As an alternative method to evaluation of slow strain rate technique (SSRT) under high-pressure hydrogen gas, Continuous Cathodic Hydrogen Charging SSRT tests were performed. Cr-Mo low alloy steel with a tensile strength of 1000 MPa grade was selected as a test material. Cathodic charging was performed in 3% NaCl aqueous solution at a current density of 400 A/m² and 1N-NaOH aqueous solution at 1.354 V constant potential test. Relative reduction of area (RRA) values obtained by tests with continuous charge at a cathode were equivalent to those performed in hydrogen gas at pressure of 69 ~ 115 MPa. The amount of hydrogen was measured using TDA. Amount of diffusible hydrogen is 0.74 ~1.09 ppm, which is equivalent to using hydrogen gas with a pressure of 69 ~ 115 MPa. Fracture surface observations were performed using scanning electron microscopy (SEM). The quasi-cleavage fracture surface of hydrogen embrittlement (QC_HE) was observed near the surface of specimen that were subjected to continuously hydrogen charged tests.

For prohibiting a global warming, fuel-cell systems without carbon dioxide emissions are a one of the promising technique. In case of a fuel-cell vehicle (FCV), high-pressure H₂ gas is indispensable for a long running range. Although there are lot of paper for studying a hydrogen embrittlement (HE), there are few paper referred to the effect of high-pressure H₂ on the HE phenomenon. Machine elements has some stress concentration parts, such as through hole, screw and so on. It is considered that a large amount of hydrogen will be accumulated in the high stress field at the stress concentration site. Therefore, it is afraid that machine elements having stress concentration site may be severely affected a hydrogen embrittlement. In this study, an effect of high-pressure H₂ gas on fatigue strength of notched specimen made of SCM435 steel and SUS316L stainless steel were investigated. A V notch specimen having different three notch root radius for different stress concentration factor were designed by FEM analysis. After then, fatigue test were carried out in ambient air and in ultra-high pressure (70MPa) H₂ gas environment. For case of SCM435, it is found that fatigue strength of V-notched specimen tested in 70MPa H₂ gas environment are affected by heat treatment condition. On the other hand, for case of SUS316L, fatigue strength of V-notched specimen are scarcely affected by 70MPa H₂ gas.

In this study, hydrogen was charged into TIG-welded joints of austenitic stainless steel SUS316L by a cathodic electrolytic method, and the effect of δ ferrite on the hydrogen content was investigated. EBSD analyses of the welded joint revealed that δ ferrite remained in the fusion zone of the weld, in which the shape of remained δ ferrite was vermicular. The amount of δ ferrite was qualitatively estimated by a ferrite scope as the volume fraction of about 12.2 % (top side) and 5.7 % (bottom side). Hydrogen was charged into both base metal and weldment, in which 3% NaCl aqueous solution with 3 g/L ammonium thiocyanate (NH₄SCN) at 50℃ was used. Both samples were kept in the solution with cathodic potential for 48 hours. Subsequently, hydrogen contents were measured by a thermal desorption spectrometry (TDS) method. The hydrogen release peaks were observed at around 200 ℃ for both the base metal and weldment. The cumulative amount of hydrogen was larger for the weld than for the base metal. That was due to the presence of remained δ ferrite phases, whose hydrogen diffusion rate was much higher than austenitic phase.

Engineering materials usually exhibit heterogeneity such as that observed in the polycrystalline structure of metals, and this heterogeneity affects the nonuniform deformation of a material. The experimental results of the nonuniform deformation of polycrystalline copper specimen with a curved gage section clarified that the randomness of the polycrystalline structure suppressed the deformation localization of the specimen. The micro- to macroscopic computational simulation based on the second-order homogenization method could not predict such a decrease in the macroscopic strain concentration in the specimens because the macroscopic structure is uniform owing to the periodic condition given to the microscopic structure. Therefore, the experimental-based inelastic nonlocal constitutive equation is attempt to be formulated by extending the elastic nonlocal constitutive equation. In the formulation process, the strain gradient caused by the microscopic heterogeneity is added to conventional elastic and plastic strain gradients, and the inelastic nonlocal constitutive equation is derived based on the J2-flow theory.

Crystalline polymers may have some size effects that show different deformation responses depending on size of crystalline phase with respect to that of specimen. In the previous report, the cooling method for solidification of polypropylene from a molten state has some problems. In the present report, the authors attempt to control the crystalline phase size precisely by improving the cooling method. Furthermore, conducting some tensile tests on a polypropylene specimen, the effect of difference in crystal size on deformation response is investigated. In addition, it is indicated that a shape of crystalline phase should be changed in the unit cell of homogenization method.

An indicator, named slip operation factor (SOF), to predict the ease of slip operation in crystalline materials was developed. SOF is a function of Schmid factor (SF) and CRSS, and considers mechanical interactions among plastically “soft” and “hard” regions. A microstructural map of polycrystal α-titanium was obtained by electron back-scatter diffraction (EBSD), and several spatial distributions of SOF were obtained based on the map with changing the influence range of mechanical interactions among regions. The distributions were compared with the spatial distribution of slip strain obtained by a crystal plasticity finite element method, and they showed good agreement with each other when the influence rage was appropriate. The accuracy in the prediction of slip strain by SOF was higher than those by SF and normalized SF which is a type of SF considering the difference of critical resolved shear stresses (CRSSs) among slip systems.

The “key” feature of FTMP (Field Theory of Multiscale Plasticity) is the evolutionary aspects of the incompatibility-based microscopic degrees of freedom, η－μDOFs, responsible for the “description” of evolving inhomogeneous fields of concern.

