A unified constitutive model considering dynamic strain aging effect was developed in order to describe inelastic deformation behavior of modified 9Cr-1Mo steel precisely. The inelastic behavior of the material was summarized as follows. A rate-dependent deformation was observed above 500°C, and there was no rate-dependency under 400°C. However, stress relaxation behavior under constant strain was observed even at rate independent temperature region. Further, the stress after relaxation depended on prior loading strain-rate, and it showed a higher value as the strain-rate was decreased. A feature of the proposed constitutive model was that an applied stress consisted of three components:a back stress, an overstress and an aging stress which corresponded to dynamic strain aging effect and showed a negative strain-rate-dependency. The aging stress was measured by stepwise strain-rate change tests, and it showed a larger value at smaller strain-rate and lower temperature. The back stress and the overstress were measured by strain dip tests. The back stress was approximately rate-independent below 400°C, however it showed rate-dependency above 500°C. The overstress showed a larger value as the strain-rate or the temperature was increased. Material constants involved in the constitutive model were determined systematically based on the measured values of these stress components. In order to evaluate the validity of the constitutive model, numerical simulations were conducted for various inelastic deformation behavior of modified 9Cr-1Mo steel. The simulations agreed with experimental results very well in all cases.

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The objective of the present study is to exploit the feasibility of piezoelectric polymer film sensors to evaluate in-plane static strain distributions of structural components. In contrast to ordinary use of piezoelectric films as strain and strain-rate sensors detecting electric changes or currents in a closed circuit, the proposed strategy consists of directly measuring the distribution of electric potentials induced in the piezoelectric film mounted on the surface of a deforming structural component. Strain distributions are determined from the measured potentials taking into account the piezoelectric constitutive law of the film material. As an illustrative example, thin films of polarized polyvinylidene fluoride(PVDF) are mounted on a holed elastic plate subjected to in-plane loading, and the induced potential distributions are measured on the film surface by an electrostatic voltmeter. It is demonstrated that the determined strain distributions are in fair conformity with those predicted by the theory of linear elasticity.

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Microscopic sintering behavior in compacts formed by pressing ceramic granules is examined to develop a constitutive model for macroscopic sintering deformation analysis. Spray-dried alumina granules are compacted by CIPing and the compacts are fired at various temperatures. The internal structure composed of fractured and unfractured granules, and large crack-like cavities caused by their inhomogeneous shrinkage during sintering are observed. The macroscopic sintering rate becomes slow because of the formation of the large cavities. A basic constitutive equation for sintering of ceramic powder compacts is proposed with the grain boundary diffusion and grain growth taken into account. The relationship between the change in the microstructure and the shrinkage rate of the powder compacts is modelled by using the basic constitutive equation. The constitutive model is applied to the finite element analysis to predict the shape change of sintering bodies. The calculated results show good agreement with the experimental results.

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First, the concepts of separated dynamic J integral and separated energy release rate were presented for dynamic interfacial fracture mechanics. The separated dynamic J integral has the physical meaning of the energy flow rate to a propagating interfacial crack tip from each material component. Next, a moving finite element method for dynamic interfacial fracture analysis was developed to make it possible to analyze transonic and supersonic interfacial crack propagation. The moving finite element simulations revealed the shock waves(Mach waves)emanated from transonically and supersonically propagating crack tips. The dynamic J integral and the separated dynamic J integrals showed excellent path independence for all crack-velocity regimes even for supersonic interfacial crack propagation. It was found that, in the subsonic crack-velocity-regimes, the compliant material supplies larger fracture energy than the stiff material does. From the energy flow rate to the propagating interfacial crack tip, the theoretical limit of interfacial crack velocity without macrocontact zone was found to be the shear wave velocity of the compliant material.

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In this paper, we demonstrate the formulation of the principle of stationary potential energy in rate form applied by the selective integration method and the mixed method. We carried out three-dimensional numerical calculations for laminated rubber bearings after studying the effect of the finite elements and the integration rules and then compared the experimental test results with the numerical analyses data. Rubber bearings composed of thin rubber and steel layers have been used to protect important structures. These bearings are capable of supporting the weight of the entire structure while maintaining sufficient flexibility to eliminate the horizontal seismic force. For the finite element analysis of hyperelasticity such as that found in rubber materials, both the mixed variational method and the selective integration method have been used to alter the ratio of volumetric constraints to the degree of freedom. In the mixed variational method, the mean stress and the deviatoric strain are decomposed and reformulated. In the selective integration method, the reduced and full integration rules are applied to the terms including the mean stress and strain.

