The demand for high-strength steel is rising due to its economic efficiency. Low-cycle fatigue (LCF) tests have been conducted to investigate the nonlinear behaviors of high-strength steel. Accurate material models must be used to obtain reliable results on seismic performance evaluation using numerical analyses. This study uses the combined hardening model to simulate the LCF behavior of high-strength steel. However, it is challenging and complex to determine material model parameters for specific high-strength steel because a highly nonlinear equation is used in the model, and several parameters need to be resolved. This study used the particle swarm algorithm (PSO) to determine the model parameters based on the LCF test data of HSA 650 steel. It is shown that the model with parameter values selected from the PSO accurately simulates the measured LCF curves.

An irradiation hardening of Inconel 718 produced by selective laser melting (SLM) was studied based on the microstructural observation and mechanical behavior. Ion irradiation for emulating neutron irradiation has been proposed owing to advantages such as low radiation emission and short experimental periods. To prevent softening caused by the dissolution of ' and '' precipitates due to irradiation, only solution annealing (SA) was performed. SLM SA Inconel 718 specimen was ion irradiated to demonstrate the difference in microstructure and mechanical properties between the irradiated and non-irradiated specimens. After exposing specimens to Fe3+ ions irradiation up to 100 dpa (displacement per atom) at an ambient temperature, the hardness of irradiated specimens was measured by nanoindentation as a function of depth. The depth distribution profile of Fe3+ and dpa were calculated by the Monte Carlo SRIM (Stopping and Range of Ions in Matter)-2013 code under the assumption of the displacement threshold energy of 40 eV. A transmission electron microscope was utilized to observe the formation of irradiation defects such as dislocation loops. This study reveals that the Frank partial dislocation loops induce irradiation hardening of SLM SA Inconel 718 specimens.

PURPOSES : In this study, to improve the quality and construction performance of backfill materials for road excavation and restoration, the basic properties of rapid-hardening materials and stone sludge are analyzed to propose an optimal mix design. METHODS : To utilize rapid-hardening materials and stone sludge as controlled low-strength materials for pipeline construction in downtown areas, specimens were prepared for each compounding condition of fast-hardening materials. Flow, slump, and compressive strength tests were performed at various setting times. Subsequently, the physical and mechanical characteristics of the rapid-hardening backfill material for each mixing factor were analyzed. RESULTS : When ultrafast hardening cement and stone sludge are used, a setting time exceeding 30 min is required for a water–binder (W/B) ratio of 200% or higher. Considering the economic feasibility of ultrafast hardening cement, a W/B of 300% is considered the most suitable when high-performance superplasticizer and retarders are mixed. A flow test was performed on the rapid-hardening backfill material and the results show that if the mixing time exceeds 10 min, then the fluidity decreases rapidly, which necessitates a higher amount of superplasticizer. When ultrafast hardening cement is used, the initial strength (based on 4 h) is 0.7 MPa or higher for all formulations at a W/B ratio of 300%, and the compressive strength decreases slightly as the amount of superplasticizer is increased by 0.1%. CONCLUSIONS : Based on the fluidity and strength of the backfill material, which is composed of a rapid-hardening material and stone sludge, the most optimal performance is achieved when ultrafast-hardening cement with a W/B ratio of 300% is used in addition to a highperformance fluidizing agent 0.3% (wt./B) and retarder 0.2% (wt./B).

벌목 개미과의 일본열마디개미는 국내 토착종이다. 지금까지 야외에서 이 종의 월동기작을 이해하기 위한 내한성 연구는 진행되지 않았다. 저온에서 다양한 온도별 노출시간에 따른 발육태별 저온 저항성을 조사하였다. 성충인 일개미가 다른 발육태와 비교하여 5°C와 10°C의 저온에서 높은 생존율을 보였으며, 급속내한성 유기 조건인 15°C에서 12시간 노출 후 내한성을 획득하였다. 급속내한성 유기는 10°C에서 최대 44%까 지 생존율이 향상되었으며, 체내과냉각점과 체내빙점은 각각 -10.0°C에서 -14.2°C, -11.3°C에서 -15.3°C까지 낮아졌다. 저온처리는 저온 또는 스트레스 관련 유전자인 글리세롤 인산화효소와 열충격 단백질의 발현을 증가시켰다. 이상의 결과는 일본열마디개미의 내한성이 급속내한성 유기에 의해 야기된다는 것을 의미한다.

