Elsevier BV Acta Medica Okayama 2238-7854 45 2026 Enhancement of mechanical properties in a cast hypereutectic Al–Si alloy via rapid cooling in heated mold continuous casting 485 494 EN Shuhei Takeuchi Graduate School of Environment, Life, Natural Science and Technology, Okayama University Shota Nakagawa UACJ Corporation Yoshifumi Shinzato UACJ Corporation Tadashi Minoda UACJ Corporation Naotaka Ohtsuka UACJ Corporation Mitsuhiro Okayasu Department of Mechanical and Systems Engineering, Okayama University To enhance mechanical properties in cast hypereutectic Al–Si alloys, Al–14.5Si samples were produced by the heated mold continuous casting (HMC). The HMC process was conducted under unidirectional solidification at cooling rates (CRs) ranging from 4.6 × 10−1 to 1.3 × 103 K/s, which were obtained by controlling the casting speed (CS). The microstructure basically consisted of α-Al dendrite, Al–Si eutectic and primary Si, while their area fractions (fα-Al, fe, and fp-Si) varied depending on the CR. At the low CR of 4.6 × 10−1 K/s, their area fractions were as follows: fα-Al = 0.2%, fe = 97.3%, and fp-Si = 2.5%, which is the typical microstructural morphology of a hypereutectic Al-Si alloy. In contrast, at the high CR of 1.3 × 103 K/s, those area fractions were altered to fα-Al = 32.3% and fe = 67.7%, while primary Si was strongly suppressed (fp-Si ≈ 0%) despite the hypereutectic Al–14.5Si alloy. Moreover, at the high CR, the aluminum matrix appears to exhibit a nearly uniform crystal orientation along <101>. These microstructural changes may be related not only to high CR but also the difference in growth kinetics between primary Si and α-Al dendrites. Accordingly, an apparent eutectic composition shifted from 12.6 to 19.7 wt% Si. The atypical microstructural formation led to a significant improvement in the tensile properties: the ultimate tensile strength of 400 MPa and fracture strain of 17%. These tensile properties are more than twice those of the conventional cast hypereutectic Al–14.5Si alloy. No potential conflict of interest relevant to this article was reported.

Springer Science and Business Media LLC Acta Medica Okayama 1939-5981 2026 Micro-segregation of Primary Si in ADC14 (Al–17Si–4Cu) Alloy Produced by Unidirectional Continuous Casting EN Shuhei Takeuchi Graduate School of Environment, Life, Natural Science and Technology, Okayama University Shota Nakagawa UACJ Corporation Yoshifumi Shinzato UACJ Corporation Tadashi Minoda UACJ Corporation Naotaka Ohtsuka UACJ Corporation Mitsuhiro Okayasu Department of Mechanical and Systems Engineering, Okayama University An upgrading approach for hypereutectic Al–Si alloys was investigated through controlled segregation of Si using a unidirectional casting process. The precipitation behavior and spatial distribution of primary Si in the hypereutectic ADC14 (Al–17Si–4Cu) alloy were systematically examined at different casting speeds (0.06, 1.9, and 10 mm/s). Microstructural observations revealed that high casting speed suppresses primary Si formation due to rapid solidification, whereas intermediate speed leads to a relatively uniform distribution of primary Si. In contrast, low casting speed combined with a holding period for 2 min promotes pronounced segregation and coarsening of primary Si in localized regions. Energy-dispersive X-ray spectroscopy analysis confirmed significant fluctuations in Si concentration along the casting direction, particularly after process interruption. Based on these results, a preliminary upgrading process was proposed, involving the selective removal of Si-enriched regions followed by remelting. This approach resulted in a reduction of Si content to approximately 13.9 wt.%, corresponding to a decrease of about 3%. The results demonstrate that controlling solidification behavior to induce phase separation provides a promising and energy-efficient strategy for upgrading recycled Al–Si alloys. No potential conflict of interest relevant to this article was reported.

