The behavior of nanostructured materials/small-volume structures and biological/bio-implantable materials, so-called “nano” and “bio” materials, is currently much in vogue in materials science. One aspect of this field, which has to date received only limited attention, is their fracture and fatigue properties. In this paper, we examine two topics in this area, namely the premature fatigue failure of silicon-based micron-scale structures for microelectromechanical systems (MEMS), and the fracture properties of mineralized tissue, specifically human bone.

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The present paper reviews some recent developments of the measurements of the macrostress and microstress by diffraction using X-rays, synchrotron and neutrons especially in Japan. These three methods are based on the same principle of the diffraction of crystals, and have different advantages. The conventional X-rays detect the stress very near the surface, while the neutron diffraction takes the stress in the interior of the materials. High-energy X-rays from synchrotron sources have the penetration depth in between and are suitable for the measurement of subsurface stresses. After describing the developments of the fundamentals of the methods, the paper covers the recent applications of the diffraction methods to the residual stress analysis in textured thin films, the nondestructive determination of the subsurface distribution of residual stress in shot-peened materials, local stress measurements near the crack tip, the stress measurements of single crystals, macrostress and microstress measurements in composites, and the determination of the internal distribution of the residual stress in welded joints.

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High-speed holographic microscopy is applied to take three successive photographs of fast propagating cracks at the moment of bifurcation. The cracks are propagated in PMMA plate specimens at a speed about 660m/s. From the photographs, crack opening displacement (COD) is measured along the cracks as a function of distance r from the crack tips. The measurement results show that the CODs are proportional to √r before bifurcation. After bifurcation, the CODs of mother cracks are proportional to √r, however, the CODs of branch cracks are not always proportional to √r. Crack speed is also measured from the photographs. As a result, discontinuous change of crack speed is not observed at the moment of bifurcation. The energy release rate and energy flux toward crack tips are obtained from the COD data, and are found to be continuous across the bifurcation point. The energy release rate and energy flux increase gradually across the bifurcation point.

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This study deals with the measurement of the two-dimensional deformation of wood joints under compressive loads using an electronic speckle pattern interferometry (ESPI) technique. A mortise and tenon joint and a dovetail joint of western hemlock (Tsuga heterophylla) are used as specimens. Results reveal that a large two-dimensional deformation of the wood joints can be measured using the ESPI technique, the deformation values significantly vary with parts, and the accuracy of the fabricated wood joints has a significant effect on the two-dimensional deformation of the wood joints.

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Ultrasonic in-situ observation of alumina particles in molten aluminum at temperature up to 800°C is presented. A focused ultrasonic sensor is employed for the high temperature measurement with a high spatial resolution. The sensor mainly consists of a conventional piezoelectric transducer, a taper-shaped clad buffer rod as a waveguide and a cooling system. Martensitic stainless steel is used as a material for the buffer rod and an acoustic lens is fabricated at the probe end of the rod. In order to examine the focusing ability of the acoustic lens, the acoustic field near the focusing zone is numerically evaluated by a finite difference method. Using the developed focused ultrasonic sensor, backscattered echoes from alumina particles of 160µm suspended in the molten aluminum at 800°C have been observed clearly in pulse echo mode at 10MHz. The effect of the size and the aggregation condition of the particle on the backscattered echoes has also been examined.

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In this paper, we describe an effective transmission method of high frequency ultrasound into a silicon chip via the polymer layers. The layer is inserted between water and the chip, and the pressure of about 0.1MPa is applied to the contact interface between the layer and the chip. The polyvinylidene chloride and polyvinyl chloride layers of 9µm thick bring the ultrasonic resonance between water and silicon, and the ultrasound in the frequency range of 20 to 80MHz is transmitted into the chip more effectively than the usual water immersion case. In practice, we carry out the acoustic imaging of the flip chip package via the layer, and clearly visualize the defective solder bumps beneath the chip under the dry-contact condition. Besides, the quality of the dry-contact image is equivalent to the water immersion image.