To this, the theory asserts that the conversions or redistributions of deformation-induced excessive sorts of elastic strain energy into such η－μDOFs mainly act as the “driving forces” for the field evolutions, including those leading ultimately to various fracture modes. This means that, as far as relevant η－μDOFs are introduced in, e.g., hardening moduli of the constitutive model being used, the corresponding fields of inhomogeneity, including both their morphological aspects and the stress-supporting abilities, are relatively readily reproduced. These energy conversion processes are hypothesized as “flow-evolutionary law” in the FTMP framework.

Phase-field models are widely used to numerically reproduce the evolution of microstructure. Among them, Kobayashi-Warren-Carter (KWC) phase-field model are frequently used to analysis of microstructure formation with crystal rotation. However, this model cannot simultaneously express the evolutions of phase state and crystal orientation of each grain since it uses only one order parameter and one orientation parameter to express phase state continuously distributed over the analysis area. In the present report, we extend KWC model by introducing interface field in reference to multi-phase-field (MPF) model to handle a large number of grains. In addition, we perform an FDM analysis on a nucleation phenomenon from subgrains using this model and show its validity.

CZ silicon single crystals were deformed in tensile tests along the [1̅34] direction at between 1173 K and 1373. Yield point phenomenon were observed deformed at below 1273 K while continues yield was observed deformed at above 1323 K. Work-hardening rates in stage II were consistent with those reported in other fcc crystals. The onset of stage II was found to have been active before the Schmid factor of the second slip system becomes larger than that of the primary slip system. It supports Takamura's theory that the formation of kink bands contributes to the onset of stage II.

Strain distribution due to martensitic transformation in a Fe-Ni alloy has been investigated using high-precision markers drawn by electron beam lithography. Particular attention has been paid on the strain distribution inside lenticular martensite, which develops in the Fe-31mass%Ni alloy below martensite start temperature:223K. Since the width of the developed lenticular martensite was 5-20 μm, the fine grid marker was drawn in the spacing of 0.5μm on the flat surface of specimen before cooling. The strain distribution evaluated by measuring the displacement of each intersection using the grid marker revealed that the amount of strain at the middle area of the lenticular martensite is larger than that near the grain boundary. This result qualitatively corresponds to an estimated strain distribution by phenomenological theory of martensite crystallography based on the observation of microstructures in lenticular martensite, where the accumulation of fine transformation twins(so-called midrib) is observed in the middle area of the lenticular martensite. This suggests that the measured strain distribution is influenced by manner of lattice invariant deformation accompanied by martensitic transformation. In addition, the effects of electrochemical charged hydrogen on the strain distribution inside lenticular martensite in the Fe-31mass%Ni alloy are also examined.

Strain-induced martensitic transformation (SIMT) plays an essential role in generating the outstanding mechanical properties of TRIP steels such as strength, toughness and ductility. Therefore, deep understanding of the SIMT at microstructural scale is very important to predict and control accurately the superior macroscopic mechanical properties of TRIP steel. In the past, it is predicted that the austenitic grain size influence strongly the expected properties by the generalized model for the kinetics of SIMT. Additionally, martensitic embryo nucleates heterogeneously due to the dislocation initiating inhomogeneously on slip systems during plastic deformation. The complicated nucleation of martensite is of course size-dependent. Hence, it is necessary to have a good approach to describe martensitic transformation phenomenon including specific length scale. In this study, a developed continuum crystal plasticity theory including the concept of microforce proposed by Fried and Gurtin is employed in the framework of finite element method in order to simulate the size-dependent martensitic transformation of single crystal TRIP steel.

During tensile tests at room temperature using thin specimens made of SUS304, the propagation of X-shaped strain localization with serrations in flow stress occurs in the later stage of deformation. As a mechanism of the phenomenon, it can be considered that the necking in this material can be strengthened by strain-induced martensitic transformation (SIMT). On the other hand, the mechanism of the phenomenon can be dynamic strain aging (DSA) which cause the similar phenomenon called Portevin-Le Chatelier (PLC) band observed frequently in the aluminum alloys. That is, the mechanism has not been fully-concluded. In the past, it is reported that the propagation of strain localization bands can be generated by nonlocality of deformation in order to represent local necking and size effects of the specimen accurately. The analysis with nonlocality is quite hard to express the propagation of X-shaped strain localization with serrations. In another previous study, the model of DSA is introduced into the stress-strain, strain rate, temperature relationship for either austenite or martensite phase and that the propagation of X-shaped strain localization and serrations is confirmed. In the analysis which introduce the DSA, a use of value for the coefficient parameter n might be incorrect. Therefore, it can be said hardly that the analysis can express proper phenomena. The purpose of this study is to elucidate the mechanism of the phenomenon. The analysis considering the nonlocality with the damage or DSA solely with different value of parameter n are done by including them into the finite element method. Then, all the results including experimental ones are compared.

To clarify the effect of specimen size on the nonuniform deformation of polycrystalline copper, the tensile test of specimens having curved gage section with various sizes was performed. The digital image correlation method was used to evaluate the distribution of nonuniform strain on the specimen surface during the tensile deformation. A series of the experiment indicate clarified that the size effect on the mechanical property of polycrystalline copper. For large specimens, a symmetric strain distribution was observed in the center of the specimens. On the other hand, because the crystal grains are relatively large when the size of the specimen is small, the deformation is likely to be influenced by factors in the microscopic region due to the crystal orientation.

The impact of crystal orientation on incipient plasticity (in particular, pop-in behavior) was investigated via both experimental and numerical methods. The results obtained from nano-indentation testing reveal that the incipient plasticity is influenced by its orientation. The pop-in load and pop-in width for indentation to basal plane are higher and larger as compared with those for indentation to prismatic plane. From deformed microstructural observations, dislocations having <c> components are activated in the sample which indented to basal plane; however, such dislocation traces are unlikely to be confirmed in the case of indentation to prismatic plane. Numerical results through molecular static simulations provide a first activation of basal <a> dislocations and then occurrence for pyramidal dislocation activities.

