The present paper is concerned with the formulation of a constitutive model which can describe the hysteresis loop of a stress-strain relationship of blood vessels under cyclic loading conditions. It is assumed that this hysteresis loop is described by the superposition of elastic deformation and viscoplastic deformation. For this reason the total strain is expressd as the sum of the elastic part and the inelastic part on the basis of the finite deformation theory. Then the elastic part is established by postulating a pseudo strain energy density function of the exponential type, while the inelastic part is formulated by modifying the non-linear kinematic hardening rule in the viscoplastic model proposed by Chaboche et al. A comparison of the numerical result with the literature shows that the present model can describe the hysteresis loop qualitatively.

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An investigation has been carried out concerning 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. In both composites, water absorption lowers the strength of the interface, resulting in a decrease in the tensile strength, an elongation at the break, and besides, 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, cooling effects by water circulation around specimens become predominant, so that the fatigue life increases in a higher stress region. We also pointed out the usefulness of a scanning acoustic microscope to examine the internal damage of the composites.

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This paper is concerned with the soundproof characteristics of infinitely long, cylindrical sandwich shells composed of orthotropic face layers and a honeycomb core. The shell is excited by axisymmetric acoustic waves travelling within the shell. To simplify the shell governing equations it is assumed that the facings resist only bending moments and the honeycomb core resists only transverse shear forces. The sound transmission loss for the shell wall, TL, is derived and calculated numerically for various values of the physical parameters involved.

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The present paper deals with the strength characteristics of T-type butt adhesive joints combined with bolts, in which two T-flanges are clamped by two sets of bolts and nuts with an initial clamping force after they are joined by adhesion. Firstly, the stress distributions in adhesives, the variation of bolt axial force and the strength of the combination joints are analyzed when an external bending moment is applied to the combination joint. For verification, experiments are performed. Analytical results are in fairly good agreement with experimental ones. Then, it is found that the strength of the combination joint is greater than that of the adhesive joint and that the shape as a joint is maintained after the adhesive layer is ruptured in the combination joint. The characteristics and the availabilities of a combination joint are made clear.

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Fine ceramics offer excellent high strength and durability characteristics at elevated temperature ; however a brittle material shows catastrophic failure without any plastic deformations. By considering these characteristics, we discuss the structural design concepts which must be established to make the best use of ceramics for high temperature machines for which high reliability is required. Based on the ceramic oriented structural design concepts, a ceramic/metal hybrid structure of 1 st stage ceramic stator vanes in industrial gas turbines was developed. In this hybrid stator vane, the components to be exposed to a high temperature and a corrosive environment are made of ceramics, and metal is used as the strength member. Moreover, a thermal shock testing method for a ceramic was proposed to evaluate the thermal shock resistance which is most important in putting the ceramic component into practice.

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Long-term reliability against thermal fatigue is required for solder joints of surface mount IC packages. This study was carried out in order to estimate thermal fatigue strength of the solder joints of the surface mount IC packages. First, a simple elastoplastic analysis of the strain produced in the solder joint was developed and the propriety of the analysis was confirmed by the stiffness measurement of the soldered leads. Next, in order to obtain data used for strength estimation, the torsion fatigue test of bulk solder and solder joint specimens was carried out. Finally, the mechanical and thermal fatigue tests of the solder joints of IC packages were carried out. It was found that the fatigue life of the solder joint by the thermal cycling test can be estimated based on the strain calculated by the present analysis and the mechanical fatigue test data of the solder joint specimens or of the solder joints of the real IC packages.

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The relation between the total fatigue life and the fatigue crack initiation life of a single spot weld tensile shear specimen was determined. Based on the results, the reason why the initial stress intensity factor could control the toota fatigue life was discussed. During the investigation, the methods of determination of fatigue crack initiation at the spot weld were developed, and related phenomena were elocidated.

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Fatigue lives of plain carbon steel with residual stress were studied with special reference to the initiation and the propagation of surface cracks. Tensile residual stresses did not have influences on crack initiation lives, but increased the fatigue crack propagation rate for surface fatigue cracks. The propagation rate of a surface fatigue crack was controlled by the parameter of {(ΔK)^0.5(K_max)^0.5} in which ΔK and K_max were, respectively, the stress intensity factor range and stress intensity factor calculated from the maximum stress distribution containing residual stress measured at the stress cycles of the initiation of surface cracks. This parameter also served to help understand surface fatigue crack shape in a residual stress field. Finally, the equation of (ΔK)^p(K_max)^q≒K_max-p·K_min was derived under condition of both p+q=1 and minimum stress intensity factor |K_min|<K_max, which enabled us to discuss effects of K_min (<0) on fatigue crack propagation from the point of mechanical behavior of the plastically deformed layer left in the wake of the advancing crack.

