• Title/Summary/Keyword: properties with stress

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Effects of Tempering Condition on the Microstructure and Mechanical Properties of 30MnB5 Hot-Stamping steel (핫스탬핑용 30MnB5강의 템퍼링 조건에 따른 미세조직 및 기계적 물성 연구)

  • Jeong, Junyeong;Park, Sang-Cheon;Shin, Ga-Young;Lee, Chang Wook;Kim, Tae-Jeong;Choi, Min-Su
    • Korean Journal of Metals and Materials
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    • v.56 no.11
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    • pp.787-795
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    • 2018
  • The effects of tempering condition on the microstructure and mechanical properties of 30MnB5 hot stamping steel were investigated in this study. Before the tempering, hot-stamped 30MnB5 steel was composed of only ${\alpha}^{\prime}$-martensite microstructure without precipitates. After the tempering at $180^{\circ}C$ for 120 min, nano-sized ${\varepsilon}$-carbides were precipitated in the ${\alpha}^{\prime}$-martensite laths. After tempering at $250^{\circ}C$ for 60 min, cementite was precipitated along the ${\alpha}^{\prime}$-martensite lath boundaries. The cementite was also observed in the specimens tempered at $350^{\circ}C$ for 30 min and $450^{\circ}C$ for 6 min, respectively. The globular ${\alpha}$-ferrite appeared at $350^{\circ}C-30min$ tempering, and the volume fraction of ${\alpha}$-ferrite increased when the tempering temperature was increased. The yield strength increased after tempering, and it reached a peak with the tempering condition of $180^{\circ}C-120min$, due to the nano-sized precipitates in the ${\alpha}^{\prime}$-martensite lath. After the tempering, the steel's ultimate tensile strength (UTS) was decreased due to the reduction in dislocation density and C segregation to lath boundaries. The highest elongation was observed at the $180^{\circ}C-120min$ tempering condition, due to the reduction of residual stress, and the lack of precipitates along the lath boundaries. The $180^{\circ}C-120min$ tempering condition was considered to have outstanding crash performance, according to toughness and anti-intrusion calculation results. In drop tower crash tests, the 30MnB5 door impact beam tempered at $180^{\circ}C$ for 120 min showed better crash performance compared to a 22MnB5 door impact beam.

Seismic Fragility Analysis based on Material Uncertainties of I-Shape Curved Steel Girder Bridge under Gyeongju Earthquake (강재 재료 불확실성을 고려한 I형 곡선 거더 교량의 경주 지진 기반 지진 취약도 분석)

  • Jeon, Juntai;Ju, Bu-Seog;Son, Ho-Young
    • Journal of the Society of Disaster Information
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    • v.17 no.4
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    • pp.747-754
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    • 2021
  • Purpose: Seismic safety evaluation of a curved bridge must be performed since the curved bridges exhibit the complex behavior rather than the straight bridges, due to geometrical characteristics. In order to conduct the probabilistic seismic assessment of the curved bridge, Seismic fragility evaluation was performed using the uncertainty of the steel material properties of a curved bridge girde, in this study. Method: The finite element (FE) model using ABAQUS platform of the curved bridge girder was constructed, and the statistical parameters of steel materials presented in previous studies were used. 100 steel material models were sampled using the Latin Hypercube Sampling method. As an input ground motion in this study, seismic fragility evaluation was performed by the normalized scale of the Gyeongju earthquake to 0.2g, 0.5g, 0.8g, 1.2g, and 1.5g. Result: As a result of the seismic fragility evaluation of the curved girder, it was found that there was no failure up to 0.03g corresponding to the limit state of allowable stress design, but the failure was started from 0.11g associated with using limit state design. Conclusion: In this study, seismic fragility evaluation was performed considering steel materials uncertainties. Further it must be considered the seismic fragility of the curved bridge using both the uncertainties of input motions and material properties.