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Mode I fracture behavior of rubber toughened PMMA(RT-PMMA) was studied over five decades of displacement rates(10^-4-13 m/s)using a high speed tensile testing machine. Two kinds of RT-PMMA, extruded RT-PMMA containing 20 wt.% rubber particles(EM20) and pressed RT-PMMA containing 40 wt.% rubber particles(PM40), exhibited different rate dependencies of the maximum mode I stress intensity factor, K_{I max} and the maximum mode I energy release rate, G_{I max}. K_{I max} and G_{I max} of EM20 decreased rapidly at high rates(1-11m/s). This suggests that the toughening effect due to rubber blending was dramatically reduced at the high rates. PM40, on the other hand, retained high K_{I max} and G_{I max} values at all the rates tested, thus, maintaining the toughening effect even at a rate of up to 13 m/s. Neat PMMA was also examined, for comparison, and its K_{I max} was found to increase with increase in the displacement rates while G_{I max} remained constant. The rate-dependent K_{I max} and G_{I max} values are discussed, taking(K_{I max})²/G_{I max} into account, and the fracture surface morphology of the specimens is also considered.

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Three-dimensional finite element analysis has been carried out on the compact normal and shear(CNS) specimens under mixed-mode loading. The complex stress-intensity factor K associated with an elastic interface crack is discussed by the virtual crack extension method. The effect of Young's modulus and Poisson's ratio on stress intensity factors is discussed under various kinds of mixed-mode loading. The distribution of stress intensity factors along the crack front is investigated. A polynomial fitting is proposed to evaluate the stress-intensity factors at the midsection of CNS specimen with an interface crack subject to mixed-mode loading. It is possible to evaluate the stress-intensity factors of CNS specimen with high accuracy by the present polynomial evaluation.

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Following the theory of linear piezoelectricity, we consider the electroelastic problem for a piezoelectric layer with a crack bonded to two elastic half planes under antiplane shear loading. The crack parallel to the interfaces is in the mid-plane of the piezoelectric layer. Fourier transforms are used to reduce the problem to the solution of a pair of dual integral equations. The solution of the dual integral equations is then expressed in terms of a Fredholm integral equation of the second kind. Numerical values of the stress intensity factor for some piezoelectric laminates are obtained, and the results are plotted to display the electroelastic interactions.

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This paper presents an exact analysis of the problem of an external circular crack in a transversely isotropic piezoelectric solid subjected to normal stress as well as electric charge loadings that are symmetric with respect to the crack plane. The recently proposed general solution is used and the potential theory method is employed. To take account of the effect of the electric field, a new potential of a simple layer is introduced. The derived Green's functions for point force and point charge are completely exact and expressed in terms of elementary functions. Simple form expressions for intensity factors are also obtained. Numerical examples are finally performed.

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In the present paper, the order of stress singularity at the corner where four free surfaces and interfaces in three-dimensional joints meets is investigated by solving an eigenequation derived from a finite element formulation. The order of stress singularity for three typical joints, referred to as the 1/8 - 1/8, 1/8 - 1/4 and 1/8 - 1/2 joints, between two rectangular blocks with different properties is investigated and compared with that of two-dimensional joints with the same cross section as that of the three-dimensional joints. Dundurs' composite parameters, α_3D and β_3D for three-dimensional joints are newly introduced and the order of stress singularity plotted on ordinal Dundurs' parameters, the α and β plane, is rearranged on the α_3D - β_3D plane. The order of stress singularity at the vertex in the three-dimensional joints is larger than that in the two-dimensional ones, although, the boundary at which the stress singularity vanishes varies little on the α_3D - β_3D plane. Furthermore, it is shown that the order of stress singularity at a vertex, where some singular lines with different orders meet, varies with the combination of material properties.

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Interferometric strain-displacement gauge(I.S.D.G.) testing system was developed for the measurement of the crack opening displacement at high temperatures. Helium-Neon gas laser and center-cracked specimens of type SUS304 austenitic stainless steel were used. Fatigue crack growth tests were conducted at 450, 550, 650 and 700°C at stress ratios of R=-0.1 and 0.5. Using I.S.D.G.for the measurement of crack closure modified using platinum plate and optical filter, crack opening displacement was found to be measured with good accuracy at all temperatures tested. Results showed that crack closure was observed at R=-0.1, while no crack closure was observed at R=0.5 even at 650°C. From the results of the measurement of fatigue crack closure in the near-threshold regime at all temperatures investigated, it was found that rapid increase and decrease in crack growth rate da/dN were observed when crack opening ratio U showed rapid increase and decrease, respectively.