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A method to measure moisture in encapsulant resin of IC packages by microwaves was demonstrated, which can determine moisture directly without drying and weighing the packages. An coaxial line sensor acts both as a source and receiver of microwave signal that is transmitted into and reflected from the package. A frequency of 100GHz was used to increase the measurement sensitivity. The relationship between the measured amplitude of the reflection coefficient and the moisture content in the packages was found to be linear. The amplitude difference, which is corresponding to the attenuation of microwave, in the cases of packages with and without moisture content, increases linearly with the increase of the thickness of the resin above the chip pad. For any kinds of packages, if the thickness of the packages is the same, the moisture content can be determined by the microwave amplitude measurement after testing two reference packages; if the thickness of the packages is known, the proposed method can be used directly after measuring a dry package.

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This paper describes an experimental study on full-field stress separation from thermoelasticity and photoelasticity measurements and its application to estimation of stress intensity factor and the J-integral. Thermoelastic stress analysis (TSA) and photoelastic stress analysis (PSA) have been developed as full-field visualization methods of stress distribution. Only the sum of the principal stresses can be measured by TSA, while only the difference of the principal stresses can be measured by PSA. In this study, the hybrid stress separation measurement technique developed by the present authors using both of these methods was applied for determining distribution of all individual stress components in a center-cracked plate subjected to mechanical load. Stress intensity factor and the J-integral were calculated from the obtained stress distribution. In addition to the conventional calculation method, near-tip exclusive domain integral method was proposed, in which the J-integral was evaluated without using degraded experimental stress distribution data near the crack tip. It was found that these fracture mechanics parameters can be evaluated with good accuracies by the present technique.

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Thermoelastic stress analysis (TSA) is a non-contact and full-field type method of experimental stress analysis. Since TSA provides only the sum of the principal stresses, many studies have been carried out for developing techniques of stress separation. Unfortunately, most of the techniques developed hitherto are rather complicated and require much labor in practical application. Recently, the authors have developed a simple technique by utilizing the nonlinearity of the thermoelastic effect. In this technique, principal stresses are determined from two sets of temperature amplitude data measured under sinusoidal loadings having same amplitude but different mean values. However, the difference between temperature amplitudes obtained at different mean loadings is very small and, therefore, the result of stress separation becomes very noisy. In this paper, several smoothing techniques are applied to the temperature amplitude data in order to improve the accuracy of stress separation. It is found that some simple smoothing techniques are effective.

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Residual stresses in TiN and TiAlN films on steel substrate were investigated by ultra high X-rays of synchrotron radiation. The specimens prepared in this study were single-, double- and multi-layer TiN and TiAlN films deposited on high speed steel substrate by arc-ion plating. The minimum thickness available for the residual stress measurement was 0.8µm by in-lab equipment whereas below 0.1µm by synchrotron radiation. Extremely large compressive residual stresses were found in the films. Residual stresses in TiAlN films were more than twice larger than those in TiN films, resulting to reduce the average residual stress in the whole film system by making double- or multi-layer film construction comparing to that in the single TiAlN film.

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It is possible to measure nondestructively the residual stress in the interior of the top coating in the thermal barrier coating (TBC) using hard synchrotron X-rays, which have a large penetration depth and high brightness. A new hybrid method is proposed to estimate the distribution of the spalling stress in the top coating by combining the synchrotron data with the stress data measured by the conventional X-ray method utilizing a Cr-Kα radiation. The new hybrid method was applied to estimate the distribution of the spalling stress in the top coating of TBC which had a zirconia top coating with a thickness of 0.24mm and a NiCoCrAlY bond coating with a thickness of 0.2mm. The residual stress, σ₁₁-σ₃₃, within the top coating was determined by synchrotron X-rays of 73keV energy level, where σ₃₃ was the stress perpendicular to the surface and σ₁₁ was an in-plane stress. The distribution of residual in-plane stresses, σ₁₁ and σ₂₂, in the top and the bond coating was determined with the conventional X-ray method by repeating the measurement after successive removal of the surface layer. From the data obtained by synchrotron and conventional X-rays, the distribution of stress component, σ₃₃, responsible for spalling was determined. The estimated value of the spalling stress was very small beneath the surface and increased to about 75MPa near the interface between the top and the bond coating.

