개시제 및 촉진제가 EPS 혼입 폴리메타크릴산메틸 모르타르의 사용가능시간 및 강도특성에 미치는 효과

이철웅,최낙운,소양섭 대한건축학회 2004 대한건축학회 학술발표대회 논문집 - 계획계/구조계 Vol.24 No.1(구조계)

The purpose of this study is to investigate the working life control of polymethyl methacrylate(PMMA} mortars with EPS using initiator-promoter system PMMA mortars are prepared with various initiator contents and promoter-initiator ratios, and tested for working life, flexural and compressive strengths. As a result, the working life of the PMMA mortars is shortened with increasing initiator content and promoter-initiator ratio. Their flexural and compressive strengths are decreased with an increase in the initiator content while their strengths are scarcely affected by promoter-initiator ratio. In general, the flexural and compressive strengths of heat-cured PMMA mortars are much higher than those of dry-cured PMMA mortars. In conclusion, the initiator content and promoter-initiator ratio of PMMA mortars with EPS should be adjusted relatively to the balance of their strength development.

RC 사각단면 기둥의 전단거동특성과 축방향철근비를 고려한 초기전단강도

이종석,선창호,김익현 한국지진공학회 2010 한국지진공학회논문집 Vol.14 No.2

횡하중을 받는 RC 기둥의 전단강도는 기둥의 변위연성도가 증가함에 따라 감소하는 것으로 알려져 있다. 연성도의 증가에 따른 전단강도의 감소율은 초기전단강도에 따라 크게 좌우되므로 이를 합리적으로 예측하기 위해서는 초기전단강도의 평가가 매우 중요하다. 기둥의 전단거동은 단면모양, 형상비, 축력, 축방향철근비, 연성도 등 다양한 요인에 의하여 영향을 받아 복잡하다. 본 연구에서는 형상비, 단면의 중공비, 축방향철근비, 중공 및 중실단면을 변수로 하는 시험체를 제작하여 실험적 연구를 수행하여 전단거동특성을 살펴보았다. 또한, 축방향철근이 전단강도에 미치는 영향을 분석하여 형상비와 축력을 고려한 기존의 초기전단평가식을 보완하였으며, 그 타당성을 검증하였다. It is well known that the shear strength of an RC column subjected to a lateral force decreases with the increase of the displacement ductility of column. This decreasing rate of shear strength is quite dependent on the initial shear strength. Therefore, the evaluation of the initial shear strength is important to predict the shear strength with reasonable accuracy. The shear behavior is complex because many parameters, such as the sectional shape, aspect ratio, axial force, longitudinal bars and ductility, are mutually interactive. In this study, the initial shear strength has been investigated by experiments varying parameters such as the aspect ratios, void ratios, ratio of longitudinal bars and sectional types. A new empirical equation for the initial shear strength, considering the ratio of the longitudinal bars, has been proposed and its validity has been assessed.

Influence of initial imperfections on ultimate strength of spherical shells

Yu, Chang-Li,Chen, Zhan-Tao,Chen, Chao,Chen, Yan-ting The Society of Naval Architects of Korea 2017 International Journal of Naval Architecture and Oc Vol.9 No.5

Comprehensive consideration regarding influence mechanisms of initial imperfections on ultimate strength of spherical shells is taken to satisfy requirement of deep-sea structural design. The feasibility of innovative numerical procedure that combines welding simulation and non-linear buckling analysis is verified by a good agreement to experimental and theoretical results. Spherical shells with a series of wall thicknesses to radius ratios are studied. Residual stress and deformations from welding process are investigated separately. Variant influence mechanisms are discovered. Residual stress is demonstrated to be influential to stress field and buckling behavior but not to the ultimate strength. Deformations are proved to have a significant impact on ultimate strength. When central angles are less than critical value, concave magnitudes reduce ultimate strengths linearly. However, deformations with central angles above critical value are of much greater harm. Less imperfection susceptibility is found in spherical shells with larger wall thicknesses to radius ratios.