Springer Science and Business Media LLC Acta Medica Okayama 1939-5981 2025 Effect of Repeated Gravity Casting on the Microstructure and Mechanical Properties of 6061 Aluminum Alloy EN Mitsuhiro Okayasu Department of Mechanical Systems and Engineering, Okayama University Shouei Makino Department of Mechanical Systems and Engineering, Okayama University Shota Nakagawa Research & Development Center, Marketing & Technology Division, UACJ Corporation Shuhei Takeuchi Department of Mechanical Systems and Engineering, Okayama University Yoshifumi Shinzato Research & Development Center, Marketing & Technology Division, UACJ Corporation Tadashi Minoda Research & Development Center, Marketing & Technology Division, UACJ Corporation Naotaka Ohtsuka Research & Development Center, Marketing & Technology Division, UACJ Corporation This study systematically investigates the effects of repeated gravity casting on the microstructure and mechanical properties of 6061 aluminum alloy. With an increasing number of casting cycles from one to ten, grain coarsening and a decrease in dislocation density were observed, mainly due to the significant depletion of magnesium from 1.03 to 0.01% and titanium from 0.009 to 0.005%. These microstructural changes led to a decrease in solid-solution strengthening and grain-boundary strengthening, resulting in a 30% reduction in tensile strength, while ductility increased by about three times. Moreover, work hardening decreased with increasing the casting cycle, which can be attributed not only to the microstructural changes but also to the increase in stacking fault energy (SFE) associated with compositional evolution. From the transmission electron microscopy (TEM) observations, in the 1-cycle sample, Mg2Si precipitates were finely dispersed and a high amount of Mg element in the matrix, resulting in significant dislocation accumulation, whereas the 10-cycle sample exhibited weaker dislocation tangling. These microstructural evolutions provide insight into the degradation of mechanical performance in aluminum alloys subjected to multiple casting processes. No potential conflict of interest relevant to this article was reported.

Springer Science and Business Media LLC Acta Medica Okayama 2510-1560 2025 Enhanced electric power generation in PZT ceramics via stress control EN Mitsuhiro Okayasu Department of Mechanical Systems and Engineering, Okayama University Itsuki Shimazu Department of Mechanical Systems and Engineering, Okayama University This study aimed to enhance the electric power generation of lead zirconate titanate piezoelectric (PZT) ceramics by optimizing stress distribution. Specifically, it focused on applying high stress over a broad area of the PZT ceramic to induce shape deformation in the PZT plate. Pre-straining the PZT plate into an arch shape improved voltage generation, reaching its peak at a maximum deflection of 0.04 mm due to the expanded and intensified stress distribution. However, exceeding this deflection threshold led to a decline in voltage output due to material degradation, including crack formation and 90° domain switching. Finite element analysis confirmed that the increased stress distribution in the pre-strained PZT plate contributed to higher voltage output. Additionally, electron backscatter diffraction analysis revealed that at higher pre-strains (deflection of 0.08 mm), 90°domain switching occurred, resulting in increased internal strain and potential crack formation. Experimental investigations using bulk PZT rods further demonstrated that moderate pre-straining effectively enhanced voltage output. No potential conflict of interest relevant to this article was reported.

Springer Science and Business Media LLC Acta Medica Okayama 1939-5981 20 4 2025 Upgrading Recycle Technology for Iron Removal in ADC12 Alloy Using Gravity and Magnetic Force 2354 2361 EN M. Okayasu Department of Mechanical Systems and Engineering, Okayama University S. Takeuchi Department of Mechanical Systems and Engineering, Okayama University M. Syahid Department of Mechanical Engineering, Hasanuddin University T. Ikeda Department of Mechanical Systems and Engineering, Okayama University As there is a technical issue to remove iron elements during aluminum recycling process, an attempt was made to evaluate the effectiveness of magnetic and gravitational separation methods for removing iron from Al-Si-Cu alloy (ADC12). A rare-earth samarium–cobalt (SmCo) magnet was employed during the solidification process to attract Fe-rich eutectic structures. The microstructural analysis revealed that block-like Fe-Cr-Si-based phases formed preferentially near the magnet and at the bottom of the crucible, suggesting that magnetic and gravity attraction contributed to the localized segregation of these phases. However, other Fe-based phases, including Fe-Si-based ones, are not strongly affected by magnet. Additionally, prolonged heating in the solid–liquid coexistence (SLC) region at 577 °C for 10 h led to the settling of a largely grown Fe-Cr-Si-rich crystal at the bottom of the crucible due to gravity. Other structures, such as Si-rich eutectic phases, were not influenced by gravity, which may be caused by the low density of Si compared to Fe one. From this approach, combining magnetic attraction and gravitational settling is a promising method to promote the removal of iron impurities from aluminum alloys. No potential conflict of interest relevant to this article was reported.