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We develop an experimental evaluation method of interface strength for ductile submicron-dots on a hard substrate without collapse of the dot. The validity is examined by a copper (Cu) submicron-dot on a silicon dioxide (SiO₂) substrate with the rigid-layer of tungsten (W), which restrains the deformation and decreases the influence of complicated stress field due to the contact of tip. The diamond tip is dragged horizontally along the SiO₂ surface and the load is applied to the side edge of the W layer at a constant displacement rate using a modified atomic force microscopy. Both the lateral and the vertical load and displacement are continuously monitored during the test. The lateral load, F_l, increases almost in proportion to the lateral displacement, δ _l, and the Cu dot with the W layer is clearly separated from the SiO₂ along the interface. The restraint by the W layer works well so that there are little damages in both the delaminated W/Cu dot and the substrate. The delamination lateral load, F_lC, is successfully measured.

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Ultrafine-grained specimens with the average grain size of less than 2µm and medium-grained specimens were prepared from steel plates produced by an advanced thermo-mechanical control process. The smooth specimens were fatigued under axial tension compression at room temperature in air. The fatigue crack initiation process was investigated by orientation imaging microscopy based on EBSP in combination with atomic force microscopy and scanning electron microscopy. The results show that fatigue cracks initiated in the simple slip lines in the medium-grained specimens. On the other hand, in the ultrafine-grained specimens, complex slip deformation was formed in the vicinity of the grain boundaries prior to the fatigue crack initiation. Fatigue cracks were nucleated at the boundary between the grains with the concentrated complex slip deformation. The crystallographic orientation analysis revealed that the complex slip deformation was formed by the cross slip of active slip systems with the largest Schmid factors. It was found that the relation between the fatigue limit and grain size of the ultrafine-grained specimens does not conform to the Hall-Petch relation of conventional ferritic-pearlitic steel due to the texture and cross slip.

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The opened-up configuration of the artery wall has long been assumed to be stress-free. This is questionable at a microscopic level: The aortic media has a laminated structure consisting of an elastic lamina (EL) and a smooth muscle-rich layer (SML). The ELs are corrugated in the opened-up configuration, suggesting their buckling. We found that the ELs were much stiffer than the SMLs from a radial compression test of the porcine aortas. Such mechanical heterogeneity may cause microscopic residual stress, which is hardly released by the radial cutting except in the area close to the cut surface, where the release may cause hills and valleys. To check this hypothesis, we measured the topography and the stiffness distribution of the cut surface of the aortas with a scanning micro indentation tester to find stiff hills (EL) and soft valleys (SML). Residual stress estimated from the measurements was almost comparable to the conventionally estimated values and was large enough to cause the buckling. Fairly large stress may still reside in the opened-up aortic wall.

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Process induced thermal residual stresses and matrix failure of unidirectional CFRP has been investigated by finite element methods. Partial discrete model composites consisting of a microscopic area of fibers and matrix surrounded by a homogeneous area were chosen. Four cases have been investigated concerning the formation of residual stresses and initial matrix failure: A free UD-laminate, a constrained UD-laminate, a cross ply laminate and a thick laminate which is subjected to a temperature gradient during cooling down. On the basis of experimental results from thermo-mechanical tests of the neat resin, the temperature dependent matrix stress-strain behavior as well as the parabolic failure criterion were formulated and introduced into the finite element program. The actual stress state on the microscopic level depending on different boundary condition could be described. The authors showed that the approach of a partial discrete model is suitable to determine the initial matrix failure of different macroscopic specimens under consideration of micro-mechanical effects. The results showed that high tri-axial stresses occur in the constrained laminate and the cross ply laminate, which lead to initial matrix failure in the 90°-ply. The consideration of a temperature gradient affects the stress distribution in the matrix though the influence on the maximum residual stress values is small. In this case, initial matrix failure can be excluded.

