The objective of this study were to develop an above-knee prosthesis focused on the ankle joint motion, and to confirm the usefulness of the developed prosthesis. Based on the problems of the previous prototype for prosthesis, an improved prosthesis was developed. The ankle joint of the prosthesis had a spring which enabled the passive joint motion due to the fluid force acting on the foot. An experiment with a subject swimmer attaching the developed prosthesis was conducted. The joint angles during flutter kick in the sagittal plane were measured. The time for 25m crawl swimming was recorded and questionnaire evaluation was also conducted. Four types of the spring constant (rigid, strong, weak and free) were tested. It was observed that the ankle joint motion changed according to the change of the spring constant. It was also found that there was the spring constant most comfortable for the subject swimmer. This result was supported by the experimental result that the swimming with the most comfortable spring brought the fastests wimming speed.

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In this study, we have development of four-wheel electric power-assisted personal mobility to support going out such as the elderly person who had a decline in the function of legs or the elderly person that a walk function decreased. This equipment, a safely reliable and physical burden is small, and there is movement going out easily while moving lower limbs. In order to check the performance of mobile support equipment, we have experimented for six healthy male subjects using this equipment. The purpose of this experimental is to evaluate the physical load of user by the oxygen uptake values and heart rate while they are running a flat road course and 8% slope course. These results can be used for the development of mobile support equipment and evaluation methods.

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The purpose of this study is to develop a haptic perception device evoking five elements (pressure, vibration, warmth, coldness, and pain) in different conventional those ways. The 3D Haptic Map was proposed as the representation method by the device. It contained X axis: a temperature shift axis displaying both warmth and coldness, Y axis: a pressure shift axis displaying both pressure and pain, Z axis: a time shift axis displaying vibration. The display was consisted of the peltier device, the pressure sensor, and the DC vibration motor on the basis of the map. An evaluation experiment was carried out on 30 subjects of early 20s. The experiment method was that they were ordered to put their fingertip on the device. After presenting senses, they answered orally subjectively-perceived senses. From these results showed that the device was able to display the five elements. In the vibration and warmth/coldness combination experiment, the pseudo-sense (e.g. itch, sore) expressed on their fingertip, instead of warmth/coldness. Thus, the device using the map was able to display both the five elements sense and the pseudo-sense, instead of the sense itself evoked by the physically presented stimuli.

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For supporting hemiplegic, active rehabilitation training that patients oneself carry out with own intention is effective. As one method to implement it, an intelligent master-slave system is proposed. A current many master-slave control system uses a large power source and a lot of sensors. Therefore, it is complicated, and a work place and time is limited. In this study, both characteristics of actuator and generator of a motor are used for energy regeneration. This system with only lightweight battery having force sense without force or motion sensor system can be developed. So this system can work on bilaterally, namely, use both motors as the master side or the slave side. Furthermore it can exert assist or resistant force on a slave side. By this, active rehabilitation training is carried out safely. In this report, it is shown from fundamental experiment that performance of the system is improved by addition of H-bridge circuit and gear system and the velocity of the slave motor almost accords with the master motor by simple control law. In addition, at tracking control, without a force sensor, the master side has almost same force sense as the slave side.

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We have developed a waist power assist device to support the welfare and nursing operation. In order to realize the human friendly configuration, a soft and light-weight pneumatic rubber artificial muscle is used as an actuator. In this paper, we describe the outline of developed assist device and its fundamental characteristics. Then, the power assist effect is shown through the experiments of lifting the weight and of supporting standing up motion of human. As a result, the developed device can be used as a practical waist power assist device in nursing and various fields.

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Prosthetic limbs are essential for amputees. A report from World Health Organization says eighty percent of amputees live in developing countries. Therefore, prosthetic limbs are to be developed under consideration of developing world conditions. In this paper, first we set requirements which reflect developing world conditions and propose an upper-limb prosthesis with using pneumatic artificial muscles as actuators. Second, we examine characteristics of the artificial muscle. As a result, we confirm that the maximum contraction displacement rate and the maximum contraction force of the artificial muscle are 35.4 % and 15.7 N, respectively. Next, we develop the prosthesis which consists of a hand and three artificial muscles and demonstrate that the prosthesis can grasp some objects with various shapes. The height, the width and the mass of the prosthesis are approximately 320 mm, 80 mm and 117 g, respectively. In addition, we demonstrate the prosthesis can grasp a mass of 500 g. Finally, we confirm that the prosthesis satisfies the requirements which we set.

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A water-mat including liquid and preparing some weirs and some orifices in the baggy mat is used for prevention of bedsores, which improves the body pressure dispersion of patients by controlling the flow of internal liquid. The water-mat has been developed to use for supine position, however, some patients lie by half side-lying position. So we developed a new water-mat for half side-lying position, then measured maximum body pressure of three young and three old people to inspect the effectiveness of it. Gatch up angle for a new water-mat of the half side-lying position was 0, 10, 20 and 30 degrees. From the experimental results using a mattress with the new water-mat, it was shown that the new water-mat has an obvious effect on dispersion of body pressure, and maximum body pressure has decreased by 22% on the average at Gatch up angle 30 degree. In addition, the pressure of the thigh at the time of Gatch up was also decreased.