Springer Science and Business Media LLC Acta Medica Okayama 0361-5235 54 7 2025 Electric Power Generation of PZT Piezoelectric Ceramics Using Both Direct and Inverse Piezoelectric Effects 5143 5150 EN Mitsuhiro Okayasu Department of Mechanical Systems and Engineering, Okayama University Itsuki Shimazu Department of Mechanical Systems and Engineering, Okayama University The power generation characteristics of lead zirconate titanate (PZT) piezoelectric ceramics (E-PZT) were experimentally investigated using a specialized PZT system which utilizes both the direct and inverse piezoelectric effects inherent to PZT materials. Specifically, electric voltage was generated from the vibration of E-PZT through the inverse piezoelectric effect, induced by mechanical energy transferred from the vibration of a PZT piezoelectric ceramic plate, such as a buzzer (B-PZT). In this system, an insulating material was placed between the B-PZT and E-PZT plates to address the electrical conductivity of the PZT ceramic. Various insulating materials with different thicknesses and different hardness were prepared. Additionally, the PZT systems were mounted in several distinct configurations to evaluate their power generation performance: a fully fixed around the PZT plate and a free-hanging setup. The influence of insulation materials and mounting conditions on electrical output was analyzed at various loading conditions, e.g., loading value and frequency. The results demonstrated that the generated electric voltage decreased with increasing insulation thickness and hardness, suggesting that thinner and softer insulating materials enhance output voltage. Conversely, when the PZT system was securely fixed around the PZT plate with an appropriate fixture, a higher and more stable electric voltage was generated. The voltage generated also varied by the loading condition, which is related to the strain value of the E-PZT plate, demonstrating a linear relationship between the strain and the output voltage. Notably, the strain was significantly influenced by resonant frequencies, which played a crucial role in achieving higher voltage outputs. Based on these experimental results, two power generation systems have been proposed. No potential conflict of interest relevant to this article was reported.

Springer Science and Business Media LLC Acta Medica Okayama 1939-5981 2025 MATERIAL PROPERTIES OF DIE-CASTING DIE AROUND HEAT-CHECKING CREATED BY A HIGH-PRESSURE ALUMINUM ALLOY DIE-CASTING OPERATION EN Mitsuhiro Okayasu Department of Mechanical Systems Engineering, Okayama University Junya Shimazu Department of Mechanical Systems Engineering, Okayama University In this study, the material properties of a nitride die-casting die exhibiting heat-checking after the die-casting process were experimentally investigated using various methods. Based on the obtained results, the authors believe that several possible mechanisms underlying the formation of heat-checking can be identified. The microstructure of the die-casting die near the heat-checking region is characterized by equiaxed grains along the vicinity of the prior γ-grain boundaries, resulting from the lath martensitic formation. Additionally, numerous Cr–Mo–V-based nitride particles, approximately 100 nm in diameter, are precipitated. The surface hardness of the die-casting die, enhanced by nitriding, induces compressive residual stresses and increases adhesive forces. As a result of changes in microstructural characteristics and crack formation, the stress state near the die-casting die is altered, where compressive residual stresses, observed in the die-casting die, are released, leading to the tensile residual stresses. This phenomenon could accelerate the formation of a large number of heat-checking cracks. No potential conflict of interest relevant to this article was reported.

