Dynamic SCC behavior of Ti-6Al-4V alloys has been studied for different microstructures and orientations in 3%NaCl solution, and the effect of crack size on crack growth behavior was discussed. Three microstructures, namely annealing at 705°C (AN705) and 850°C (AN850) and solution treatment and aging (STA), were used. Tests were performed at a frequency of 10 Hz and a stress ratio of 0.9 using CT specimens for long cracks and surface-cracked specimens for small cracks. The K_{I SCC} values in L-T orientation for long cracks were higher than those in T-L orientation. These values were almost the same as, or higher than, the K_{D SCC} values in each microstructure and orientation. In both orientations, the K_{D SCC} values for long cracks were considerably lower than those for small cracks in all microstructures. The crack-size dependence in the crack growth behavior related to dynamic SCC was confirmed in Ti-6Al-4V alloy.

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Nondestructive evaluation of bifurcated cracks is a key issue in maintenance of tracks for high-speed trains. Magnetic flux density for a rectangular parallelepiped material in which direct current flows is analyzed. The material contains an embedded and through-wall horizontal crack and a bifurcated crack from the horizontal one. The magnetic flux density in the air near the top surface of the rectangular specimen is obtained by using a 3-D finite-element method. The maximum change due to the cracks in the component of magnetic flux density in the direction of the width of the rectangular parallelepiped is shown to be related to the length and the depth of the horizontal crack and the bifurcated crack. A technique of quantitative nondestructive evaluation of the vertical component of the bifurcated crack is proposed and is verified by experiment.

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Rotating bending fatigue tests were carried out on three kinds of cast aluminum alloys after hot isostatic pressing (HIP) treatment. The HIP treatment was carried out to reduce cast defects and porosity of cast aluminum alloys. Efficacy of HIP treatment varied from material to material, but in the material which treatment was most effective, namely AC4CH, the fatigue strength was markedly improved. In the HIP-treated AC4CH, the fatigue crack initiation site was not a cast defect but a part of the specimen surface with a high density of eutectic silicon particles. Comparing the HIP-treated AC4CH with conventional AC4CH, crack propagation behavior was the same for both, but crack initiation life was longer for the former than the latter. Fatigue life was successfully evaluated considering lives of both crack initiation and crack propagation. Here, the crack initiation life was defined as involving scatter immediately after crack initiation, and the crack propagation life was expressed in one relation for the HIP-treated materials and the conventional material.

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The effect of hard shot-peening (HSP) on the fatigue reliability of Austempered Ductile Iron (ADI) was investigated. The main results obtained were as follows : (1) The fatigue life, that is, the number of cycles to failure, could be improved about tenfold through HSP. (2) Microporosity was always found at the origin of the fatigue crack. It was observed at or near the surface for non HSP-treated ADI. On the other hand, it was observed more than 300 μm from the surface for HSP-treated ADI. (3) The origin of the fatigue crack was transferred from the surface to subsurface with compressive residual stress induced by HSP. This explains why the fatigue life was improved by HSP. (4) From an S-N diagram under ultrahigh-cycle testing of over 10⁷, it was recognized that the fatigue limit could not be improved by HSP.

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A rotating-bending fatigue testing machine was newly developed for the evaluation of the fatigue strength of a shape memory alloy wire. The rotating-bending fatigue tests were successfully performed for the TiNi shape memory alloy wire at various temperatures. The results on fatigue were summarized as follows. (1) If the maximum strain amplitude was found in the completion region of the rhombohedral phase transformation, the fatigue life shortened as the strain amplitude increased. However, if the maximum strain amplitude was found in the intermediate region of the rhombohedral phase transformation, the fatigue life lengthened. (2) The higher the temperature, the shorter the fatigue life. (3) The higher the rotational speed, the shorter the fatigue life.

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R 6 method proposed by U. K. CEGB (Central Electricity Generating Board, present Nuclear Electric plc) was applied to fracture evaluation using a failure assessment diagram (FAD). Since FAD has been developed based on J-integral criterion, J-integral can be inversely estimated using FAD. Because the fatigue crack growth rate is determined by J-integral value, it is suggested that R 6 method can be applied not only to fracture assessment but also to low-cycle fatigue crack growth assessment. Carbon steel pipes with a defect were monotonically and cyclically fractured to confirm the applicability of the crack growth assessment method using FAD. In the monotonic bending tests, J-resistant curve obtained by R6 method agreed with that obtained by η-Factor approach. In the cyclic bending tests, fatigue lives could be successfully estimated by the analysis using R 6 method.

