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