start-ver=1.4 cd-journal=joma no-vol=13 cd-vols= no-issue=4 article-no= start-page=139 end-page= dt-received= dt-revised= dt-accepted= dt-pub-year=2025 dt-pub=20250402 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=An Implementation of Creep Test Assisting System with Dial Gauge Needle Reading and Smart Lighting Function for Laboratory Automation en-subtitle= kn-subtitle= en-abstract= kn-abstract=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. en-copyright= kn-copyright= en-aut-name=KongDezheng en-aut-sei=Kong en-aut-mei=Dezheng kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=FunabikiNobuo en-aut-sei=Funabiki en-aut-mei=Nobuo kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 ORCID= en-aut-name=FangShihao en-aut-sei=Fang en-aut-mei=Shihao kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=3 ORCID= en-aut-name=NopriantoMitsuhiro en-aut-sei=Noprianto en-aut-mei=Mitsuhiro kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=4 ORCID= en-aut-name=OkayasuMitsuhiro en-aut-sei=Okayasu en-aut-mei=Mitsuhiro kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=5 ORCID= en-aut-name=PuspitaningayuPradini en-aut-sei=Puspitaningayu en-aut-mei=Pradini kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=6 ORCID= affil-num=1 en-affil=Graduate School of Environmental, Life, Natural Science and Technology, Okayama University kn-affil= affil-num=2 en-affil=Graduate School of Environmental, Life, Natural Science and Technology, Okayama University kn-affil= affil-num=3 en-affil=Graduate School of Environmental, Life, Natural Science and Technology, Okayama University kn-affil= affil-num=4 en-affil=Graduate School of Environmental, Life, Natural Science and Technology, Okayama University kn-affil= affil-num=5 en-affil=Graduate School of Environmental, Life, Natural Science and Technology, Okayama University kn-affil= affil-num=6 en-affil=Department of Electrical Engineering, Universitas Negeri Surabaya kn-affil= en-keyword=creep test kn-keyword=creep test en-keyword=Raspberry Pi kn-keyword=Raspberry Pi en-keyword=dial gauge kn-keyword=dial gauge en-keyword=needle reading kn-keyword=needle reading en-keyword=smart lighting kn-keyword=smart lighting END start-ver=1.4 cd-journal=joma no-vol=13 cd-vols= no-issue=8 article-no= start-page=1368 end-page= dt-received= dt-revised= dt-accepted= dt-pub-year=2023 dt-pub=20230729 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Microstructural Control and Alloy Design for Improving the Resistance to Delayed Fracture of Ultrahigh-Strength Automotive Steel Sheets en-subtitle= kn-subtitle= en-abstract= kn-abstract=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. en-copyright= kn-copyright= en-aut-name=SenumaTakehide en-aut-sei=Senuma en-aut-mei=Takehide kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=OkayasuMitsuhiro en-aut-sei=Okayasu en-aut-mei=Mitsuhiro kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 ORCID= en-aut-name=MohrbacherHardy en-aut-sei=Mohrbacher en-aut-mei=Hardy kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=3 ORCID= affil-num=1 en-affil=Department of Mechanical and Systems Engineering, Okayama University kn-affil= affil-num=2 en-affil=Department of Mechanical and Systems Engineering, Okayama University kn-affil= affil-num=3 en-affil=NiobelCon BV kn-affil= en-keyword=delayed fracture kn-keyword=delayed fracture en-keyword=hydrogen embrittlement kn-keyword=hydrogen embrittlement en-keyword=high-strength steel kn-keyword=high-strength steel en-keyword=automotive steel sheets kn-keyword=automotive steel sheets en-keyword=microstructural control kn-keyword=microstructural control en-keyword=alloy design kn-keyword=alloy design END start-ver=1.4 cd-journal=joma no-vol=14 cd-vols= no-issue=6 article-no= start-page=312 end-page= dt-received= dt-revised= dt-accepted= dt-pub-year=2023 dt-pub=20230529 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=An Edge Device Framework in SEMAR IoT Application Server Platform en-subtitle= kn-subtitle= en-abstract= kn-abstract=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. en-copyright= kn-copyright= en-aut-name=PandumanYohanes Yohanie Fridelin en-aut-sei=Panduman en-aut-mei=Yohanes Yohanie Fridelin kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=FunabikiNobuo en-aut-sei=Funabiki en-aut-mei=Nobuo kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 