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A water-mat including water in the baggy mat was developed for persons in need of nursing care. A flow of water in this mat is controlled by the positions, sizes, number and shape of some weirs and some orifices in the water-mat. This mat is designed to have a good body pressure distribution and to follow smoothly the posture of patient. Now we already developed a lightweight water-mat including liquid with flexible materials. This lightweight water-mat is however, too heavy for elder people to use more easily. If more lightweight water-mat can be developed and good body pressure distribution at high back raising angle can be accomplished, more people can use it in home care. So we developed more lightweight and new form water-mat including liquid with flexible materials We call this new water-mat as the discrete type. We verified the pressure dispersion of the lightweight discrete type water-mat by comparing it with the lightweight water-mat until now and the marketed bedsore prevention mattiess.

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Pressure ulcer is consequence of intense and prolonged mechanical loading of vascularized soft tissues, which causes cell death through metabolic deprivation and/or critical deformation. Now a pressure ulcer is concern in our country with increase bedridden elderly with expeditious advent of aging society. Therefore in this research we focused attention on the external causes of pressure ulcer generating mechanism. We measured shear stress and pressure on the skin surface under the occiput, the scapula, the calcaneal and the sacrum. Furthermore, the stress states in the body were numerically examined using viscoelastic finite element method. It was shown that the stress on uppermost of subcutaneous tissue under the sacrum greatly depended on the projection shape and the size of the sacrum.

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The durability test for a newly developing axial-flow ventricular assist device (VAD) with hydrodynamic bearings was conducted under pulsatile flow condition for six months to obtain a long-term reliability. A mock circulation was consisted of a diaphragm pump with a mechanical heart valve, a reservoir, a compliance tank, a resistance and simple-layout flow paths that were made of polymer or titanium. The VAD was installed behind the diaphragm pump submerged in saline solution. A blood analog fluid was saline added with glycerin whose viscosity coincided with that of blood at the temperature of 37 ℃. The pulsatile flow condition was set within the flow rate range to realize positive flow rate and positive head at the impeller rotational speed obtaining the flow rate of 5 L/min and the pressure of 100 mmHg. The pump characteristics were monitored for flow rate, pressure head, impeller rotational speed, and so on. The mock circulation characteristics were maintained for fluid temperature, fluid density and pulse rate of the diaphragm pump, and so on. The mock circulation realized the pulsatile flow rate to achieve 0±1 L/min at the systolic phase, 9.5±1 L/min at the diastolic phase and 5±1 L/min in average at the pulse rate of 72 bpm. The durability tests were conducted for eight axial-flow VADs. For six months, the experimental conditions have been maintained that were the average flow rate of 4.4 (± 0.2) ± 0.05 (± 0.04) L/min, the diastic flow rate of 0.1 (± 0.1) ± 0.1 (± 0.1) L/min, the systolic flow rate of 10.9 (± 0.2) ± 0.1 (± 0.03) L/min, the average head of 80 (± 3) ± 2 (± 2) mmHg, the pulse rate of 72.1 (± 0.3) ± 0.2 (± 0.1) bpm, the fluid temparature of 37.2 (± 0.2) ± 0.2(± 0.1)℃, the fluid viscosity of 3.2(±0.1)±0.3(±0.1) cP, in which the value in the bracket means individual device differences. The metal components were hardly detected in the working fluids. The long-term durability of the developing axial-flow VAD for six months was confirmed.

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Extracorporeal Membrane Oxygenation (ECMO) has been widely applied to treatment of severe pulmonary and/or circulatory failure, but the durability of the device is one of the drawbacks toward its prolonged use. We have developed a compact centrifugal blood pump that has a unique hydrodynamic bearing system to realize superior antithrombogenicity. This pump, together with the membrane oxygenator with the durable antithrombogenic coating, will form an durable ECMO system that can be operated over a month with a minimum amount of anticoagulant and antiplatelet therapy. This study reports on the chronic animal experiments to evaluate biocompatibility of the newly developed ECMO system with the centrifugal pump.

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The purpose of this study is to establish an optimal design of the multi-arc hydrodynamic bearing in a centrifugal blood pump for improvement of bearing stiffness and hemolysis level. The multi-arc bearing was designed to fulfill the required specification: (i) ensuring the uniform bearing stiffness against various bearing angles, (ii) ensuring the higher bearing stiffness than the centrifugal force to prevent the impeller whirl, and (iii) adjusting bearing clearance as much as possible to reduce hemolysis. First, we performed the numerical analysis to optimize three design parameters of the multi-arc bearing: number of arc N, bearing clearance C and groove depth H. To validate the accuracy of the numerical analysis, we measured the impeller trajectories. Finally, in vitro hemolysis test was conducted to evaluate the hemolysis level of the multi-arc bearing. As a result of the numerical analysis, the optimal parameter combination of the multi-arc bearing was determined as follows: N of 4, C of 100 μm and H of 100 μm. In the measurements of the impeller trajectory, the optimal parameter combination was found out to be as follows: N of 4, C of 90 μm and H of 100 μm. This result showed high reliability of the numerical analysis. In the hemolysis test, the relative hemolysis level of the multi-arc bearing was 0.8-times higher than that of the cylindrical bearing. It was found that the multi-arc bearing can reduce the hemolysis level. In conclusion, we could optimize the multi-arc bearing for improvement of bearing stiffness and hemolysis level.