Plane bending fatigue tests were conducted using coarse-grained magnesium (Mg) alloy, AZ31, at stress ratio R = -0.6. Prior to the fatigue tests, grain orientations were analyzed by EBSD to investigate fatigue crack initiation mechanism and the effect of grain orientations. Since annealing was performed for grain coarsening process, there was no texture as seen in the as-received Mg alloy. Transgranular crack initiation was observed in the fatigue tests at R = -1 and 0.1 in the previous studies. But fatigue cracks predominantly initiated along grain boundaries at R = -0.6. Crystallographic effects on intergranular crack initiation were summarized as follows. Fatigue cracks initiated along grain boundaries where Schmid factors of basal slips of two grains across the grain boundary were very high. In addition, the misorientation angles of c-axes of both grains were large. Grain boundary with those characteristics tends to induce accumulation of dislocations. Subsequently, fatigue crack initiated along that grain boundary. In the present study, fatigue test results at different stress ratios of R = -1，0.1 and -0.5 were evaluated using equivalent stress amplitudes based on SWT (SmithWatson-Topper) method. However, there was a large scatter in the fatigue lives depending on the stress ratios, which could be attributed to the different crack initiation mechanism at different stress ratios.

In this study, effects of yttrium (Y) addition on basal slip have been investigated by micropillar compression at room temperature. Micropillar specimens were machined with a focused ion beam apparatus in grains of pure magnesium (Mg) or Mg-1at%Y alloy polycrystals. The c-axis of the micropillars was inclined from the loading axis at an angle of approximately 45 degrees. The estimated critical resolved shear stress (CRSS) of basal slip was 14MPa for pure Mg and 30MPa for Mg-Y respectively, and moreover, the stress-strain curves of pure Mg and Mg-Y micropillars were different. The solid solution strengthening by Y was discussed with atomistic calculations.

The aim of present study is to investigate the relationship between deformation twinning avalanche behavior and macroscopic yield stress arising in polycrystalline pure Ti under mechanical loading. First, a commercial polycrystalline pure Ti palate is prepared, and the two types of micropillar specimens are fabricated from the plate. One is single crystal and bicrystal micropillar specimens which size is several micro meter, fabricated by Focus Ion Beam (FIB) technique. The other is polycrystalline micropillar specimens which size is from several dozen to several hundred micro meter, fabricated by in-house processing machine. Second, compression tests are performed by in-house micro compression test machines for the micropillar specimens. At the same time, acoustic emission (AE) monitoring is conducted to measure deformation twinning initiation. The relationship between deformation twinning avalanche behavior and macroscopic yield stress arising in polycrystalline pure Ti is discussed from the present experimental results.

In this study, cylindrical cup-drawability of a Grade 2 CP-Ti sheet was investigated by means of experiments and crystal-plasticity finite-element simulations. In the experiments, four ears were observed at 45° from the rolling direction, and the texture at the side wall was significantly different in the circumferential direction due to the difference in twinning activity. In particular, twinning was very active in the transverse direction, while twinning was not active in the rolling direction. The simulation results were in good agreement with the experimental results. Numerical experiments suggested that the twinning activity hardly affected the earing formation, indicating that the earing formation would be governed primarily by slip activities.

Mg-based LPSO phase is known to contribute to increase in both of strength and ductility of Mg alloys. As a deformation mode in the LPSO phase, kink-band formation is recently focused. In the present state, however, its formation criteria have not yet been clarified. According to the study on the LPSO phase, its unique crystal structure which is constructed by the alternative stacking of soft and hard layers, called mille-feuille structure, are supposed as plausible factors to govern the formation of deformation kink bands. To confirm these assumptions, in this paper we examined the deformation behavior of directionally solidified Mg/Mg₁₇Al₁₂ eutectic alloy with lamellar microstructure as a model material.

As a result, kink band formation was indeed confirmed when stress was applied parallel to the lamellar interface. The present results give a new insight to develop the noble strategy for the aggressive usage of deformation kink band to improve the mechanical properties of the materials.

Magnesium (Mg) alloys with long-period stacking ordered (LPSO) phase are potential candidates for next generation light-weight metallic materials because the wrought alloys show quite good mechanical properties compared with conventional Mg alloys. Whereas a number of researches on deformation behavior of LPSO-type Mg alloys have been done during last 20 years, understandings of active deformation modes of these alloys are still limited. In this study, active deformation modes during plastic deformation are examined based on evolution of lattice strain for both α-Mg phase and LPSO phase. Experimentally, lattice strains for various crystallographic planes were measured by in-situ neutron diffraction. The measured evolution of lattice strain was quantitatively evaluated by crystal plasticity analysis.

Magnesium alloys with the long period stacking order (LPSO) structure show the superior strength and are expected as the next generation structural material. In the mechanical behavior of LPSO-structured magnesium, the kink band in the LPSO phase may play an important role. In this study, to evaluate the deformation around kink band, a higher-order gradient crystal plasticity model is adopted. The reproducing kernel particle method (RKPM), which is a kind of meshfree method, is introduced to solve the higher-order crystal plasticity. The numerical integration scheme is essential in a meshfree analysis, and the stabilized conforming nodal integration (SCNI) is utilized. A numerical analysis of a specimen with kind band is demonstrated using the present method, and it is shown that kind band increases the macroscopic flow stress of material. Also, the effect of kink band shape on strengthening of flow stress is discussed.

