• Title/Summary/Keyword: aging properties

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A Study on Mechanical Characteristic of Hydrogen Charged Al-6.3Zn-2.4Mg Alloy (Al-6.3Zn-2.4Mg 합금의 수소충전에 따른 기계적 특성 연구)

  • Kim, Dae-Hwan;Choi, Tae-Young;Shim, Sung-Young;Lim, Su-Gun
    • Journal of Korea Foundry Society
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    • v.34 no.2
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    • pp.54-59
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    • 2014
  • In this study, the extruded Al-6.3Zn-2.4Mg alloys were selected among the 7000 series aluminum alloys sensitive to hydrogen environment in order to examine the effects of both the aging conditions and the length of hydrogen charging period on the mechanical properties of the alloy. The specimens were aged for 24hours at $100^{\circ}C$ (under aging (UA)), $120^{\circ}C$ (peak aging (PA)), and $160^{\circ}C$ (over aging (OA)), respectively. Charging tests were performed at RT for 12, 24, 36 hours under potentiostatic conditions (-2000 mV vs (Ag/AgCl)) for 12, 24 and 36 hours in 1M $H_2SO_4$ and 0.1%$NH_4SCN$ solution. The fracture surface was examined by scanning electron microscopy (SEM). X-ray diffraction (XRD) pattern in peak aged sample was obtained before and after hydrogen charging from extruded Al-6.3Zn-2.4Mg alloys. The decreasing rate of tensile strength and elongation is represented in order of over aging < under aging < peak aging, and it is believed that the hydrogen recharge is more sensitive to elongation than tensile strength. The formation of $AlH_3$ in hydrogen charged Al-6.3Zn-2.4Mg alloys has been confirmed by X-ray diffraction studies.

A Study on the Age-related Remodeling of Femur in Normal Korean Adult (연령증가에 따른 정상 한국인 대퇴골의 재형성에 관한 연구)

  • Kang, S.B.;Ba, T.S.;Choi, J.B.;Choi, K.
    • Proceedings of the KOSOMBE Conference
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    • v.1997 no.11
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    • pp.489-492
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    • 1997
  • The general pattern of adaptation in the appendicular skeleton with aging is that the subperiosteal apposition of bone occur along with endosteal absorption. This remodeling of diaphysis to a cylinder of larger diameter is hypothesized to serve a mechanical compensatory unction by increasing the moment of inertia as the cortex thins with aging. These findings is only true of the diaphysis of long bone. Measuring the area and inertia at each section of femur, the age-related change of proximal emur and diaphysis is observed. After screening by physical and radiological examination, 200 normal Korean adults divided 5 groups in both male and female based on age. Twenty persons were in each group. One femur in each person was analyzed using CT images. femur scanned with 60 to 80 slices and this images were digitized. Then 2-D images were reconstructed into 3-D images. Using the nonlinear method, normalization and interpolation technique, 7 locations of interest (trochanteric area: 1, 2 subtrochanteric area: 3, 4, isthmic area: 5, 6, 7) were determined. On the each cross section at each location, the area (total, cortical and medullary) and 5 inertia of moment were measured. The results were analyzed statistically. With aging, significant area change occurred mainly in diaphysis and female. In trochanteric area, no significant change was noted. With aging, total and medullary area were increased, but cortical area was not changed. In diaphysis, lateral bendingresistanceincreasedsignificantly. No inertia change was noted in trochanteric area. Anteroposterior bending resistance was constant with aging. In more than age 60, total area and medullary area were larger than that of others. Lateral bending resistance was higher especially in diaphysis. In diaphysis, with aging, the decreased properties is compensated with the increased lateral bending resistance by geometric remodeling. In trochanteric area, no compensation occur. With aging, especially in more than age 60, the higher rate of trochanteric fracture is expected.

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Recovery Behaviors of NR, SBR and BR Vulcanizates from Circular Deformation (NR, SBR, BR 가황물의 원형 변형으로부터의 회복 거동)

  • Jang, Joong-Hee;Choi, Sung-Seen
    • Elastomers and Composites
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    • v.44 no.4
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    • pp.442-446
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    • 2009
  • Recovery behaviors of unfilled NR, BR, and SBR vulcanizates after aging with a circular deformation were compared to prevent the influence of reinforcing agent. Samples were aged at room temperature, 50, 70, and $90^{\circ}C$ for 10 days. Recovery increased by increasing the measurement time. Instantaneous recoveries less than 1.0 sec were obtained using the recovery variations with the measurement time. For aging at room temperature, difference in the recoveries of the rubber samples was not significant because the aging time was too short. However, for accelerated thermal aging at 50, 70, and $90^{\circ}C$, difference in the recoveries of the rubber samples was significant. Degree of recovery of BR specimen was higher than those of the others, while that of SBR was lowest. However, for accelerated thermal aging at $90^{\circ}C$, recovery of the NR sample was higher than that of the BR one. The initial recovery decreased by increasing the aging temperature and the decrement of SBR was larger than the others. The experimental results were explained with the resilience properties of rubbers and the crosslink density changes by thermal aging.