Evaluation of Soil Disturbance Due to Bucket Installation in Sand (모래지반에서 버켓기초 설치에 의한 지반교란 평가)

  • Kim, Jae-Hyun;Lee, Seung-Tae;Kim, Dong-Soo
    • Journal of the Korean Geotechnical Society
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    • v.34 no.11
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    • pp.21-31
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    • 2018
  • Bucket foundations are widely used in offshore areas due to their various benefits such as easy and fast installations. A bucket is installed using self-weight and the hydraulic pressure difference across the lid generated by pumping out water from inside the bucket. When buckets are installed in high permeable soil such as sands, upward seepage flow occurs around the bucket tip and interior, leading to a decrease in the effective stress in the soil inside the buckets. This process reduces the penetration resistance of buckets. However, the soil inside and outside the bucket can be disturbed due to the upward seepage flow and this can change the soil properties around the bucket. Moreover, upward seepage flow can create significant soil plug heave, thereby hindering the penetration of the bucket to the target depth. Despite of these problems, soil disturbance and soil plug heave created by suction installation are not well understood. This study aims to investigate the behavior of soil during suction installation. To comprehend the phenomena of soil plug heave during installation, a series of small-scale model tests were conducted with different testing conditions. From a series of tests, the effects of tip thickness of bucket, penetration rate, and self-weight were identified. Finally, soil properties inside the bucket after installation were approximated from the measured soil plug heave.

Evaluation of Mechanical Characteristics and Concentration Target Layer Applicability of Silty Sand by Fines Content (실트질 모래의 세립분 함유율에 따른 역학적 특성 및 압밀 대상층 적용성 평가)

  • Jung-Meyon Kim;Min-Seo Kang;Jong-Joo Kim;Seung-Joo Lee;Young-Seok Kim;Chan-Young, Park;Yong-Seong, Kim
    • Journal of the Korean Geosynthetics Society
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    • v.22 no.3
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    • pp.37-46
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    • 2023
  • In this paper, the physical properties, stress deformation and strength characteristics, density and permeability characteristics of silty sand (SM) by fines content were analyzed through indoor tests. also based on the results of the indoor tests, a compact analysis was performed according to the content of SM, and the applicability of SM ground to the compacted target layer was evaluated by comparing it with the measurement data of the actual problem site. As a result of indoor tests and compression analysis, SM changed its mechanical properties from sandy soil to viscous soil when the fine particle content was 35% or higher, and using field measurement data, SM was found to have a higher compression tendency than direct subsidence. Therefore, the mechanical characteristics of SM above Fc 35% are considered to be similar to that of viscous soil, which is different from the compression characteristics of the tendency of immediate subsidence to conventional sandy soil, so it is necessary to present the mechanical characteristics of SM through further research. The research findings highlight the importance of considering consolidation settlement in silty sand (SM) when evaluating soft soil conditions. These findings can aid in revising criteria for assessing weak ground conditions by providing essential engineering property data based on varying fines content in silty sand.

Numerical Modeling of Hydrogen Embrittlement-induced Ductile Fracture Using a Gurson-Cohesive Model (GCM) and Hydrogen Diffusion (Gurson-Cohesive Model(GCM)과 수소 확산 모델을 결합한 수소 취화 파괴 해석 기법)

  • Jihyuk Park;Nam-Su Huh;Kyoungsoo Park
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.37 no.4
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    • pp.267-274
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    • 2024
  • Hydrogen embrittlement fracture poses a challenge in ensuring the structural integrity of materials exposed to hydrogen-rich environments. This study advances our comprehension of hydrogen-induced fracture through an integrated numerical modeling approach. In addition, it employs a ductile fracture model named the Gurson-cohesive model (GCM) and hydrogen diffusion analysis. GCM is employed as a fracture model that combines the Gurson model to illustrate the continuum damage evolution and the cohesive zone model to describe crack surface discontinuity and softening behavior. Moreover, porosity and stress triaxiality are considered as crack initiation criteria . A hydrogen diffusion analysis is also integrated with the GCM to account for hydrogen enhanced decohesion (HEDE) mechanisms and their subsequent impacts on crack initiation and propagation. This framework considers the influence of hydrogen on the softening behavior of the traction-separation relationship on the discontinuous crack surface. Parametric studies explore the sensitivity to diffusion properties and hydrogen-induced fracture properties. By combining numerical models of hydrogen diffusion and the ductile fracture model, this study provides an understanding of hydrogen-induced fracture and thereby contributes significantly to the ongoing efforts to design materials that are resilient to hydrogen embrittlement in practical engineering applications.