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This paper describes observations of thrombus formation process on orifice flows by laser sheet. In the observation of thrombus formation process, the brightness of CCD image corresponds to protein or thrombus concentration. In this paper, thrombus formation rate was estimated by the gradient of brightness history near the wall. In addition, we changed flow rate using the same orifice type to compare the difference of the thrombus formation rate. As a result, the difference in thrombus formation process was seen by changing flow rate, and it was found that the threshold of the shear rate for the thrombus formation existed because of the platelet activation.

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Recently, the development of miniature size ventricular assistance devices (VAD) has made it easier for the heart patients to get discharged from the hospital and rest at home. However, thrombus formation is a major problem for such prosthetic devices. But, there is no proper mechanism to detect the thrombosis in real-time. Therefore, a 3-D visualization system is studied here to visualize the cross-sectional concentration of red blood cell so as to determine the possible thrombus. The applicability of electrical process tomography technique, which is capable of showing the concentration distribution across the cross-section, has been analyzed. In-vitro experiment was carried out using bovine blood. Thrombus was created by adding calcium chloride to the blood. The experiments showed the change in conductivity distribution when thrombus was passed through the cross-section of interest. The thrombus passing through the channel caused increase in higher electrical resistance in its path. It shows the possibility of developing reliable sensor to detect the thrombus.

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Stent implantation in intracranial arteries is termed as endovascular treatment. The number of such cases has been increasing worldwide because the surgical damage resulting from stenting seem to be less than that of other treatments. A side wall type idealized aneurysm shape reconstructed by straight pipe and half sphere were used, Z-type stent was used. CFD analysis was performed each aspect ratio aneurysm and stent strut pattern. The optimization by the process of Multi-Objective Genetic Algorithm and Kriging was performed to the CFD results From the results, we report the development of new stent strut pattern in cerebral aneurysm using the computational fluid dynamics (CFD) and optimization.

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To produce an optimal design of stents for cerebral aneurysm is attracted for reducing the flow in the aneurysm efficiently. This report demonstrates the optimization for 3-D aneurysm with two different objectives. As the result, the optimum stent for the maximum velocity has denser struts on distal of the neck. On the other hand, the optimum stent for average velocity has denser struts on proximal of the neck.

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We have been developing a micro porous covered stent as a newly device for cerebral aneurysm treatment to adapt large and giant cerebral aneurysm with a broad neck. This stent has a porous film to control among thrombus formation, rapid neointimal formation and intimal hyperplasia. It is expected that the neointimal formation becomes earlier by using much larger pores. But there is a possibility that the covered stent with large pare cannot embolize an aneurysm by increasing inflow from parent vessel. The purpose of this study is optimization of pore design to ensure compatibility between reliable embolization and controlling early neointimal formation, in-vitro experiment based on flow similarity low has been conducted by using a 2D parent vessel model with a side wall type aneurysm model. The flow visualization result shows that three kinds of flow pattern in the aneurysm were observed namely, viscous shear induced flow, pressure drop induced flow and those coexistence flow. According to PIV measurement result, area mean shear rate in the aneurysm after stenting was decreased to less than 1/5 of before stenting. Especially, when the covered stents of which aperture diameter was lower than 200μm and aperture ratio was 60% were installed, shear rate in aneurysm was less than 1 s^<-1> which was a threshold of F-IX activating necessary for venous thrombus formation.

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To provide basic data for assistance of the development of the medical guide-wire, we examined the mechanical properties of the guide-wire in blood vessel model. As the first step of this study, we noticed the rotation of the guide-wire, and measured torque transmission and rotational response of the guide-wire in the blood vessel model. Material of the blood vessel models are PVA-H (polyvinyl alcohol hydrogel ) and PVA-H(D) which mixed DMSO to PVA-H. Shape of the blood vessels model is square pillar, and the guide-wire was inserted in the central hole. During the experiment of torque transmission measurement, the torque meter was attached to both ends of the guide-wire. Rotational torque was generated by stepping motor of the proximal end side. During the experiment of the rotation response measurement, two arms were attached to both ends of the guide-wire, and their rotational angle were taken by video camera. As the result, we found that the greater stiffness of blood vessel model and proximal rotational speed affect the torque and rotational losses of guide-wire.

