WileyActa Medica Okayama8756-758X2026Fatigue Life Evaluation Using the Damage]Equivalent Strain for 7075]T6 Aluminum Alloy Under Bending and Torsion Bending VibrationsENJunjiSakamotoFaculty of Environmental, Life, Natural Science and Technology, Okayama UniversityNaoyaTadaFaculty of Environmental, Life, Natural Science and Technology, Okayama UniversityTakeshiUemoriFaculty of Environmental, Life, Natural Science and Technology, Okayama UniversityThe vibrations caused by external factors (such as fluids) or internal factors often pose strength-related problems in mechanical and structural components. Although several studies have investigated the material fatigue characteristics during vibration, reports on complex vibration modes such as torsion bending are limited. In this study, we addressed this gap by conducting experiments and finite element analyses on I- and L-shaped aluminum alloy specimens under bending and torsion bending vibrations, respectively. We established a reliable method to estimate the strain at the notch by utilizing the strain measured at a position outside the notch and a ratio derived from finite element analysis. This method allows for accurate assessment of the critical strain history without interfering with crack observation. Using the strain range at the crack initiation site effectively unified the fatigue life evaluation for both specimens.No potential conflict of interest relevant to this article was reported.Elsevier BVActa Medica Okayama2352-4928502026Effects of grain size and crystal orientation on tensile properties of pure titanium thin wires114240ENJunjiSakamotoFaculty of Environmental, Life, Natural Science and Technology, Okayama UniversityNaoyaTadaFaculty of Environmental, Life, Natural Science and Technology, Okayama UniversityTakeshiUemoriFaculty of Environmental, Life, Natural Science and Technology, Okayama UniversityTo clarify the effects of the grain size and crystal orientation on the tensile properties of pure titanium thin wires, tensile and stepwise tensile tests were conducted on pure titanium wires with diameters of approximately 180 ƒÊm and different average grain sizes (52, 37, 23, and 3.8 ƒÊm). When the grain size was large, the fracture strain was significantly smaller, the variation in tensile strength was larger, and the grain size threshold for such properties was a grain-size ratio to wire diameter of 0.13 or greater. For larger grain sizes, the slip system with the highest modified Schmid factor (MSF), which is the Schmid factor divided by the critical resolved shear stress of each slip system, was activated in all 15 grains whereas for smaller grain sizes, the percentage of slip systems activated with the highest MSF was slightly lower. In addition, the fracture location in a thin wire with larger grain sizes was highly correlated with the average MSF of the grains in the cross-section.No potential conflict of interest relevant to this article was reported.Informa UK LimitedActa Medica Okayama0960-34094312025Creep damage parameters based on the distribution of cavities on grain boundaries4557ENNaoyaTadaFaculty of Environmental, Life, Natural Science and Technology, Okayama UniversityWhen polycrystalline heat-resistant steels are subjected to static or cyclic loading at high temperatures, they can exhibit various fracture modes and processes. This paper begins by outlining representative methods for life assessment under creep-dominated conditions. It then discusses the fracture processes and the underlying mechanisms. Under creep-dominated conditions, the initiation and growth of cavities serve as the primary form of material damage, making their quantitative assessment essential. Several parameters have been proposed to evaluate cavity distributions quantitatively. However, the relationship between these parameters and the actual cavity distribution in materials, as well as their physical significance, has remained unclear. In this study, a simple cavity distribution model was employed to clarify these issues. The results suggest that the area fraction of cavities is an appropriate damage evaluation parameter for transgranular fracture, while the fraction of cavities on grain boundary line is suitable for intergranular fracture.No potential conflict of interest relevant to this article was reported.IOP PublishingActa Medica Okayama1742-658828922024Crystal Grain Rotation during Tensile Test of Polycrystalline Pure Titanium Thin Sheet Based on Surface Height and Crystal Orientation012002ENNaoyaTadaOkayama UniversityHiroakiOhashiOkayama UniversityTakeshiUemoriOkayama UniversityJunjiSakamotoOkayama UniversityThin sheets and wires of polycrystalline pure titanium are important materials for various devices used in electrical, mechanical, dental, and medical fields. Since pure titanium shows strong anisotropy in elastic and plastic deformation, and the individual grains comprising a polycrystalline body have different orientations and geometries, inhomogeneous deformation always occurs on the microscopic scale. This