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Low cycle fatigue tests and microcrack propagation tests were carried out under strain cycling with two-step variable plastic strain amplitude on annealed low carbon steel and commercial pure iron. The applicability of Miner's law to the extremely low cycle fatigue has been discussed in relation to the fracture mode transition and the damage accumulation mechanism in the extremely low cycle regime. It was found that the surface microcrack initiated at a low plastic strain Δε_p1 in low to high variable amplitude tests becomes nonpropagating at a high plastic strain Δε_p2 because of its blunting under large plastic strain, and that in such a situation, final failure occurs in a different fracture mode from the surface microcracking by the striation mechanism. The total fatigue life is controlled by the development of internal microvoid ahead of the crack in pure iron and by the initiation of an internal crack associated with the pearlite cracking in low carbon steel. In such a case, the damage accumulation does not occur linearly with strain cycling and the value of Σn_i/N_fi becomes larger than unity.

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Fatigue crack growth behavior from a semi-elliptical surface crack under shear loading has been investigated. The fatigue tests of rectangular bar specimens with a semi-elliptical surface crack were made on an aluminum alloy 2017-T4 and on a weldable structural steel SM41A, using the four-point-shear loading method. Under this loading condition, the crack front of these semi-elliptical surface cracks is subjected to mixed mode II-III deformation, and the ratio of K_III/K_II varies depending on the position along the crack front. Macroscopically, two kinds of crack growth morphology-tensile mode growth and shear mode growth-were observed. SM41A showed the tensile mode growth which grew in a plane different from the pre-crack and formed complicated three-dimensional planes. On the other hand, in 2017-T4, the shear mode growth occurred in the same plane as the pre-crack. The planes formed by the tensile mode growth and those by the shear mode growth obtained by the tests have shown good agreement with those predicted by the σ_max-criterion and the τ_max-criterion, respectively. A method was proposed to predict the shear mode fatigue crack growth in 2017-T4 under mixed mode II-III loading. It was found that, by this method, the da/dN-ΔKτ_max relation of a a semi-elliptical surface crack under shear loading can be predicted from the mode II and the mode III fatigue crack growth characteristics, where ΔKτ_max=Δ(√(K_II²+K_III²).

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Crack propagation behavior has been observed in A7003-T6 aluminum alloy under low cyclic loading with hold time, over the frequency range 4×10^-3∼1 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 are measured by metallographic examination, and the actual crack tip stress intensity factor was estimated.

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High-cycle fatigue tests, low-cycle fatigue tests, and static tensile tests on notched specimens of a maraging steel were conducted. not only is the fatigue fracture toughness K_fc approximately constant for high-cycle and low-cycle fatigue, regardless of applied stresses and strains, but also K_fc is approximately equal to the static fracture toughness K_IC;K_fc<cong>K_IC<cong>36 MPa·m^1/2. Moreover, for its high tensile strength (yield stress σ_0.2=2440 MPa, tensile stress σ_B=2490 MPa), the maraging steel has an extremely small value of K_IC in comparison with other low-and medium-strength steels. Considering that the crack propagation period occupies only 20-30% of total life in high-cycle fatigue and also that the crack lengths at final fracture in low-cycle fatigue are very small in comparison with specimen size, the fatigue life prediction method on the basis of the integral of crack growth rate equation is inadequate and should not be applied to high-strength steels such as maraging steels. Instead, K_fc will be useful to predict the final fracture of maraging steels.

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This investigation has been carried out to determine the influence of specimen size and side groove on elastic-plastic fracture toughness parameters. Elastic-plastic fracture toughness J_IC and tearing modulus T_mat were evaluated by the unloading compliance method which describes ASTM E813-81 standards. A compact tension specimen was prepared from SUS316LN and the test was conducted at cryogenic temperature 4.2K. It is understood that J_IC and T_mat were independent of specimen size when the specimen satisfied ASTM standard size requirements. J_IC and T_mat decrease with the increase of side groove for 0-12.5%, and they are independent of the side groove when the side groove is 12.5-37.5%. These results suggest that a 0.5 CT small specimen with a 25% side groove can provide a proper J_IC and T_mat independent of specimen size and side groove.