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Mobile-bearing type knee prosthesis has been used in total knee arthroplasty (TKA) to improve the mobility of the knee joint. In this type of knee prosthesis, UHMWPE tibial insert is not fixed to the tibial component and able to move freely on the top surface of tibial component. Although deep flexional motion can be expected using the mobile-bearing prosthesis, the safety of the prosthesis, especially the stress state of the tibial insert has not been clarified yet. The purpose of this study was to understand the stress variation in the tibial insert under deep knee flexional motion using the dynamic finite element analysis. It was found that if the movement of the mobile-bearing system is firmly restrained during flexional motion, the stress level tends to increase up to 90 MPa, while the maximum stress level is settled down at 55 MPa when the system works very smoothly.

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In this study, influence of phospholipid and protein constituents on friction and wear behavior of artificial hydrogel cartilage was investigated. A sliding pair of a spherical specimen of poly(vinyl alcohol)(PVA) hydrogel and a flat specimen of PVA hydrogel was tested in reciprocating friction test. Dipalmitoylphosphatidylcholine (DPPC) was selected as phospholipid constituent and was dispersed in saline as liposome. Fluorescent-labeled albumin and γ-globulin were used as protein constituents in lubricants at high concentration such as 1.4wt%. After reciprocating friction test, the boundary film formed on the surface of PVA hydrogel and the worn surface of PVA hydrogel were observed by using fluorescent microscope and confocal laser scanning microscope, respectively. When only albumin or γ-globulin was added to lubricant, adhesive wear pattern was significantly observed and large breaking-off of surface structure of PVA hydrogel occurred Lubricants that contain proteins and 0.01 wt% DPPC showed reduction of friction and suppression of large breaking-off of surface structure of PVA hydrogel. Under coexistence of protein and 0.02wt% DPPC, friction increased compared to that of in lubricants that contain 0.01wt% DPPC and wear patterns were almost the same as those in lubricants that contain only proteins. Therefore, not only concentration but also relative ratio of proteins and phospholipids are important factors to function those as excellent boundary lubricant for PVA hydrogel.

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Hip replacement arthroplasties have been increasing in number as the number of patients with coxarthrosis is increasing. Prosthetic hip joints of the surface replacement type with metal-metal contact are considered to be an effective choice for bone preservation. It is however shown that the metal-metal contact type prosthetic hip joint could be toxic to human cells when the abrasion powder of the Co-Cr alloy, a component of the joint, is ionized. In the present study we examined ceramic-coated metal pieces of the Co-Cr alloy. Using the Pin-On-Disk abrasion test method, we investigated their abrasion resistance and the elution of the metal ions into a pseudo body fluid. As a result, the metal pieces with DLC coating(a-C:H and ta-C) showed the best performances in terms of the frictional coefficient, the abrasion resistance and the elution property of the ions.

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ACL injuries occur when an athlete rapidly decelerates, followed by a sharp or sudden change in direction. In order to improve surgical results and understand the disease, it is necessary to evaluate how kinematics of the knee changes. Rotational instability in ACL insufficient knee addresses the symptom or the abnormal motion, which can be subjectively evaluated in the clinical exam. The clinically available quantitative measurement for this instability has not been established, and this prevents providing the definite diagnosi. In order to solve the problem, a measurement system for 6 degree of freedom in knee motions has been developed. This system consists of two plates connected by six linear potentiometers that expand or contract to fit the knee movement. By using this system, the pivot shift test was evaluated in the ACL injured knee.

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Total hip arthroplasty (THA) is an effective treatment to remove the pain for patients who suffer from rheumatoid arthritis or osteoarthritis of the hip joint. In THA, the artificial hip joint dislocation is one of the most serious problems to be solved. The dislocation of the artificial hip joint occurs depending on the hip joint angles and hip contact force. Specifically, the muscle forces of the patients who suffer from hip osteoarthritis become weaker because they cannot move the hip joint enough due to pain. In this paper, we discuss the influence of the hip contact force on artificial hip joint dislocation when the muscle forces around the hip joint become weaker. To clarify the influence, the experiments are carried out using the hip joint simulator which can generate the desired hip joint angle and the joint contact force simultaneously.

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Total hip arthroplasty (THA) and resurfacing hip arthroplasty (RHA) has been the standard treatment for patients with progressive osteoarthritis and for relatively young patients with femoral head necrosis, respectively. Although the joint functions are dramatically improved due to THA, sometimes large strains or stresses in the vicinities of the implants have been associated to the cause of bone fracture. The purpose of this study was to investigate the bone fracture mechanisms in THA and RHA on the basis of the finite element method with use of damage mechanics. Microscopical damage formations with microcracking and final bone fracture were successfully reproduced by this modeling procedure.

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We have developed our own manufacturing method of the material and new artificial models of bone mainly made of polyurethane. It is for operation training and medical education for doctors, because the properties of cutting and bone drilling of existing bone models are not completely the same as real bone. In the new bone model, we can change its structure by changing the ratio of the porous foam of polyurethane. This leads to control and change in the cutting and drilling properties relating to the structure and mechanical behaviors of the material. In this study, to clarify the relationship between the porous distribution and the drilling properties of the models and develop the fundamental technique of order-made new bone models, we evaluated the cutting and drilling properties of the models by compression test, push out screw test and observation by scanning electron microscope (SEM). We found characteristic differences of force-displacement curve by compression test, maximum load values, decreasing force rate and residual force values by screw push out test. In addition, SEM observations showed the differences of size and number of the pores in the materials, suggesting that the characteristic mechanical behaviors are caused by the differences of micro scale structures. Availability of the properties obtained by our proposed experiments as indicators to evaluate the cutting and drilling properties of the bone model are discussed.

