Mechanical property of bone is inhomogeneous and the range of its variation depends on individual. It influences on the total stiffness and stress condition of the bone. Therefore, mechanical analysis considering inhomogeneous property of the bone is necessary for patients oriented evaluation of bone in clinic. If the finite element method is used, the inhomogeneous analysis is possible by giving a material property to an element one by one. So that, extreme fine meshing is required for precise analysis of bone with inhomogeneous property. In this study, we improved the “ADVENTURE system”, which had developed by JSPS (Japan Society for the Promotion of Science) as a large-scale finite element analysis system, to be applicable to stress analysis of inhomogeneous bone problems. We applied the improved program to a composite beam model with graded material property and ensured is validity by comparing between the theoretical and calculated results. Furthermore, it was applied to stress analysis of proximal femur based on CT images and its efficiency was discussed.

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Individual stress analysis of a bone based on X-ray CT data provides useful information for diagnoses and medical treatments. Many studies on the stress analyses have been reported, however little attention has given to partial volume effect in the CT data. The partial volume effect may cause lower reliability in the analytical results because CT values on a bony part are changed by the effect. This paper proposes a method to correct CT values influenced by the partial volume effect. The correction method transforms CT values using a regression curve of an exponential function. The validity of the proposed method is confirmed by use of CT images of femurs of a pig and human mandibles.

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This paper is concerned with an individual finite element modeling system for femur and biomechanical evaluations of the influences of loading conditions, bone shape and bone density on risks of hip fracture. Firstly, a method to construct an individual finite element model by morphological parameters that represent femoral shapes was developed. Using the models with different shapes constructed by this method, the effects of fall direction, posture of upper body, femur shape and bone density on hip fracture were discussed. The results showed that the fall direction influences the fracture type but its effects depend on the sex. A backward posture increases a risk of a cervical fracture. Diameter of femur neck showed significant influence on fracture type. Though osteoporosis does not cause a fatal decrease of bone strength, it increases the risk of hip fracture.

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In order to devolop the total hip prosthesis design fitted for Japanese osteoar throsis (OA) femurs, the authors analyzed their canal shapes geometrically. The canal shapes of Japanese OA femurs were classified into three types, and prosthetic stem designs corresponded to each femur type were proposed in our previous paper. 3-dimensional CAD models of the proximal femurs based on computed topographic (CT) images were used in the classification and the design. Shape accuracy estimation of the CAD models is required to establish the classification. In this paper, femur CAD models were constructed from not only the CT Images but real images of sliced femur specimen, and proximal canal shapes of the models were compared each other in same coordinate. Shape differences of the models were estimated quantitatively, and accuracy of the model based on CT images was entablished. Furthermore, a prosthetic stem design was improved to increase fill rate of the stem to femoral canal. Finite-element analysis of proximal femur with the improved prosthesis was carried out. Stress distribution of bone around the stem was compared between case of the improved and previous design. Effect of increasing the canal fill ratio on the stress distribution was discussed.

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In order to prevent hip fracture among the elderly, hip protectors are expected to be one of the most effective methods. In the present paper, we performed dynamic finite element analyses to elucidate the mechanism of hip fracture prevention by hip protectors and to suggest a design guide. Firstly, we constructed an elderly Japanese female finite element model. The femur, soft tissue of thigh and the other body segments were incorporated into the model. Then various types of protectors were modeled, and the analyses to simulate fall were carried out by using them. The results of the simulations showed that a hollow structure pad was effective for fracture prevention, and that the mechanism of fracture prevention is not only the attenuation of impact by hip pad, but also the reduction of load on the greater trochanter due to load distribution to the surrounding soft tissue.

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In bone tissue engineering, a porous scaffold plays an important role as a functional substitute to provide a mechanical load-bearing construct and to direct new bone formation. Bone regeneration process consists of scaffold degradation and bone formation, in which scaffold-bone construct needs to keep a desired mechanical function with well-organized functional transition between two components. Therefore, a design of biodegradable porous scaffold needs to be evaluated based on functional change of the structure in bone regeneration process. In this study, a framework to design a porous scaffold is proposed using a computational simulation for bone regeneration. First, rate equations for scaffold degradation and new bone formation were proposed, and computational simulations for bone regeneration was conducted using a simple scaffold stucture. As a result, it was demonstrated that the proposed simulation method could express the bone regeneration process in which new bone formed with increasing mechanical function while scaffold degraded with decreasing its load-bearing function. Second, a new design method for porous scaffold structure using a bone regeneration simulation was proposed. As a design objective function, difference in strain energy between bone-scaffold construct and ideal bone in regeneration process was used, and optimum design valuable that minimize the objective function was searched by simulating bone regeneration process. Through these simulation studies, the proposed method is expected to have a potential for the actual porous scaffold design.

