start-ver=1.4 cd-journal=joma no-vol=11 cd-vols= no-issue=6 article-no= start-page=24-00129 end-page= dt-received= dt-revised= dt-accepted= dt-pub-year=2024 dt-pub=2024 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Effect of artificial defect on tensile properties of thin titanium alloy wire en-subtitle= kn-subtitle= en-abstract= kn-abstract=This 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. en-copyright= kn-copyright= en-aut-name=SAKAMOTOJunji en-aut-sei=SAKAMOTO en-aut-mei=Junji kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=TADANaoya en-aut-sei=TADA en-aut-mei=Naoya kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 ORCID= en-aut-name=UEMORITakeshi en-aut-sei=UEMORI en-aut-mei=Takeshi kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=3 ORCID= en-aut-name=OISHIKoyo en-aut-sei=OISHI en-aut-mei=Koyo kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=4 ORCID= affil-num=1 en-affil=Okayama University kn-affil= affil-num=2 en-affil=Okayama University kn-affil= affil-num=3 en-affil=Okayama University kn-affil= affil-num=4 en-affil=Okayama University kn-affil= en-keyword=Ti-6Al-4V kn-keyword=Ti-6Al-4V en-keyword=Thin wire kn-keyword=Thin wire en-keyword=Tensile properties kn-keyword=Tensile properties en-keyword=Defect kn-keyword=Defect en-keyword=Focused ion beam kn-keyword=Focused ion beam en-keyword=Net-section nominal stress kn-keyword=Net-section nominal stress en-keyword=Fracture surface kn-keyword=Fracture surface en-keyword=Fracture strain kn-keyword=Fracture strain END start-ver=1.4 cd-journal=joma no-vol=23 cd-vols= no-issue= article-no= start-page=102405 end-page= dt-received= dt-revised= dt-accepted= dt-pub-year=2024 dt-pub=202409 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Crystal plasticity analysis of fatigue crack initiation site considering crystallographic orientation in Ti-22V-4Al alloy en-subtitle= kn-subtitle= en-abstract= kn-abstract=In this study, plane bending fatigue tests were conducted on Ti-22V-4Al alloy, a beta-type titanium alloy, to examine the fatigue crack initiation behavior in detail. In addition, the prediction of fatigue crack initiation points was investigated from the perspectives of the Schmidt factor (SF) and crystal plasticity finite element method (CP-FEM). The slip system contributing to fatigue crack initiation can be accurately predicted by assessing the magnitude relationship of SF. Also, this prediction is already indicated in a lot of paper by using out of component of slip activity. However, the location where the fatigue crack will occur can be not estimated by SF on polycrystalline. Therefore, prediction of grains where fatigue cracks will occur could be achieved with high accuracy by constructing a CP-FEM that considers the mechanical interaction of polycrystals and grain boundary. Utilizing advanced methodologies such as CP-FEM and numerical calculation techniques, it is strictly investigated that the factors influencing fatigue crack initiation in polycrystalline materials. Our research concluded the understanding of fatigue crack initiation on polycrystal grains by considering the mechanical interaction of polycrystals and grain boundary. en-copyright= kn-copyright= en-aut-name=ArakawaJinta en-aut-sei=Arakawa en-aut-mei=Jinta kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=HirazumiKoki en-aut-sei=Hirazumi en-aut-mei=Koki kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 ORCID= en-aut-name=UemoriTakeshi en-aut-sei=Uemori en-aut-mei=Takeshi kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=3 ORCID= en-aut-name=TakemotoYoshito en-aut-sei=Takemoto en-aut-mei=Yoshito kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=4 ORCID= affil-num=1 en-affil=Graduate School of Natural Science and Technology, Okayama University kn-affil= affil-num=2 en-affil=Graduate School of Natural Science and Technology, Okayama University kn-affil= affil-num=3 en-affil=Graduate School of Natural Science and Technology, Okayama University kn-affil= affil-num=4 en-affil=Graduate School of Natural Science and Technology, Okayama University kn-affil= en-keyword=ƒÀ-Ti kn-keyword=ƒÀ-Ti en-keyword=Fatigue crack initiation kn-keyword=Fatigue crack initiation en-keyword=Schmidt factor kn-keyword=Schmidt factor en-keyword=Crystal plasticity FEM kn-keyword=Crystal plasticity FEM en-keyword=Polycrystalline kn-keyword=Polycrystalline END start-ver=1.4 cd-journal=joma no-vol=153 cd-vols= no-issue= article-no= start-page=107623 end-page= dt-received= dt-revised= dt-accepted= dt-pub-year=2023 dt-pub=202311 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Prediction 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 orientation en-subtitle= kn-subtitle= en-abstract= kn-abstract=Thin 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. en-copyright= kn-copyright= en-aut-name=TadaNaoya en-aut-sei=Tada en-aut-mei=Naoya kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=UemoriTakeshi en-aut-sei=Uemori en-aut-mei=Takeshi kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 ORCID= en-aut-name=SakamotoJunji en-aut-sei=Sakamoto en-aut-mei=Junji kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=3 ORCID= affil-num=1 en-affil=Faculty of Environmental, Life, Natural Science and Technology, Okayama University kn-affil= affil-num=2 en-affil=Faculty of Environmental, Life, Natural Science and Technology, Okayama University kn-affil= affil-num=3 en-affil=Faculty of Environmental, Life, Natural Science and Technology, Okayama University kn-affil= en-keyword=Mechanical engineering kn-keyword=Mechanical engineering en-keyword=Microdevices made of thin metal sheet kn-keyword=Microdevices