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Mechanical tests on two types of short femoral nail (SFN), namely, currently used "Lag Screw (LS)" and newly developed "Grasping Pin" with a "Lag Pin (LP)" for osteosynthesis have been performed so as to make a comparison between their initial stability. Both LS and LP were implanted in human femoral heads taken from the patients who were suffered from femoral neck fracture, and then tested under cyclic compressive and quasi-static torsional loading. No "Cut-out" was observed in both LS and LP under cyclic compression and LS clearly showed less amount of subsidence than LP. An almost constant resistance to torsional loading was found in LS independently of rotation, while LP demonstrated the linear or monotonic increase of torsional resistance with an increase of rotation. These results were remarkably different from the results of the previous study where the polyurethane foams were used as simulated materials of cancellous and cortical bone.

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Biomechanical measurements are often performed by FEM analysis and Mechanical test but there are few reports which analyze the combination of FEM analysis and Mechanical test together to determine their relational accuracy. In the current study we use FEM and Mechanical tests to evaluate their relationship in a posterior lumber interbody fusion disorder in an effort to develop the Spinal interbody fusion implant. First, CAD data of the lumber spine (L4, L5) and lumber implant were created. FEM analysis and Compression test were performed with a load of 1000N and displacement was recorded. Only the anterior-superior aspect of the L4 lumber spine was displaced in the FEM analyses but the L4 was displaced downward overall in the Mechanical test. The boundary condition between the lumber spine and screw in the Mechanical test is fastened in a manner that allows transverse motion but is completely fixed in the FEM analysis. Improving the boundary conditions between the lumber spine and the screw in FEM analysis should help give close agreement with the results of the Mechanical test. Thereby improving the development of better Spinal interbody fusion spacer.

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In recent years, there has been increased the osteoporosis patient, and it has become important to elucidate how the bone loss of lumber vertebra has an influence on the compression fracture. This study investigated the stress and deformation of the osteoporotic lumber vertebra injected by bone cement during prolonged uniform load using the growth-strain method. First, 3D FEM models on the lumber vertebras and lumber vertebras injected by bone cement with bone loss 30, 50% were determined by changing the Young's modulus. Then, growth criterion parameters of the strain energy density on various parts of the lumber vertebra were determined by analyzing these FEM models. Finally, the strain energy density of osteoporotic cervical spine models injected by bone cement receiving the uniform load were analyzed using the growth-strain method, and the bone growth behavior was compared. As a result, it was clarified that the 4th lumber vertebra had highest risk of the compression fracture.

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Today the development of most orthopedic implants makes great use of Mechanical testing and FEM analysis. At Mechanical testing however, it is difficult to know about the conditions within implant and results are prone to error. Additionally, in FEM analysis, results can change even when something as simple as boundary conditions are chosen incorrectly. In this study, the evaluation of mechanical and FEM analysis using an intertrochanteric femur fracture model was performed. An intertrochanteric femur fracture fixed with a femoral nail was first designed in CAD software. The mechanical model was tested under single compression and the displacement deviation between before and after compression was measured with a contactless 3D-Scan. In the FEM analysis, constraint conditions were defined similar to Mechanical testing conditions. Displacement was used to compare the results. The deformation method of the mechanical test was similar to that of the FEM analysis. However, displacement values of the FEM analysis were twice than the mechanical displacement. The elastic modulus of the inner urethane foam duplicates cancellous bone changes because the applied loads crumpled air holes within the urethane foam. The results of the FEM analysis will differ from Mechanical testing due to the fact that the elastic modulus used for FEM calculations is non-linear.

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The purpose of this study was to validate the cartilage contact behavior in the tibiofemoral joint evaluated using an image matching technique. Two human cadaveric knees were used for this study. Each knee underwent CT scanning to create 3D femoral and tibial bone models and MR imaging to create 3D femoral and tibial cartilage layer models. Tactile pressure sensors were inserted into the medial and lateral compartments of the knee. Calibrated biplane radiographic images of the cadaver knee were obtained during axially loaded using a lever arm apparatus. The 3D positions of the femoral and tibial bone models were recovered by matching their projected outlines with the bone contours in biplane radiographs. The contact area and contact depth were determined from the intersection of the femoral and tibial cartilage layer models. The proximity was obtained between the femoral and tibial bone models. The location of the contact area corresponded to that measured with the pressure sensors. The distributions of contact depth and the proximity also corresponded to the pressure distribution. These data indicate that the image registration technique could be used to evaluate the in vivo articular cartilage contact behavior of the knee joints.

