallic materials is developed from phenomenological and continuum mechanics points of view. The constitutive modeling is based on the irreversible thermodynamics for internal state variable theories, where the thermodynamic potentials, i.e., free energy and dissipation energy functions, are defined using hardening and damage variables. The material damage is assumed to be isotropic. We first derive a damage coupled kinematic-hardening model in the invariant form on the basis of the Malinin-Khadjinsky model. Then, an isotropic-hardening model which includes a coupling with damage is formulated by assuming a particular representation of the kinematic hardening variable. The evolution equation of the hardening variable is prescribed by the Bailey-Orowan format which includes the effect of damage. The damage rate is governed by the magnitude of the assumed strain hardening variable. These models can describe a transition from primary to tertiary creep stages, and it is applicable to variable loading conditions. In a particular case the expression for the creep rupture time has a similar form to the Kachanov-Rabotnov type, although it depends on the time and damage at the instant of a hardening saturation under the applied stress condition.

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A model is presented to have insights into the shear stress relaxation around a fiber break in unidirectional metal matrix composites reinforced with long brittle fibers. A cylindrical cell containing a broken fiber is considered, and a bilinear approximation of the fiber stress distribution in the broken fiber is employed to derive a simple differential equation for the shear stress relaxation. The resulting relaxation equation is applied to the cell subjected to either constant or increasing strain. It is thus shown that the shear stress relaxes very slowly in comparison with the axial normal stress in the matrix, and that the analytical solution obtained in the case of constant strain agrees well with the numerical analysis performed by Du and McMeeking. It is also shown that the relaxation equation under constant strain is almost derivable on the basis of the overall balance of energy in the cell. In addition effect of the radial gradient of shear stress in the matrix is discussed.

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Dynamic behaviour of a bias-type actuator using Ti-Ni shape memory alloy is examined theoretically as well as experimentally. The constitutive and the heat equations for the shape memory alloy, derived in the framework of continuum thermomechanics with phase transformation taken into account, are employed to describe the response of the considered actuator to applied electric input varying in time. Material parameters in the constitutive model adopted are determined from uniaxial loading-unloading tests at different temperatures. An experimental setup of the actuator, consisting of a shape memory alloy wire and a bias spring connected serially, is also manufactured, and the response of the actuator to cyclic electric input is measured. The experimental results obtained are compared with the predictions of the analytical model, which proves promising to describe the behaviour of the actuator very well in terms of its dependence on various factors such as the rigidity of the bias spring, as well as the magnitude and the period of cyclic input.

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The dependence of slip band occurrence at the periphery of microcircular holes formed by photoetching in electrodeposited copper foil upon the number of cycles and cyclic stress magnitude for plane bending and cyclic torsion is examined. The results show that the principal stresses in an element under biaxial stresses, which are undetectable by the conventional copper electroplating method, can be evaluated using an equation based on the probability of slip occurrence, which takes into account both cyclic stress magnitude and the number of cycles.

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In this work, a theoretical analysis of the axisymmetric thermal stress problem and the associated thermal stress intensity factor K_I is developed for Kassir's nonhomogeneous body with a penny-shaped crack with radius a subjected to a uniform heat supply from the crack surfaces. Assuming that the thermal conductivity λ, shear modulus of elasticity G and coefficient of linear thermal expansion α vary with the axial coordinate z according to the relations λ(z)=λ_o(|z/a|+1)^β, G(z)=G_o(|z/a|+1)^m and a(z) = α_o(|z/a|+1)ⁿ, the axisymmetrical steady temperature solution is obtained. Then, the associated thermal stress distribution and the thermal stress intensity factor at the crack tip are evaluated theoretically using the method of superposition. Numerical calculations are carried out for three different cases taking into account the nonhomogeneity of the above-mentioned material properties, and the numerical results obtained are shown in graphical form. The influences of the nonhomogeneous material properties on the temperature distribution, the corresponding thermal stress distribution and the stress intensity factor are examined.

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Microfracture processes of microcracking and crack propagation are simulated along with fracture strengths for 2-dimensional alumina polycrystals which have thermal anisotropy within a grain. Microcracks are generated by thermally induced residual stresses at a grain boundary. The stress concentration near the microcrack is calculated numerically by the body force method, and superposed on the preexisting residual stress. Stress intensity factors at the microcrack tip are also obtained by the method, and the location at which the next microfracture occurs is determined by the competition between microcracking and crack propagation in the new stress state. The microfracture stress increases with the progress of the fracture and decreases after maximum indicating a fracture strength. In many cases, the propagation of microcracks induces an unstable fracture. With decreasing grain size and increasing grain boundary toughness, the number of microfractures prior to the unstable state decreases, while the fracture strengths increase. For alumina of grain size 17.5 μm, when the fracture toughness of the grain boundary is 0.6 times that of the grain or greater, unstable fracture occurs prior to stable microcracking.

