Formulations are conducted to analyse the effect of flexible flagellum of swimming bacteria. In the present model, the single-flagellated bacterium is assumed to consist of a rigid cell body of the prolate spheroidal shape and a flexible helical flagellum. The resistive force theory is applied to estimate the forces exerted on the flagellum. The torsional as well as the bending moments determine the curvature and the torsion of the deformed rod according to the Kirchhoff model for elastic rod. The unit tangential vector along the deformed flagellum is calculated applying a generalized type of the Frenet-Serret equation, and also the deformed shape of the flagellum is obtained.

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In order to understand the process of the shape change of a red blood cell (RBC), a mathematical model of an RBC was developed based on the energy principle. The model was constructed by dividing the whole membrane of an RBC into small triangular elements having their own resistances to the changes in the stretch of each edge, the contact angle between the elements, and the area of each element and the whole membrane. The shape of an RBC with a given volume was determined by moving the mass points assigned to each node of the elements so as to minimize the total elastic energy of the membrane generated by these elastic resistances. It was shown that a spherical RBC transformed itself into a biconcave discoid shape and a cupped shape depending on the elastic resistance for shear deformation, and a spiculate shape temporarily when the volume was suddenly decreased. From these results, it was confirmed that it was possible to simulate various shape changes of an RBC using our model developed in the present study.

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Flow-induced mechanical stress affects morphology of endothelial cells. The morphological remodeling of the cells is adaptive response by the mechanical stimulus. To address the mechanisms for the response, it is necessary to examine how the mechanical environment influences the adaptation process. Therefore, we tracked the same group of cultured endothelial cells during flow exposure, and measured surface geometry of the cells by confocal laser scanning microscopy. Flow field near the measured cell surface was then simulated by computational fluid dynamics, and the shear stress distribution on the cell surface was determined. When the cells, which were polygonal without alignment at the beginning of the flow exposure, elongated and aligned with the flow direction, mean shear stress of the cell group was decreased with time course. However, there were some cells on which mean shear stress per cell was increased, and morphological change of each cell was not always adaptive. The results show importance of interaction with surrounding cells for the adaptive response as cell layer.

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Effects of initial stretch conditions of aortic wall segments on shape and cytoskeletal structure of endothelial cells were studied in static culture conditions. Considering the stretch conditions in vivo we cultured the aortic wall segments in six different situations, mostly for 72 h (maximum up to 216 h). Changes in cell shape and the cytoskeletal structure were observed by a light microscope and a confocal laser scanning microscope. It was found that the initial shapes, that is, flat or cylindrical, and the initial stretch conditions of aortic wall segments significantly affected the changes in cell shape and cytoskeletal structure by culture duration. Especially the effect of the circumferential strain was quite large. The importance of mechanical environment for endothelial cells was pointed out to keep their configuration.

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It has been suggested that smooth muscle contraction alters intramural strain distribution in the artery wall. To examine this hypothesis, change in in vivo strain distribution following smooth muscle contraction was compared between elastic and muscular arteries. Tubular and short ring-like segments of common carotid and femoral arteries were excised from rabbits as an example of elastic and muscular arteries, respectively. Pressure-diameter relationship of the tubular specimens and opening angle of the ring-like segments were measured under various levels of smooth muscle contraction to calculate in vivo strain distribution in the wall. The distribution became uniform in both arteries at a certain level of smooth muscle contraction. The level of the contraction was lower in the muscular artery than in the elastic artery.

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The purpose of this study was to establish a method for measuring the circumferential difference in the deformation of artery walls during pressurization. Thoracic aortas of Japanese white rabbits were stretched to their in vivo length and pressurized to 80 mmHg in a physiological saline at room temperature. Four 5-mm long small needles (φ0.4 mm) were stuck perpendicularly into the aortic wall at equal intervals on a circumference. Displacement of the needles during pressurization from 0 to 200 mmHg was observed from longitudinal direction with a CCD camera and laterally with two cameras placed in an opposite direction across the aorta. The images of the cameras were used to identify the points at penetration of each needle and to obtain circumferential length between the needles. Circumferential stretch ratio was significantly higher in the ventral side than in the dorsal, indicating that mechanical heterogeneity exists even in healthy arteries. The present method may be useful for further understanding of vascular mechanics.

