Dislocations emitted from a crack tip in silicon single crystals have been investigated using a high voltage electron microscopy (HVEM). The influence of those crack tip dislocations on the fracture toughness has been discussed based on the 3-D stress analysis of crack-dislocation interaction. Pure screw dislocations were introduced not only ahead of a crack tip but also behind the tip. The dislocations ahead of the crack tip have the sign of Burgers vectors opposite to that of the dislocations behind the tip. These configurations of crack tip dislocations are understood by dislocation loop expansion from sources near the crack tip. The contribution to the fracture toughness by those crack tip dislocations was calculated, and it was found that 70∼90% increase in the fracture toughness was caused by a dislocation configuration corresponding to that observed in the early stage of dislocation emission from a crack tip.

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Slip deformation in the vicinity of a spherical shaped inclusion, which is embedded in metal matrix is analysed by a finite element technique. Spatial gradient of the plastic shear strain on slip systems is calculated to evaluate the density components for the geometrically necessary dislocations. Graphical image for the three dimensional structure of the dislocations around the inclusion is reconstructed from the numerical data for edge and screw components of dislocation segments. The obtained results show loop shaped structure around the inclusion, dislocation walls growing nearly perpendicular to the slip plane, and some smaller dislocation loops. Development of these structures is discussed in conjunction with the fluctuation of stress field, which takes place after nonuniform slip process.

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Relation of microhardness to the indentation depth has been experimentally investigated for two single crystalline materials of silicon and aluminum. For the case of silicon, the microhardness is strongly affected by the coupled behavior between phase transition induced by the hydrostatic pressure from the diamond structure to the β-tin and dislocation emission. Increase of hardness at the depth less than about 2μm is observed at the case of aluminum, which has already been reported for the other ductile materials discussing with the evolution of the dislocation network. The onset of the increase is, however, dependent on the surface characterization. The elastic constants estimated from the unloading curves don't show the drastic change according to the indentation depth. The assumption on a paraboloid of revolution as an indenter in the process defining the hardness is also verified and its error is found to be small within the present measurable range.

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Applying the theory of soliton system, we mathematically analyze the mechanical properties of an atomic chain model in order to understand the mechanical behavior of nano-scale metallic contact. We use the typical atomic chain model which includes the topological defect and consists of the thermal effect, the interactions of atoms, the friction from the environment and the external force. The dynamics of the chain model is given by the thermal overdamped sine-Gordon equation. Solving the equation by the perturbation expansion, we derive the strain of the atomic chain model under the constant applied force. We show that the strain against time behaves viscoelastically like the response induced by Voigt model. The properties in temperature and applied force support the well-known results of the experimental data.

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The dislocation behavior, i.e. density of mobile dislocation and eigen-frequency of dislocation strings, are closely related to fatigue damage of materials. We can estimate the density of mobile dislocation under fatigue process by measuring ultrasonic wave velocities with three-different propagating frequencies via Granato-Lucke's dislocation string theory. In the present paper, the correlation of the mobile dislocation density with fatigue damages both of aluminum alloy and chromium-molybdenum alloy steels was examined. The results obtained are as follows. The ultrasonic wave velocities with three-different propagating frequencies (5, 10 and 15 MHz) decreased due to increasing of number of fatigue cycles in the both cases of aluminum alloy and chromium-molybdenum alloy steel. The density of mobile dislocation in the both cases estimated by Granato-Lucke's model increased in the fatigue damage progress.

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We carried out an in situ neutron diffraction study on tensile deformation using the time-of-flight method with a spallation neutron source. We have installed a tensile testing machine which was designed in such a way that the center of a specimen did not move during tensile deformation in high resolution powder diffractometer Sirius. Using an IF steel, we have succesfully measured changes in various (hkl) lattice plane spacings during tensile deformation at room temperature. In this experiment, lattice plane spacings along tension direction and perpendicular direction were measured simultaneously. We obtained macroscopic average starins of the [hkl] grains in elasto-plastic deformation of the bcc polycrystalline specimen.

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Tensile tests below room temperature were conducted to investigate effects of temperature, strain rate and ferrite grain size on tensile flow stress for ferrite-pearlite (FP) steels with ferrite grain sizes between 3.6 and 46.2 μm. The temperature and strain rate sensitivity of flow stress for the FP steels is almost independent of ferrite grain size. The flow stress for the FP steels is expressed by Hall-Petch equation; σ=σ₀+KD^-1/2, where D refers to ferrite grain size and σ₀ and κ constants. The slope κ of the equation is almost identical being independent of strain, temperature and strain rate. By summarizing the experimental results, it is possible to describe the flow stress of the FP steels by the following equation, σ=σ_t+182+5.8D^-1/2+900ε where σ_t and ε mean thermal component of stress and true strain, respectively; σ_t is influenced by ε, temperature and strain rate.