Comparative Study on Mechanical Properties and Dimensional Stability of Staypak and Wood-Polymer Composites from Populus alba × P. Glandulosa wood (현사시나무로 제조(製造)된 열압축목재(熱壓縮木材)와 목재(木材)-고분자(高分子) 복합체(複合體) 재질(材質)의 비교연구(比較硏究))

  • Pak, Sang-Bum;Ahn, Won-Yung
    • Journal of the Korean Wood Science and Technology
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    • v.13 no.2
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    • pp.14-34
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    • 1985
  • One of the techniques for altering the properties of wood that has received considerable attention in the last twenty years is the formation of a wood-polymer composite (WPC) by irradiation and heat-catalyst polymerization of a monomer incorporated into the wood matrix. Wood-polymer composites are the new products having the superior mechanical and physical properties and the combinated characteristics of wood and plastic. The purpose of this experiment was to obtain the basic data for the improvement of wooden materials by manufacturing WPC and Staypak. The species examined was Hyunsasi-Namoo (Populus alba ${\times}$ P. glandulosa) which had not been utilized yet. Methylmethacrylate (MMA) as monomer, benzoyl peroxide (BPO) as initiator and methyl alcohol as bulking agent were used. The monomer containing BPO was impregnated into wood pieces by the dipping and the vacuum process for 2 hours. After impregnation, the treated samples were polymerized on the hot press with pressure and heat-catalyst methods. The results obtained were summarized as follows 1. The monomer loading into wood by the dipping process was 12.13 percent and 29.99 percent by the vacuum. The polymer loading into wood by the dipping process was 6.79 percent and 15.44 percent by the vacuum. 2. Comparing with Staypak, antishrink efficiency (ASE) of WPC was 12.5 to 13.6 percent on the radial direction and 14.70 to 18.63 percent on the tangential. Antiswelling efficiency (AE) was 14.40 to 17.22 percent on the radial direction and 17.18 to 42.1 8 to 42.14 percent on the tangential. Reduction in water absorptivity (RWA) was 8.19 to 15.5 percent. As a whole, the vacuum process was better than the dipping. 3. The specific gravity of control, Staypak and WPC were 0.44, 0.66 and 0.61 to 0.62, respectively. 4. In the bending strength test, the strength in case that the load direction is on the radial surface was greater than that which the load direction is on the tangential. 5. Increasing rate of stress at proportional limit in compression perpendicular to grain was 72.26 percent in case of WPC by the dipping process, 78.93 percent by the vacuum and 99.09 percent in case of Staypak.

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Antioxidant Properties of Red Yeast Rice (Monascus purpureus) Extracts (홍국쌀(Monascus purpureus) 추출물의 항산화 작용)