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The effects of the long-term injection of a quite small amount of a polymer substance, Separan, on blood viscosity were studied in detail using 24 Japanese white rabbits. The same effects for rabbits fed on a cholesterol-rich diet were also studied. The rabbits were divided into 4 groups: Control group (CO), Separan group (SE), cholesterol group (CH), and cholesterol-Separan group (CS). Every rabbit were given the same amount of diets. The rabbits in the SE and CS groups were injected intravenously a small volume of Separan solution 3 times a week to maintain its concentration in plasma at approximately 60 ppm, while the rabbits in the CO and CH groups were injected the same volume of saline. Blood was sampled at regular intervals to monitor the changes in blood compositions. Blood viscosity was measured at 20 weeks. It was found that blood viscosity and it's non-Newtonianity was significantly lowered by injecting Separan. Red blood cells decreased by injecting Separan, while other blood compositions didn't change drastically. These results indicate that the alteration of blood viscosity can achieve in vivo by the oresent method, in which Separan affects blood viscosity by lowering hematocrit in either case of diet feeding to rabbits.

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Flow simulation is useful for understanding and quantifying fluid phenomena which arise in the circulatory system. The blood flow in vivo, however, is complicated because of its unsteadiness and complex viscoelastic property of blood vessel wall. Conventional one-dimensional models do not involve the effects of the unsteady viscousity and the viscoelastic behavior of the arteries which are important in analyzing the pulse wave propagation along the arteries. We thereby proposed a one-dimensional model which can accurately calculate the effect of the unsteady viscosity and using tube law expressed in the generalized viscoelastic model of arterial wall, aiming at performing numerical simulations of blood flows in the systemic arteries. The simulated results show good agreement with the measurements of pressure waves in a silicone rubber tube and indicate that the influence of the "unsteady viscous resistance and the viscoelasticity of the wall is significant and hence should be accounted for even in the one-dimensional model.

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To investigate the effects of hemodynamic factors on the development of atherosclerosis and intimal hyperplasia, we carried out a computer simulation of the adaptive changes in the thickness of the wall of a human coronary artery with a multiple bend. This was done by assuming that only the arterial wall where wall shear stress (WSS) is lower than a certain threshold value increases its thickness, and shifting the luminal surface of the vessel step by step in the direction normal to the wall based on the value of WSS obtained by the calculation of blood flow through the artery under conditions of a steady flow. It was found that thickening of the vessel wall occurred and progressed at the inner wall of curved segments where WSS were low in the initial state. However, the final thickness of the wall at the completion of adaptive changes was not determined by the value of WSS in the initial state, but was determined as a result of the interaction between the change in vascular geometry caused by the thickening of the vessel wall and the flow affected by it.

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A concern about fatigue has been toning up these days. Although the evaluation of muscle fatigue has been developing based on physiology lately, these are invasive ones. Muscle fatigue accompanies the change of its biomechanical characteristics in general. The authors examined the relation between muscle fatigue and biomechanical characteristics (visco-elasticity) with a biomechanical impedance measurement system non-invasively. First, it was confirmed that our system could detect the visco-elasticity of muscle with experimental models. Next, isometric contraction was applied to a subject's forearm with 10 and 15% of maximum voluntary contraction (MVC) for a certain constant period until one got fatigued. As a result, the elasticity decreased and the viscosity increased under contraction. The tendency was the opposite with no load. The amount of load did not affect the tendency but the fatiguing speed.

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It is difficult to directly measure the muscle force in living subjects. Since many muscles act cooperatively in a human shoulder motion, computer simulation will be useful to analyze the muscle force. This paper describes a method of numerical analysis of muscle force during shoulder abduction. Three-dimensional skeletal muscle model was constructed from normal volunteer's computed tomography. Muscles were modeled by each straight line vector from the insertion to the origin. Because muscle forces could not be calculated from only the equilibrium equations of force or moment, the optimization method using SQP method was applied to this analysis. The objective function was defined as the square sum of the muscle force divided by the physiological cross sectional area. To determine the vector of the muscle which originated from the wide area, the optimization method was also used to select the adequate origin point for each abduction angle. The results of the analysis showed qualitatively good agreement with the results of electromyography.