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As an effective approach, biphasic theory has been successfully applied to mechanical modeling of hydrated soft tissues. In this research, by virtue of weighted residual method, a nonlinear finite element formulation based on biphasic theory was developed by adopting solid phase before deformation as reference configuration. Although, in biphasic theory, both solid and fluid phases are assumed to be intrinsically incompressible, the structural compressibility of solid structure in biphasic mixture has to be taken into account to avoid obtaining unrealistic results. This requirement can be satisfied by introducing to the elastic potential an additional term accounting volume change of solid structure. Furthermore, viscoelastic behaviors of biphasic mixture were investigated by comparing analytical solutions of confined compression of biphasic model and uniaxial compression of Voigt viscoelastic model, and also, the results of finite element analysis for two types of unconfined compression of biphasic model. It is found that the similarity between classic viscoelastic model and biphasic mixture exists under specific conditions but the mechanical behaviors are significantly influenced by the boundary conditions and deformation.

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By regarding hydrated charged soft tissues as a fluid phase composed of water, movable electrolytes, and a solid phase mainly composed of collagen fibrils and negatively charged proteoglycans, triphasic theory has been proposed to understand the coupling mechanisms between mechanical, chemical and electrical phenomena in hydrated charged soft tissues. In this research, a finite element formulation based on triphasic theory for large deformation analyses was developed by introducing a reference configuration defined at undeformed solid phase. The weak form was obtained by introducing weighted residual method. Numerical results of confined compression problem were presented to demonstrate the mechanical and electrochemical behavior of triphasic structures. The effects of mechanical load on the stiffness of tissue, fixed charge density, ion concentration and electric potential were also exemplified.

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Recently, it is reported that risk of rupture of aneurysms is further less than risk of surgical complications. Therefore, to avoid unnecessary surgical operations, prediction of rupture of aneurysms is necessary. Because wall shear stress is known to play an important role for a vascular disease, the authors have investigated the relationship between wall shear stress and cerebral aneurysms. In this paper, numerical fluid-structure interaction analyses are performed to investigate influences of wall deformation on hemodynamic factors. The results show several patterns of arterial wall deformations and their influences on blood flow behavior and hemodynamic factors.

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We have developed a numerical method on Cartesian grid for image-based blood flow simulation. Cartesian grid has advantages for grid generation for the complex and moving boundary problems. Interpolated Differential Operator (IDO) scheme with Local Mesh Refinement method are effectively introduced for blood flow simulations. In order to simulate flow interacting with elastic vessel on Cartesian grid, a new technique INTERGRID has been developed and it is shown that the simulation of fluid-structure interaction problems that structure does not displace over the resolution of grid is carried out.

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In the present study, an image-based simulation system has been developed in order to investigate the relationship between vascular morphology and cerebral hemodynamics. The simulation system consists of medical image-based geometric modeling, grid generation, finite element fluid simulation, and scientific visualization. The paper has developed an effective smoothing method for over-tessellated polygonal surfaces by combining polygon reduction and smoothing techniques. The simulations are conducted for 19 cases of the bifurcation segment of middle cerebral artery branches. The multiple regression analysis is performed based based on 19 cases to examine the effects of cerebrovascular morphology on wall shear stresses. As a result, diameter of MCA, ratio of diameter of branching artery to that of MCA, and bifurcation angle between MCA and the branching artery are important morphological factors in determining the maximum wall shear stresses.

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The arterial branch from abdominal aorta to renal artery is reported to be one of the prediction sites of atherosclerosis, which can either block up the blood flow into the kidney, or, result in the formation and the break-down of rental thrombosis. Quantitative prediction of the relationship between hemodynamics and rental diseases is therefore of great importance and it is thought that anatomic geometry of the rental arterial branch may play a key role in the set-on and the development of rental atherosclerosis. A numerical analysis has been conducted for the rental arterial hemodynamics. We constructed a realistic geometric model for the rental arterial branch based on CT image data, using an integrated method combining an automatic shape-extracting method and an automatic grid-generation method. A recently developed in house NS solver was employed, that includes the multi-block method, the overset grid method, and the one-dimensional modeling method for arterial tree which can provide realistic physiological boundary conditions. Results are presented of velocity vectors and wall shear stresses at the rental arterial branch, which points to a close relationship between the fluid dynamic structures and the rental atherosclerosis.