Kink deformation, which occurs in the long period stacking ordered (LPSO) structure phase of Mg-TM-RE alloys, is considered to affect the excellent mechanical properties of this alloy. Although the mechanism of kink band formation was explained by segregation and rearrangement of dislocation, it is recently attempted to express the kinking process from the viewpoint of a rotational line defect called disclination. We developed a new model of Cosserat continuum consistent with the framework of the crystal plasticity by describing the microscopic plastic rotation as a quantity of each slip system and conducted meshfree analysis for a plate of a LPSO single crystal. However, a meshfree method imposing boundary conditions using Lagrange multipliers is not exactly consistent with the principle of virtual work. In this study, finite element method (FEM) using penalty parameters for boundary conditions is adopted to the dislocation-based crystal plasticity Cosserat model considering disclination density and it is shown that FEM can also reproduce the kink formation by use of disclination quadrupole structure and array structure of GN dislocation formed in the vicinity of the kink band as well as meshfree method. Furthermore, a size effect owing to the intrinsic length scale of Cosserat model is properly expressed under a boundary condition on rotational degree of freedom.

Kink-strengthening for mille-feuille structures has attracted many attentions in recent years. This study aims at identifying the kink formation/strengthening mechanisms via numerical reproductions of emerging kink-like morphologies based on FTMP (Field Theory of Multiscale Plasticity)-incorporated FE simulations, where incompatibility-based relevant underlying microscopic degrees of freedom for twinning are introduced, in addition to the slip modes. The targeted phenomena here include an experimentally-observed unique feature recently reported based on the combined ND–AE (neutron diffraction - acoustic emission) technique, i.e., scale-free-like energy release before (precursor) and during kink formations. This study uses a Mg single crystal model with alternatingly aligned soft and hard layers in parallel to the basal plane under c-axis plane-strain compression, where the soft/hard regions are controlled by the activity/inactivity of the twin model. The simulated results are demonstrated to exhibit power-law type distributions both in the strain energy fluctuation and the incompatibility from the early stage of deformation even before the massive emergence of kink-like regions, which are analogous to the above-mentioned ND–AE observations. They lead us to tentatively conclude that the layered structure associated with the incompatibility-based relevant degrees of freedom, in addition to a sufficient constraint of the basal slip activity, can play pivotal roles in reproducing the targeted feature.

Nanodiamond (ND) particles are nano-scale materials that have recently been attracting major attention for biological purposes, owing to their high biocompatibility and chemical stability. ND also possesses nanostructures, which makes it an ideal size for various purposes especially in nanotechnology.

An MRI contrast agent could be a suitable target for the practical use of nanodiamond particles. MRI contrast agents with a diameter of 3–10 nm could be selectively ingested by lymphatic vessels through simple subcutaneous injection, which could be then filtered in the kidney. However, ordinary contrast agents (Gd-DTPA) were smaller than 1 nm in diameter, and thus the MR imaging of the lymphatic system had not been successfully achieved. In this study, highly-dispersive carboxylated-nanodiamond (CND) particles with a diameter of ~5 nm were employed as a platform for the subsequent condensation of gadolinium-complexes (Gd-DTPA-CND). CND particles were employed not only for their nanoscale size, but also for the evasion of unnecessary aggregations of ND particles in water.

The diameter of Gd-DTPA-CND particles in distilled water was measured by the dynamic light scattering (DLS), revealing that the particles possessed a diameter of 4-5 nm, which was an adequate size for the selective uptake by limphs and for the final excretion at the kidney. The dispersity and the MRI visibility of Gd-DTPA-CND particles in human serum were evaluated by the transmission electron microscopy (TEM) and the 1.5T MRI, respectively. It was found that high-contrast imaging could be established by the Gd-DTPA-CND particles, indicating that the Gd-DTPA-CND particles possessed high MRI visibility in distilled water. Furthermore, the Gd-DTPA-CND particles also presented high dispersity and MRI visibility even in human serum, suggesting that the particles could be used intravitally. Therefore, it was concluded that Gd-DTPA-CND particles could be promising MRI contrast agents for the imaging of the lymphatic system through subcutaneous injection.

Anterior Cruciate Ligament (ACL) plays an important role in controlling tibial anterior translation and tibial internal rotation. But knee rotational instability does not improve after ACL Reconstruction (ACLR) for ACL Injury. Therefore, there is surgery to perform ACLR and Anterolateral Ligament Reconstruction (ALLR) at the same time. Anterolateral Ligament(ALL) controls tibial internal rotation. However, it has been reported that the reconstruction position of ALL affects tibial internal rotation. In this study, we first made a 3D knee joint model consisting of the femur, tibia, and fibula. Next, in the knee joint model which ALL, ACL, Posterior Cruciate Ligament (PCL), Lateral collateral ligament (LCL), and Medial collateral ligament (MCL) were attached, the effect of the attachment position of ALL on the internal rotation control function was evaluated by the finite element method (FEM). Using a 3D digitizer, we performed 3D scanning while rotating the right knee model by 20 °. The ligament model was made with a linear spring. When an anterior drawer force of 135 N was applied to the tibia, there was no difference in the tibial anterior translation amount with and without ALL. On the other hand, when an internal rotation torque of 5 N·m was applied, there was a difference in the tibial internal rotation amount with or without ALL.

The anterior cruciate ligament (ACL) prevents the tibia from moving forward toward the femur and the torsion of the knee. From an anatomical perspective, ACL composed of Antero-Medial (AM) and Postero-Lateral (PL) bundles. Therefore, ACL surgery is currently performed in two ways: single-bundle and double-bundle reconstruction. However, both methods have the problem of being damaged immediately after surgery. Therefore, it is important to elucidate the mechanical properties of the fiber bundles that make up the ACL. In this study, as part of elucidating the mechanical properties of ACL, we investigated the tensile speed dependence. In order to evaluate the anterior tibial braking performance of ACL, we applied a load to the front of the tibia at different angles and measured the amount of anterior movement of the tibia using the developed 6 degree-freedom testing machine. As a result, it was found that the greater the knee joint angle, the smaller the forward movement of the tibia. In addition, in order to evaluate the load speed dependency, the load was applied to the front of the tibia at the speeds of 1.0 mm / s, 0.1 mm / s, and 0.01 mm / s, and the amount of forward movement of the tibia was measured. As a result, it was found that the amount of forward tibial movement decreased as the loading speed increased.