This study deals with the yielding behavior and strain aging properties of three bake hardening steels with dualphase microstructure, fabricated by varying the annealing temperature. Bake hardening and aging tests are performed to examine the correlation of martensite volume fraction with yielding behavior and strain aging properties of the bake hardening steels with dual-phase microstructure. The volume fraction of martensite increases with increasing annealing temperature. Roomtemperature tensile test results show that the yielding behavior changes from discontinuous-type to continuous-type with increasing volume fraction of martensite due to higher mobile dislocation density. According to the bake hardening and aging tests, the specimen with the highest fraction of martensite exhibited high bake hardening with low aging index because solute carbon atoms in ferrite and martensite effectively diffuse to dislocations during the bake hardening test, while in the aging test they diffuse at only ferrite due to lower aging temperature.

Insect cuticle tanning (pigmentation and sclerotization) is a complex and vital physiological process that begins with tyrosine and is responsible for production of both melanin- and quinoid-type pigments. In addition, these quinones undergo isomerization to quinone methides and cross-linking reactions with cuticular proteins for cuticle sclerotization. In this study, we studied the functions of TmDDC and TmY-y as well as TmNAT1, TmADC and Tmebony from Tenebrio molitor, which are involved in the tyrosine-derived melanin- and quinoid-type pigment productions, respectively. The temporal and spatial expression patterns of the genes were analyzed by real-time PCR. RNA interference was performed to understand the genetic regulation and molecular mechanism underlying the darkening and hardening of beetle cuticle.

자갈 궤도는 부설 후 궤도틀림이 발생하여 지속적인 유지·보수 작업이 필요하다. 이를 개선하기 위하여 기존의 자갈 궤도 에 급속경화 모르타르를 주입하여 단시간 내에 콘크리트 궤도로 치환할 수 있는 급속경화궤도가 개발되었다. 교량에 부설되 는 급속경화궤도는 교량과 궤도의 거동을 일치시키기 위하여 후설치 앵커를 궤도 세그먼트 중앙부에 시공한다. 본 논문은 앵커로 교량과 연결된 급속경화궤도와 교량의 궤도-교량 상호작용 해석을 수행하여 레일 및 앵커의 안전성을 검토하였다. 이때 앵커의 강성 및 강도, 급속경화 콘크리트의 재령, 급속경화궤도와 교량 사이의 마찰을 고려하였다. 이를 바탕으로 급속 경화궤도 부설 후 적절한 앵커의 설치시기 및 열차 정상운행 가능시기를 검토하였다.

Insect cuticle/exoskeleton covering the entire external surface of the body is essential for protecting insects from various environmental stresses. Tyrosine metabolism plays a major role in not only the darkening of cuticle but also its hardening. In this work, we have focused on the functional analysis of nine genes involved in tyrosine-mediated cuticle tanning (pigmentation and sclerotization) pathway in Tenebrio molitor, which has a unique adult cuticle coloration, dark/black dorsal thorax and elytron, and reddish ventral thorax and abdomen. The temporal and spatial expression patterns of the genes were analyzed by real-time PCR, and RNA interference (RNAi) was performed to study the functional importance of these genes in cuticle coloration and/or hardening in T. molitor. This work was supported by NRFs (NRF-2015R1A2A2A01006614 and NRF-2015R1A6A3A04060323).

목적 : 본 연구는 산재근로자를 대상으로 작업능력강화프로그램이 자기효능감, 우울, 재활동기에 미치는 효 과와 원 직무복귀에 따른 그룹 간 차이를 알아보고자 하였다. 연구방법 : 2015년 6월부터 2016년 8월까지 경상남도 소재의 C병원에서 작업능력강화프로그램을 실시한 산재근로자 49명을 대상으로 실시하였다. 작업능력강화프로그램은 1일 1회 3시간 이상 주 5회, 총 4~8 주간 실시하였고, 프로그램 중재 전･후 자기효능감, 우울, 재활동기를 측정하였다. 산재요양기간 종료 후 2개월 뒤 추적관찰을 통해 원 직무복귀 그룹과 원 직무복귀 실패 그룹을 나누어서 두 집단 간 차이를 알아보았다. 결과 : 작업능력강화프로그램 실시 후 자기효능감, 우울, 재활동기에서 유의한 차이가 있었다(p<.05). 산재 요양기간 종결 2개월 뒤 원 직무복귀 여부에 따라 두 집단 간 차이를 확인했을 때 자기효능감의 변화량 에서 유의한 차이를 보였다(p<.05). 결론 : 본 연구는 작업능력강화프로그램이 산재근로자의 자기효능감, 우울, 재활동기 향상에 효과적임을 보 여주었고, 자기효능감이 원 직무복귀 성패에 중요한 요인임을 제안한다.