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Effects of impact damage on fracture mechanisms of plain woven CFRP composite are studied by means of acoustic emission monitoring. The maximum load and the AE characteristics of 0 specimen differ from those of 45 specimen, where 0 and 45 are the angles between the directions of yarn and loading. When a load P_b is determined by AE energy gradient method, the ratio of P_b/P_b(N) is used to estimate the residual strength, when P_b is the load at which the damage mechanisms are changed and P_b(N) is the maximum load of a non-impact specimen. It is found that the reliability of CFRP with the impact damage can be evaluated by the load ratio.

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The influence of notch shape on the fatigue reliability of carbon-fiber (CF) -reinforced PA 46 was examined and compared with that of glass-fiber (GF)-reinforced PA 46, CF. PA 66 and GF. PA 66. The main results were as follows : (1) In terms of the fatigue strength of U-notched specimens, CF. PA 46 is markedly superior to the other three materials. On the other hand, the fatigue strength of V-notched specimens was divided into two groups of CF materials and GF materials. Then, this is inferior to that. (2) For U-notched specimens, three stages were observed in the diagram showing the relation between notch root heating ⊿ T and number of cyclic stress N. The temperature of the notch bottom is increased rapidly at the first stage and kept constant during the second stage. Then, crack tip heating is promoted with crack growth at the final stage. On the other hand, for V-notched specimens, the one and only final stage was found in ⊿ T-N diagram. From ⊿ T-N diagram, it could be suggested that the crack initiating in U-notched specimens required a half fatigue life and that the crack propagating in V-notched specimens had a majority in fatigue life. (3) By micro fractography using SEM, it was recognized that the fracture surface of V-notched specimens was brittle and flat, while that of U-notched specimens was ductile and rough. Therefore, it is assumed that fatigue reliability of U notched specimens could be improved at the crack initiating through the superior heat resistance of CF. PA 46 and also the higher rigidity and heat conductivity of carbon fiber.

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Very high cycle fatigue tests were conducted on austempered ductile iron finished by buffing (called material A) and that finished by electropolishing (called material EA) for comparison of what please clarity. An S-N curve of rotating bending fatigue of material A represented a characteristic of a two-stage bending resembling extremely high-strength materials. This phenomenon clarified the occurrence of different fracture mechanisms through the intermediary of nonpropagating cracks. In material EA, the structural sensitivity was lower owing to the removal of the work hardening layer on the material surface. Consequently, its S-N curve of rotating bending fatigue was unexceptional, because mechanical properties of its matrix structure resemble those of its pearlitic structure. Fatigue stress amplitudes of both materials were σ_w = 382 MPa.

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The purpose of this study is to understand the mechanical properties of the human cranium in order to develop a FEM simulation model of the head. Craniectomy samples, autoclave bone flaps and dry cadaver skulls were tested using values of radial bending moment considered typical in the case of head injury. In this study, we developed a procedure for estimation of the mechanical properties of the cranium by assuming a proportional relation between the bone mineral density and Young's modulus. The mechanical properties of the human cranium have been determined from the three-point bending test and the bone mineral density measured by the dual energy X-ray absorptiometry. The human cranium consisted of inner and outer tables (cortical bones) and a diploe (a cancellous bone). The stress on the cortical and the cancellous bones in the field of bending stress was assumed that the cranium was a beam in which two different materials were combined. The experiment showed that fresh cranial fractures start at the inner table and the diploe and then propagate to the outer table. The fracture of a cranium taken out of a human being will exhibit elastic-plastic fractures. This fact implies that the inner table and the diploe fractures can occur even if no fracture is detected using plain X-rays in cases of acute extradural hematomas (EDH).

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The experiments on the temperature difference for exfoliation of a three-dimensional joint have been performed to investigate crack initiation and the difference between two-and three-dimensional joints using specimens made from resin and steel. When the edge angle is less than 90 degrees, the crack initiates at the side, therefore the temperature difference for exfoliation of the 3D joint equals that of the 2D joint. Under the other conditions, namely the edge angle being greater than or equal to 90 degrees, the crack initiates at the corner and the temperature difference of the 3D joint is slightly less than that of the 2D joint.

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A model is presented to express the relaxation of the interfacial shear stress acting on the ineffective part of a broken fiber in a unidirectional metal matrix composite 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 relaxation of the interfacial shear stress. The resulting equation is applied to the cell subjected to constant or increasing strain. It is thus shown that the interfacial shear stress relaxes very slowly in comparison with the axial 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. The effect of the radial gradient of matrix shear stress on the interfacial shear stress relaxation is also discussed.

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Stress intensity factors of modeled fiber-reinforced composite materials are calculated by the finite difference method based on the linear two-dimensional theory of elasticity. In order to bound the region to be analyzed, cracks and fibers are periodically arrayed in an infinite region. The bounded region is conceptually divided into two regions by a square boundary centered at the crack tip. The general solution about the crack tip is employed to describe the displacement on and within the square boundary. The region outside the square is devided into finite differences. The effects of several parameters such as fiber length and crack length on the stress intensity factors are examined for two kinds of configuration.