inhomogeneity is more significant in thin films than in bulk materials. It is therefore important to investigate the inhomogeneous deformation of pure titanium thin sheets to ensure the reliability of various titanium devices. In this study, thin-sheet specimens made of polycrystalline pure titanium were subjected to tensile testing. Inhomogeneous deformation was evaluated on the basis of two kinds of crystal grain rotations based on surface height and crystal orientation. The results under elastic and plastic tensile conditions were compared.No potential conflict of interest relevant to this article was reported.Elsevier BVActa Medica Okayama2452-3216682025Method for predicting crack size using amplitude change in titanium alloy under bending vibration13191323ENJunjiSakamotoOkayama University, Faculty of Environmental, Life, Natural Science and TechnologyNaoyaTadaOkayama University, Faculty of Environmental, Life, Natural Science and TechnologyTakeshiUemoriOkayama University, Faculty of Environmental, Life, Natural Science and TechnologyThe natural frequency of a material decreases owing to the presence of cracks. Thus, when a crack initiates in a material under vibration, the amplitude of the vibration changes with the crack propagation. In this study, we investigated a method for predicting crack size using the amplitude change in a plate specimen of a titanium alloy under bending vibration. The bending displacement amplitudes were measured using high-speed camera images of the specimens. The crack sizes were measured using optical microscopy images of plastic replicas of the specimen surfaces that were obtained after interrupting tests at specified intervals. By using the relationship between the total area of the cracks and bending displacement amplitude for tests at two different vibration frequencies as well as the relationship between the vibration frequency and bending displacement amplitude for an undamaged specimen, the bending displacement amplitude at any vibration frequency can be monitored to predict the total area of the cracks.No potential conflict of interest relevant to this article was reported.Japan Society of Mechanical EngineersActa Medica Okayama2187-97451162024Effect of artificial defect on tensile properties of thin titanium alloy wire24-00129ENJunjiSAKAMOTOOkayama UniversityNaoyaTADAOkayama UniversityTakeshiUEMORIOkayama UniversityKoyoOISHIOkayama UniversityThis study investigated the effects of artificial defects, introduced via focused ion beam (FIB) processing, on the tensile properties of thin titanium alloy wires (Ti-6Al-4V). Results indicated that the defective wires fractured when the net-section nominal stress reached the ultimate tensile strength of the smooth wires, probably because of localized stress concentrations relaxing due to plastic deformation around the defects. The effect of defects on tensile properties was classified into three regions based on the size of the defect area. In the case of small defects, wires fractured at the smooth area away from the defects where the cross-sectional strength was lower. In this case, the defects minimally affected the tensile properties. This is attributable to variations in the cross-sectional strength of the wire, which resulted in some sections with lower strength as compared with the defect area. In the case of medium-sized defects, the fracture strain decreased gradually as the defect area increased. Finally, in the case of large defects, the fracture strain was extremely small. The boundary between the medium-sized and large defects indicates the transition from plastic deformation to no plastic deformation in the smooth area.No potential conflict of interest relevant to this article was reported.ElsevierActa Medica Okayama1350-63071532023Prediction of slip activity of crystal grains around semi-circular and semi-elliptical notches in thin-sheet specimens of pure titanium using formulated macroscopic stress distribution and crystal orientation107623ENNaoyaTadaFaculty of Environmental, Life, Natural Science and Technology, Okayama UniversityTakeshiUemoriFaculty of Environmental, Life, Natural Science and Technology, Okayama UniversityJunjiSakamotoFaculty of Environmental, Life, Natural Science and Technology, Okayama UniversityThin metal sheets and wires are important materials for various devices used in electrical, mechanical, and medical fields. With the downsizing of these devices, demand for thinner sheets and wires has increased. Amongst the many metals available, pure titanium has been attracting much attention for use in medical and dental devices because of its good biocompatibility in addition to its light weight and high corrosion resistance. However, thin metal sheets and wires are usually polycrystalline materials and, with the downsizing of materials, there is a loss of homogeneity during deformations. Inhomogeneous deformation becomes significant in thin sheets and wires, owing to the different crystal orientations and geometries of crystal grains. Furthermore, the