A subtropical insect species, Maruca vitrata, is invasive to temperate zones. Supercooling capacity of M. vitrata was confirmed in all developmental stages, in which egg exhibited the lowest supercooling point (SCP) at –22.5oC. However, low temperature lethality was observed at much higher temperatures than SCPs in all developmental stages. In addition, this nonfreezing injury increased with incubation time at rearing condition. Uncontrolled phenoloxidase activation appeared to cause the nonfreezing injury. Preexposure to a cool temperature before lethal low temperature significantly increased survival of M. vitrata. This cold hardening accompanied with increase of glycerol content in hemolymph. Transcriptome of M. vitrata under cond-hardening was assessed.

A rapid cold hardening (RCH) and supercooling capacity usually play crucial roles in survival during the overwintering period in the tobacco budworm, Helicoverpa assulta, a freeze-susceptible species. Cryoprotectants such as polyol or sugar affect RCH and maintain fluid status of hemolymph. This study is performed to identify cryoprotectants as a RCH factor in H. assulta. Pre-exposure of H. assulta larvae to 4℃ significantly increased survival at -10℃ in all developmental stages from egg to adult. RCH was dependent on the duration of the pre-exposure period. RCH also significantly enhanced the supercooling capacity. Analysis of cryoprotectants from the hemolymph revealed that the pre-exposure treatment allowed the larvae to accumulate glycerol and trehalose among polyols examined. In addition, unknown materials from 2 peaks were also increased. TIC analysis revealed 3 predicted formulas for unknown materials, C26H24O20S or C3H4N6OS and C22H20O21. Glycerol-3-phosphate dehydrogenase (GPDH) and glycerol 3-phosphatase (G3P) that involving in glycerol biosynthesis were identified from the transcriptome of H. assulta 4th instar larvae. Based on the expression level of transcripts, the expressions of GPDH and G3P were relatively increased when compared to that of the control, suggesting that these genes contribute to overwintering and biosynthesis of glycerol.

The tobacco budworm, Helicoverpa assulta, is a freeze-susceptible species that overwinters in temperate zones with pupa diapause. A rapid cold hardening (RCH) and supercooling capacity usually play crucial roles in survival during the overwintering period. This study is performed to identify a cryoprotectant as a RCH factor in H. assulta. Pre-exposure of H. assulta larvae to 4°C significantly increased survival at -10°C in all developmental stages from egg to adult. RCH was dependent on the duration of the pre-exposure period. RCH also significantly enhanced the supercooling capacity. Cryoprotectant analysis using HPLC showed that the preexposure treatment allowed the larvae to accumulate glycerol in the hemolymph. Two genes, glycerol-3-phosphate dehydrogenase (GPDH) and glycerol 3-phosphatase (G3P), that involing in glycerol biosynthesis were identified from the transcriptome of H. assulta 4th instar larvae. From the result of transcriptome, the expressions of GPDH and G3P were relatively increased when compared to that of the control, suggesting that these genes contribute to overwintering and biosynthesis of cryoprotectant.

In recent years, industrial demands for superior mechanical properties of powder metallurgy steel components with low cost are rapidly growing. Sinter hardening that combines sintering and heat treatment in continuous one step is cost-effective. The cooling rate during the sinter hardening process dominates material microstructures, which finally determine the mechanical properties of the parts. This research establishes a numerical model of the relation between various cooling rates and microstructures in a sinter hardenable material. The evolution of a martensitic phase in the treated microstructure during end quench tests using various cooling media of water, oil, and air is predicted from the cooling rate, which is influenced by cooling conditions, using the finite element method simulations. The effects of the cooling condition on the microstructure of the sinter hardening material are found. The obtained limiting size of the sinter hardening part is helpful to design complicate shaped components.