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The purpose of this study is to evaluate correlation between extracellular matrix and mechanical properties of articular cartilage. Collagenase and hyaluronidase were used to degrade colloagen fibril and proteoglycan respectively. Indentation test, dynamic visco-elasticity measurement and tensile test were carried out to evaluate mechanical properties before and after the enzyme treatment. Acoording to indentation test, maximum strain was increased and recovery ratio (=recovery strain/maximum strain) was decreased with treatment time for both enzyme treatments. There were no significant differences in tensile strength before and after the hyaluronidase treatment, where as the strength was decreased by the collgenase treatment. Result of dynamic visco-elasticity measurement showed that peak value and peak frequency of tan δ were shifted to a higher value with treatment time after the hyaluronidase treatment. These results suggest that compressive modulus and visco-elastic properties are much affected by collagen-proteoglycan network and tensile strength is affected mainly by collagen fibers.

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Damaged articular cartilage has a very limited capability of self-healing. The need for improved treatment of cartilage defects, which involve over 1 percent of population in Japan, has motivated research to create regenerated cartilage. Regenerated cartilage is engineered by culturing autologous chondrocytes on biodegradable scaffolds. We studied changes in biomechanical property, especially dynamic visco-elasticity during 6 weeks of in vitro culture. The results suggest that the ability of water holding was increased by new extracellular matrix (ECM) synthesis during 4 weeks of in vitro culture, although the ability of solid matrix (ECM and scaffold) to resist compression elastically was reduced.

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Poly (lactic acid) was molded under four different kinds of condition to obtain samples with different microstructures. A single crystal was not observed in the specimen molded at 0°C. The size of spherulites became larger with increase of molding temperature. The density of spherulites increased with increase of molding time. Mode I fracture toughness, K_IC was measured at a static (1 mm/min) and an impact loading rate (1 m/s). K_IC became lower with increase of degree of crystallization at the static loading rate. This is mainly due to suppression of craze formation in the vicinity of crack-tip. On the other hand, at the impact loading rate, K_IC increased with increase of degree of crystallization. Thus, the results showed that crystallization has significant influence on K_IC, and its effect on the static K_IC was different from that on the impact one. Relationship between fracture toughness and fracture micromechanism was discussed on the basis of the results of fracture tests and microscopies.

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In this study, fatigue experiments of stress ratio 0.1 were conducted using the bovine-cortical-bone specimen under stress frequency of 0.3 and 20 Hz. It was clarified that the fatigue lives of bovine bone increased with an increase in the stress frequency, however the rate of fatigue crack growth lowered with the stress frequency. By considering the crack growth behavior during the fatigue process, computer simulation of the tensile fatigue process of the bovine bone was conducted to clarify the fatigue mechanism of the bone. The obtained S-N curve from the simulation agrees well with the experimental one, and leads the different fatigue lives with the stress frequency.

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Reliable stress analysis of a bone requires not only precision in shape of the finite element model but also proper setting of material constants for the model. This paper deals with estimation of Young's modulus to the finite elements based on the X-ray CT data. At first, partial volume effect on the modeling was discussed by analytical and experimental ways using acrylic cylindrical specimen. Second, a simple correction method which transforms the CT value around border of the object was proposed. In this correction method, CT value larger than the threshold value was pulled up to the target CT value. To confirm validity of the proposed correction method, a load test and stress analyses using a dry mandible were performed. Analytical displacement between condyles and maximum principal strains were well coincided with these of experiments.

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It is known that the metallic oxide film of bearing surfaces markedly affects the wear process. Influence of dissolved oxygen in the lubricating liquid containing principal constituents of synovial fluid on wear characteristics of Co-Cr-Mo alloy used in a metal-on-metal artificial hip joint has been investigated by using a pin-on-plate wear machine. Concentration of the dissolved oxygen was adjusted by N₂ injection in the enclosure which covered pin and plate. It was observed that the decrease in oxygen concentration, which was similar to be in vivo, caused the wear to decrease. The material properties of the bearing surface were controlled by the oxygen concentration. The bearing surface tended to be smooth in lower oxygen concentrations. The friction coefficient increased in the low oxygen concentration. The experimental results indicated that the decrease in oxygen concentration made the adhesion between bearing surfaces increase. The increase in adhesion leads to a high frictional force. The high adhesion and frictional force brought about work hardening and fine structure of the bearing surface, so that the wear was decreased.