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Fatigue crack growth tests were conducted at 450, 550, 650 and 700(°C)using type 304 stainless steel. Crack closure level was measured using the interferometric strain/displacement gage(I.S.D.G.), described in the previous paper. Crack growth rates for stress ratio R= -0.1 plotted against stress intensity factor range, ΔK, deviated from those for R=0.5. Using the effective stress intensity factor range, ΔK_eff and effective J-integral range, ΔJ_{f, eff} which were calculated using crack opening ratio determined from the I.S.D.G. measurement, the crack growth behaviors for R=0.1 and 0.5 were reconciled at each test temperature. A threshold value, ΔK_{eff, th} of fatigue crack growth was determined at each temperature investigated. It was found that the threshold value reached a maximum at a temperature between 450 and 550(°C).

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Residual stress distributions in a 4-inch-diameter carbon-steel pipe butt-welded joint were evaluated using five methods. The analytical evaluation methods used were inherent strain analysis and thermal elastic-plastic analysis. The experimental methods were X-ray diffraction and strain-gauge measurement for the surface residual stress and as well as neutron diffraction for the internal stress. The residual stress distributions determined using these methods agreed well with each other, both for surface stress and internal stress. The characteristics of the evaluation methods were summarized, and it was found that the most suitable method for any particular situation can be selected depending on the purpose by considering the evaluated location and the operating conditions of the object to be evaluated.

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A precise method for estimating the axial stress is proposed for the short and highly stressed bolts used for automobile. These bolts show non-linear extension, because of local plastic deformation as well as non-uniform stress distribution in bolt cross section. The proposed method consists of(a)precise measurement of the time-of-flight of longitudinal and transverse waves using a digital pulse-echo technique, (b)to establish the calibration curves which take into account of nonlinear extension due to non-uniform stress distribution based on simultaneous measurement of the axial elongation, time-of-flight of longitudinal and transverse waves and(c)evaluation of the axial stress with the change in the time-of-flight and the assumed length of equivalent stressed length. The axial stress is estimated within 1% error for one type bolts and within 2% error for another type bolts.

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In order to find an effective method to control the residual coating stress after thermal spraying, an analysis and experiment were carried out on a cylindrical member of 80Ni20Cr/SUS304. Temperature measurements during the processes of thermal spraying, heating and cold thermal shock were carried out. Using these measured results, thermal stress analyses were perfomed by the finite element method(FEM) and a proposed simplified method for estimating the coating stress. Thermal stress of the coating obtained by FEM was compared to that obtained by the simplified method and good agreement was obtained between them. Moreover, the residual coating stress after the thermal spraying was measured by the X-ray diffraction method and compared with the estimated results, and good agreement was obtained between them. Based on the simplified method, a control method of the residual coating stress after the thermal spraying was proposed. According to this control method, compressive residual stress can be expected by controlling the preheating temperature of the substrate irrespective of the magnitude of the thermal expansion coefficient of the coating and that of the substrate.

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The stresses of joints combining the bonding force of adhesives with the clamping force of bolts is analyzed using axisymmetrical theory of elasticity and FEM, when an internal pressure is applied to the combination joint in which two pipe flanges are clamped together by bolts and nuts with an initial clamping force after being joined by anaerobic sealant. The anaerobic sealant is applied at the interfaces partially instead of formed gaskets in pipe flange connections. In the numerical calculations, the effect of the bonding area and position and Young's modulus of sealant on the contact stress at the interfaces are clarified. In addition, using the interface stress distribution, the strength of the combination joint is predicted. Experiments were performed and the analytical results are consistent with the experimental results concerning the variation in axial bolt force and the strength of combination joints. It is found that the joint strength changes as the bolt pitch circle diameter, the bonding position and its area, the initial clamping force and the adhesive material properties change. Furthermore, it is seen that the sealing performance of such combination joints in which the interfaces are bonded partially is improved over that of pipe flange connection with metallic gaskets.

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The static strength of a quasi-isotropically reinforced random chopped glass/polypropylene composite is studied theoretically and experimentally. In the previous paper⁽¹⁾ a fracture model is proposed which simulates probabilistically the damage accumulation process. On the basis of the percolation theory, the model can estimate the static strength of the FRPP as the critical point on condition that the fiber volume fraction is 30%wt. In this paper, by applying the model, the strengths of a discontinuous fiber composite are predicted as a function of the volume fraction of glass fiber. By comparing with the experimental data, the validity of the model is confirmed in terms of the fiber volume fraction.

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