MDPI Acta Medica Okayama 2227-7080 13 4 2025 An Implementation of Creep Test Assisting System with Dial Gauge Needle Reading and Smart Lighting Function for Laboratory Automation 139 EN Dezheng Kong Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Nobuo Funabiki Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Shihao Fang Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Noprianto Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Mitsuhiro Okayasu Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Pradini Puspitaningayu Department of Electrical Engineering, Universitas Negeri Surabaya For decades, analog dial gauges have been essential for measuring and monitoring data at various industrial instruments including production machines and laboratory equipment. Among them, we focus on the instrument for creep test in a mechanical engineering laboratory, which evaluates material strength under sustained stress. Manual reading of gauges imposes significant labor demands, especially in long-duration tests. This burden further increases under low-lighting environments, where poor visibility can lead to misreading data points, potentially compromising the accuracy of test results. In this paper, to address the challenges, we implement a creep test assisting system that possesses the following features: (1) to save the installation cost, a web camera and Raspberry Pi are employed to capture images of the dial gauge and automate the needle reading by image processing in real time, (2) to ensure reliability under low-lighting environments, a smart lighting mechanism is integrated to turn on a supplementary light when the dial gauge is not clearly visible, and (3) to allow a user to stay in a distant place from the instrument during a creep test, material break is detected and the corresponding message is notified to a laboratory staff using LINE automatically. For evaluations, we install the implemented system into a material strength measuring instrument at Okayama University, Japan, and confirm the effectiveness and accuracy through conducting experiments under various lighting conditions. No potential conflict of interest relevant to this article was reported.

Springer Science and Business Media LLC Acta Medica Okayama 1598-2351 25 5 2025 Hydrogen Embrittlement Characteristics of Austenitic Stainless Steels After Punching Process 1158 1167 EN Mitsuhiro Okayasu Department of Mechanical and Systems Engineering, Okayama University Xichang Li Department of Mechanical and Systems Engineering, Okayama University Tomohisa Kawakami SHOYO SANGYO Co., Ltd. This study investigates the influence of microstructural characteristics on the hydrogen embrittlement of SUS304 austenitic stainless steel. The investigation utilized SUS304 sheets with a thickness of 1.5 mm, which were processed by punching with an 8 mm diameter to make specimens. Severe plastic deformation was localized near the punching edge, with the extent of deformation determined by the punching speed. Slower punching speeds induced more pronounced plastic strain, which was closely associated with work hardening and strain-induced martensitic (SIM) transformation. The SIM phase was predominantly observed within a depth of approximately 0.1 mm from the punched edge when processed at a punching speed of 0.25 mm/s, corresponding to roughly 10% of the cross-sectional area of the sample. These microstructural changes led to a significant reduction in tensile and fatigue strength, thereby exacerbating susceptibility to severe hydrogen embrittlement, despite the limited extent of microstructural alteration. Based on these findings, a modified Goodman diagram for SUS304 austenitic stainless steel, incorporating mechanical properties and hydrogen embrittlement behavior, was proposed. No potential conflict of interest relevant to this article was reported.

Springer Science and Business Media LLC Acta Medica Okayama 1939-5981 20 3 2025 Study of the Mechanical Properties of Al–Mg ADC6 Aluminum Alloy Produced by Unidirectional Casting Under Various Cooling Rates 1951 1963 EN S. Takeuchi Graduate School of Environment, Life, Natural Science and Technology, Okayama University M. Okayasu Department of Mechanical Systems and Engineering, Okayama University To create the high strength and high ductility of Al–Mg-based aluminum alloy (JIS–ADC6), ADC6 samples were produced by the unidirectional continuous casting (HMC). The HMC process was conducted with direct water cooling to melt ADC6, which can make fine microstructures and control crystal orientation. The cast samples were prepared under various cooling rates (CRs): 6.3, 34, and 62 K/s. The microstructure and crystal orientation of the samples were altered with CR. At CRs of 34 K/s and 62 K/s, the α-Al phases and intermetallic compounds, e.g., Mg2Si and Al15(Fe, Mn)3Si2, became finer and more spherical. The secondary dendrite arm spacing for the sample at 62 K/s was 8.7 µm—more than 70% smaller than the ADC6 sample (ingot) made by a gravity casting process. Notably, at a CR of 34 K/s, the crystal orientation was predominantly arranged with the (101) plane. Tensile properties—ultimate tensile strength (σUTS), 0.2% proof stress (σ0.2), and failure strain (εf)—varied with the CR. The tensile strength (σUTS and σ0.2) consistently increased with increasing the CR. The improvement in the tensile strength resulted from the refined microstructures, such as the α-Al phase and intermetallic compounds. Similarly, the failure strain also increased with increasing CR, which was severely affected by the finer and more spherical intermetallic compounds. In this case, the εf value of the sample at 34 K/s was, however, slightly higher than that at 62 K/s, due to more uniformly organized crystal orientation, while their ductility was much higher than that of the gravity cast sample. The tensile properties in detail were further analyzed using their failure characteristics. No potential conflict of interest relevant to this article was reported.