ORCID= en-aut-name=ItoSho en-aut-sei=Ito en-aut-mei=Sho kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=3 ORCID= en-aut-name=HusnaRadhiatul en-aut-sei=Husna en-aut-mei=Radhiatul kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=4 ORCID= en-aut-name=KuribayashiMinoru en-aut-sei=Kuribayashi en-aut-mei=Minoru kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=5 ORCID= en-aut-name=OkayasuMitsuhiro en-aut-sei=Okayasu en-aut-mei=Mitsuhiro kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=6 ORCID= en-aut-name=ShimazuJunya en-aut-sei=Shimazu en-aut-mei=Junya kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=7 ORCID= en-aut-name=SukaridhotoSritrusta en-aut-sei=Sukaridhoto en-aut-mei=Sritrusta kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=8 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=Graduate School of Natural Science and Technology, Okayama University kn-affil= affil-num=8 en-affil=Department of Informatic and Computer, Politeknik Elektronika Negeri Surabaya kn-affil= en-keyword=Internet of Things kn-keyword=Internet of Things en-keyword=edge device kn-keyword=edge device en-keyword=framework kn-keyword=framework en-keyword=application server platform kn-keyword=application server platform en-keyword=SEMAR kn-keyword=SEMAR END start-ver=1.4 cd-journal=joma no-vol=807 cd-vols= no-issue= article-no= start-page=140851 end-page= dt-received= dt-revised= dt-accepted= dt-pub-year=2021 dt-pub=20210311 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Effects of microstructural characteristics on the hydrogen embrittlement characteristics of austenitic, ferritic, and γ–α duplex stainless steels en-subtitle= kn-subtitle= en-abstract= kn-abstract=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. en-copyright= kn-copyright= en-aut-name=OkayasuMitsuhiro en-aut-sei=Okayasu en-aut-mei=Mitsuhiro kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=FujiwaraTakafumi en-aut-sei=Fujiwara en-aut-mei=Takafumi kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 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= en-keyword=Hydrogen embrittlement kn-keyword=Hydrogen embrittlement en-keyword=Stainless steel kn-keyword=Stainless steel en-keyword=Austenite kn-keyword=Austenite en-keyword=Ferrite kn-keyword=Ferrite en-keyword=Duplex phase kn-keyword=Duplex phase END start-ver=1.4 cd-journal=joma no-vol= cd-vols= no-issue= article-no= start-page= end-page= dt-received= dt-revised= dt-accepted= dt-pub-year=2020 dt-pub=20200708 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Failure Characteristics of PZT Ceramic During Cyclic Loading en-subtitle= kn-subtitle= en-abstract= kn-abstract=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. en-copyright= kn-copyright= en-aut-name=OkayasuMitsuhiro en-aut-sei=Okayasu en-aut-mei=Mitsuhiro kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=OgawaTsukasa en-aut-sei=Ogawa en-aut-mei=Tsukasa kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 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= en-keyword=Piezoelectric ceramic kn-keyword=Piezoelectric ceramic en-keyword=lead zirconate titanate ceramic kn-keyword=lead zirconate titanate ceramic en-keyword=electrical power generation kn-keyword=electrical power generation en-keyword=domain switching kn-keyword=domain switching en-keyword=cyclic loading kn-keyword=cyclic loading END start-ver=1.4 cd-journal=joma no-vol=791 cd-vols= no-issue= article-no= start-page=139598 end-page= dt-received= dt-revised= dt-accepted= dt-pub-year=2020 dt-pub=20200618 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=The effect of precipitations (NbC and carbide) in Fe–C–Mn-xNb steels on hydrogen embrittlement characteristics en-subtitle= kn-subtitle= en-abstract= kn-abstract=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. en-copyright= kn-copyright= en-aut-name=OkayasuMitsuhiro en-aut-sei=Okayasu en-aut-mei=Mitsuhiro kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=SatoMasaya en-aut-sei=Sato en-aut-mei=Masaya kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 ORCID= en-aut-name=IshidaDaiki en-aut-sei=Ishida en-aut-mei=Daiki kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=3 ORCID= en-aut-name=SenumaTakehide en-aut-sei=Senuma en-aut-mei=Takehide 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=Steel