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Carbon Fiber Reinforced Plastic (CFRP) is composed of electric conductive carbon fibers and electric insulator resin. Self-monitoring system has been reported utilizing electric resistance change of unidirectional CFRP due to fiber breakages and to applied strain. Piezoresistivity is electric resistance change with applied strain. Many researchers have already reported the piezoresistivity of unidirectional CFRP. There is, however, large discrepancy in the measured piezoresistivity even in the fiber direction during tensile loading: both positive piezoresistivity (electric resistance increase) and negative piezoresistivity (electric resistance decrease) are reported during tensile tests. Electric resistance change at electrodes due to poor electric contacts are reported to be a main cause of this large discrepancy. In the present study, therefore, basic properties of piezoresistivity were measured with specimens made from single-ply and multi-ply laminates using a four-prove method. Many cases of electric resistance changes in the fiber direction transverse direction were measured during tensile loading. Effect of shear loading was also investigated using a shear test. To investigate the effect of poor electric contact at the electrodes, electrodes were made without polishing specimen surface and a tensile test was performed with measuring piezoresistivity. After the test, the specimen surface was polished, and a tensile test was performed again using the identical specimen. As a result, positive piezoresistivity was obtained for both single-ply and multi-ply specimens and negative piezoresistivity is confirmed that it was caused by the poor electric contact at electrodes.

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To find out the degradation behavior of polymer in the real space, space exposure experiments utilizing the International Space Station (ISS) were scheduled. PEEK sheets under tensile stresses were exposed to the environment around the ISS orbit, and were irradiated by atomic oxygen (AO), ultraviolet ray, and electron beam (EB) in the ground test facility. This study introduces the outline of these experiments, and shows the results of AO and EB pilot irradiation tests as follows: (1) Test piece surfaces after AO exposure exhibited significant morphological damages characterized by micron-sized conical pits. (2) Thickness reductions of the test pieces by AO exposure increased with increasing tensile stress. (3) Residual strength after AO exposure could be estimated by taking account of thickness reduction. (4) No significant change was observed on surface morph, mass, chemical structure, and tensile properties of the test pieces after EB exposure regardless of tensile stress.

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This paper applies a constitutive model proposed previously by the authors to three lead-free solder alloys of Sn/Ag, Sn/Bi and Sn/Zn. First, the material constants in the constitutive model are determined using the so-called “plasticity-creep separation method” by simple tests such as pure tensile tests. The constitutive model is incorporated into a general purpose Finite Element Method program ANSYS using the stress integration method. The material constants for the lead-free solders could be simply determined using only the data obtained by the pure tensile tests with three strain rates. The basic mechanical deformation such as creep and cyclic deformation are simulated by the constitutive model using the material constants determined using the “plasticity-creep separation method”. Thermal deformation during a reflow process with electronic packaging is also simulated by the constitutive model.

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Isothermal axial-strain-controlled creep-fatigue tests of a eutectic alloy Sn-37Pb were carried out at room temperature. Four kinds of triangular strain waveforms, so-called fast-fast, fast-slow, slow-fast and slow-slow, were used. First, constant-amplitude fully-reversed creep-fatigue tests were performed in order to obtain the creep-fatigue properties of the material as the partitioned inelastic strain range versus life relationships; that is, Δ ε_ij-N_ij relationships (ij=pp, pc, cp, and cc). The obtained Δ ε_ij-N_ij relationships were compared with the literature data. Second, two-step variable-amplitude fully-reversed creep-fatigue tests, so-called low-high and high-low, were conducted under fast-fast and slow-fast straining conditions. The results were analyzed and discussed based on the creep-fatigue damage rule proposed by the author and his colleague in a previous study for other high-temperature materials. Finally, the effects of ratcheting strain on creep-fatigue life were studied by conducting creep-fatigue tests under the strain waveforms involving small tensile ratcheting strain.