  • Kwon, Chong-Suk
    • Journal of the Korean Society of Food Science and Nutrition
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    • v.41 no.4
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    • pp.437-442
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    • 2012
  • Red yeast rice (RER) has been used in China for centuries for its medicinal properties and is an increasingly popular alternative lipid-lowering treatment. This study was carried out to estimate the antioxidant properties of RER extracts. The ethyl acetate extract exhibited the DPPH radical scavenging activity of 85% at 0.2 mg/mL and $IC_{50}$ 0.13 mg/mL. A significant proportion of hydroxyl radicals in a cuvette were scavenged: 44.2% at 2.5 ${\mu}g$/mL, 74.1% at 5.0 ${\mu}g$/mL, and >100% at 10 ${\mu}g$/mL. The $HepG_2$ cells pre-treated with RER ethyl acetate extract reduced the hydroxyl radicals significantly compared to the control cells. Oxidative DNA damage was measured using a Comet assay. The RER ethyl acetate extract did not induce any DNA damage per se, and appeared to enhance the resistance to DNA damage caused by an oxidant challenge with $H_2O_2$, whereas lovastatin increased the level of DNA damage in the cells in both the unstressed (no oxidant) and those stressed with $H_2O_2$. The relative gene expression of the antioxidant enzymes in $HepG_2$ cells were also affected by the RER ethyl acetate extract. The $HepG_2$ cells were pre-incubated with the RER ethyl acetate extract, and then stressed with $H_2O_2$ or left unstressed (no oxidant). In the unstressed cells, superoxide dismutase (Cu/Zn SOD) and glutathione peroxidase (GPx) were increased significantly 3.25-fold and 2.67-fold, respectively, whereas in the stressed cells, the catalase (CAT) level was increased by 4.64-fold and 7.0-fold at 5 ${\mu}g$/mL and 10 ${\mu}g$/mL, respectively, compared to those of the control. From these results, RER appears to be effective in suppressing oxidative stress.

FINITE ELEMENT ANALYSIS OF THE INFLUENCE OF ESTHETIC POSTS ON INCISORS (심미 포스트가 전치에 미치는 응력과 변위에 관한 삼차원 유한요소법적 분석)

  • Kwon Tae-Hoon;Hwang Jung-Won;Kim Sung-Hun;Shin Sang-Wan
    • The Journal of Korean Academy of Prosthodontics
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    • v.41 no.5
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    • pp.582-595
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    • 2003
  • Statement of problem : Most posts are metallic, but in response to the need for a post that possesses optical properties compatible with an all-ceramic crown. an esthetic post has been developed. Although there have been many studies about the esthetic post materials, 3-dimensional finite element studies about the stress distribution of them are in rare. Purpose : The purpose of this study is to investigate comparatively the distribution of stresses of the restored, endodontically treated maxillary incisors with the esthetic post materials and the displacement on the cement layer on simulated occlusal loading by using a 3-dimensional finite element analysis model. Material and method : Four 3-dimensional finite element models were constructed in a view of a maxillary central incisor, a post, a core, and the supporting tissues to investigate the stresses in various esthetic posts and cores and the displacement on the cement layer (Model 1 ; Cast gold post and core, Model 2 ; Glass fiber post with composite core, Model 3 ; Zirconia post with composite core. Model 4 ; Zirconia post with ceramic core). Force of 300N was applied to the incisal edge and the cingulum (centric stop point) with the angle of 135-degree to the long axis of the tooth. Results : 1. The stresses and displacement on the incisal edge were higher than on the cingulum 2. The stresses in dentin were the highest in Model 2 (Glass fiber post with composite core), and the second was Model 3, the third Model 1, and the lowest Model 4. 3. The stresses in post and core were the highest in Model 4 (Zirconia post with ceramic core), and the second was Model 1, the third Model 3, and the lowest Model 2. 4. The displacement on the cement layer was the highest in Model 2 (Glass fiber post with composite core), and the second was Model 3, the third Model 1, and the lowest Model 4. Conclusion : When a functional maximum bite force was applied, the distribution of stresses or the esthetic post and core materials and the displacement on the cement layer were a little different. It seems that restoring extensively damaged incisors with esthetic post and core materials would be decided according to the remaining tooth structure.

Review on Wandering Behavior in Persons with Dementia (치매 노인의 배회행동에 관한 문헌 조사)