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Computational fluid dynamics of intraventricular flow during diastole was carried out to investigate the relationship between a left ventricular (LV) diastolic function and a color M-mode Doppler (CMD) echocardiogram. Results showed that a vortex ring, which was generated around a ventricular filling flow, locally increased velocity of the inflow due to a vena contracta effect and whereby created a maximum velocity point (MVP) there. Growth of the vortex ring with a ventricular expansion shifted MVP towards the apex. Although this occurred regardless of goodness of LV diastolic function, growth of the vortex ring was decelerated or reduced with deterioration of LV diastolic function, which resulted in a decrease in traveling distance and speed of MVP. It was reflected to shortening of an aliasing area in CMD echocardiogram. In a physiological range, a good correlation was found between traveling distance and speed of MVP and LV diastolic function. These findings validated the utility of the CMD echocardiographic technique for assessing LV diastolic function.

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A finite element analysis using structural optimization method was performed to simulate the remodeling of bovine aortic endothelial cells (BAECs) under flow condition. BAECs showed marked elongation and aligned in the flow direction by exposing to a steady shear stress of 2 Pa for 24 h. An atomic force microscope (AFM) system was used to obtain cell surface topography, showing that the cell height decreased significantly from 2.8±1.0μm to 1.4±0.5μm with exposure to fluid flow. The fluorescent images of cells stained by rhodamine-phalloidin showed that control cells exhibited dense peripheral bands of actin filaments, while sheared cells exhibited centrally located actin stress fibers parallel to the flow direction. In the analysis, the two-dimensional mesh was generated based on the cell surface data measured by AFM and then elastic modulus of each element was changed in accordance with an object stress, together with update of cell shape. Numerical results showed that the cell height decreased with fluid flow and the higher elastic modulus appeared in the upstream region of the nucleus at the final step, which may correspond with cytoskeletal structure. The present analysis should be effective for elucidating the remodeling of endothelial cells.

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This paper describes fundamental investigation to apply penetration of micro jet to disintegrate microcapsules in Drug Delivery System (DDS). Deformation processes of a bubble near curved elastic wall by shock wave observed by optical shadowgraph method using a high-speed camera. It is found that a bubble generates micro jet toward a wall and opposite side whose characteristics are affected by wall elasticity, wall curvature and a position of an initial bubble. Maximum velocity reaches 77 m/s, which corresponds to 28 MPa as water pressure. Changing wall elasticity, wall curvature and an initial bubble position can control penetration force by micro jet.

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Quantitative evaluation of level set contour segmentation method applied to three dimensional images detecting image edge based on threshold is discussed. The integration of two popular level set methods, i.e., reinitialization method and geodesic active contour method, leads to success in development of robust, with high accuracy, level set based segmentation method. The applications of this method to both synthetic and clinical medical images are shown. Accuracy of the propose method, in the view of both averaged contour location and standard deviation of curvature in the vicinity of contour, calculated using obtained level set function is discussed.

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A material test system combined with X-ray computed tomography (CT) is newly developed for material characterization of biological tissue in non-invasive manner. An identification method is investigated for internal displacement field of inhomogeneous body through the CT images from the system. Two voxel models are constituted by laying up thicken pixels of the cross-sectional tomograms taken under unloaded and loaded conditions. Representing the displacement field in terms of the Fourier series, we pose an inverse problem to identify unknown Fourier coefficients by using unloaded and actually loaded voxel models. A virtually deformed voxel model is embodied through an image processing technique to transform the unloaded voxel model via the tentative Fourier series. An error function between actually loaded and virtually deformed voxel model is defined by the voxel values, which indicate brightness of voxels. The error is minimized with respect to unknown coefficients by means of the SCE-UA method (Shuffled Complex Evolution Method Developed at the University of Arizona). The validity of the proposed method is demonstrated through an experimental example.

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A defect inspection and sizing technique for the corrosion of thin-walled pipes with circumferential SV waves is extended to precise sizing of defects at inner surface. The conventional angular transducers placed on the outer surface of pipes excite SV waves of different refraction angles depending on the incident position. Thus, refracted SV beams diverge markedly, which results in non-uniform distribution of the wave amplitude throughout the cross section of the pipe. In this study, a special angle beam transducer that excites SV wave of the same refraction angle in the pipe wall is designed and applied to sizing of inner axial defects. With this transducer, the wave amplitudes passing through the defects are nearly proportional to the defect depth with a fixed width. The transducer also excites circumferential guided waves, therefore, the modes and group velocities are measured with a laser ultrasonic detector of an ultra broadband. The use of the circumferential guided waves of various modes gives us more information of defect features.