The anterior cruciate ligament is prone to tearing due to abrupt valgus and rotation during intense sports, and natural healing is difficult, so reconstruction and replacement surgery are required. The ligament and bone tissue are not independent tissues, but cortical bone, calcified fibrocartilage, non-calcified fibrocartilage, and ligament from bone tissue to ligament tissue. Divided into hierarchies, they are collectively referred to as enthesis. In this study, 23-month-old bovine femur specimens were prepared, and Raman spectroscopic measurements were performed on each layer. First, the composition of substances contained in dry and wet specimens was measured in an unloaded state, and the spectra were compared using the strength ratio of the contained substances and FWHM as indicators. Contrary to the expectation that B and L showed the prominent properties of hard and soft tissues, significant peaks were observed for CFC and FC, which are intermediate substances. Since the cause is unknown at present, the results of this study will be considered in detail by increasing the sample size and measuring under tensile load.

Beauty roller is a device that expects activation of the subcutaneous tissue by massaging them with the roller. Although it is qualitatively clear that an effective massage using a beauty roller can be used instead of massage by human hand, further clarifying the deformation and stress behavior contributes to the improvement of the equipment and future design. In this study, we created a hyperelastic human model and analyzed the deformation and stress generation behavior caused by the rotation of the beauty roller by FEM. It was found that the used part deformed in such a way that it is picked up by two rollers, and the stress concentrates in the vicinity of the contact area between the roller and the part being picked up. Further verification of such behavior is going to help create a more efficient massage device.

Pressure ulcer occurs due to the closure of microvessels with prolonged load, i.e., pressure and shear loads, on the skin surface. The aim of this study is to identify the mechanical factors which determine the conditions of venous closure in the soft tissue. In the previous study we analyzed the deformation behavior of cephalic vein in the forearm for two healthy men by compressing the skin surface with a probe of medical ultrasound scanner. Based on the measurement data, we obtained the changes of the venous height and width and the compressive load with the vertical displacement of the probe. We found that the load increased exponentially and the height of the vein decreased almost linearly while the width was almost kept during the displacement of the probe by 3-4 mm. We also conducted three-dimensional finite element analysis to simulate the deformation behaviour of the cephalic vein in the subcutaneous tissue with a compression of the skin surface by the probe. The closure of the vein was accompanied with a compression of the layer of skin and subcutaneous tissue which was located at the side of the vein. We found that the noncircular cross section of vein under venous pressure and the change of load under the displacement of the probe were similar to the measured one for subjects.

To determine the stiffness of the medial (MCL) and lateral (LCL) collateral ligaments in varying knee flexion angles. Strain ultrasound elastography with an acoustic coupler as the reference was applied to obtain relative stiffness of the proximal, middle, distal portions of the superficial MCL (sMCL) and LCL, and meniscofemoral and meniscotibial portions of the deep MCL (dMCL) in 10 healthy males while placing the knee in different flexion angles. The relative stiffness of the ligaments was defined using strain ratio (SR); strain develops in the target tissue to that in the reference. Reliability of the SR values were tested using Intraclass correlation coefficient (ICC). The intra ICC (1, 3) and interrater ICC (2, 3) values for the SR measurements were good (0.6–0.9) for all the ligament portions. The relative stiffness was highest in 0°, and it was decreased when increasing the knee flexion in the MCL. However, LCL have shown a fluctuating stiffness behavior through the flexion pathway. Strain ultrasound elastography is a reliable and feasible tool in routine clinical practice to monitor stiffness of the collateral ligaments. The ligament stiffness decreased from knee extension to flexion.

The demand of artificial bones as substitutes of natural bone for producing bone grafts is increasing and the ways to recalcify collagen are examined. One of the methods to do so is called PILP process. This mothed is different from previous ones and it was reported that this method could imitate the structure of natural bone. Previous researches have investigated ultra-scale bone structures by SEM, TEM and so on, but only few mechanical tests were conducted. The purpose of this study is to examine mechanical behaviors of recalcified bone through PILP process, by tensile test and X-ray diffraction. Specimens were cut from the cortical bone of the lateral aspect of the middle diaphysis of an adult right bovine femur. Specimens were fully decalcified by 10 % formic acid and then recalcified by recalcification solution. There were 4 conditions of specimens, intact specimens, decalcified specimens, 5 days recalcified specimen and 7 days recalcified specimen. The elastic modulus was determined by tensile test under optical microscope. The microscopic strain of HAp crystal was measured by X-ray diffraction. The elastic moduli of recalcified specimen were much lower than intact specimen. The reasons why that were thought to be that the time to recalcify specimens was too short and anisotropy of 7 days recalcified specimen decreased. The relationship between tissue strain and microscopic strain of HAp crystal at (211) crystal plane in intact specimen was positive. The relationship in recalcified specimen was a slightly positive. In recalcified specimens, because the amount of HAp crystals was small and the stress was concentrated on collagen, the lattice strain was small and correlation became weak. As the recalcification progressed, the anisotropy characteristic became decreased when comparing to natural bone. But, the mechanical behavior of recalcified specimen is similar to natural bone.

Osteoporosis of elder people has been one of the primary clinical orthopedic problems in Japan. Deformation and fracture behavior of osteoporotic cancellous bones must be clarified in order to understand the mechanism of bone fracture due to osteoporosis. In the present study, micro-CT images of real femoral head of an elder patient were used to fabricate cancellous bone plastic models using 3D-printing technique and furthermore, to construct a finite element model of the cancellous bone. Compressive mechanical tests of the plastic 3D models and the FE model were conducted and the stress-strain relations obtained from the different tests were compared. It was found that the FEA with micro-CT images can predict the experimental behavior very well.