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On-site measurement of the outer diameter of rodlets and hot cell examination of typical rodlet tips were carried out for the rod cluster control assembly (RCCA) of a PWR plant after 10 cycles. The main objectives of the examination are to investigate the extent of degradation of control rods and to determine the cracking mechanism involved since cracks are observed in a number of cladding tubes near the tips. In this study, the crack initiating limit for cladding tubes of PWR RCCA rodlets subject to absorber swelling is investigated. Although the cladding tube material consists of a ductile material, 304 S. S., it should be treated as low ductile material that is intermediate between a ductile and a brittle material because its ductility is reduced by neutron irradiation. The crack initiating strain limit for the low ductile material is investigated and is obtained as follows. ε_cr =ε_ue+1/2ε_up where ε_cr : crack initiating strain, ε_ue : elastic component of uniform strain, ε-<up> : plastic component of uniform strain The proposed crack initiating strain limit shows good agreement with the results of on-site examination. Axial cracking in RCCA rodlets can be prevented if RCCAs are replaced when the total amount of neutron fluence reaches approximately 8×10²¹ n/cm² (E >1 MeV). Moreover, it is possible to increase the lifespan of a RCCA by increasing the gap between the cladding tube and the absorber.

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Three-dimensional microscopic models of powder compacts for viscoplastic finite element analysis are developed to investigate the deformation behavior of powder particles during sintering. The repeating unit cells containing three types of pore with a regular arrangement are analyzed. Pore shrinkage due to surface tension during the intermediate stage of sintering is simulated. The volumetric strain rates of the unit cells are compared with that in a spherical shell model and the effect of the pore shape on the shrinkage rate and the sintering stress is discussed. A constitutive equation for sintering is proposed on the basis of the analyzed results. The sintering is described as the deformation process of viscous porous bodies under the action of the sintering stress. The proposed constitutive equation gives a good fit to the results obtained by experiment as well as the finite element analysis.

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This paper is concerned with an analytical formulation and a numerical solution of the thermal stress and deformation for axisymmetrical shells of functionally graded material (FGM) subjected to thermal loading due to fluid. The temperature distribution through the thickness is assumed to be a curve of high order, and the temperature field in the shell is determined using the equations of heat conduction and heat transfer. The equations of equilibrium and the relationships between the strains and displacements are derived from the Sanders elastic shell theory. The fundamental equations derived are numerically solved using the finite difference method. As numerical examples, functionally graded cylindrical shells composed of SUS 304 and ZrO₂ subjected to thermal loads due to fluid are analyzed. Numerical computations are carried out for various compositional distribution profiles in FGM. The results show that the present method gives correct temperature distributions and that the temperature distributions, stress distributions and deformations vary significantly depending on these compositional distribution profiles.

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This article concerns a theoretical analysis of heat conduction in a transient state and the associated thermoelastic behavior for a multilayered anisotropic laminated plate subjected to nonuniform heat supply. As an analytical model, we consider a laminated rectangular plate consisting of a diagonal stack of layers having orthotropic material properties, i.e., an angle-ply laminate. The three-dimensional temperature solution in a transient state and the associated thermoelastic behavior of the plate with simply supported edge conditions are formulated using the functional approach based on the variational principle. For the analysis of the thermoelastic field, the higher-order shear deformation theory of the plate is used to evaluate the shear stress components. As an example, numerical calculations are carried out for a 2 layered angle-ply laminate, and the numerical results for temperature distribution, out-of-plane deflection, normal and shear stress distributions are discussed in detail.

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The transient dynamic response of a panel structure subjected to blast loading was investigated, as simulated by the step function and the exponentially decaying function. Based on the Bauer methodology, and applying Galerkin's method, the von Karman nonlinear equations of plates could be transformed into Duffing-type nonlinear ordinary differential equations and then solved by adopting the Lindstedt-Poincare perturbation method. The complete analysis of square plates was carried out for all-clamped and all-simply supported edge conditions. The results of deflection history and stress resultants using one perturbation term were sufficiently correlated with results both from related literature and obtained by the finite-element method.

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A mathematical model for asymmetrical sheet rolling is proposed, using the stream function method and the upper bound theorem to investigate the plastic deformation behavior of the sheet at the roll gap. The curvature of the rolled product obtained under various rolling conditions of roll speed ratio, roll radius ratio, friction factor ratio, and inlet angle of the sheet at the entrance of the roll gap, are discussed systematically. The predicted curvature of the rolled product and rolling force are in good agreement with those of experimental measurements. Therefore, the proposed analytical approach is considered to be applicable for simulating asymmetrical sheet rolling.