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This paper deals with the improvement of density and surface roughness of Ti alloy compacts produced by laser forming (or selective laser melting). Laser forming process, as advanced additive manufacturing technique is very reliable technique for the manufacturing of complex shaped parts in low cost and fast processing time. However, the improvement of density and surface roughness is strongly required for the commercial manufacturing process. In this study, we focused on the feeding powder layer height (FLH), which affects to the amount of melting pool. Single layer specimens and multi-layer specimens were fabricated in various FLH under the optimized laser condition. Comparing single and multi-layer specimens, it was confirmed that small FLH is very effective to improve the surface roughness due to the homogeneous powder melting. Moreover, improved surface roughness results good adhesion between layers, and nearly full density (99.8%) could be obtained. Also, high tensile strength (1080 MPa) that is higher than that of ASTM, was obtained in small FLH.

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To simulate the rigid motion of particles and the grain growth behavior in powder compacts during sintering, a sintering model for coupling phase-field method (PFM) and discrete-element method (DEM) is proposed. The sintering forces and the contact areas in a chain of powder particles are evaluated from the phase field variables, computed in PFM, and taken into consideration in the calculation of the rigid motion of particles in DEM. Two-dimensional simulations of sintering shrinkage and grain boundary migration process are implemented for basic two-particle models, including the case with different particle sizes. The changes in the neck size and the center-to-center distance between particles are well reproduced by using the proposed sintering model.

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This study aims to manufacture the micro-MIM parts exhibiting excellent soft magnetic properties. The effects of solid loading of feedstock and injection speed on the sintered density and the coercive force were investigated. The feedstock composed of Fe-47Ni powder and binders was prepared by changing the solid loading of 60-67% and were injection-molded into micro-dumbbell specimen with 0.16mm in parallel portion and 2.52mm in diameter of chucking parts. The internal mould pressure was measured in the chucking parts. The filling behavior of feedstock into the micro-dumbbell specimen was investigated by comparing the results of flow simulation and short shot test, then the internal pressure drop and jetting phenomena were revealed. It could be concluded that the coercive force of the sintered parts was significantly influenced by the density reduction and the remaining carbon content, thus the solid loading of feedstock and injection speed in addition to debinding-sintering conditions should be optimized.

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This study aims to demonstrate the usefulness of digital image measurement for the optimization of manufacturing condition and the quality management of MIM parts. New types of measuring systems were used to measure the 3D coordinate and strain filed of Ti-MIM parts with very complex shape. Debinding and sintering were carried out under the three types of setting conditions: 1) laying and 2) standing on Al_2O_3 plate, and 3) embedding in Al_2O_3 powder. The effects of the setting condition on the shape of sintered parts could be clarified quantitatively and visually by the digital image measurement. Also the difference in shape between the measured data of sintered parts and the 3D-CAD data could be visualized, and less-visible flaw mark could be detected easily. Thus it is concluded that the digital image measurement has a great potential to inspect precisely the shape error and strain field of complex shaped MIM parts under loading.

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In this study, the fabrication conditions of tool steel powder by direct selective laser sintering were investigated. The effects of powder size and laser scanning conditions on the state of laser-sintered body were examined to fabricate a sound laser-sintered body of tool steel. The optimum laser power, scan speed and scan pitch were examined by experiments. As a result, it is difficult to fabricate a sound laser sintered body by using SKD11 powder of 10 μm. It was, however, found that the continuously smooth single-scan track can be obtained at wider range between laser power and scan speed by using SKD11 powder below 45 μm. The laser-sintered body could be fabricated at a laser power of 10 W, a scan speed of 10 mm/s and a scan pitch of 0.08 mm by using SKD11 powder below 45 μm.

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Pure aluminum and iron powders were mechanically alloyed (MAed) using a vibrational ball mill, and the MAed powders were consolidated into bulk materials by spark plasma sintering (SPS). Magnetic properties of the SPS materials were evaluated by vibrating sample magnetometer (VSM). The saturation magnetic flux density of the SPS materials increased with the amount of the iron content. The amount of the Al_<13>Fe_4 and Al_5Fe_2 was increased with an increase in sintering temperature. As the formation of intermetallic compounds, the saturation magnetic flux density of the SPS materials decreased by an increase in sintering temperature.

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In recent years, AlN attracts attentions as heat sink materials for discrete semiconductor devices because AlN has the characteristics necessary for heat sink. But it can't be formed complex shape by net shape. So we try to establish mass production technology of sintered AlN parts having high thermal conducting and complex shape by vibrational compaction process and milliwave sintering. The frequency of vibration and the amplitude is controlled as frequency condition. The compaction is evaluated by measuring sedimentation speed, compaction speed and relative density. As a result, compaction speed and particle filling rate are improved by the molding method. But compaction speed is improved by minute vibration against particle filling rate improved by large vibration. Maximum impression speed is 5.5 times as fast as spontaneous sedimentation that. But it is not enough to improve particle filing rate in this energy rage and compaction don't have high packing dencity. So clearly sintering characteristic is confirmed by milliwave sintering.