kn-keyword=Steel en-keyword=Hydrogen embrittlement; kn-keyword=Hydrogen embrittlement; en-keyword=Trapping site kn-keyword=Trapping site en-keyword=Niobium carbide; kn-keyword=Niobium carbide; en-keyword=ε-carbide kn-keyword=ε-carbide END start-ver=1.4 cd-journal=joma no-vol=10 cd-vols= no-issue=6 article-no= start-page=743 end-page= dt-received= dt-revised= dt-accepted= dt-pub-year=2020 dt-pub=20200603 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Friction-Induced Martensitic Transformation and Wear Properties of Stainless Steel under Dry and Wet Conditions en-subtitle= kn-subtitle= en-abstract= kn-abstract=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. en-copyright= kn-copyright= en-aut-name=LeeYoon-Seok en-aut-sei=Lee en-aut-mei=Yoon-Seok kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=KondoYuta en-aut-sei=Kondo en-aut-mei=Yuta kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 ORCID= en-aut-name=OkayasuMitsuhiro en-aut-sei=Okayasu en-aut-mei=Mitsuhiro 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= en-keyword=stainless steels kn-keyword=stainless steels en-keyword=friction-induced transformation kn-keyword=friction-induced transformation en-keyword=lubricant kn-keyword=lubricant en-keyword=wear kn-keyword=wear en-keyword=martensite kn-keyword=martensite END start-ver=1.4 cd-journal=joma no-vol=790 cd-vols= no-issue= article-no= start-page=139418 end-page= dt-received= dt-revised= dt-accepted= dt-pub-year=2020 dt-pub=20200506 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Microstructure-dependent hydrogen diffusion and trapping in high-tensile steel en-subtitle= kn-subtitle= en-abstract= kn-abstract=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. en-copyright= kn-copyright= en-aut-name=OkayasuMitsuhiro en-aut-sei=Okayasu en-aut-mei=Mitsuhiro kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=MotojimaJun en-aut-sei=Motojima en-aut-mei=Jun kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 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= en-keyword=High-tensile steel kn-keyword=High-tensile steel en-keyword=Hydrogen embrittlement kn-keyword=Hydrogen embrittlement en-keyword=Hydrogen trapping kn-keyword=Hydrogen trapping en-keyword=Hydrogen diffusion kn-keyword=Hydrogen diffusion en-keyword=Carbide kn-keyword=Carbide en-keyword=Lattice structure kn-keyword=Lattice structure END start-ver=1.4 cd-journal=joma no-vol=8 cd-vols= no-issue=4 article-no= start-page=509 end-page=518 dt-received= dt-revised= dt-accepted= dt-pub-year=2019 dt-pub=20191204 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Effects of loading contact on electric-power generation of lead zirconate titanate piezoelectric ceramic plate en-subtitle= kn-subtitle= en-abstract= kn-abstract=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. en-copyright= kn-copyright= en-aut-name=OkayasuMitsuhiro en-aut-sei=Okayasu en-aut-mei=Mitsuhiro kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=OgawaTsukasa en-aut-sei=Ogawa en-aut-mei=Tsukasa kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 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= en-keyword=piezoelectric ceramic kn-keyword=piezoelectric ceramic en-keyword=lead zirconate titanate ceramic kn-keyword=lead zirconate titanate ceramic en-keyword=electric power generation kn-keyword=electric power generation END start-ver=1.4 cd-journal=joma no-vol=4 cd-vols= no-issue=4 article-no= start-page=577 end-page=583 dt-received= dt-revised= dt-accepted= dt-pub-year=2019 dt-pub=20191014 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Mechanical and fatigue properties of long carbon fiber reinforced plastics at low temperature en-subtitle= kn-subtitle= en-abstract= kn-abstract=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. en-copyright= kn-copyright= en-aut-name=OkayasuMitsuhiro en-aut-sei=Okayasu en-aut-mei=Mitsuhiro kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=TsuchiyaYuki en-aut-sei=Tsuchiya en-aut-mei=Yuki kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 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= en-keyword=CFRP kn-keyword=CFRP en-keyword=Carbon fiber kn-keyword=Carbon fiber en-keyword=Tensile strength kn-keyword=Tensile strength en-keyword=Fatigue strength kn-keyword=Fatigue strength en-keyword=Low temperature kn-keyword=Low temperature END