Trapeziometacarpal joint (TMC joint) is one of the joints having a complicated shape which enables to generate a wide variation of finger movements in daily life. It is important to clarify the in vivo contact behavior of healthy TMC joint when evaluating artificial joint design and post-operative joint movements. Thus, author analyzed right-side TMC joint contact behavior in 4 different finger positions of 8 healthy males using magnetic resonance imaging (MRI) system. From MR images, 3D bone models were constructed and a 3D coordinate system was defined by the shape of each 3D model. Then, three bone axial angles of each 4 positions in the TMC joint were calculated: abduction-adduction, extension-flexion, pronation-spination. Furthermore, contact area of the articular cartilage in each 4 positions were clarified from MR images.

Although the teeth are arranged three-dimensionally (3D) in the oral, generally the dental arch is determined in 2D. However, 3D information is needed in computer aided diagnosis, in designing customized implants and in planning orthodontics procedures. Therefore, this study aimed at a method of expressing the dental arch three dimensionally. The 3D models of maxillary and mandibular jaws were constructed from CBCT images of five adults. A 3D world coordinate system in the oral was developed from three feature points of the jaw models. Then, 3D tooth surface models of all the teeth except the third molar were constructed and determined the center of gravity (COG) of each model. The COGs of the all teeth were projected on X-Y(axial), X-Z(coronal) and Y-Z(sagittal) planes of the 3D world coordinate system. The projected COGs of each maxillary and mandibular teeth were regressed as Quadratic to Seventh-order function in each plane. Then the regressed curves were examined using residual sum of squares (RSS) and with aesthetic point of view.

Magnesium (Mg) would be promised as biodegradable material for producing a stent applied in blood vessels. Though Mg had the advantage properties of biocompatibility and adjustment in body, it had the disadvantage properties of low corrosion resistance and so strength. We had tried to conduct two kinds of immersion tests for corrosion behavior with 99.9wt% Mg ribbon. One is that an immersion test was conducted under physiologic saline (0.9%NaCl) and the other is that under simulated body fluid (SBF) at 37℃ for 0, 48, 120 hours. The corrosion behavior was evaluated to focus on any corrosion products, tensile strength and surface morphology. It resulted that specimens immersed in 0.9%NaCl produced Mg(OH)₂ as corrosion products and showed general corrosion. The tensile strength decreased with the surface roughness increased. The specimens immersed in SBF produced Ca₃(PO₄)₂ and showed pitting corrosion, and the tensile strength decreased with the increase of surface roughness. As a result, a corrosion behavior can have an effect on the relationship between surface roughness and tensile strength. Both solutions relationship between surface roughness and tensile strength was different and corrosion state affected mechanical property. Next, the immersion test was conducted that the specimens were applied some loads with the equipment designed by ourselves. Then, the test solution was 0.9%NaCl and temperature was at 37℃. Consequently, the specimen was fractured for shorter time because of accelerating anodic reaction at specimen surfaces concentrated on impurities and then cracking.

Friction and wear properties of titanium-based materials are improved by nitriding; however, conventional nitriding decreases their strength owing to the grain-coarsening at high temperature (approximately 900 oC). The purpose of this study is to develop the rapid nitriding for titanium-based materials at room temperature in air without heating. This approach forms the nitrided layer on titanium-based materials using the transfer of nitrided commercially pure titanium particles during fine particle peening (FPP). Plasma nitriding was performed at 600 or 700 oC to form a nitrided layer on the surface of CP-titanium particles, and FPP was performed for 1, 10, 30 s using the nitrided particles. Nitrided layer could be found on titanium alloy (Ti-6Al-4V) due to the transfer of nitrided CP-titanium particles. Nitrogen concentration tended to increase with the particle nitriding temperature. Furthermore, the thickness of nitrided layer tended to increase with the treating time. Formation rate of nitrided layer by the developed process was higher than that by the conventional nitriding. In addition, nitrogen concentration of the treated surface on CP-titanium was higher than that by Ti-6Al-4V alloy and β-type titanium alloys.

Co-Cr alloy is widely used as implant materials. The design life of artificial joints is 10 to 20 years and the increase in durability is required as the aging of society is expected. Most of the artificial joints are currently made by European and American manufacturers and their applications to small physiques, including Japanese women, are not fully expected. There are difficulties in current materials to create thinner and longer implants to suit and fulfill the requirements depending on the bone shape. Therefore, it is necessary to improve the fatigue properties of Co-Cr alloys. Shot peening (SP) is one of the methods to improve these parameters. In this study, bending fatigue tests and observation of surface morphology, crystalline structure analysis were conducted on SP-treated medical grade Co-Cr alloys. Surface roughness and hardness distribution showed typical values compared to present research. EBSD analysis showed strain-induced martensitic transformation (SIMT) and refinement of crystal grains near the SP-treated surface. These effects were remarkable among specimens treated by high hardness projection materials and high coverage. Fatigue test revealed that the fatigue limit of the SP-treated specimen was improved by 77%. However, there were no significant differences in fatigue strength between SP-treated specimens under various conditions. Saturation of martensite transformation near the surface and equivalent compressive residual stress may be the primary effect to fatigue properties compared to surface roughness and hardness.