Convergence Study on Preparation of Anti-aging Peptides from Fish Collagen Hydrolysates (콜라겐 단백가수물을 이용한 항노화 펩타이드 제조에 대한 융합 연구)

  • Bae, In Young;Han, Yoo Kyung;Je, Hyun Jeong;Lee, Hyun Jun;Lee, Hyeon Gyu
    • Journal of the Korea Convergence Society
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    • v.11 no.5
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    • pp.61-72
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    • 2020
  • An anti-aging peptide was prepared from fish collagen hydrolysate (FCH) by ultrafiltration (MWCO; 1 kDa) and reversed-phased high performance liquid chromatography (RP-HPLC). Its anti-aging properties were evaluated based on the procollagen-synthesizing and MMP-1-inhibiting activities in Hs68 cells. A potent anti-aging peptide (fraction I-I) increased collagen synthesis by 46% and also inhibited MMP-1 secretion by 77%, compared with unpurified FCH. The amino acid sequence of fraction I-I was identified to be Gly-Arg-Arg-Gly-Asn-Lys (GRRGNK; the repeating Gly-X-Y sequence in collagen), and it had a molecular mass of 686.175 Da. It revealed that the anti-aging activity of GRRGNK was mainly due to skin protective effects. These results demonstrated that fish collagen hydrolysate may be a potential source of anti-aging peptides, which could be utilized in various field, including foods, cosmetics, and pharmaceuticals.

Physico-chemical Properties for Utilization of Aging Index of Cold Storage Beef Tenderloin (냉장우육의 숙성도 지표로 활용하기 위한 물리화학적 특성)

  • 정인철;김미숙;신완철;문윤희
    • Journal of the Korean Society of Food Science and Nutrition
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    • v.26 no.4
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    • pp.647-653
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    • 1997
  • To establish the index of aging stage for cold storage beef tenderloin, shear force value(SFV), Mg-ATPase activity, myofibrillar fragmentation index(MFI), myofibrillar fragmentation ratio(MFR) and appearance of 30KD(30KD) were measured as the parameters for the indices of aging stage. Aging index of air-packed beef tenderloin stored for 14 days at 3$^{\circ}C$ were useful in the order of SFV(r=-0.893)>MFR (r=0.863) >30KD(r=0.853)>MFI(r=0.814)>Mg-ATPase activity(г=0.804). Vacuum-packed beef tenderloin stored for 28 days at 3$^{\circ}C$ were useful in the order of MFR(r=0.880)>30KD(r=0.836). In case of the correlation between aging indices of air-packed beef tenderloin, MFR had relation with SFV, Mg-ATPase activity, MFI and 30KD. In case of the correlation between aging indices of vacuum-packed beef ten- derloin, MFR had relations with 30KD.

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Study on the Thermal Degradation Behavior of FKM O-rings

  • Lee, Jin Hyok;Bae, Jong Woo;Choi, Myoung Chan;Yoon, Yoo-Mi;Park, Sung Han;Jo, Nam-Ju
    • Elastomers and Composites
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    • v.53 no.4
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    • pp.213-219
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    • 2018
  • The degradation mechanism and physical properties of an FKM O-ring were observed with thermal aging in this experiment. From X-ray photoelectron spectroscopy (XPS) analysis, we could observe carbon (285 eV), fluoro (688 eV), and oxygen (531 eV) peaks. Before thermal aging, the concentration of fluoro atoms was 51.23%, which decreased to 8.29% after thermal aging. The concentration of oxygen atoms increased from 3.16% to 20.39%. Under thermal aging, the FKM O-ring exhibited debonding of the fluoro-bond by oxidation. Analysis of the C1s, O1s, and F1s peaks revealed that the degradation reaction usually occurred at the C-F, C-F2, and C-F3 bonds, and generated a carboxyl group (-COOH) by oxidation. Due to the debonding reaction and decreasing mobility, the glass transition temperature of the FKM O-ring increased from $-15.91^{\circ}C$ to $-13.79^{\circ}C$. From the intermittent CSR test, the initial sealing force was 2,149.6 N, which decreased to 1,156.2 N after thermal aging. Thus, under thermal aging, the sealing force decreased to 46.2%, compared with its initial state. This phenomenon was caused by the debonding reaction and decreasing mobility of the FKM O-ring. The S-S curve exhibited a 50% increase in modulus, with break at a low strain and stress state. This was also attributed to the decreasing mobility due to thermal aging degradation.