  • HongSon, Gwi-Ryung
    • Perspectives in Nursing Science
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    • v.3 no.1
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    • pp.35-45
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    • 2006
  • In Korea, about 8.3% over aged 65 are suffering from Alzheimer's disease or other type of dementia. Among dementia-related behaviors, wandering is the one of strongest factors on burden and stress of caregivers. On Lee and Kwon's report with community living persons with dementia, upto 85% of caregivers reported wandering as a problem. Wandering is a frequently encountered problem in communities and long-term care facilities, but it is among least understood dementia. related behavior. Despite the prevalence of wandering, its significant adverse outcomes, and the increase in persons with dementia in Korea, no systematic research has been conducted in Korea. The purpose of this study is to review on literature related to wandering behavior among persons with dementia. The specific topics related to wandering are included: definition, the prevalence of dementia and wandering behavior, the influencing factor on wandering, outcomes of wandering behavior, and the measurement method. Wandering is defined as "aimless walking" and "Meandering, aimless or repetitive locomotion that exposes one to harm and is incongruent with boundaries, limits, or obstacles". Wandering is viewed as a problematic behavior, however, it has to be understood as need-driven compromised behavior. For example, wandering may be an expression of searching for familiar person and/or place. Recently, in Korea, there is an effort for establishing the therapeutic environment for elders who are wanderers in long-term-care facilities. Cognitive impairment of persons with dementia is found to be a consistent factor on wandering behavior through many national and international studies. The adverse outcomes of wandering are serious problem in persons with dementia as well as their caregivers. The adverse outcomes include falls, fractures, getting lost, use of restraints, or even death. In fact, wandering is one of the major reasons for a patient to be institutionalized. For measurement of wandering behavior, two methods are broadly used: observation using stop watch, and survey form. A revised instrument of the Korean version of Algase wandering scale (K_RAWS) is established the psychometric properties (Son, Song, & Lim, 2006) demonstrating valid and reliable instrument in measuring wandering behavior among persons with dementia who are residing in communities. K_RAWS has a 39 items with six subscales including persistent walking, repetitive walking, spatial disorientation, eloping behavior, negative outcome, and mealtime impulsivity. In conclusion, studies including the prevalence of wandering behavior and predictive factors on wandering should be conducted to understand wandering clearly before developing any types of intervention.

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Effects of Microstructural Change in Joint Interface on Mechanical Properties of Si3N4/S.S316 joint with Ni Buffer layer (Ni buffer layer를 사용한 Si3N4/S.S316 접합체에서 접합계면의 미세구조 변화가 접합체의 기계적 특성에 미치는 영향)

  • 장희석;박상환;권혁보;최성철
    • Journal of the Korean Ceramic Society
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    • v.37 no.4
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    • pp.381-387
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    • 2000
  • Si3N4/stainless steel 316 joints with Ni buffer layer were fabricated by direct active brazing method (DIB) using Ag-Cu-Ti brazing alloy only and double brazing method (DOB) using Ag-Cu brazing alloy with Si3N4 pretreated with Ag-Cu-Ti brazing alloy. For the joint brazed by DIB method, Ti was segregated at the Si3N4/brazing alloy interface, but was not enough to form a stable joint interface. In addition, large amounts of Ni-Ti inter-metallic compounds were formed in tehbrazing alloy near the joint interface, which could deplete the contents of Ti involved in the interfacial reaction. However, for the joint brazed by DOB method, segregation of Ti at the joint interface were enough to enhance the formation of stable interfacial reaction products such as TiN and Ti-Si-Ni-N-(Cu) multicompounds, which restricted the formation of Ni-Tio inter-metallic compounds in the brazing alloy during brazing with Ni buffer layer. Fracture strength of Si3N4/S.S 316 joints with Ni buffer layer was much improved by using DOB method rather than DIB method. It could be deduced that the differences of fracture strength of the joint with Ni buffer layer depending on brazing process adapted were directly affected by the formation of stable joint interface and the change in microstructure of the brazing alloy near the joint interface. It was found that fracture strength of Si3N4/S.S 316 joints with Ni buffer layer was gradually reduced as the thickness of interface. It was found that fracture strength of Si3N4/S.S 316 joints with Ni buffer layer was gradually reduced as the thickness of Ni buffer layer in the joint was increased from 0.1 mm to 10 mm. It seems to due to the increased residual stress in the joint as the thickness of Ni buffer layer is increased. The maximum fracture strength of Si3N4/S.S 316 joints with Ni buffer layer was 386 MPa, and the fracture of joint was originated at Si3N4/brazing alloy joint interface and propagated into Si3N4 matrix.

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