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Coating of cutting tool tips is demanded to obtain not only good surface properties but also good adherence to a substrate. The former are related to high stability and high strength, and the latter to bonding characteristics between film layer and substrate. WC-TiN gradient coating was conducted by rf magnetron sputtering using multi-S-guns. In order to explain the gradient coating mechanism, various analyses were carried out : X-ray diffraction for inspection of crystalline structures, Auger electron spectral analysis for inspection of chemical compositions, and scanning electron microscopy for observations of sectioned film layers. Two mechanisms play important roles in improving the bonding characteristics. One is that sputter-deposited elements of each layer are composed of the same crystalline structure as NaCl. The other is that some carbon from WC diffuses into the substrate. The deposition of β-WC_1-x, in a stable state at high temperature, is due to rapid cooling and removal of partial carbon.

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This paper concerns the evaluation of the normal inhomogeneity of functional gradient materials by means of spectrum analysis of ultrasonic waves. We first derive a theoretical method for the measurement of continuously changing acoustic impedance in the normal direction by spectrum analysis, by integrating the inverse Fourier transform of the ratio of the spectrum of the reflected wave to that of the incident wave. Next we apply this method to materials such as clad material, functional gradient material and powder compact, and it is proven to be useful in nondestructive inspection.

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We present an efficient strength optimization approach on laminated composite structures under in-plane loading where layer orientation angles in addition to layer thicknesses are used as design variables. A high-quality approximation of stress components is generated by a linear approximation of stress resultants with respect to intermediate design variables. An approximation method is then applied to a minimum-weight design of laminated panels under strength constraints. The validity of the present approach is verified through several optimization examples of laminated panels.

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Assuming a spherical void in an infinite rigid plastic material, Gurson proposed a yield function for isotropic porous solids. It is, however, well known that the Gurson model gives harder response than those predicted by experimentation on actual porous solids. In numerical studies to check the validity of Gurson's model, most of the past researchers have introduced a cubic unit cell model, in which a spherical void is placed at the center of the cube. The cubic model can be a good approximation of a porous solid, if the void volume fraction is very small. The cubic model, however, may be not appropriate for the study of porous solids with high ratio of void volume fraction since the model automatically introduces an orthotropy effect due to the geometrically repetitive distribution of voids in three orthogonal axis directions. This research will propose a new unit cell model which is appropriate for the study of the yield functions for isotropic porous materials. The model is also favorable for the study of the anisotropic effect due to the void shape because the unit cell includes less of the anisotropy based on the distribution than the cubic model does.

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Three-dimensional elastoplastic analysis is carried out using the finite-element method (DYNA3D) in order to determine know the stress distribution and to optimize the shape of link chains subjected to combined loads of torsion and impact tension. The stress is evaluated using von Mises' criterion. The effects of various dimensions and twisted contact angle of the link chains on the stress distributions are shown. Experiments were performed on deformation and strain of link chains subjected to the combined loads. Fairly good agreement is seen between the numerical and the experimental results. As a result, it is clarified that von Mises' equivalent stress of twisted link chains can be improved by optimizing the chain width. von Mises' equivalent stress of chains subjected to the combined loads when the contact torsional angle θ is between 22. 5 and 30 degrees, which is about 13% greater than that when θ is zero degrees.

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This paper gives analytical solutions of an optimization problem for beams with rectangular cross section which are supported by statically indeterminate conditions and are subjected to a uniformly distributed load. The problem is based on the inverse variational principle in which the shape and displacement that make the total potential energy stationary are considered under the condition of volume constancy. The problem becomes one of searching for the positions where the sign of the bending moment changes. The beams obtained have the property of uniform strength.

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A measuring method for coefficients of impulsive friction is presented for the case of slip occurring at the interface of two bodies subjected to impulsive loads. The mechanism of an apparatus is based on the Hopkinson bar method. Three specimens clamped by normal force are sandwiched between two long pressure bars. The loading initiated by impacting the incident pressure bar with the striker bar generates slip between the contact surfaces of specimens. The shearing force on the contact surfaces of specimens is measuring by means of strain gages mounted on the transmitter pressure bar. By measuring coefficients of impulsive friction for steel specimens, it is found that coefficients of impulsive friction decrease with the increase of normal force. The experimental results are useful to clarify the loosening mechanism of screw threads subjected to impulsive loads.