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Strength degradation of pristine silica optical fibers immersed in water at stress-free condition, i.e., “aging”, is believed to result form the roughness development of corroded glass surface. This study has investigated in detail the geometrical properties of the roughness development. High-resolution topography was obtained by atomic force microscopy for aged samples. Simulations of surface roughening were also conducted by means of stochastic differential equation for heterogene-ous dissolution of silica. The experiments and simulations suggested that (1) the corroded surface has self-affine geometry, where the Hurst exponent is kept to 0.85 during the roughness development, (2) the roughening is caused by fluctuations of dissolution rate of silica, and (3) the roughness increases in a power law of aging time with an exponent of 0.8. Boundary element stress analyses for the self-affine surface was also carried out to obtain a relationship between the roughness and the strength, where the surface process layer was introduced to prevent difficulties concerning on stress singularity and the stress concentration factor was adopted as a fracture parameter.

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The fatigue strength of eutectoid steel wires was investigated by rotating bending tests under various corrosive environments. The high cycle fatigue strength was remarkably lower in air at relative humidity of 70% as compared with those at 30 to 50% and even in distilled water. Although the strength in NaCl aqueous solution was lower than that in distilled water, no appreciable difference was found among the NaC1 solution with concentration of 1% and 0.1% and also in the solution analogous to that in the tire absorbed solution. Although the effect of dissolved oxygen concentration in the tire absorbed solution on the fatigue strength was small, that of the hydrogen ion concentration was large in the region of PH7 to 10, slightly smaller at pH 2 and no effect at pH 12. Fractographic observations revealed that pitting corrosion is dominant in pH 7 to 10, while the general corrosion is dominant in pH 2.

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Pulsed holographic microscopy is applied to take photographs of a rapidly bifurcating crack in a PMMA plate specimen. The crack is the opening mode and propagates at a speed more than 600 m/s. Two photographs are simultaneously taken on the both sides of the specimen about 15μs after bifurcation. Crack opening displacements, CODs, of branch cracks are measured from the photographs on both specimen surfaces. It is found that one of the two branch cracks appears as a surface crack. Also found is that the two branch cracks propagate at the same speed even though one of the two branch cracks is not linked to the mother crack on one side of the specimen. And the CODs of the branch crack that didn't perfectly connect with the mother crack become smaller near the bifurcation point. This fact indicates clearly that the rapid crack bifurcation is three-dimensional phenomenon.

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The effect of moisture absorption on the static and fatigue properties for plain woven CF/epoxy composite were examined with changing humidity at each stage ; mixing, lamination, storage and testing stage. The experimental results showed that the static strength and fatigue life of plain woven CFRP were significantly improved when the material was protected from moisture absorption during the mixing and lamination stage. This prevention improved the resistance of crack growth in DCDC test and interfacial shearing strength at the interface between fiber and matrix in micro droplet test. Such improvement of fiber/matrix interfacial properties contributed to the enhancement of the static strength and fatigue life of plain woven CFRP.

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The plastic strain range of stress-strain curve during fatigue process was measured for an annealed and rolled carbon steel S 45 C, SUS 304, aluminum, and copper alloys. The plastic strain range was evaluated from the movable dislocation density. It was found that the variation in movable dislocation density was expressed as a function of the number of stress cycles by the logistic curve based on the multiplication and annihilation processes of dislocations. It was concluded that the logistic curve is able to calculate the variation in plastic strain range and also the cumulative damage by taking into account the incubation period of cumulative in dislocation in the initial stage.

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A new formulation for an adhesive force and the penetration depth of an indenter considering surface stresses is presented using the minimum of free energy in the present paper. Surface stresses, are originated from surface energy, are related with a reconstruction of surface atoms. Contact pressure in an adhesion is derived analytically by simplifying the exact formulation of integral equation for the contact pressure. The adhesive force in the present theory includes that of JKR theory, and the method for deducing the relationship between the adhesive force and the penetration depth of the indenter is applied easily for deducing that with a different profile. Surface stresses influence upon the adhesive force just before the detachment between the indenter and a substrate. The adhesive force in the theory is compared with the experiment conducted by the other researchers, and both are well agreed with each other. The formulation for adhesive force and the penetration depth of the indenter in case where the adhesion area is relatively large with the size of the indenter is newly deduced, and the radius of adhesion area estimated by the theory is compared with Rimai's experiment. Both are well agreed with the experimental results.

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Railway vehicle has been required to achieve higher safety during its collision. In order to protect passengers during collision, energy absorber for crashworthy structure is developed using annealed aluminium alloy hollow extrusion. At first, to assure characteristics of annealed aluminium, tensile strength test and quasi-static crash test using column was carried out and these results revealed that annealed alloy has good characteristics for energy absorber. Second, box-shaped energy absorber was designed and quasi-static crash test was carried out. To predict crash characteristics of the absorber, numerical simulation was carried out in parallel to the experiment. As a result, load efficiency of the box energy absorber achieved 82% and numerical simulation had a good agreement with the results of experiment in deformation and crash characteristics. From above results, railway vehicle's characteristics in crashworthiness can be achieved higher performance with the absorber developed in the paper.

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