made of thin metal sheet en-keyword=Pure titanium kn-keyword=Pure titanium en-keyword=Deformation kn-keyword=Deformation en-keyword=Microscopic characterization and microanalysis kn-keyword=Microscopic characterization and microanalysis en-keyword=Plastic deformation kn-keyword=Plastic deformation en-keyword=Microscopic inhomogeneity and stress kn-keyword=Microscopic inhomogeneity and stress en-keyword=concentration kn-keyword=concentration en-keyword=Slip activity control kn-keyword=Slip activity control END start-ver=1.4 cd-journal=joma no-vol=143 cd-vols= no-issue=2 article-no= start-page=021502 end-page= dt-received= dt-revised= dt-accepted= dt-pub-year=2020 dt-pub=2020105 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Prediction of the Fracture Location by Tensile Tests of Gray Cast Iron Based on the Dimensional Changes of Graphite Flakes en-subtitle= kn-subtitle= en-abstract= kn-abstract=Gray 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. en-copyright= kn-copyright= en-aut-name=TadaNaoya en-aut-sei=Tada en-aut-mei=Naoya kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=UemoriTakeshi en-aut-sei=Uemori en-aut-mei=Takeshi kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 ORCID= en-aut-name=SakamotoJunji en-aut-sei=Sakamoto en-aut-mei=Junji kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=3 ORCID= affil-num=1 en-affil=Graduate School of Natural Science and Technology, Okayama University kn-affil= affil-num=2 en-affil=Graduate School of Natural Science and Technology, Okayama University kn-affil= affil-num=3 en-affil=Graduate School of Natural Science and Technology, Okayama University kn-affil= END start-ver=1.4 cd-journal=joma no-vol=10 cd-vols= no-issue=14 article-no= start-page=4883 end-page= dt-received= dt-revised= dt-accepted= dt-pub-year=2020 dt-pub=20200716 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Finite Element Study of the Effect of Internal Cracks on Surface Profile Change due to Low Loading of Turbine Blade en-subtitle= kn-subtitle= en-abstract= kn-abstract=Turbine 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. en-copyright= kn-copyright= en-aut-name=SakamotoJunji en-aut-sei=Sakamoto en-aut-mei=Junji kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=TadaNaoya en-aut-sei=Tada en-aut-mei=Naoya kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 ORCID= en-aut-name=UemoriTakeshi en-aut-sei=Uemori en-aut-mei=Takeshi kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=3 ORCID= en-aut-name=KuniyasuHayato en-aut-sei=Kuniyasu en-aut-mei=Hayato kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=4 ORCID= affil-num=1 en-affil=Graduate School of Natural Science and Technology, Okayama University kn-affil= affil-num=2 en-affil=Graduate School of Natural Science and Technology, Okayama University kn-affil= affil-num=3 en-affil=Graduate School of Natural Science and Technology, Okayama University kn-affil= affil-num=4 en-affil=Shimadzu Corporation kn-affil= en-keyword=nondestructive inspection kn-keyword=nondestructive inspection en-keyword=crack detection kn-keyword=crack detection en-keyword=low loading kn-keyword=low loading en-keyword=surface profile kn-keyword=surface profile en-keyword=turbine blade kn-keyword=turbine blade en-keyword=finite element analysis kn-keyword=finite element analysis END start-ver=1.4 cd-journal=joma no-vol=9 cd-vols= no-issue=7 article-no= start-page=783 end-page= dt-received= dt-revised= dt-accepted= dt-pub-year=2019 dt-pub=20190712 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Effect of Lubrication and Forging Load on Surface Roughness, Residual Stress, and Deformation of Cold Forging Tools en-subtitle= kn-subtitle= en-abstract= kn-abstract=Cold 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. en-copyright= kn-copyright= en-aut-name=KarunathilakaNuwan en-aut-sei=Karunathilaka en-aut-mei=Nuwan kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=TadaNaoya en-aut-sei=Tada en-aut-mei=Naoya kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 ORCID= en-aut-name=UemoriTakeshi en-aut-sei=Uemori en-aut-mei=Takeshi kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=3 ORCID= en-aut-name=HanamitsuRyota en-aut-sei=Hanamitsu en-aut-mei=Ryota kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=4 ORCID= en-aut-name=FujiiMasahiro en-aut-sei=Fujii en-aut-mei=Masahiro kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=5 ORCID= en-aut-name=OmiyaYuya en-aut-sei=Omiya en-aut-mei=Yuya kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=6 ORCID= en-aut-name=KawanoMasahiro en-aut-sei=Kawano en-aut-mei=Masahiro kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=7 ORCID= affil-num=1 en-affil=Graduate School of Natural Science and Technology, Okayama University kn-affil= affil-num=2 en-affil=Graduate School of Natural Science and Technology, Okayama University kn-affil= affil-num=3 en-affil=Graduate School of Natural Science and Technology, Okayama University kn-affil= affil-num=4 en-affil=Graduate School of Natural Science and Technology, Okayama University kn-affil= affil-num=5 en-affil=Graduate School of Natural Science and Technology, Okayama University kn-affil= affil-num=6 en-affil=Graduate School of Natural Science and Technology, Okayama University kn-affil= affil-num=7 en-affil=Zeno Tech Co., Ltd kn-affil= en-keyword=cold forging kn-keyword=cold forging en-keyword=high-speed tool steel kn-keyword=high-speed tool steel en-keyword=lubrication kn-keyword=lubrication en-keyword=residual stress kn-keyword=residual stress en-keyword=surface roughness kn-keyword=surface roughness en-keyword=tool deformation kn-keyword=tool deformation END