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It is important to evaluate the penetration of surface cracks in a Leak-Before-Break analysis. Because the stress intensity factors for surface cracks in pre/post penetration had not yet been analyzed, the authors carried out three-dimensional boundary element analyses in order to obtain them. First, the authors developed the technique of nodal breakdown appropriate for cracks with short ligament length in a two-dimensional boundary element analysis. Next, analyses of stress intensity factors for surface cracks in pre/post penetration were carried out using the technique of nodal breakdown for cracks with short ligament length and the three-dimensional boundary element code BEM3D which was designed for a supercomputer.

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This paper is concerened with the stress analysis of the vicinity 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 an internal pressure. By using the generalized Abel transform, we reduce the problem to the Hilbert problem with infinite unknown functions. The general method 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 a constant pressure.

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A method of the finite element synthesis is formulated which is based on a new notion : that the objective design is searched in the vicinity of the baseline design, while the structural response to the objective value is approximated by the first-order Taylor series expansion of the response with respect to the design variables. A functional is comprised 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 that the concentrated stresses around the hole in a square plate under bi-axial tension and along the roots of gear tooth under bending are lowered.

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A unified constitutive equation is formulated to determine the plastic-creep behavior of metals under a combined stress state. The elastoplastic constitutive equation with a distribution function of yield stresses is extended by including the viscoplastic property. This theory is applied to predict the plasticity-creep stress-strain relation of SUS304 stainless steel. Two different nonlinear visco-plastic models are proposed for an elevated temperature and room temperature. The "steady-state" creep term is added into the elevated-temperature model. It is found that the properties of primary creep and the effect of creep on plasticity arise from the plasticity-creep interaction caused by the distribution of internal stresses. The rate sensitivity with "over stress" is considered for the room-temperature model. The time-dependent stress-strain relation, cyclic creep behavior and biaxial creep behavior are calculated and compared with the experimental results of SUS304 stainless steel.

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Fracture of blades or disks due to centrifugal force in rotary machines has often caused serious accidents. Branched cracks are frequently encountered in the unstable fracture of various brittle materials. (Furthermore, branched cracks have been observed behavior for the mixed mode with complicated geometry.) In this paper, stress intensity factors K_I and K_II were determined by using the photoelastic and caustics method, as a function of the branched crack of length ratio a_II/a_I and at different values of the branched crack angles 2θ at two velocities. The interaction in branched cracks was also discussed, together withacomparison of the results of these experimental methods.

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The erosion-corrosion characteristics of a carbon steel commonly used as a piping material subjected to an impinging gas-liquid two-phase jet were investigated. The localized damage was observed, and the range of the erosion rate under the experimental conditions was beteen 45 mm/year and 87 mm/year. It became clear that the principal mechanism of this damage was the occurrence of pitting corrosion caused by the corrosion potential distribution on a specimen and the rapid growth of pits. The significance of flow-induced potential distribution on a specimen was demonstrated by use of an array of test pieces insulated electrically from each other. This potential distribution induced by the flow distribution on a specimen also gave crucial effects on the location where the erosion-corosion damage occurred. Namely, erosion-corrosion damage took place locally, just at the part of the specimen where the corrosion potential was shifted to more nobler than the pitting potential of the condition of interest. This corrosion potential distribution was caused by the distribution of the oxygen supply rate and deposition and/or removal of oxydizer corrosion product (γ-FeOOH). These were originally caused by the flow distribution. This erosion-corrosion damage was completely inhibited by keeping the pitting potential nobler than the corrosion potential ; for example, by the addition of NaNO₂ to the system.

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An ultrasonic method is presented for the nondestructive evaluation of texture in cold-rolled steel sheets. Three 4-th order orientation distribution coefficients are determined from the propagation velocities of longitudinal and shear waves, and SH_o plate mode. A simple rule of mixture allows the estimation for the concentration of crystallite orientation around the principal components of the rolling recrystallization texture. The concentration is then used to predict the plastic strain ratio (γ-value) and to draw the ultrasonic pole figures ; both show good correspondence with the conventional methods. Practically important is the correlation between the average γ-value and the longitudinal/shear wave velocity ratio, which is explained by the dominant concentration on {111} components.

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