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Grain refinement is the only one method to increase both strength and toughness for low carbon steel. However, ultrafine-grained steel has some problems. One of these is the shortness of uniform elongation. Ashby et al. show that an increase in volume fraction of second phase and a decrease in its diameter increase strain hardening rate and therefore increase uniform elongation. We have tried to apply this idea to the low carbon ultrafine-grained steel by using carbides as the second phase. Superior uniform elongation is promised by increasing the carbon content to lead an increase in the volume fraction of carbide (f) or by decreasing the rolling temperature to make the diameter of carbide (d) finer. It is evident that an increase in f/d increases the strain hardening rate or the uniform elongation of low carbon ultrafine-grained steel.

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The Bauschinger effect of metals is explored by the multi-scale modeling based on the mathematical homogenization theory without any phenomenological constitutive models such as kinematic hardening. Although this peculiar mechanical behavior was discovered in 19th century, and has been introduced as one of the most typical plastic phenomena for metals in most of basic textbooks for plasticity, the study of this mechanism has been superficial so for. First, we conduct experiments under cyclic loading for specimens with two kinds of microstructures; the pearlite and the spheroidized cementite structures. Then, these experiments exhibiting the Bauschinger effect are simulated by the global-local analysis technique. By focusing our attention to the micro-scale mechanical behavior, we try to explain why and how the effect comes out in experiments.

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Various defects are accompanied in steel heat treatment process. Heat convection and steam film cause non-homogeneity of heat transfer. The technique that the quenchant is put into stirring in order to prevent these heat treatment defects are proposed. In addition, the heat transfer coefficient is identified in order to carry out the simulation promoted recently. The purpose of this paper is to propose a method of identification of heat transfer coefficient and verify effect of the quenchant on internal structure and mechanical behavior. Here, the stirring quenching experiment was carried out using ring specimen of carbon steel SCM 420. Then, heat transfer coefficient was identified from measured temperature on surface of the specimen. The heat transfer coefficient was input into simulation data, and the calculation using the finite element method was carried out. Simulation results were compared and verified with the experimental value, and identification result of the heat transfer coefficient and effectiveness of the stirring of quenchant were confirmed.

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Authors reported the formulation procedure for the constitutive equations of polycrystalline shape memory alloy under complex loading conditions in the previous paper (First Report). In the second report, several unique deformation behavior of shape memory alloy obtained by the systematic experiments under complex loading conditions were shown and discussed. In this paper, the results of experiments and predicted results obtained by the proposed constitutive equations are compared and, the reliability of the constitutive equations is confirmed.

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In this work, a series of biaxial ratchetting tests and numerical simulations are carried out. Experimental results obtained using the tubular specimen of SUS 304 stainless steel subjected to cyclic shear staining under the superposed axial stress show the dependence of the amount of superposed axial stress, the cyclic shear strain amplitude and the shear strain rate. Even under zero superposed stress, the ratchetting strain is induced in the axial direction. Finally, the unified constitutive model proposed by authors is used for the predictions of these biaxial ratchetting. The characteristic features of biaxial ratchetting are well described by the numerical simulation.

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Analytical solutions are presented for stochastic temperature, thermal deformation and thermal stress in a laminated plate including functionally graded material layer (FGM layer) subjected to random surface temperatures. The laminated plate has arbitrary nonhomogeneities of thermal and mechanical properties corresponding to arbitrary gradual change in the material composition, and temperature variation only through the thickness of plate. The surface temperatures are expressed by stochastic functions with respect to time. The transient temperature field is determined by solving the nonhomogeneous heat conduction problem in a multilayered plate with piecewise linear nonhomogeneous thermal conductivity, and different, constant specific heat and density in each layer. Analytical expressions of the response autocorrelation functions for temperature, thermal stress and curvature are derived under the condition that the randomly varying surface temperatures of the laminated plate can be modeled as a stationary random process. Numerical calculations are carried out for a case that the random variation of the surface temperature is a white noise, and the FGM laminated plate is composed of PSZ and SUS 304.

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The thermomechanical properties of polyurethane-shape memory polymer foam were investigated experimentally. The results obtained are summarized as follows. (1) By cooling the foam after deformation at high temperature, stress decreases and the deformed shape is fixed. Stress decreases markedly in the region of temperature below the glass transition temperature T_g during the cooling process. (2) By heating the shape-fixed foam under no-load, the original shape is recovered. Strain is recovered markedly at the temperature region in the vicinity of T_g. (3) The ratio of shape fixity is 100% and that of shape recovery 98%. Both ratios do not depend on the number of cycles. (4) Recovery stress increases by heating under constraint of the fixed shape. Recovery stress is about 80% of maximum stress. Relaxed stress at high temperature is not recovered. (5) The shape deformed at high temperature is maintained for six months at T_g-60 K under no-load without depending on maximum strain, and the original shape is recovered by heating. (6) If the deformed shape is kept at high temperature, the original shape is not recovered. The factors to influence the shape irrecovery are strain, temperature and time during keeping the deformed shape.