MDPI Acta Medica Okayama 2227-7080 13 4 2025 An Implementation of Creep Test Assisting System with Dial Gauge Needle Reading and Smart Lighting Function for Laboratory Automation 139 EN Dezheng Kong Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Nobuo Funabiki Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Shihao Fang Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Mitsuhiro Noprianto Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Mitsuhiro Okayasu Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Pradini Puspitaningayu Department of Electrical Engineering, Universitas Negeri Surabaya For decades, analog dial gauges have been essential for measuring and monitoring data at various industrial instruments including production machines and laboratory equipment. Among them, we focus on the instrument for creep test in a mechanical engineering laboratory, which evaluates material strength under sustained stress. Manual reading of gauges imposes significant labor demands, especially in long-duration tests. This burden further increases under low-lighting environments, where poor visibility can lead to misreading data points, potentially compromising the accuracy of test results. In this paper, to address the challenges, we implement a creep test assisting system that possesses the following features: (1) to save the installation cost, a web camera and Raspberry Pi are employed to capture images of the dial gauge and automate the needle reading by image processing in real time, (2) to ensure reliability under low-lighting environments, a smart lighting mechanism is integrated to turn on a supplementary light when the dial gauge is not clearly visible, and (3) to allow a user to stay in a distant place from the instrument during a creep test, material break is detected and the corresponding message is notified to a laboratory staff using LINE automatically. For evaluations, we install the implemented system into a material strength measuring instrument at Okayama University, Japan, and confirm the effectiveness and accuracy through conducting experiments under various lighting conditions. No potential conflict of interest relevant to this article was reported.

MDPI Acta Medica Okayama 2075-4701 13 8 2023 Microstructural Control and Alloy Design for Improving the Resistance to Delayed Fracture of Ultrahigh-Strength Automotive Steel Sheets 1368 EN Takehide Senuma Department of Mechanical and Systems Engineering, Okayama University Mitsuhiro Okayasu Department of Mechanical and Systems Engineering, Okayama University Hardy Mohrbacher NiobelCon BV The demand for higher-strength automotive steel sheets has increased significantly for lightweight and safe body concepts. However, the increment of the steel strength is often limited by the potential occurrence of delayed fracture. This paper discusses proper microstructure control and alloy design to improve the resistance against the delayed fracture of ultrahigh-strength automotive steel sheets in order to increase the usable upper limit of their strength and provides basic data serving as a practical guide for solving the problem of delayed fracture in ultrahigh-strength automotive steel sheets. It is confirmed that grain refinement, the appropriate dual-phase structure of martensite with ferrite or retained austenite, and surface decarburization, increase the resistance to delayed fracture. In terms of alloy design, the effects of Nb, Mo, and B on the delayed fracture resistance of hot-stamped steels have been investigated. The results suggest that there are other reasons for Nb to improve delayed fracture resistance in addition to grain refinement and the ability to trap hydrogen by its precipitates, as has been conventionally believed. Regarding Mo, it was clearly demonstrated that the segregation of this element at the grain boundary plays a main role in improving the delayed fracture resistance. No potential conflict of interest relevant to this article was reported.