Performance Evaluation of Machine Learning Model for Seismic Response Prediction of Nuclear Power Plant Structures considering Aging deterioration (원전 구조물의 경년열화를 고려한 지진응답예측 기계학습 모델의 성능평가)

  • Kim, Hyun-Su;Kim, Yukyung;Lee, So Yeon;Jang, Jun Su
    • Journal of Korean Association for Spatial Structures
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    • v.24 no.3
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    • pp.43-51
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    • 2024
  • Dynamic responses of nuclear power plant structure subjected to earthquake loads should be carefully investigated for safety. Because nuclear power plant structure are usually constructed by material of reinforced concrete, the aging deterioration of R.C. have no small effect on structural behavior of nuclear power plant structure. Therefore, aging deterioration of R.C. nuclear power plant structure should be considered for exact prediction of seismic responses of the structure. In this study, a machine learning model for seismic response prediction of nuclear power plant structure was developed by considering aging deterioration. The OPR-1000 was selected as an example structure for numerical simulation. The OPR-1000 was originally designated as the Korean Standard Nuclear Power Plant (KSNP), and was re-designated as the OPR-1000 in 2005 for foreign sales. 500 artificial ground motions were generated based on site characteristics of Korea. Elastic modulus, damping ratio, poisson's ratio and density were selected to consider material property variation due to aging deterioration. Six machine learning algorithms such as, Decision Tree (DT), Random Forest (RF), Support Vector Machine (SVM), K-Nearest Neighbor (KNN), Artificial Neural Networks (ANN), eXtreme Gradient Boosting (XGBoost), were used t o construct seispic response prediction model. 13 intensity measures and 4 material properties were used input parameters of the training database. Performance evaluation was performed using metrics like root mean square error, mean square error, mean absolute error, and coefficient of determination. The optimization of hyperparameters was achieved through k-fold cross-validation and grid search techniques. The analysis results show that neural networks present good prediction performance considering aging deterioration.

The Variation of Thermal Cycle on the Transformation Temperature and Mechanical Properties of CuZnAi Shape Memory Alloy (CuZnAI형상기억합금의 변태온도에 미치는 열사이클 및 기계적성질 변화)

  • Yang, Gwon-Seung;Park, Jin-Seong;Gang, Jo-Won
    • Korean Journal of Materials Research
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    • v.4 no.5
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    • pp.524-534
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    • 1994
  • The effects of transformation temperature and mechanical properties by thermal cycle of CuZnAl shape memory alloy with a small of misch metal and Zr contents were investigated. The addition of misch metal and Zr was very effective for reducing the grain size. After solution treatment, the specimens were post-quench aged or step quenched at $100^{\circ}C$ to $350^{\circ}C$ for variation of Rockwell hardness value. It was found that the Rockwell hareness value was very increased at $200^{\circ}C$ and $250^{\circ}C$. The fracture strength and ductility have been significantly increased with the increase of misch metal conten when tensile tested below $M_f$ temperature. Also, the fracture strength has been more increased in the case of post quench aging treatment than that of the as-quenching treatment. Aging of the $\beta$-phase decreases the $M_s$ temperature, but that of the martensite phase increases the $A_s$ temperature. The change in $A_s$ temperature with post-quench aging can be attributed to recovery of order in the $\beta$phase. The hystersis of transformation temperature ($A_s-M_s$) has an increasing tendency by thermal cycles.

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Comparison of Drying Yield, Meat Quality, Oxidation Stability and Sensory Properties of Bone-in Shell Loin Cut by Different Dry-aging Conditions

  • Cho, Soohyun;Kang, Sun-Moon;Kim, Yun-Seok;Kim, Young-Chun;Ba, Hoa Van;Seo, Hyun-Woo;Lee, Eun-Mi;Seong, Pil-Nam;Kim, Jin-Hyoung
    • Food Science of Animal Resources
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    • v.38 no.6
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    • pp.1131-1143
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    • 2018
  • This study aimed to investigate the drying yield, meat quality, oxidation stability and sensory properties of Hanwoo beef loin subjected to different dry-aging conditions. A total of 54 Hanwoo beef loins (bone-in, $6^{th}-13^{th}$ ribs) with fat cover at 2 d postmortem were assigned to four groups and hung in a dry-aging room at a controlled temperature ($2^{\circ}C-4^{\circ}C$), humidity (65%-85%) and air velocity (3 m/s). Four treatment conditions were tested; the respective temperature, humidity and treatment duration are as follows: T1, $2^{\circ}C$, 85%, 60 d; T2, $2^{\circ}C$, 65%, $20d+2^{\circ}C$, 75%, $20d+4^{\circ}C$, 85%, 20 d; T3, $2^{\circ}C$, 75%, $20d+4^{\circ}C$, 85%, 40 d; T4, $4^{\circ}C$, 85%, 60 d. The drying yield, total aerobic counts and fat contents increased, whereas the moisture content, meat color (CIE $L^*$, $a^*$, and $b^*$), and Warner-Bratzler shear force values decreased significantly during the aging period for all treatments (p<0.05). The cooking loss (%) did not change significantly until 40 d, and it was significantly higher in T1 and T4 than in T2 and T3 at 60 d (p<0.05). The water-holding capacity, pH and lipid oxidation [thiobarbituric acid reactive substance (TBARS) values] increased during aging (p<0.05). The sensory scores for tenderness, juiciness, flavor, and overall acceptability of dry-aged loin muscles increased as the aging period increased. T2 and T3 had significantly higher sensory scores and T1 had significantly lower scores for tenderness, juiciness, flavor, and overall acceptability at 20, 40, and 60 d for loin muscles (p<0.05).