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As model specimens of surface film-bonded materials with or without resin interlayer, pure copper or commercial grade iron films were bonded to the surface of steel base plates by epoxy resin bonding or by diffusion bonding. The film thickness was 100 and 50µm for the copper and 100µm for the iron, respectively. In the fatigue testing results using these specimens, very few slips were observed around the crack initiated relatively early during fatigue on the film bonded with epoxy resin, while many slips were observed during fatigue on the film bonded by diffusion. As for the fatigue life, the epoxy bonding layer restrains the fatigue crack propagation from the surface film to the inner base plate, thus increasing the fatigue crack propagation life of the film-bonded plates with epoxy resin. In this connection, both the compressive residual stress on the iron film and the smaller tensile residual stress on the thinner copper film increased the fatigue crack propagation life significantly as compared with the larger tensile residual stress on the thicker copper film. Finally, the effect of the epoxy bonding layer on the fatigue crack propagation rate of the surface film was discussed in terms of the measured crack opening displacement range at 250µm from behind the crack tip, Δ φ₂₅₀.

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The growth of dominant crack is sometimes affected by distributed small cracks in multiaxial low cycle fatigue. Considering such a situation, crack initiation in biaxial fatigue was first modeled in this work. In modeled grains, normal directions of slip planes and slip directions on respective planes were independently given at random. A slip-band crack was presumed to be initiated along the given slip direction on the specified slip plane when the resolved shear stress in the slip direction exceeded a critical shear stress. The crack initiation life was also evaluated using a dislocation pile-up model. Simulations on crack initiation were conducted under the same loading conditions as experiments. Simulated directional distribution of initiated cracks was compared with experimental results obtained in biaxial fatigue tests using tubular specimens of pure copper, and it showed a good agreement with the experimental observation.

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The fatigue crack growth test under mode II dominant condition is conducted. It is found that the crack growth direction can not be predicted by the conventional method. By the fracture surface observation, it is also found that the thickness effect strongly affects this behavior. Three dimensional elastic-plastic FEM analyses are conducted for this problem considering the Bauschinger effect. The change of the crack tip stress field during fatigue crack growth is studied. The criteria to predict the fatigue crack growth direction are studied and new criteria are discussed.

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A simulation method for microscopic creep damage at grain boundaries in the fine-grain heat-affected zone of low-alloy steel welds involving high energy piping was proposed on the basis of the combination of elastic-creep FEM analysis and random fracture resistance modeling of the materials. First, the initiation and growth-driving forces of small defects were concretely determined based on microscopic observation of the damage progress at the grain boundaries of the material, taking into account dependence on stress and temperature. Then, a simulation procedure combining the stress distribution from elastic-creep FEM and the random fracture resistance model was proposed, and this procedure was applied to the simulation of the microscopic damage progress in a welded joint model test and in actual power piping. The results in terms of the simulated number density of small defects throughout the wall thickness were in good agreement with the observed results.

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This paper describes the applicability of passive electric potential CT (computed tomography) method which does not require electric current application for damage detection. In this method, piezoelectric film is glued on the surface of structures as a sensor. Electric potential values on the piezoelectric film change due to the strain distribution on the structure, when the structure is subjected to external load. The strain distribution of the cracked body induces a characteristic electric potential distribution on the piezoelectric film. Therefore passively observed electric potential values on piezoelectric film can be used for the defect identification. An inverse method based on the least residual method was applied to the crack identification from the electric potential distribution. In this inverse method, square sum of residuals is evaluated between the measured electric potential distributions and those computed by using the finite element method. This method may be applied to develop an intelligent structure with a function of self-monitoring of flaws and defects. The electric potential on piezoelectric film was measured by the contact type and the non-contact type methods. The measured electric potential distribution was used to identify a crack by using the present inverse method. It was found that the location, size and depth of the crack can be quantitatively identified by the passive electric potential CT method.

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A fatigue life prediction method is presented based upon the data obtained due to flow-induced vibration. In the experimental program a small wind tunnel was used to produce flow-induced vibrations of a Styrofoam cylinder. These vibration was transmitted to an attached fatigue specimen. The specimen was made of a medium carbon steel with a small hole drilled into its surface to simulate a defect and to localize the fatigue crack propagation process. A small portable strain histogram recorder (Mini Rainflow Corder, MRC) was used to acquire the service strain histogram and also to measure the variation of natural frequency. Fatigue damage, D, was defined by the Modified Miner's Rule and was determined by using the strain histogram of the early portion of the test record. The values of D were all smaller than 1.0 and ranged from 0.2 to 0.8. The effect of the size of the simulated defect on the values of D was clarified by focusing on the relationship between small crack growth behavior and the strain histogram.