MDPI Acta Medica Okayama 2078-2489 14 6 2023 An Edge Device Framework in SEMAR IoT Application Server Platform 312 EN Yohanes Yohanie Fridelin Panduman Graduate School of Natural Science and Technology, Okayama University Nobuo Funabiki Graduate School of Natural Science and Technology, Okayama University Sho Ito Graduate School of Natural Science and Technology, Okayama University Radhiatul Husna Graduate School of Natural Science and Technology, Okayama University Minoru Kuribayashi Graduate School of Natural Science and Technology, Okayama University Mitsuhiro Okayasu Graduate School of Natural Science and Technology, Okayama University Junya Shimazu Graduate School of Natural Science and Technology, Okayama University Sritrusta Sukaridhoto Department of Informatic and Computer, Politeknik Elektronika Negeri Surabaya Nowadays, the Internet of Things (IoT) has become widely used at various places and for various applications. To facilitate this trend, we have developed the IoT application server platform called SEMAR (Smart Environmental Monitoring and Analytical in Real-Time), which offers standard features for collecting, displaying, and analyzing sensor data. An edge device is usually installed to connect sensors with the server, where the interface configuration, the data processing, the communication protocol, and the transmission interval need to be defined by the user. In this paper, we proposed an edge device framework for SEMAR to remotely optimize the edge device utilization with three phases. In the initialization phase, it automatically downloads the configuration file to the device through HTTP communications. In the service phase, it converts data from various sensors into the standard data format and sends it to the server periodically. In the update phase, it remotely updates the configuration through MQTT communications. For evaluations, we applied the proposal to the fingerprint-based indoor localization system (FILS15.4) and the data logging system. The results confirm the effectiveness in utilizing SEMAR to develop IoT application systems. No potential conflict of interest relevant to this article was reported.

Elsevier Acta Medica Okayama 0921-5093 807 2021 Effects of microstructural characteristics on the hydrogen embrittlement characteristics of austenitic, ferritic, and γ–α duplex stainless steels 140851 EN Mitsuhiro Okayasu Graduate School of Natural Science and Technology, Okayama University Takafumi Fujiwara Graduate School of Natural Science and Technology, Okayama University Hydrogen embrittlement (HE) characteristics of γ (AS), α (FS), and γ–α duplex (DS) stainless steels were examined experimentally and numerically. Severe HE occurred in the DS sample, whereas weak HE was detected in the AS and FS samples. This was attributed to the high hydrogen concentrations at the DS-trapping sites. Hydrogen trapping occurred in the low atomic density zones in the boundaries between α and γ phases in DS sample. The chemical bonding between atomic-scale phase boundaries was weakened by hydrogen penetration. This resulted in a crack growth along the DS α/γ phase boundaries. The ductility of DS decreased as the hydrogen content increased, especially when it exceeded 15 ppm. In contrast, the weak HE observed among AS and FS samples was attributed to the small hydrogen levels that infiltrated both samples. Finally, HE mechanism was proposed on the basis of these experimental results. No potential conflict of interest relevant to this article was reported.

MDPI Acta Medica Okayama 2075-4701 10 6 2020 Friction-Induced Martensitic Transformation and Wear Properties of Stainless Steel under Dry and Wet Conditions 743 EN Yoon-Seok Lee Graduate School of Natural Science and Technology, Okayama University Yuta Kondo Graduate School of Natural Science and Technology, Okayama University Mitsuhiro Okayasu Graduate School of Natural Science and Technology, Okayama University The wear characteristics of SUS304 and SUS316 stainless steels were evaluated at the rotation speeds of 100 m/s, 200 m/s, and 300 m/s under dry and wet conditions. The transition of friction-induced martensite occurred in wear-affected regions of two materials, regardless of the wear test conditions. The specific wear rates (W-s) of both stainless steels increase with increasing rotation speeds, regardless of the circumstances. Moreover,W(s)of SUS304 and SUS316, obtained under dry conditions, is significantly higher than that of SUS304 and SUS316 obtained under wet conditions, respectively. This is because that the water film on the wet ring can act as a liquid lubricant between the ring and the block during the tests. After the wear tests, the hardness changes of both SUS304 and SUS316 are much higher under dry conditions, compared to those under wet conditions. No potential conflict of interest relevant to this article was reported.