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We describe the calculation of mechanical properties of solids using the molecular dynamics method. The thermal expansion coefficient and elastic constants of α-Fe are calculated using an empirical potential, that is, the Johnson potential. The thermal expansion coefficient is calculated using a differential operation of the temperature dependence of the lattice constant obtained from the NPT ensemble molecular dynamics analysis. Reasonable agreement is found between the analytical results and measured data up to the phase transition temperature. The elastic constants are calculated from the stress-strain curves obtained from the NVT ensemble, the initial lattice constant of which is modified based on the result of the NPT ensemble. The analytical results agree reasonably well with the measured data up to 400 K.

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In general, structural integrity depends on material performance under cyclic loading. It is therefore very important to characterize the fatigue strength characteristics of ceramic/metal joints for wide use in structural applications of engineering ceramics. In this work, in order to clarify the strength characteristics of alumina joints, static strength and cyclic fatigue tests were carried out for joints of Al₂O₃/Al₂O₃ and Al₂O₃/Mo/SUS 304/Mo/Al₂O₃ formed with Ticusil and Cu₈₀ Ti₂₀ fillers in vacuum. Static tests were conducted at room temperature and elevated temperature. Fatigue tests were conducted at constant stress ratio R(=0.1) and constant frequency f(=50Hz) at room temperature. The strength characteristics of the joints of Al₂O₃/Al₂O₃ formed using Ticusil were similar to the strength characteristics of Al₂O₃. The strength characteristics of the joints of Al₂O₃/Mo/SUS 304/Mo/Al₂O₃ were mainly determined by those of the joint of Mo/Al₂O₃.

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The effect of phosphorus doping on the crystallization-induced stress of silicon thin films is discussed experimentally. Amorphous silicon thin films are deposited on thermally-oxidized silicon substrates using chemical vapor deposition. Phosphorus is doped to the film during film deposition using PH₃ gas. The initial residual stress of the phosphorus doped films is constant at-200 MPa, regardless of dopant concentration. The internal stress of the films changes to a tensile stress of 800 MPa during crystallization due to film shrinkage. Although the magnitude of the stress change is independent of the dopant concentration, the crystallization temperature of the film decreases with an increase of dopant concentration. The doped phosphorus at the film/substrate interface affects the crystallization process, i.e., the structure and crystallinity of the silicon thin films. The surface condition of the substrate also affects the crystallinity and crystallization-induced stress of the film.

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The spot-welded joint is widely used as a structural part. In the quality control of the joint, one of the most important issues is to quantitatively estimate connective strength such as tension shearing load from the information detected by nondestructive testing as accurately as possible. In this paper, a system based on an ultrasonic inspection device and a neural network is proposed to evaluate the tension shearing load of each spot-welded joint. The network is configured by learning the pattern sets dealing with the interaction between the scanning graphs of the welded region using ultrasonic testing and tension shearing load of the joints. The input of the network is the echo height at each scanning position of the welded region. The output from the system was examined by comparing it with the experimental results, and the validity of the system was thereby confirmed.

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AE (Acoustic Emission) generation behavior during microfracture process of 2-dimensional alumina polycrystals is simulated along with its characteristic parameters, by assuming that a microfracture corresponds to an AE event. The microfracture process is simulated by using the body force method. Various AE generation behaviors are predicted as a function of the grain boundary toughness (K_cb), the grain size and the distribution state of residual stresses due to crystalline anisotropy. The predicted AE events have a tendency to occur at higher stress with increasing K_cb and with decreasing grain size. By the fracture-mechanical calculation of the crack opening volume, the relative variation of AE amplitude is also simulated. The actual AE measurements are tarried out in vacuum for two kinds of alumina with different grain size, and compared with the simulated results. The cumulative AE event curve for 11.5 μm grain size shows good agreement with the simulation when the K_cb is 0.35 times the grain toughness (K_cg), and that for 28.2 μm shows good agreement with the simulation at K_cb = 0.45K_cg. The results of AE location for both the simulation and the measurement show the similar characteristics of the scattered distribution over the stressed fields.

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This paper is dedicated to the problems of nondestructive testing of rubberlike materials. A new method which we call an audiosonic contact impedance evaluation is developed. It is based on mechanical contact impedance evaluation (MCIE) at the local contact area between a piezo active sensor and specimen. A theoretical model consisting of quasistatically loaded and consequently connected dissipative Voigt's elements is discussed and solved analytically. A resonance equation used for MCIE at the local contact area consists of two impedances: mechanical impedance of PZT sensor and mechanical impedance of the specimen. Analytical results are compared with the results obtained from the simulation using the finite element method (FEM). Simultaneous measurements of the contact impedance and compliance associated with rubberlike materials having different hardnesses are accomplished by the multilayered piezo active sensor. A dynamic response obtained from the experimental sensor highly correlates with mechanical and rheological parameters.

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