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Wear debris of ultra high molecular weight polyethylene abbreviated as UHMWPE were clarified to be a major cause of osteolysis. So the wear rate evaluation of UHMWPE has to be performed in the research of artificial joint using UHMWPE. But wear evaluation of UHMWPE requires scrupulous procedure. As the wear rate of UHMWPE is strongly correlated to the coefficient of friction, this study was designed to assess a change of the coefficient of friction for various contact conditions. It was found that the contact condition strongly affected the coefficient of friction. Furthermore contact temperature was measured by means of the infrared radiometric microscope and was compared to the lubricant temperature. Temperature rise up to about 12°C was observed in 30 minutes under a condition of the mean contact pressure p = 12.7 MPa and sliding speed 50 mm/s. There was a linear relation between contact temperature and lubricant temperature.

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Total en bloc spondylectomy is the most efficient surgical treatment to prevent recurrence of malignant vertebral tumors. In this surgery, a tumorous vertebra is totally removed and replaced with a titanium mesh cage filled with bone autograft, and spinal instrumentation is carried out by using pedicle screw system. Two types of reconstruction method are available in clinical use. One is the multilevel posterior instrumentation (MLP), and another is the short posterior and anterior instrumentation (SPA). MLP has posterior fixations using pedicle screws and spinal rods connecting the two vertebrae above and adjacent to the removed bone and the two below the removed. SPA has anterior and posterior fixations in left side at one level above and below the removed vertebra. It is believed that bone fusion and remodeling of the grafting depend on mechanical stress condition, although mechanical stress condition has not been sufficiently investigated. In this study, experiment and analysis of the reconstructed structure were carried out to determine its stress distribution. The main results are as follows: (i) SPA was favorable to reduce stress of posterior instruments; (ii) MLP was advantageous to promote bone fusion between bone graft and vertebra.

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In this study, stress condition of the femur with fixation using the Gamma nail, which is widely used as the intramedullary nail device of trochanteric fracture, is investigated by three-dimensional finite element method. Imitation bone model, which has mechanical properties as same as the human bone, is used to analyze. The stress analysis of the femur before and after the implantation of the nail is carried out in detail. As the results, the stress considerably decreases at the proximal part by the nail insertion, but the stress concentration appears around the nail tip. The stress rapidly increases, when the gap between nail and cancellous bone becomes small. The existence of the locking screw does not affect the stress distribution of the circumference. In the meantime, the stress distribution is considerably similar to the intact bone, when the nail is made of titanium alloy, which has material properties closer to the cortical bone in comparison with stainless steel.

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Temporomandibular joint (TMJ) disorder relates to the biomechanical irregularity of the structual joint components, and the behavior of soft tissue components is considered as a key to understand the biomechanical condition in the TMJ. The configuration of joint components, however, deeply depends on individual patient. In this study, the attention has been focused on the stress and displacement of irregular TMJs with anterior disc displacement (ADD). Using biplane MRI, typical ADD-TMJs of patients have been modeled individually. The stress distribution in ADD-TMJs has been compared with that in normal-TMJs. The parameter study with the elastic modulus has been carried out and revealed that the stress distribution in the TMJ is very dependent on the connective tissue modulus as well as disc modulus in the case of ADD-TMJ, and that the disc displacement due to jaw opening movement depends on disc modulus in normal subjects but depends on retrodiscal connective tissue in ADD subjects.

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We suppose that most organisms have the optimized structures under various environment, but its mechanism has the most complex and many unknown factors. In this paper, we propose that it is useful in engineering to obtain the mechanism of a bamboo structure using the laminate sheet model, through the experiments and the observation of the organizational structure within fibers of a bamboo. Based on the fundamental research of the fiber contents and strength of the bamboo's slices, we could learn how to construct the more fiber or the laminated composite structures by numerical analysis of the elastic-plastic FEM. This paper denoted that it is applicable to obtain the organizational properties of bamboo by the laminate sheet model.