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The dynamic behavior of monodispersed particulate aggregation subjected to projectile impact at velocities less than 16m/s is investigated numerically by the discrete element method (DEM). The particulate aggregation consists of mono-size nylon spheres arranged regularly and three-dimensionally in a rectangular parallelepiped container. A steel sphere vertically strikes a nylon sphere or several nylon spheres near the center in the top layer of aggregated particles. In particular, the effects of several impact conditions on the rebound velocity of the steel projectile are discussed in detail. As a result, it is found that the rebound velocity of the steel projectile depends upon the lateral gap between nylon spheres, the ratio of the radius of the steel projectile to the radius of nylon spheres and the impact position of the steel projectile.

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A combined instrument for ultra-microhardness testing and atomic force microscopy (AFM) has been developed. The instrument could be employed to conduct hardness tests with a diamond indenter and its Si tip allowed high-resolution AFM images to be obtained at the same position on the specimen. Ultra-microhardness tests and AFM observations were carried out on electrolytically polished specimens of a tungsten single crystal and JIS-SCM415 and JIS-SCM440 low-alloy steels. The SCM415 and 440 steels were tempered at 873K and 723K, respectively. The benefits of using a Si tip instead of a diamond indenter for AFM observation are clearly shown by the better profile of the indent mark on the tungsten single crystal and the clearly distinguishable images of the fine carbides of the steels. The ultra-microhardness of the steels was influenced by the local microstructures such as the carbide density and the presence of a ferritic phase.

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In this paper, the behavior of an interface crack between isotropic and orthotropic elastic half-planes subjected to a uniform tension is investigated by use of the Schmidt method under the assumption that the effect of the crack surface overlapping very near the crack tips is negligible and there is a sufficiently large component of mode-I loading so that the crack essentially remains opening. The upper half-plane is isotropic elastic materials and the lower half-plane is orthotropic composite materials. By use of the Fourier transform, the problem can be solved with the help of two pairs of dual integral equations in which the unknown variables are the jumps of the displacements across the crack surfaces. Numerical examples are provided for the stress intensity factor of the cracks. Here, we just give an approach to solve the problem of the interface crack. As in a special case, we also give solutions of the ordinary crack in homogeneous materials and of the interface crack between two dissimilar isotropic materials. These solutions have been compared with each other.

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In this paper, the problem of a crack along an interface between inhomogeneous orthotropic media is solved by using a new method, named the Schmidt method. To make the analysis tractable, it is assumed that the Poisson's ratios of the mediums are constant and the material modulus varies exponentially with coordinate parallel to the crack. By use of the Fourier transform, the problem can be solved with the help of two pairs of dual integral equations in which the unknown variables are the jumps of the displacements across the crack. To solve the dual integral equations, the jumps of the displacements across the crack surfaces are expanded in a series of Jacobi polynomials. Numerical examples are provided to show the effects of the length of the crack and the parameter describing the functionally graded materials upon the stress intensity factor of the cracks. When the material properties are continuous across the crack line, the numerical results are the same as those obtained so far. When the material properties are not continuous across the crack line, an approximate solution of the interface crack problem is given under the assumptions that the effect of the crack surface overlapping very near the crack tips is negligible. Contrary to the previous solution of the interface crack, it is found that the stress singularities of the present interface crack solution are similar with ones for the ordinary crack in homogenous orthotropic materials.