shapes of such devices are not uniform, unlike, say, a simple rod. Therefore, macroscopic stress and strain concentrations should be taken into consideration when designing these devices as they affect the localization of deformation and the resultant fracture. In this study, semi-circular and semi-elliptical notched specimens made of thin-sheet polycrystalline pure titanium are subjected to tensile testing. Inhomogeneous deformation caused by crystallographic slip is observed near the notch root. Analysis of the crystal orientation and observation of the slip line show that the slip initiation in crystal grains is affected by the macroscopic stress distribution and can be predicted from the slip activity calculated from both the critical resolved shear stress on the slip systems and the resolved shear stress acting on prospective slip planes obtained from the macroscopic multiaxial stress distribution.No potential conflict of interest relevant to this article was reported.ASME InternationalActa Medica Okayama0094-993014322020Prediction of the Fracture Location by Tensile Tests of Gray Cast Iron Based on the Dimensional Changes of Graphite Flakes021502ENNaoyaTadaGraduate School of Natural Science and Technology, Okayama UniversityTakeshiUemoriGraduate School of Natural Science and Technology, Okayama UniversityJunjiSakamotoGraduate School of Natural Science and Technology, Okayama UniversityGray cast iron has been used as a component in various mechanical parts, such as the blocks and heads of automobile and marine engines, cylinder liners for internal combustion engines, and machine tool bases. It is desirable because of its good castability and machinability, damping characteristics, and high performance-to-cost ratio. On the other hand, weak graphite flakes present in gray cast iron serve as stress concentrators and adversely affect the material strength. Therefore, it is crucial to examine the relationship between the distribution of graphite flakes and the strength or fracture of gray cast iron. In this study, tensile tests on gray cast iron were carried out using a plate specimen and observed by scanning electron microscopy, and the microscopic deformation was observed on the specimen surface. Particularly, the change in the size of graphite flakes during the tensile tests was examined, and the observed trend was discussed. The experimental results reveal that the dimensional changes in the graphite flakes vary in the observed area and that the final fracture occurs in an area where a large dimensional change is observed, suggesting that the fracture location or critical parts of gray cast iron can be predicted from the dimensional changes of the graphite flakes at an early stage of deformation.No potential conflict of interest relevant to this article was reported.MDPIActa Medica Okayama2076-341710142020Finite Element Study of the Effect of Internal Cracks on Surface Profile Change due to Low Loading of Turbine Blade4883ENJunjiSakamotoGraduate School of Natural Science and Technology, Okayama UniversityNaoyaTadaGraduate School of Natural Science and Technology, Okayama UniversityTakeshiUemoriGraduate School of Natural Science and Technology, Okayama UniversityHayatoKuniyasuShimadzu CorporationTurbine blades for thermal power plants are exposed to severe environments, making it necessary to ensure safety against damage, such as crack formation. A previous method detected internal cracks by applying a small load to a target member. Changes in the surface properties of the material were detected before and after the load using a digital holographic microscope and a digital height correlation method. In this study, this technique was applied in combination with finite element analysis using a 2D and 3D model simulating the turbine blades. Analysis clarified that the change in the surface properties under a small load varied according to the presence or absence of a crack, and elucidated the strain distribution that caused the difference in the change. In addition, analyses of the 2D model considering the material anisotropy and thermal barrier coating were conducted. The difference in the change in the surface properties and strain distribution according to the presence or absence of cracks was elucidated. The difference in the change in the top surface height distribution of the materials with and without a crack was directly proportional to the crack length. As the value was large with respect to the vertical resolution of 0.2 nm of the digital holographic microscope, the change could be detected by the microscope.No potential conflict of interest relevant to this article was reported.MDPIActa Medica Okayama2075-4701972019Effect of Lubrication and Forging Load on Surface Roughness, Residual Stress, and Deformation of Cold Forging Tools783ENNuwanKarunathilakaGraduate School of Natural Science and Technology, Okayama UniversityNaoyaTadaGraduate School of Natural Science and Technology, Okayama UniversityTakeshiUemoriGraduate School of Natural Science and Technology, Okayama