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To evaluate the mechanical strength of fiber reinforced composites it is necessary to consider singular stresses at the end of fibers because they cause crack initiation, propagation, and final failure. To obtained the magnitude of the singular stress, in this paper, an interaction among a hexagonal array of cylindrical inclusions under longitudinal tension is considered. The body force method is applied to a unit cell region; then, the problem is formulated as a system of singular integral equations, where unknowns are densities of body forces distributed in infinite bodies having the same elastic constants as those of the matrix and inclusions. The unknown functions are expressed as piecewise smooth functions using fundamental densities and power series. Here, the fundamental densities are chosen to represent the symmetric strees singularity, and the skew-symmetric stress singularity. Then, generalized stress intensity factors at the fiber end are systematically calculated with varying the elastic ratio, length, and spacing of fibers. The region when the interaction effect is less than 1% is shown in a figure as a function of fiber length.

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This paper deals with a stress concentration problem of an ellipsoidal inclusion of revolution in a semi-infinite body under biaxial tension. The problem is formulated as a system of singular integral equations with Cauchy-type or logarithmic-type singularities, where unknowns are densities of body forces distributed in the r-and z-directions in semi-infinite bodies having the same elastic constants of the matrix and inclusion. In order to satisfy the boundary conditions along the ellipsoidal boundary, four fundamental density functions proposed in the previous paper are used. Then the body force densities are approximated by a linear combination of fundamental density functions and polynomials. The present method is found to yield repidly converging numerical results for stress distribution along the boundaries of both the matrix and inclusion even when the inclusion is very close to the free boundary. Then, the effect of free surface on the stress concentration factor is discussed with varing the distance from the surface, shape ratio, and elastic ratio. Also the present results are compared with the ones of an ellipsoidal cavity in a semi-infinite body.

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In designing web-handling machinery for papers, steel sheets, endless belts, etc., the line management of strips is one of the most important technologies. Since these strips are very thin, they easily walk in the lateral direction when running on rolls, due to the roll misalignment, thickness imperfection and/or heterogeneity of strips and some other reasons. For a narrow strip with an infinitely long span, some researchers have succeeded in analyzing the lateral walking, taking account of the misalignment of a roll. However, for a wide strip with a short span, the infinite boundary conditions for the strip is no longer valid, because the deflections of adjacent rolls strongly affect the deformation of the strip. In this paper, a new theoretical approach for analyzing the lateral walking phenomena of wide strips is proposed, where the deflection of all the adjacent rolls are considered. The effects of the roll misalignment, roll crown, the friction between rolls and a strip, as well as the line tension, to the lateral walking are discussed.

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This paper deals with the stress concentration problem of a hollow circular thick walled elastic cylinder with a semicircular groove under internal pressure. A method of solution is presented for the problem by applying Green's functions for axisymmetric body force problems of a thick plate. The Green's functions are defined as solutions for a thick plate subjected to axisymmetric body forces acting along a circle in the interior of the plate. A principle of the method of solution is to imagine a hollow cylinder with a notch and to distribute axisymmetric body forces in the thick plate so as to satisfy the boundary conditions of the hollow cylinder. The problem is formulated by an intergral equation with unknown functions of body forces. Stress concentrations at the notch are investigated by numerical calculations and stress distributions near the notch and form factors are shown. The maximum stress appears at the bottom of notch or the inner boundary of smallest cross section depending on the inner radius of cylinder and the notch radius.

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The plane strain dynamic singular stress problem for glassfiber reinforced plastics with surface cracks at low temperatures is considered. The layered composite is made of a layer bonded between two layers of different physical properties, and the surface layers contain the cracks normal to the interfaces. Laplace and Fourier transforms are used to formulate the problem in terms of a singular integral equation. The singular integral equation is solved by using the Gauss-Jacobi integration formula. Numerical calculations are carried out, and the effects of the crack length and the temperature on the dynamic stress intensity factors of the embedded and edge cracks are shown graphically.