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On-demand duplication process of net-shaped ceramic parts is developed. The essential problem of ceramic duplication process is shrinkage during sintering, that is, green compacts cannot be made by replica of teeth, for example. To compensate such shrinkage, we develop a resin expansion process using supercritical fluid impregnation technique. A shell type mold with enlarged product shape cavity is taken from expanded original mold. The shell mold is buried into alumina slurry and compacted by high-speed centrifugal compaction process (HCP). In this research, appropriate resin for expansion process is selected and relationship between impregnation condition and expanding ratio is evaluated. The HCP with buried shell mold is also performed and obtained densely packed green compacts. A hydrostatic pressure generated during the HCP avoids collapse of weak shell mold during the compaction. The shell mold is thermally decomposed completely in subsequent heating process.

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We aim to develop a new powder metallurgy process for producing next generation common-rail diesel nozzles having tiny and multiple holes. In the process, a resin core which makes tiny holes in the products is combined with the high-speed centrifugal compaction process (HCP). Powder can be filled up to all the corners of complicated shaped molds by the HCP. Moreover, during the HCP, only isotropic hydrostatic pressure is applied to a resin core, so that, the core is buried in a green compact without collapse even if the core has scarce strength. A resin core is removed by thermal decomposition method. A nozzle sample with tiny multiple holes are successfully produced by this process.

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ZrB_2-SiC-ZrC (ZSZ) ceramics with four different compositions containing 16 vol% SiC were sintered by hot press and spark plasma sintering. The relative density of all the ZSZ ceramics made by both methods reached around 95%. These ZSZs oxidized continuously up to 1500℃ using thermo gravimetric analysis. The ZSZ containing the highest ZrB_2 indicated the lowest weight gain, and that containing the highest ZrC indicated the highest weight gain. After the oxidization, the microstructure of the samples' surface and cross section were studied by X-ray diffraction analysis, optical microscope and field emission scanning electron microscope along with X-ray dispersive spectroscopy. Results of these analyses for the samples revealed that ZSZs have oxidation resistance due to formation of the oxide scale, which act as the barrier for oxygen diffusion into the unoxidized substrate. In the next study, ZSZ ceramics was heated continuously up to 1700℃ in air using zirconia ultra high temperature furnace. Oxidation test was earned out at 1700℃ by IR image furnace. The surface of the oxidized specimen had a number of bubbles and appeared to be covered with zirconia and glassy compounds. These results suggest that the active oxidation of SiC was occurred at the interface between the oxide scale and the substrate. In addition, because the spallation between the oxide scale and the substrate was not occurred, it was implied that ZSZs showed the resistance to the active oxidation of SiC.

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The polymer impregnation and pyrolysis (PIP) method, and melt infiltration with silicon (Si-MI) method are conventional processing routes of Carbon-fiber-reinforced SiC matrix (C/SiC) composites. In PIP method, due to the low volume yield of pre-ceramic polymers after pyrolysis, PIP should be repeatedly processed to obtain high-density C/SiC composites. This leads to long manufacturing time and high processing cost. For the purpose of reducing the processing cost, a slurry infiltration process was studied. In this process, the space between fibers in a 2D carbon fiber preform was impregnated with SiC powder slurry by a pressure or vacuum assisted infiltration before the PIP process, and the bulk density of the powder filled preform achieved 1.3 g/cm^3. Then, the powder filled preform was further densified by the PIP method or the melt infiltration (MI) method. Through these experiments, SiC powder infiltration behavior during a pressure and vacuum assisted slurry infiltration process was discussed, and basic mechanical properties of C/SiC composites fabricated by these processes were evaluated.

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In this research, the effects of MWCNT addition on mechanical properties and microstructures of pressureless sintered MWCNT/alumina composites were investigated by using four types of MWCNTs having different fracture characteristics and dispersibility. It was demonstrated that it is possible to fabricate MWCNT/alumina composites by pressureless sintering at a temperature of 1400℃. Fracture tests showed that the MWCNTs annealed at 2200℃ was the most effective in improving the mechanical properties of the MWCNT/alumina composites, and 0.9 vol.% MWCNT addition resulted in 25% and 45% simultaneous increase in bending strength (742.6 ± 13.1 MPa) and fracture toughness (5.83 ± 0.19 MPa m^<1/2>), respectively, compared with MWCNT-free sintered bodies. An improvement in the fracture properties may be attributed to the use of the MWCNT having a higher load carrying capacity. For the larger amount of the MWCNTs, strong correlation between mechanical properties of the composites and dispersibility of the MWCNTs was observed, and the degradation of mechanical properties was shown to be primarily attributed to the severe phase segregation. Our finding suggests that the important factor for the preparation of ceramics composites with MWCNT for higher strength and toughness will thus be the use of MWCNT having a much higher load carrying capacity as well as a good dispersion in the matrix.

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Porous carbon materials with uniform pore diameter were successfully fabricated with various processing conditions, and their microstructures and thermo-mechanical properties were evaluated. The starting material was phenolic resin with continuous micro-pores, which have almost uniform diameter of several micron-meters. Even with different carbonization temperatures, the carbon materials showed almost the same bulk density of about 0.36g/cm^3. Compressive strength and coefficient of thermal expansion were also independent of the carbonization temperatures. On the other hand, Young's modulus of the porous carbon material was increased with temperature from about 0.5GPa to more than 1GPa.

