• 한국주조공학회지
• /
• 제18권4호
• /
• pp.364-372
• /
• 1998

Effects of Si and Ca additions on the mechanical properties of AM60 based Mg alloys have been investigated. Hardness of the AM60 based Mg alloys reached a maximum value after aging for approximately 33 hours but the amount of hardness increase was negligible. The poor age hardening response of the alloys was due to low Al content, which implies that Al content must be >6 wt.% to observe age hardening effect. The tensile and yield strength increased with increasing Al, Si, and Ca content but elongation decreased with increasing Al and Si content. The best mechanical properties obtained in AM 40-2.5Si-0.2Ca alloy after T4 heat treatment were as follows; tensile strength 193.4 MPa, yield strength 79.2 MPa, and elongation 11.2%. High temperature property obtained from creep test was also improved by introducing $Mg_2Si$ which has high hardness, high melting temperature and low thermal expansion coefficient.

• Journal of Advanced Marine Engineering and Technology
• /
• 제29권4호
• /
• pp.399-406
• /
• 2005

Alloy 625 is used widely in industrial applications such as aeronautical aerospace, chemical, petrochemical and marine applications. Because of a good combination of yield strength. tensile strength, creep strength, excellent fabricability, weldability and good resistance to high temperature corrosion on prolonged exposure to aggressive environments. High qualify weldments for this material are readily produced by commonly used processes. But all of processes are not applicable to this material by reason of unavailability of matching, position or suitable welding filler metals and fluxes may limit the choice of welding processes. Recently, the flux cored wire is developed and applied for the better productivity in several welding position including the vortical position. In this study. the weldability and weldment characteristics of Alloy 625 are evaluated in FCAW weld associated with the several shielding gases($80\%Ar+20\%\;CO_2,\;50\%Ar+50\%\;CO_2.\;100\%\;CO_2$) in viewpoint of welding productivity. The results of the experimental study on corrosive characteristics of Alloy 625 are as follows; There is no remarkable difference among shielding gases. however they has a striking difference among corrosive solutions by results of distinguished density and time of corrosive solution. Generally, the shielding gases($80\%Ar+20\%\;CO_2$) was superior to the other gases on high temperature tensile and a low temperature impact. but all of the shield gases were making satisfactory results on corrosion test.

• 대한기계학회논문집A
• /
• 제25권1호
• /
• pp.161-167
• /
• 2001

The overhead transmission wires operating both at warm temperature and tighten state for a long period of time in a power transmission plant are degraded by air pollution, wind, creep and slip between steel wire and aluminium conductor. The objective of this study is to investigate to investigate the characteristics of fatigue properties with tension and bending loading of a high carbon steel wire. The fatigue behaviors have been carried out by tension-tension, 4 points bending and 3 points bending loading. In the present study, a conventional fatigue strengths between 4 points bending and tension-tension fatigue were determined by Gerber, Sorderberg and Goodmans theory and we investigated S-N diagram for bending and tensile loading.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 추계학술대회논문집A
• /
• pp.274-279
• /
• 2000

The overhead transmission wires operating both at warm temperature and tighten state for a long period of time in a power transmission plant are degraded by air pollution, wind, creep and slip between steel wire and aluminium conductor. The objective of this study is to investigate a high carbon steel wire. We tested for basic mechanical properties and 3 types fatigue behavior, tension-tension, 4 points bending and 3 points bending fatigues. In this study, a conventional fatigue strengths between 4 points bending and tension-tension fatigue were determined by Gerber, Sorderberg and Goodman's theory and we investigated S-N diagram for bending and tensile loading.