Springer Acta Medica Okayama 0361-5235 2020 Failure Characteristics of PZT Ceramic During Cyclic Loading EN Mitsuhiro Okayasu Graduate School of Natural Science and Technology, Okayama University Tsukasa Ogawa Graduate School of Natural Science and Technology, Okayama University Failure characteristics of PbZrTiO3 (PZT) ceramic plates are investigated under cyclic loading with rods of different diameters, i.e., different contact areas (0–20 mm). The voltage generated under loading by the rod with the smallest diameter (contact area) is higher than those for the larger contact areas. This is due to the high strain induced in the PZT ceramic. However, the opposite trend is seen when the loading exceeds 60 N, i.e., the voltage obtained for the smallest contact area is lower. This is caused by failure of the PZT ceramic. The voltage generated under cyclic loading by the 5-mm, 10-mm, 15-mm, and 20-mm rods drops by about 10% in the early cyclic loading stage, but then remains constant until 10,000 cycles. The reduction in voltage is influenced mainly by 90° domain switching. In this case, many grains (about 15% of the total) are switched: a random domain orientation is switched to the ⟨100⟩ direction perpendicular to the ceramic plate, i.e., a crystalline texture is formed. In contrast, there is significant reduction in voltage under loading by the 0-mm rod (point contact). As the extent of domain switching for the 0-mm rod is similar to that for the other rods, the reduction in electrical generation can be attributed to crack generation resulting from the high deformation. No potential conflict of interest relevant to this article was reported.

Elsevier Acta Medica Okayama 0921-5093 791 2020 The effect of precipitations (NbC and carbide) in Fe–C–Mn-xNb steels on hydrogen embrittlement characteristics 139598 EN Mitsuhiro Okayasu Graduate School of Natural Science and Technology, Okayama University Masaya Sato Graduate School of Natural Science and Technology, Okayama University Daiki Ishida Graduate School of Natural Science and Technology, Okayama University Takehide Senuma Graduate School of Natural Science and Technology, Okayama University Hydrogen embrittlement (HE) characteristics in Fe–C–Mn-xNb steels were examined via various analyses, including electron backscatter diffraction analysis, scanning transmission electron microscopy and three-dimensional atom-probe tomography. For the investigation, the steel samples were prepared with varying Nb contents and heat treatment processes. The material properties of steel samples that were subjected to: (i) water quenching and (ii) quenching and tempering at 170 °C for 20 min, were determined to be nearly similar, although different degrees of HE were detected. After the tempering process, ε-carbide precipitated clearly in the matrix, which could act as a trapping site for hydrogen atoms and lead to improved HE resistance. Moreover, with addition of Nb, niobium base precipitates (e.g., NbC) with a diameter of a few nanometers were obtained in the martensite matrix, which could also function as hydrogen trapping sites. There was slight improvement in the HE resistance with NbC. Hydrogen-assisted failure mechanisms under both static and cyclic loading were observed with intergranular brittle cracking for the water quenched sample, even though the brittle and ductile mix failure mode was detected for the sample after the quenching and tempering process. No potential conflict of interest relevant to this article was reported.