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In this paper, the adaptive bone remodeling is simulated by using the cellular automata (CA) method. It is assumed that each cell has a property of Bone marrow, Osteoclast, Osteoblast, Bone cell or Osteoprogenitor cell. Two types of local rule are adopted, that are the metabolism rule and adaptive bone formation rule. The metabolism rule is based on the interactions of cells and the bone formation rule is based on the adaptation against the mechanical stimulus. The history of load and memory of mechanical stimulus are also considered in the local rules. As the simulation model, two dimensional femur model is considered and the adaptive remodeling of the cancellous bone is simulated. As the result, the pattern of distribution of the bone tissue is dynamically adequate and it can be regarded as the trabecula. It is shown that the CA method is one of the simulation method to express the adaptive bone remodeling.

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In order to investigate the effect of the opening rate and the vein angles on the unfolding manner of corrugated tree leaves, five paper models with various vein angles were considered. By using vector analysis, a series of numerical simulations for the unfolding of corrugated tree leaves was carried out. The midrib extension of Monarch birch leaves was also measured as an example of corrugated tree leaves. It was found that the extension rate of midrib is very small at an initial stage of unfdlding and then it becomes almost constant. From the simulation, it was obtained that the unfolding of leaves with constant kinetic energy makes the total kinetic energy minimum and gives a similar midrib extension pattern to the pattern of a real Monarch birch leaf.

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The residual stress in thin films composing metal oxide semiconductor field emitter transistors (MOSFETs) was quantified, and a finite element method (FEM) based on the residual stress was proposed to predict stress in a scaled-down MOSFET which consists of a variety of thin films. A numerical analysis of process-induced stress in 130-nm-technology node MOSFETs was also carried out. The strain in the Si area in an actual MOSFET was measured by convergent-beam electron diffraction (CBED) and was compared with the FEM results to verify the validity of the FEM methodology. The FEM analysis results showed that (1) the magnitude of the compressive strain in the channel area increases as the source/drain length is reduced, (2) salicide reduces the magnitude of the compressive strain in the channel area, and (3) depositing tensile-stress SiN film in the sidewall spacer effectively reduces the channel strain. From a comparison of the FEM and CBED results it was found that although differences in the strain values obtained by these two methods are recognized, the results for both methods are in good agreement with regard to the shape of the strain distribution.

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Elastic interaction between bolts occurs in pipe flange connections during not only the bolt assembly process but also the disassembly process. In this study, the mechanical behaviors of pipe flange connections during the disassembly process have been systematically examined by using finite element analysis. As a result, it is shown that the maximum value of bolt preload during the bolt removing processes increases as the rating class and nominal size of pipe flange increase. The effects of the bolt removing sequence are also analyzed in order to estimate the redistributions of bolt preloads and the variations in contact pressure distributions on the gasket bearing surface. Furthermore, it is simulated how a pipe flange connection behaves when the clamping forces of some bolts are lost due to failure or loosening.

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The objective of this investigation is to study the effect of non-woven carbon tissue (NWCT) in order to fundamentally understand the impact damage mechanism of hybrid composites with NWCT. Damage mechanism of of hybrid composites was investigated under a quasi-static indentation loading condition with a steel ball as an indentor. Four kinds of cross-ply laminates were studied; i.e. CFRP laminates ([0₅/90₅/0₅] and [0₃/90₃/0₃/90₃/0₃]) and hybrid laminates ([0₅//90₅//0₅] and [0₃//! 90₃//0₃//90₃//0₃]). Here, the symbol "//" means that the NWCT layer is located at an interface between the CFRP layer interfaces. Under the same condition of the indentation energy, the total delamination area of the [0₅//90₅//0₅]hybrid specimen was about 56% smaller than that of the [0₅/90₅/0₅] CFRP specimen, and also the [0₃//90₃//0₃//90₃//0₃] hybrid specimen was about 38% smaller than that of the [0₃/90₃/0₃/90₃/0₃] CFRP specimen. The mechanism of the NWCT interleaving's effect was clarified based on the observation of damage on the specimens' crosssections cut after testing. It was found that the Mode II interlaminar fracture is predominant in the delamination by the indentation loading.