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In the previous papers, characteristics of stress fields near the apex in dissimilar materials formed from several isotropic homogeneous wedges with arbitrary angles subjected to surface traction or thermal load were theoretically clarified. The stress fields near the apex are defined by a linear combination of the singular solutions K_γ^p-1 of typeγ^p-1 on root p of an eigenequation in 0 < Re(p) < 1 or K_g logγ of type logγ on a double root p=1, no singularity ones K_γ^p-1 on root p in Re(p) > 1 and the particular solution K_pa on root p=1. The singularity of type logγ appears at the boundary where characteristics of stress fields vary from no singularity solutions to singular solutions of typeγ^p-1 or its reverse (Re(p) > 1 &harr; 0 < Re(p) < 1). For variations Re(p) > 1 &harr; 0<Re(p) < 1 of root p, the distributions of stress intensity K_j on p =p_j and K_pa on P=1 are changed at the boundary. Moreover, it is shown that characteristics of stress fields cannot be determined by only the roots of the eigenequation.

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The residual stress in a subsurface layer of austenitic stainless steel with a finished surface was evaluated by the polychromatic X-ray method. A surface of austenitic stainless steel SUS316 plate was ground and lapped as the specimen. In this method, the relation between strain and depth was approximated with a linear function or an exponential function, and it was assumed that the plane stress state existed in each subsurface layer in the depth direction of the specimen. As a result, the residual strain which was estimated under the assumption of the exponential function showed more reasonable distribution than that of the linear function. In addition, the residual stress which was calculated from the strain distribution was maximum tension at the surface of the specimen, and maximum compression at a position 3 μm below the surface. Therefore, the steep gradient of residual stress could be confirmed in a subsurface layer of the SUS316 with a finished surface.

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The dependence of slip line occurrence at the periphery of microcircular holes formed by photoetching in an 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 the element under biaxial stress, which are undetectable by the conventional copper electroplating method, can be evaluated using the equation based on the probability process of slip line occurrence, which takes into account both cyclic stress magnitude and the number of cycles.

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A method of resolution of all stress components from the first invariant of stress J₁ measured using a thermoelastic stress analyzer is shown. Not only surface stress but also internal stress can be determined by this method which is based on the following procedures. ( 1 ) Select an arbitrary domain Γ where the stresses must be determined from the structure. ( 2 ) Measure J₁ inside Γ. ( 3 ) Determine the optimum boundary traction along Γ by the least squares method so that the difference between the measured J₁ and calculated J₁ is minimum. Either FEM or BEM may be used for calculation. Examples of stress resolution for a two-dimensional stress concentration problem and a three -dimensional stress concentration problem are shown and the accuracy of stress resolution is discussed.

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It is well known that the principal directions of stress, strain and birefringence are not usually coincident with each other in a viscoelastic body. We undertook to develop and establish a convenient method for photoviscoelastic analysis using a circular disk under non-proportional loading conditions. The method is expected be applicable to the cases of moving crack or contact problems in which the boundary itself varies with time. A characteristic feature of this method is the extensive use of computer-aided image processing for photoelastic analysis based on the diagonal summation theorem.

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Dynamic behavior of a bias-type actuator using a TiNi shape memory alloy is examined theoretically as well as experimentally. The constitutive equation and the heat equation 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 behavior 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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Wavelet transform has recently been applied to the analyses of seismic or acoustic data in place of the Fourier transform. This integral transform using the localized kernel function can extract microscopic characteristic features at any location (time) with an arbitrary intensification, from the original sequential data. One of the most attractive applications of this transform is to multifractal analysis. In the present work, the eligibility of this application is first confirmed for the Cantor sets and Koch curves, the fractal dimensions of which are known exactly. Then it is applied to interfacial roughness data of the metal-polymer laminated material reported in the previous paper. We find that this method enables identification of the local inhomogeneous fractal properties including distinction from the nonfractal region or the bounds of the scale showing self-similarity.

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A renovative shape design method of defective structures is proposed to strengthen stiffness under the least weight reinforcement. The design domain is composed of discrete material elements that constitute a structure and discrete weak material elements. The structural shape is discretely modified by the exchange of the elements in the steepest descent of sensitivity function that is evaluated from the strain energy variation of the entire structure with the successive approximation procedure. In the computed structural reinforcements for the original defects, the topology and the dimensions of the structural boundary are obtained with the least additive weight to give the renovated structural shape.

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The methods used in university lectures will gradually be changing from blackboards and books to multimedia. In this investigation, we prepared for lectures on the strength of materials, using multimedia. The first step was creating an Electric Book on the strength of materials. This book contains movies, graphics, speeches, equations and texts, and also offers rich interactivity. The second step was preparing an actual lecture using multimedia. The third part term of the lecture on the strength of material consisted of multimedia information, which was projected on the screen, of the computer. Based on these experiences and questionnaires from many lecturers on the strength of materials, we propose a future vision of lectures on the strength of materials.

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