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The stress concentration near the interface edge of film/substrate, which dominates the delamination, is analyzed by the molecular dynamics (MD) analysis. Here, the thickness of film is in the nanoscale, the interatomic interaction is simulated by the Morse type model potentials. Three types of load are applied to the film/substrate in order to examine the effect of stress-concentrated region on the delamination at the interface edge. At lower applied load, the stress distribution along the interface near the edge in the MD simulation coincides well with the one obtained by a linear elastic analysis (FEM: Finite Element Method). However, after the stress near the edge reaches the ideal strength of the interface, it deviates from the FEM result. The delamination crack initiates from the free edge when the stress at y<1 nm (y: distance from the edge) reaches the ideal interface strength. This signifies the criterion of interface toughness that the delamination is governed by the stress in the region (process zone). This also suggests the limit of applicability of linear elastic fracture mechanics on the nano-scale components.

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The effects of adsorbing oxygen molecules (O₂) on the healing of the newly created surfaces of a fatigue crack of lead (Pb) are analyzed using an extended Tersoff interatomic potencial function. At first, the properties of Pb, O₂, and PbO₂ are calculated by using this function. The calculated values of the properties agree well with the observed values. Next, the simulations of the creation of new surfaces of a crack, the adsorption of O₂ to the surfaces, and the closing of the surfaces are carried out using this function. The simulation shows that the healing of surfaces is suppressed by O₂. Moreover, the effect of air pressure on the fatigue life is calculated based on an energy curve obtained from the simulation. The calculated results show good agreement with the experimental results.

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In order to investigate the mesoscopic stress field in polycrystal on the basis of the stress concentration due to the deformation constraint by the neighboring crystal, the crystallographic orientation and the 3-dimensional shape of each grain in a copper polycrystal specimen are specified by the repetition of processes: polish and observation with an orientation imaging microscope (OIM). Then, a finite element analysis for the polycrystal shows that the stress is concentrated on the region near the grain boundary. Especially the large stress concentration emerges near the twin boundary and the junction between grain boundaries. The high shear stress area, which is resolved to the crystallographic slip systems, corresponds to the location and crystallographic plane where the persistent slip bands are observed in a high cyclic fatigue test of the specimen.

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In order to clarify the fundamental mechanism of dislocations in the γ/γ' microstructure of Ni-based superalloy, three molecular dynamics simulations are conducted on the behavior of edge dislocations nucleated from a free surface and proceeding in the pure Ni matrix (γ) toward cuboidal Ni₃Al precipitates (γ') under shear force. One involves dislocations near the apices of two precipitates adjoining each other with the distance of 0.04 μm, as large as the width of the γ channel in real superalloys. Others simulate dislocations piled at the precipitates as well, however, the scale of the microstructure is smaller than that in real superalloys by one order of magnitude, and one of them have precipitates with atomistically sharp edge. Dislocations are pinned at precipitates and bowed-out in the γ channel, then they begin to penetrate into the precipitate at the edge in both the real-scale and smaller microstructures when the precipitates have blunt edges. On the other hand, an edge dislocation splits into a superpartial in the γ' precipitate and a misfit screw dislocation bridging between two adjacent precipitates at the atomistically sharp edge of γ' precipitates. It is also observed that two superpartials glide in the precipitate as a superdislocation with anti-phase boundary (APB), of which the width is evaluated to be about 4 nm.

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Hill and Hutchinson [J. Mech. Phys. Solids, 23, 239-264 (1975)]studied shear-band bifurcation which is investigated for an incompressible rectangular block constrained to undergo plane deformation. The block is assumed to be made of an incrementally-linear solid. Continuing equilibrium between both side regions separated by a shear plane gives a mode equation which is derived from the condition for the indefiniteness of velocity gradients. On the other hand, Needleman[J. Mech. Phys. Solids, 27, 231-254 (1979)]deduced the same equation based on maintaining equilibrium between these side regions in place of continuing equilibrium. However, in the process of obtaining the mode equation it is ignored in these analyses that these side regions must be under identical boundary condition. Then, this paper examines using Hencky constitutive equations whether the necessity of identical boundary condition is satisfied or not. Consequently, it is found that maintaining of identical boundary condition is disturbed. Hence, no reliance is made on the information in shear banding obtained according to these analyses.

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