We have been trying to optimize the microstructures of the HAp/collagen composite fibers, in order to enable the creation of the artificial bone mimicking the bone microstructures. Previously, we evaluated the effects of the cross-linking and HAp deposition condition on the tensile strength of the HAp/collagen composite fibers. In this study, we tried to optimize the amount of the cross-linking agent, the adhesive protein and deposited HAps. The collagen fibers were prepared by the bio-inspired method, where the fibrosis and the cross-linking are generated at the same time. The HAp particles were deposited on the collagen fibers by the biomimetic deposition method, where the collagen fibers are dipped into the pseudo body fluid alternatively. The HAp/collagen composite fibers were coated with osteonectin as the adhesive protein before the HAp deposition process. As a result, the tensile strength of the HAp/collagen composite fibers increased and then decreased with the increase of the cross-linking agent concentration, the adhesive protein concentration and the HAp deposition time. In addition, the tensile strength of the HAp/collagen composite fibers with the osteonectin coating was maximized under the moderately low EDC concentration, the intermediate adhesive protein concentration and the moderately short HAp deposition time. It is considered that the osteonecitn used as the adhesive protein would act as the additional bonding factor between the collagen fibers and HAp crystals, and would decrease the tensile strength of the HAp/collagen composite fibers in the case of the excessive interfacial bonding.

10¹¹ cycles fatigue tests were conducted on high-strength steel to clarify a new fatigue limit in very high cycle regions. The new fatigue limit had not been confirmed by fatigue tests up to 10¹⁰ cycles, while our previous study suggested that the new fatigue limit was probably confirmed by those up to 10¹¹ cycles. However, the 10¹¹ cycles fatigue testing was challenging since it took 2 months even by using ultrasonic fatigue testing at 20 kHz. In this study, 3 specimens were tested beyond 10¹⁰ cycles. Although a test on a specimen was terminated at around 5 x 10¹⁰ cycles, 2 specimens reached 10¹¹ cycles without failure. In other word, no specimen failed above 10¹⁰ cycles. These results demonstrated the existence of the new fatigue limit. The fractured specimens below 10¹⁰ cycles revealed internal fractures originating from oxidetype inclusions. When the specimens failed in very high cycle regions, clear ODAs (Optically Dark Areas) were observed on the fracture surfaces, while the ODAs were obscure in case of failure in conventional life regions. The runout specimens up to 10¹¹ cycles were forcibly fatigue-fractured at higher stress amplitudes in the conventional life regions. As the result, the ODA was observed on the forcibly fatigue-fractured surface. This meant that small internal cracks existed in the runout specimens since the ODA was a trace of small internal crack growth. Namely, non-propagating cracks were the mechanism of the appearance of the new fatigue limit.

Low- and rgiga-cycle fatigue tests were conducted for heats A and B of SUS329J3L duplex stainless steels. In the low-cycle fatigue properties, all samples revealed almost equal fatigue strength under constant strain amplitude tests. Cyclic softening and hardening were small, and cyclic yield stress was revealed to be almost equal to that of conventional steels. In the giga-cycle fatigue tests, almost all specimens showed surface fracture in case of Heat A, while Heat B showed surface and internal fractures. In the giga-cycle fatigue properties, the difference was small between the Heat A and Heat B. In this case, the rotating bending tests revealed higher fatigue strength than uniaxial loading tests.

Since SUS630 is good at strength and anticorrosion, it is used for a wide range of engineering fields, where high reliability is required for the material. Along with the aging of structural components, fatigue strength and fatigue crack growth characteristics are becoming more significant in very high cycle regime. In this study, crack growth tests were conducted using ultrasonic fatigue testing machine in order to clarify the effect of stress ratio on the crack growth characteristics of SUS630. The crack growth test results show that stress ratio have strong influence on threshold characteristics and that the crack growth rate of stress ratio, R, of 0.8 is higher than those of other R. The characteristics were compared with a standard, WES2805, published by The Japan Welding Engineering Society. Fatigue crack growth diagram of WES2805 showed conservative crack growth characteristics compared with the experimental data. Ultrasonic fatigue tests were also conducted for sharp notched round bar specimens. The fatigue test results revealed that the threshold stress intensity factor range calculated by tensile component of the cyclic stress and the notch depth regarded as a crack length is a controlling parameter for the fatigue fracture of the sharply notched specimens. Maximum stress intensity factor at fatigue limit and threshold stress intensity factor range at R of 0.5 showed similar values due to the crack closure behavior.

In order to investigate fatigue properties of magnesium alloy in very high cycle regime, the cantilever type rotating bending fatigue tests were carried out using AZ31, AZ61 and AZ80 alloys at room temperature in air. As a result of the cantilever type rotating bending fatigue test, S-N curve of AZ61 and AZ80 have the tendency of a duplex S-N curve, and S-N curve of AZ31 has tendency of the monotone decreasing that did not show a clear fatigue limit. The fatigue crack origins in high stress and low cycles area were the twin deformation at the specimen surface, and the fatigue crack origins in low stress and high cycles area were the slip deformation at the specimen surface. As a result of estimating the time strength at 10⁷ cycles using the fatigue limit estimation formula proposed by Murakami et al., the estimated value was close to the experimental value.

In this study, cantilever type rotating bending fatigue test and axial force fatigue test were carried out for the cast aluminum alloy. Three kinds of materials with different manufacturing time were prepared. The very high cycle fatigue properties and damage mechanism were investigated. As the result of the micro Vickers hardness tests, it was found that the hardness has the tendency to increase from the inside of the test specimen toward the surface. As the results of cantilever type rotating bending fatigue test, the test specimen were fractured over 1×10⁸ cycles, the S-N curve showed a tendency specific to non-ferrous metals that did not show a clear fatigue limit. The fatigue strength of the cantilever type rotating bending fatigue test was higher than that of the axial fatigue test. The fatigue crack origin was mostly a casting defect. The positions of the crack origin were a surface or close to surface. √area were almost 100 μm or less. There was no clear correlation between √area and the number of cycles to failure. It was found that √area follows a Gumbel distribution. As a result of estimating the time strength at 107 cycles using the fatigue limit estimation formula, the estimated value was close to the experimental value.