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The buckling characteristics of straight SMA (shape memory alloy) columns were investigated in this study. A parameter called anti-buckling capability was introduced and used to judge the stability of SMA columns under axial compression. The anti-buckling capability of SMA columns with different lengths and axial loads were calculated using a simple method. It was found for all considered lengths of columns that with the increase of axial load the anti-buckling capability decreases to a minimum value first, increases again to a maximum value and at last decreases monotonically to negative. This special anti-buckling capability versus axial load curve of SMA columns is due to the special non-linearity of stress-strain curve of the SMA. The anti-buckling capability at the minimum point can be either positive or negative depending on the length of a column. Since a SMA column buckles at the smallest value of the axial load, at which the antibuckling capability becomes negative, the sign of the anti-buckling capability at the minimum point of the anti-buckling capability versus axial load curve is critical to the buckling load of column. If the anti-buckling capability at the minimum point is negative, the column buckles at a significantly low axial load. However, the absolute value of the negative anti-buckling capability is relatively small and it can easily be changed to positive by very simple strengthening so that tthe buckling load of the column can be significantly increased.

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Thermal cycle tests of thermal barrier coated type 304 stainless steel were conducted. 8 mass% Y₂O₃-ZrO₂, Al₂O₃, CoNiCrAlY, NiCr coatings were used for the thermal barrier coatings (TBCs). Surface strain behavior during the thermal cycle test was measured using the laser speckle strain! displacement gauge (SSDG) in order to examine the delamination damage process. Surface strain was found to decrease when interface delamination occurred. Fatigue processes were discussed with the results of both surface strain measurement and microscopic observation of the specimen. Cracking occurred in ceramics layer and the crack grew parallel to the interface between the ceramics layer and the bond coating layer in the ceramics layer near the interface. The number of cycles to delamination decreased with increasing of the maximum temperature and hold time at its temperature. LPPS bond coating was found to be effective in extending the thermal cycle fatigue life of thermal barrier coated material.

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The three dimensional theoretical solution of a concentrated tangential force on the free surface of a coating material is deduced in detail, by introducing the infinite mirror points of the load point, and applying the Dirichlet's uniqueness theorem. The deduction is based on the basic equations of the Papokovitch's formula for three dimensional elastic problems. It is found all the harmonic stress functions corresponding to the infinite mirror points, which satisfy the continuous interface conditions and the free boundary conditions, can be deduced from the fundamental solution of a concentrated shear force at the free surface of a half infinite homogeneous solid. It is also found that only the stress functions corresponded to the first several mirror points can give the accurate enough solution, by comparing with the finite element analysis results. It is also found that the effect of material constants is quite complicate, and can not be described by only two Dunders' parameter. This theoretical solution can also be applied to any bonding dissimilar material with free surface parallel to its interface.

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In this report, the new method of topology optimization technique which is able to deal with the three dimensional structure with constant cross section is described. In actual design field, the structure with constant cross section is widely adopted because of manufacturing restriction and efficient design and maintenance. A key technology is to form a longitudinal group by collecting finite elements along the sweeping curve, and the structure is constructed with these groups. Since the design variables are allocated to each group instead of to each finite element, the total number of design variables is drastically reduced. Illustrative examples are shown and the effectiveness of the proposed method is discussed.

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Authors have been reported in previous paper that the S-N characteristic of high carbon-chromium hearing steel shows the "Duplex S-N Curve" which consists of two different S-N curves corresponding to the fracture modes, such as surface and internal failure mode in wide stress amplitude range. It is important to clarify the damage mechanisms under varying amplitude load cycling for the metals having quite different fatigue characteristics. In this study, fatigue behavior under high-low and low-high two-step loading fatigue tests was investigated. From the experimental results, the Palmgren-Miner linear cumulative damage rule was applicable for a bilevel loading sequence of which failure mode is same in the S-N curve. However, in case that the failure mode is different in each step amplitude loading, the problem was not quite simple and the linear-cumulative damage rule was able to apply only after obtaining the fracture mode at the second step amplitude loading. And also, it was found from the two-step loading fatigue tests that the granular-bright-facet (BCF) around a nonmetallic inclusion forms at an early stage of fatigue process.

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Pulsed holographic microscopy is applied to take photographs of rapidly bifurcating cracks in PMMA plate specimens. The cracks are of the opening mode and propagate at a speed more than 600 m/s. The photographs are simultaneously taken on the both side of the specimens about 10 μs after bifurcation. The photographs show that, in many cases, the bifurcated crack's shape on one side of a specimen is apparently different from that on the other side of the specimen. Even in the case of cracks that have similar shapes on the both sides of specimens, the crack shapes are different near the bifurcation points on the both sides of the specimens. These facts indicate that the rapid crack bifurcation in PMMA is three dimensional phenomenon. Also shown is the example that two crack branches have different crack opening displacements. It means that the bifurcation of the crack was asymmetric with respect to the line along the mother crack.

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