UniversityRyotaHanamitsuGraduate School of Natural Science and Technology, Okayama UniversityMasahiroFujiiGraduate School of Natural Science and Technology, Okayama UniversityYuyaOmiyaGraduate School of Natural Science and Technology, Okayama UniversityMasahiroKawanoZeno Tech Co., LtdCold forging is a metal forming that which uses localized compressive force at room temperature. During the cold forging process, the tool is subjected to extremely high loads and abrasive wear. Lubrication plays an important role in cold forging to improve product quality and tool life by preventing direct metallic contact. Surface roughness and residual stress also greatly affects the service life of a tool. In this study, variations in surface roughness, residual stress, and specimen deformation with the number of cold forging cycles were investigated under different forging conditions. Specimens that were made of heat-treated SKH51 (59-61 HRC), a high-speed tool steel with a polished working surface, were used. The specimens were subjected to an upsetting process. Compressive residual stress, surface roughness, and specimen deformation showed a positive relationship with the number of forging cycles up to a certain limit and became almost constant in most of the forging conditions. A larger change in residual stress and surface roughness was observed at the center of the specimens in all the forging conditions. The effect of the magnitude of the forging load on the above discussed parameters is large when compared to the effect of the lubrication conditions.No potential conflict of interest relevant to this article was reported.Faculty of Engineering, Okayama UniversityActa Medica Okayama0475-00713612001Microscopic Observation of Tensile Deformation Behavior of Polycrystalline Titanium with Scanning Probe Microscope716ENYanLiTakejiAbeNaoyaTadaMasanoriKanazawa/10.18926/46996The change in the surface morphology of polycrystalline titanium during tensile plastic deformation is studied, using the scanning probe microscope as well as the laser scanning microscope. The observation shows that the slip occurs mainly near grain boundary at the strain range of ƒÃ < 0.05. The slip develops with the applied strain, and the slip on the second slip system or the crossing of slip lines appear. The surface roughness increases linearly with the applied strain. The height difference between the
grain boundary area and the inner grain area also increases with the applied strain, though the increase rate becomes low after the applied strain of about 0.3. The nano-scale height difference of the surface step of slip lines increases with the applied strain, though it remains almost constant after the applied strain of 0.4. The averaged surface roughness measured with the scanning probe microscope is in good agreement with that measured with the laser scanning microscope.No potential conflict of interest relevant to this article was reported.Faculty of Engineering, Okayama UniversityActa Medica Okayama0475-00713612001Observation of Orientation Change During Plastic Deformation of Polycrystalline Copper by EBSD Method16ENRyoujiKondouTakejiAbeNaoyaTadaIchiroShimizu/10.18926/46995Change in crystal orientation and strain of individual grains during tensile plastic deformation are studied to clarify on the microscopic deformation behavior of polycrystalline copper. The orientation of grain is measured by electron backscatter diffraction (EBSD) technique in the scanning electron microscope. The principal strain of grain is also measured by obtaining the approximated ellipse of strain distribution. The deformation of grains dependent on their initial orientation and the rotation of the principal strain during uniaxial tension are clarified.No potential conflict of interest relevant to this article was reported.Faculty of Engineering, Okayama UniversityActa Medica Okayama0475-00713912005Microscopic Surface Change of Polycrystalline Aluminum duringTensile Plastic Deformation715ENXiaoqunWangTakejiAbeNaoyaTadaIchiroShimizu/10.18926/14135Roughening on free surface of polycrystalline metal during plastic deformation is closely related to the
inhomogeneous deformation in the respective grain at the surface. Uniaxial tensile tests are carried out on
annealed pure aluminum sheet specimens with various averaged grain sizes. The roughening is measured by
a 3-dimensional stylus instrument to examine the roughness change in both sides of specimen surfaces at each strain. The irregularities on one side are reversed on the backside, when the averaged grain size is as large as the thickness of the specimen. Discussions are made on the relation between the surface shapes of both sides adopting the cross correlation factor. The strains of respective grains are also measured from the grain boundary shape before and after plastic deformation. There are some deviations in the strains of the grains and their standard deviation increases with the applied strain.No potential conflict of interest relevant to this article was reported.