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In the surveillance program for the reactor pressure vessel, fracture toughness is estimated by assuming that the shift of transition temperature on fracture toughness is equivalent to the shift on measured Charpy impact properties. Therefore, it is necessary to establish the correlation between both shifts of transition temperature. In this study, we applied the master curve approach adopted in the ASTM E1921 method to fracture toughness testing. The materials used are five ASTM A533B class 1 steels and one weld metal. Neutron irradiation for Charpy-size fracture toughness test specimens and standard Charpy-v specimens was carried out at the Japan Materials Testing Reactor (JMTR). A correlation between the reference temperature on fracture toughness and Charpy transition temperatures before and after irradiation is established. Based on this correlation, the optimum test temperature for fracture toughness testing is suggested. The method to determine a lower bound fracture toughness curve is also discussed.

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The probabilistic fracture mechanics (PFM) analysis code PASCAL has been developed in JAERI. This code can evaluate the conditional probabilities of crack initiation and fracture of a reactor pressure vessel (RPV) under transient conditions such as pressurized thermal shock (PTS). Based on the temperature and stress distributions in the vessel wall for four cases of PTS transients in a typical 3-loop PWR, parametric PFM analyses were performed using PASCAL on the variables such as pre-service inspection method, crack geometry, fracture toughness curve and irradiation embrittlement prediction equation. The results showed that the Arakawa's model for a pre-service inspection had a significant effect on the fracture probability and reduced it by more than 3 orders of magnitude compared with no inspection case. The fracture probability calculated by the fracture toughness estimation method in Japan was about 2 orders of magnitude lower than that by the USA method. It was found that the treatment of a semi-elliptical crack after its initiation in PASCAL reduced the conservatism in a conventional method where it is transformed into an infinite length crack.

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The main purpose of this study is to develop a high frequency induction process that is capable of producing the nanoparticle suspension, as well as the investigation into the properties of nanoparticle suspension. Also the effects of the process parameters, such as cooling temperature, vacuum pressure and inert gas on the rheology of nanoparticles are investigated. Experimental results indicate that under lower vacuum pressure, the nanoparticle suspension performs a larger rheological change and produces smaller nanoparticles, whereas under lower cooling temperature, it can produce finer ones. Besides, by adding inert gas during the process, the rheology of nanoparticle suspension would change. Furthermore, by adjusting the pH value of nanoparticle suspension below 7, its surface electric potential can also be increased and subsequently acquires smaller suspension particles. Besides, the nanoparticle suspension produced by this study has a good capability of absorbing UV light.

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This paper describes an application of friction stir welding (FSW), solid phase welding, to fabricate railway car body made of aluminium hollow extrusions (double-skinned car body). The construction of double-skinned car body using FSW can reduce deformation and release process from skilled workers compared with the conventional method. In this paper, from the viewpoint of strength, we show our approach from a design of the joint's sectional shape to the final evaluation test using actual double-skinned car body fabricated by FSW. For design, reaction force in the workpiece coincident with heat input was considered. At load test, we evaluated stress levels at the joint, accuracy of the simulation of the car body and double-skinned car body's characteristics. As a result, railway car body joined by FSW can meet all the requirements for actual application. These benefits have been applied to 319 vehicles as of June 2002.

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Most failures of ductile materials in metal forming processes occurred due to material damage evolution- void nucleation, growth and coalescence of neighboring voids. Recently, Gologanu-Leblond-Devaux (J. Mech. Phys. Solids, Vol.41 (1993), pp.1723-1754) extended the classical Gurson model (ASME J. Engng. Mater. Technology, Vol.99 (1997), pp.2-15) to a ductile material containing an oblate ellipsoidal cavity. And, they proposed a new approximate yield function incorporating the initial void shape effects, which is significant especially at low stress triaxiality. In the present work, the Gologanu-Leblond-Devaux's yield function for anisotropic sheet materials containing axisymmetric prolate ellipsoidal cavities is adopted in evaluating analytically forming limits of sheet metals under biaxial stretching by Marciniak and Kuczynski (M-K) model. The effect of a void shape and growth on the forming limits of sheet metals under biaxial tensile loading is introduced and examined within the framework of the M-K model, along with the effect of including a first-order strain gradient term in the flow stress. To confirm the validity of the proposed model, the predicted FLDs were compared with experimental results for steel sheets. The predicted forming limits for the voided sheets were found to agree well with the experimental data.

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