Influence of initial imperfections on ultimate strength of spherical shells

Chang-Li Yu,Zhan-Tao Chen,Chao Chen,Yan-ting Chen 대한조선학회 2017 International Journal of Naval Architecture and Oc Vol.9 No.5

Comprehensive consideration regarding influence mechanisms of initial imperfections on ultimate strength of spherical shells is taken to satisfy requirement of deep-sea structural design. The feasibility of innovative numerical procedure that combines welding simulation and nonlinear buckling analysis is verified by a good agreement to experimental and theoretical results. Spherical shells with a series of wall thicknesses to radius ratios are studied. Residual stress and deformations from welding process are investigated separately. Variant influence mechanisms are discovered. Residual stress is demonstrated to be influential to stress field and buckling behavior but not to the ultimate strength. Deformations are proved to have a significant impact on ultimate strength. When central angles are less than critical value, concave magnitudes reduce ultimate strengths linearly. However, deformations with central angles above critical value are of much greater harm. Less imperfection susceptibility is found in spherical shells with larger wall thicknesses to radius ratios.

노치 반경과 재료 강도에 따른 고강도강 SENT 시편의 균열 개시 위치 분석

김재윤(Jae-Yoon Kim),황진하(Jin-Ha Hwang),김윤재(Yun-Jae Kim),마사키 오미야(Masaki Omiya) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11

The Sheet Metal Forming process is important in manufacturing a car body. Cracking defects are one of the serious problems that reduce quality in sheet metal forming process. In this study, the effect of notch radius and material strength of the Single Edge Notched Tension (SENT) specimen on the crack initiation location of the high-strength steel was analyzed. Through the SENT experiment, it was confirmed that the crack initiation locations were different at the notch radius of 0.5mm and 5mm. Also, the crack initiation occurred at the back of the crack tip as the material strength increased. The experiment was simulated by Finite Element Analysis. The Stress Field according to the distance from crack tip was compared and analyzed. In this study, by introducing damage criterion, we were able to simulate the difference in crack initiation locations depending on the notch radius and material strength.

Effect of curing treatments on the material properties of hardened self-compacting concrete

Salhi, M.,Ghrici, M.,Li, A.,Bilir, T. Techno-Press 2017 Advances in concrete construction Vol.5 No.4

This paper presents a study of the properties and behavior of self-compacting concretes (SCC) in the hot climate. The effect of curing environment and the initial water curing period on the properties and behavior of SCC such as compressive strength, ultrasonic pulse velocity (UPV) and sorptivity of the SCC specimens were investigated. Three Water/Binder (W/B) ratios (0.32, 0.38 and 0.44) have been used to obtain three ranges of compressive strength. Five curing methods have been applied on the SCC by varying the duration and the conservation condition of SCC. The results obtained on the compressive strength show that the period of initial water curing of seven days followed by maturation in the hot climate is better in comparison with the four other curing methods. The coefficient of sorptivity is influenced by W/B ratio and the curing methods. It is also shown that the sorptivity coefficient of SCC specimens is very sensitive to the curing condition. The SCC specimens cured in water present a low coefficient of sorptivity regardless of the ratio W/B. Furthermore, the results show that there is a good correlation between ultrasonic pulse velocity and the compressive strength.

Rock wool wastes as a supplementary cementitious material replacement in cement-based composites

Wei-Ting Lin,An Cheng,Ran Huang,Yuan-Chieh Wu,Ta-Yuan Han 사단법인 한국계산역학회 2013 Computers and Concrete, An International Journal Vol.11 No.2

The use of rock wool waste, an industrial by-product, in cement-based composites has positive effects on the environment because it reduces the problems associated rock wool disposal. The experiments in this study tested cement-based composites using various rock wool waste contents (10, 20, 30 and 40% by weight of cement) as a partial replacement for Portland cement in mortars. The pozzolanic strength activity test, flow test, compressive strength test, dry shrinkage test, absorption test, initial surface absorption test and scanning electron microscope observations were conducted to evaluate the properties of cement-based composites. Test results demonstrate that the pozzolanic strength activity index for rock wool waste specimens is 103% after 91 days. The inclusion of rock wool waste in cement-based composites decreases its dry shrinkage and initial surface absorption, and increases its compressive strength. These improved properties are the result of the dense structure achieved by the filling effect and pozzolanic reactions of the rock wool waste. The addition of 30% and 10% rock wool wastes to cement is the optimal amount based on the results of compressive strength and initial surface absorption for a w/cm of 0.35 and 0.55, respectively. Therefore, it is feasible to utilize rock wool waste as a partial replacement of cement in cement-based composites.