Elsevier Acta Medica Okayama 09215093 790 2020 Microstructure-dependent hydrogen diffusion and trapping in high-tensile steel 139418 EN Mitsuhiro Okayasu Graduate School of Natural Science and Technology, Okayama University Jun Motojima Graduate School of Natural Science and Technology, Okayama University In this work, the hydrogen embrittlement (HE) characteristics of high-tensile steel sheets with different microstructural characteristics were investigated. The sheets were fabricated via cold rolling (CR), water quenching (WQ), baking hardening (BH), and low-temperature annealing (LT), and their HE characteristics were clarified by examining the relationships between the microstructural characteristics and the severity of HE. Severe HE occurred in the WQ sample with hydrogen trapping at the boundaries of the retained austenite phases, resulting in intergranular and cleavage-like brittle failure. A reduction in HE was realized after the BH and LT processes. In these cases, hydrogen trapping was divided between the ε-carbide in the lattice spacings and at the boundaries of retained austenite, resulting in a mixed ductile/brittle failure mode. The extent of HE in the CR sample was similar to those in the BH and LT samples. However, the trapping sites were different; hydrogen trapping in the CR sample occurred in the slip band and around dislocations, resulting in delamination-like brittle failure on the slip planes. The extent of HE was also affected by the strain rate. More severe HE occurred in both the WQ and BH samples loaded slowly at 0.01 mm min−1 compared to the samples loaded 1.0 mm min−1 (i.e., intergranular failure). In this case, HE was affected by the large amount of hydrogen atoms trapped at the boundaries of the retained austenite phases. The hydrogen atoms in the lattice structure and ε-carbide migrated to the boundaries via dislocation movement. The extent of deterioration in tensile strength was two times higher in the samples loaded at the higher speed of 1.0 mm min−1 compared to those loaded at 0.01 mm min−1. Finally, the hydrogen trapping and failure mechanisms on the nano and atomic scales were discussed based on the results of the microstructural analyses. No potential conflict of interest relevant to this article was reported.

SpringerOpen Acta Medica Okayama 2226-4108 8 4 2019 Effects of loading contact on electric-power generation of lead zirconate titanate piezoelectric ceramic plate 509 518 EN Mitsuhiro Okayasu Graduate School of Natural Science and Technology, Okayama University Tsukasa Ogawa Graduate School of Natural Science and Technology, Okayama University To better understand the generation of electric power for piezoelectric PbZrTiO3 (PZT) ceramic plate (phi 25 mm), an attempt was made to investigate experimentally and numerically electric-power generation characteristics during cyclic bending under various loading fixtures (phi 0-phi 20 mm), i.e., different contact areas. Increasing the load-contact area on the PZT ceramic leads to a nonlinear decrease in the generated voltage. Decreasing contact area basically enhances the generated voltage, although the voltage saturates during loading when the contact area is less than phi 5 mm. A similar voltage is generated for phi 0 and phi 5 mm, which is attributed to strain status (ratio of compressive and tensile strain) and material failure due to different stress distribution in the PZT ceramic. On the basis of the obtained electric generation voltage, suitable loading conditions are clarified by loading with the phi 5 mm fixture, which generates a higher voltage and a longer lifetime of the PZT ceramic. From this approach, it is appeared that the area contact with the area ratio of 0.04 (phi 5 mm/phi 20 mm) is suitable to obtain the high efficiency of the electric voltage. No potential conflict of interest relevant to this article was reported.

Vietnam National University Acta Medica Okayama 24682179 4 4 2019 Mechanical and fatigue properties of long carbon fiber reinforced plastics at low temperature 577 583 EN Mitsuhiro Okayasu Graduate School of Natural Science and Technology, Okayama University Yuki Tsuchiya Graduate School of Natural Science and Technology, Okayama University The mechanical properties of long unidirectional (UD) and crossply (CR) carbon fiber reinforced plastics (CFRPs) were investigated at a low temperature (−196 °C). The CFRPs were fabricated from 60 vol.% carbon fiber and epoxy resin. The bending strength of the UD-CFRP was approximately twice that of the CR-CFRP. The high strength of the UD-CFRP was directly attributed to the amount of carbon fiber oriented along the loading direction: 60% for UD-CFRP compared with 30% for CR-CFRP. The low-temperature (−196 °C) tensile and fatigue strengths of the UD-CFRP were over 1.5 times greater than those at room temperature (20 °C). This was attributed to the increased epoxy strength at low temperatures along with the internal compressive stress arising from the different thermal expansion coefficients of the carbon fiber and epoxy. Both the epoxy strength and internal compressive strength were employed as factors in a compound law to numerically estimate the low-temperature tensile strength. This work presents a systematic analysis for changes in the CFRP material properties at low temperatures. No potential conflict of interest relevant to this article was reported.