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The microdamages in ATZ composite ceramics during 4-point bending test were monitored by acoustic emission (AE) technique, and the rapid increase in cumulative AE energy prior to the final fracture was observed, which could be related with the maincrack formation as the origin of final fracture. The critical stress for maincrack formation σ_c was determined as the stress at rapid increasing point of AE signals. The stress increased with decreasing in Alumina weight fraction without 0% By increasing in ZrO_2, the growth grain size of Al_2O_3 was restrained and the flaw size turned smaller, since σ_c depends on the dispersion in the size and the distribution of initial failure.

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Photon emission was measured during crack extension in silica glass. To detect a location of the crack tip, stripe pattern of Au thin coating was made on both tensile and side surfaces of silica glass specimen. The specimen was fractured by three-point bending test in a vacuum chamber. During fracture, the resistances of those thin coatings were monitored, and also photon emission was measured by photomultiplier tubes in the range of wavelength around 450nm and 650nm. The changes in the resistances showed that the crack ran through the tensile surface first, and then extended into the thickness. The fracture surface area was calculated to normalize the count rates of photon emission. It was revealed that photon emission per unit fracture surface area had a maximum value at the onset of fracture and then monotonously decreased with crack extension.

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A round robin with 13 laboratories was conducted to evaluate the reproducibility of indentation fracture toughness, K_<IFR> of silicon carbides sintered with B and C. K_<IFR> varied widely from 3.43 to 4.43 MPa・m^<1/2> when the crack length was measured with an optical microscope at a low magnification of 〜 100x, while those obtained by powerful microscopy with both an objective lens of 40x and a traveling stage exhibited a consistent value of 3.23 ± 0.10 MPa・m^<1/2>. The crack lengths of the returned samples were also measured by the authors and compared with the reported values from each participant to clarify the origin of the variation of K_<IFR>. The wide scatter of K_<IFR> for the former measurements was explained by the misreading of the crack length which ranged from 55 to 115μm. It was revealed that the high resolving power of the objective lens of 40x enabled to find exact crack tips easier, which resulted in the good matching of K_<IFR> between laboratories for the latter case.

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Aluminum nitride (AlN) /hexagonal boron nitride (h-BN) composites. were fabricated from AlN and h-BN nanopowders. Spark plasma sinterng. was used for densification. Boron nitride addition is varied from 0 vol. % to 20 vol. %. Gamma-AlON/h-BN composites were obtained from commercial AlN and h -BN nanopowders. Dense AlN/h-BN composites, which had higher bulk density than 95% in relative density, were obtained from AlN nanopowder synthesized by gas reaction nitndation and commercial h-BN nanopowder by optimizing sintering condition. Thermal conductivity of AlN ceramics without BN is 71.8 W/(mK) and that of AlN/ 20Vol%BN is 40 3 W/(mK).

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In the present study, fiber-reinforced self-healing ceramic, which has SiC interlayer acting as self-healing agent at alumina matrix/ alumina fiber interface, was developed. It is found that the developed composite can completely recover strength by the heat treatment for 1h at 1200 ℃ and 50 h at 1000 ℃ Furthermore, the composite was found to maintain the good ability of fiber reinforcement after self-healing treatment. From the obtained results, the composite can heal the pre-crack fast compared to particle dispersed self-healing ceramics, in order that it spread the crack to the interlayer consisting of healing agent. The results imply that the developed fiber-reinforced self-healing ceramic can ensure its structural integrity against the accidental damage, such as, crash and thermal shock.

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Effect of substrate temperature and ambient pressure on a flattening behavior of thermal sprayed particle has been investigated systematically in our lab. It was recognized from the results that splat morphology of any sprayed material changed from a splash shape to a disk one with increase of substrate temperature or decrease of ambient pressure. The most interesting feature is that this morphological change is defined as transitional phenomenon. Instead of the actual thermal spraying, freely fallen experiment was conducted in this study to measure the in-situ temperature history inside of the splat to estimate what is happening in an impact of particle onto the substrate surface. Mirror polished SUS304 plate and Cu particle were used for both substrate and droplet material, respectively. It was found from the results obtained that droplet decided its flattening pattern just after the collision onto substrate surface and ring shaped initial solidification at bottom surface of the splat might give the possibility to arrest the splashing. The contact nature between particle and substrate, namely wettability, can be the domination for this transition phenomenon.

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The purpose of this research is to propose a simpler method of evaluating adhesive strength for hydroxyapatite (HAp) coating using four-points bending test with a slit coated specimen. AE signals were recorded and delamination behavier from the edges of HAp coating was observed during fourpoints bending test in order to specify delamination points. AE signals from HAp coating specimen was observed earlier compared with that from Ti substrate. Delamination starting point of HAp coating is about 120MPa and energy release rate G_<max> is calcurated to be 8.59[N/m].

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