Effects of Solidification Structure on Fatigue Crack Initiation and Fatigue Strength in Al-Si-Mg Cast Alloys

Han, Sang-Won,Lee, Ui-Jong,Kim, Sug-Won 대한금속학회 2002 METALS AND MATERIALS International Vol.8 No.5

Rotating-bending uniaxial fatigue tests and micro-fatigue crack initiation tests were carried out using a permanent mold cast (PMC) and semi-solid die cast (SDC) with Al-7%Si-0.35%Mg composition in order to examine the relationship between solidification structures and fatigue behaviors. The crack length was measured using a replication method. Fatigue strength was improved in SDC, which was almost consistent with the predicted fatigue strength using the size of Si particle cluster. Resistance to fatigue crack initiation and fatigue strength were improved in SDC owing to the finer Si cluster and to higher ultimate tensile strength. Fatigue crack in PMC was preferentially initiated at pores. For SDC, the fatigue crack was initiated at the Si particle/matrix interface, and then sucessively grew along eutectic cell boundaries.

Property modification of a silicone acrylic pressure-sensitive adhesive with oligomeric silicone urethane methacrylate

Park, Hee-Woong,Park, Ji-Won,Lee, Jung Hyun,Kim, Hyun-Joong,Shin, Seunghan Elsevier 2019 European polymer journal Vol.112 No.-

<P><B>Abstract</B></P> <P>A silicone acrylic pressure-sensitive adhesive (SPSA) was synthesized using a silicone macro-azo-initiator as an adhesive for low surface energy substrates. The SPSA had a high peel strength value on an SUS (steel use stainless) substrate due to its low surface energy; however, it had very low peel strength values on low surface energy substrates such as PP and PE. In this study, a silicone urethane dimethacrylate (SiUDMA) oligomer was synthesized as a modifier for the SPSA. The SiUDMA had a much lower viscosity and a slightly higher surface energy than the SPSA. The addition of SiUDMA increased the peel strength of the SPSA regardless of the substrate. In the case of the PP and PE substrates, the increase of peel strength with SiUDMA addition was remarkably large when compared to the SUS substrate because SiUDMA significantly reduced SPSA viscosity and improved its fluidity, consequently facilitating the wetting of the rough surfaces of PP and PE. The rough surfaces of PP and PE could also aid the spreading of SiUDMA-modified SPSA and enlarge the interfacial area. On the other hand, UV curing of SiUDMA and the SiUDMA-modified SPSA resulted in a serious decrease in the peel strength on the PP and PE substrates due to the decrease in the fluidity of the SPSA material, but the SAFT of SPSA increased with UV irradiation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Silicone acrylic PSA (SPSA) was synthesized using a silicone macro-azo-initiator. </LI> <LI> Silicone urethane dimethacrylate (SiUDMA) oligomer was synthesized as a modifier. </LI> <LI> SiUDMA/SPSA mixture had a single <I>T<SUB>g</SUB> </I> peak in tan δ curve, showing good compatibility. </LI> <LI> On the PP or PE plate, SiUDMA modified SPSA showed remarkably improved peel strength. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Probabilistic Distributions of Plate Buckling Strength for Normal and Bridge High-performance Steels

Dang Viet Duc,Yoshiaki Okui,Koichi Hagiwara,Masatsugu Nagai 한국강구조학회 2013 International Journal of Steel Structures Vol.13 No.3

The probabilistic distributions of buckling strengths for compressive plates of normal and bridge high-performance steels were obtained through numerical analyses in order to develop a nominal design strength and a corresponding safety factor. In the numerical analyses, Monte Carlo simulation was used in combination with the response surface method to reduce the effort associated with the finite element analyses. For each value of the slenderness parameter R, a response surface of the normalized local bucking strength was determined based on the results of 114 finite element analyses using different residual stresses and initial defections. The response surface is approximated as a simple algebraic function of the residual stress and the initial deflection. Monte Carlo simulation is then carried out in order to evaluate the probabilistic distribution of the local bucking strength. The mean values obtained in the present study approach those of a mean curve proposed based on experiments. The standard deviation of the present study was approximately half that obtained based on experimental results in the range of 0.6<R<1.2.