It is well known that there are a strong correlation between emission of CO₂ gas and weight of car. Therefore, the weight saving of industrial products are one of the effective means for stopping the global warming. For this purpose, aluminum alloy are one of the candidate materials because of its excellent properties. Especially, aluminum die-casting alloy has been widely used in industrial products because of its lightweight, high dimensional stability for complex shapes and thin walls and so on. On the other hand, as compared with steel, there not enough fatigue testing data including a very high cycles regime. Also, some researcher reported that aluminum die-casting alloy takes on the so-called “interior induced fatigue fracture” in the VHCF regime, as same as high-strength steel. In this study, for considering a mechanism of the “interior induced fatigue fracture” of aluminum die-casting ally JIS ADC12, fatigue tests up to N > 10⁸ cycles were carried out in ambient air and high vacuum environment. Fatigue crack initiation and propagation behavior are also observed with a newly developed “real-time fatigue crack observing system”. Also, the FRASTA technique were applied to fatigue fracture surface. By using both fatigue crack images and FRASTA results, it is confirmed that there every possibility of unraveling the “interior induced fatigue fracture” mechanism of ADC12.

It is well known that there are a strong correlation Relationship between emission of CO₂ gas and weight of car. Therefore, the weight saving of industrial products are one of the effective means for stopping the global warming. For this purpose, aluminum alloy are one of the candidate materials because of its excellent properties. Especially, aluminum die-casting alloy has been widely used in industrial products because of its lightweight, high dimensional stability for complex shapes and thin walls and so on. On the other hand, as compared with steel, there not enough fatigue testing and/or fatigue crack data including a very high cycles regime. In this study, the real-time fatigue crack observing system for rotating bending testing machine has been improved. This system consists of (1) testing machine motor with a rotary encoder, (2) programmable logic controller(PLC) for controlling flash timing, (3) electronic flash with high-brightness white LEDs arranged on spherical surface, (4) long working distant type microscope and (5) hi-definition digital video camera. For verifying performance of this observing system, fatigue tests were carried out by using fatigue specimen having a small artificial defect. It is proved that this system can be detect a small fatigue crack and its propagation behavior during N > 10⁷ range without stopping fatigue test.

Uniaxial fatigue tests of Ti-22V-4Al alloy were carried out up to very high cycle regime at various stress ratios. In case of internal crack, so-called facets regarded as a crack initiation site were found from the fracture surface. To figure out the internal crack initiation and propagation process, fractographic analysis using 3D SEM was conducted. Material constants “C” and “m” in the Paris law were obtained by comparing the characteristics of facets around the fracture origins to estimate fatigue life caused by internal crack, and a new model of facet initiation process was proposed. As a result, the internal crack fatigue life estimation using the proposed model was clarified to be effective to evaluate experimental results.

The initiation process of internal fatigue cracks in Ti-6Al-4V in very high cycle regime was investigated via synchrotron radiation X-ray CT. A projection-type CT with a resolution of one micrometer or below and a phase contrast imaging-type CT with a resolution of sub-micrometer were used. The projection-type CT revealed that 1) more than twenty cracks initiated in one specimen, 2) fatigue life varied widely from 20% to 70% of the average fatigue life, and 3) whether the initiated crack can smoothly propagate or not was determined by the nonuniformity of surrounding microstructure. The imaging-type CT clarified that the crack initiation was caused by slip deformation in α phase and that the shape of internal crack tip was blunter than that of surface crack tip.

In Ti6Al4V alloy, the origin of fatigue fracture is usually at the surface in the high stress and lower fatigue life region, whereas in low stress and longer fatigue lifetimes in very high cycle fatigue regime, origins are generally sub-surface in nature. Observation of fracture surfaces revealed that the unique fine concave-convex agglutinate (hereinafter called Granular Region) formed on the fracture surface of sub-surface fractures. Since this peculiar area is not observed on the fracture surfaces of surface fractures, the formation mechanism of the area can be a clue to the unified comprehension of the characteristics of the sub-surface fracture. In this study, the formation mechanism of the granular region has been experimentally investigated. Test pieces with smooth and rounded surfaces were repeatedly contacted in air or vacuum environment. As a result, fine surface asperities were observed on the contact surfaces which was quite similar to that observed in the sub-surface fractures. Nanoscale-indentation tests and detailed observations using SEM were carried out on the microstructure just below the contact surface. In the indentation tests, characteristic force-displacement curves were obtained for the fine surface asperities part. Furthermore, microstructure refinement and metallic adhesion were confirmed in the observations. These phenomena probably relate to the different fatigue crack propagation properties in the surface and sub-surface fractures.

Wrinkles form when a stiff film attached to a soft substrate is compressed beyond a critical strain. As the compressive strain further increases to another critical level, the wrinkles evolve into folds. The wrinkle-to-fold transition has been exploited to fabricate functional devices and to rationalize morphogenetic features of biological systems. However, the transition is difficult to induce in practice because relatively large compressive strains need to be applied. Here, we show a method using water for triggering the transition even for strains considered suitable only to generate wrinkles and demonstrate its potential use in developing nano- and microchannels.

To clarify the effect of loading mode on exothermic chemical reaction mechanisms in Ti/Si multilayered nanofilms under mechanical loading, in situ TEM shear experiments were conducted and the results were compared to those of previous compression experiments. The in situ TEM observation indicated that plastic shear deformation occurred at the very local region under shear loading, resulting in the generation of new Ti/Si interface. Nano-beam electron diffraction analysis revealed that a new crystal structure, proposed to be Ti₅Si₄ and/or TiSi, was generated at the local region. This chemical reaction mechanism was different from that under compression where the multilayers were plastically compressed in the stacking direction and the chemical reaction occurred in a broad interface region. These findings suggest the possibility of controlling the chemical reaction by local mechanical loading mode.