• 공업화학
• /
• 제24권2호
• /
• pp.138-143
• /
• 2013

화학적 열화를 빠르게 유도할 수 있는 단파장의 자외선(254 nm)을 고밀도 폴리에틸렌의 표면에 조사하여, 생성된 carbonyl band의 변화로부터 기계적 물성 변화를 예측할 수 있는 지에 대한 가능성을 연구하였다. 오랜 시간이 요구되는 자연 태양광에 의한 옥외폭로시험이나, 제논-아크 광원에 의한 광 열화 대신에 광양자 에너지가 높은 UVC 램프를 사용함으로써, 유도되는 광열화의 화학적 특성이 동일한 기계적 물성 변화를 유발하는지를 확인하는 것에 본 연구의 의미가 있다. 인장시험과 크리프-파괴시험으로 진행된 고밀도 폴리에틸렌의 기계적 강도는 CI 변화에 유사한 양상을 보였으며, 특히 항복강도와 신장률은 자외선 노출시간과 밀접한 관계가 있음을 보여주었다. 따라서 빠른 표면 열화를 유발하는 UVC 램프를 활용한 카르보닐 지수와 기계적 물성 변화의 관계를 통하여 장시간이 요구되는 옥외에서의 기계적 물성변화를 보다 빠르게 파악할 수 있는 방법을 제시하였다.

• Computers and Concrete
• /
• 제17권6호
• /
• pp.703-721
• /
• 2016

A novel approach to modeling concrete behavior at the stage of its maturing is presented in this paper. This approach assumes that at any point in the structure, concrete is composed of a set of layers that are activated in time layer by layer, based on amount of released heat that is produced during process of the concrete's maturing. This allows one to assume that each newly created layer has nominal stiffness moduli and tensile/compressive strengths. Hence introduction of explicit stiffness moduli and tensile/compressive strength dependencies on time, or equivalent time state parameter, is not needed. Analysis of plain concrete (PC) and reinforced concrete (RC) structures, especially massive ones, subjected to any kind of straining in their early stage of existence, mostly due to external loads but especially by thermal loading and shrinkage, is the goal of the approach. In this article a simple elasto-plastic softening model with creep is used for each layer and a general layered model behavior is illustrated on one-dimensional (1D) examples.

• 한국공간구조학회논문집
• /
• 제14권3호
• /
• pp.85-92
• /
• 2014

Most of the structural forms in which ETFE film is used are the cushion(pneumatic membrane structures) and tension type(tensile membrane structures), which have been generally accepted to be the most efficient forms. Tensile membrane structures are pulled outward from the exterior to introduce initial stress. And such structures offer the advantage of a natural shape formed by tensile stress and eliminate the need for blast air. Recently, the number of tension type structures is increasing. However, there are problems of creep and relaxation of ETFE films under long-term stresses. In this paper, the stretch fabrication method is proposed for stretching the film into the plastic region during initial tensioning as a way to increase its strength. And its effectiveness is confirmed by investigating experimental and analytical test using ETFE films.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2003년도 추계학술대회논문집
• /
• pp.187-190
• /
• 2003

An Fe-25Cr steel was oxidized in Ar at 973K with or without external stesses of 30~35Mpa. A 0.1 ${\mu}{\textrm}{m}$ thick Cr$_2$O$_3$scales was formed during pre-treatment in Ar. Cracking on the oxides scales commenced at the alloy grain boundary by the end of second creep stage, arrayed almost perpendicular to the direction of the tensile directions. On the contrary, a scale formed in $N_2$-0.1%SO$_2$shows poor adherence on the metal substrate. In this case, the strength of materials is much lower than in Ar

• 한국도로학회논문집
• /
• 제6권3호
• /
• pp.9-15
• /
• 2004

아스팔트 혼합물의 균열 저항성은 일반적으로 인장 강도, 스티프니스와 같은 단일 물성치를 측정함으로써 평가된다. 그러나, 아스팔트 혼합물의 균열 성능을 평가함에 있어서 단일 물성치의 이용은 의문시되어 왔다. 따라서 본 연구에서는 아스팔트 혼합물의 균열 저항성과 관련이 있는 주요 특성치를 좀 더 심도 있게 규명하고자 하였다. 이를 위해 다양한 하중 조건 하에서 파괴 시험 크리프 시험, 강도 시험이 일반 아스팔트 혼합물과 개질 아스팔트 혼합물에 대해서 수행되었다. 시험 결과, 혼합물의 균열 저항성은 주로 미세 손상 축적 속도에 영향을 받음을 알 수 있었으며, 이 값은 파괴 에너지 한계에 영향을 주지 않으면서 m값에 반영됨을 알 수 있었다. 또한, 짧은 하중 재하 시간 (탄성거동) 동안 얻어지는 스티프니스는 혼합물의 균열 저항성의 차이를 규명하는데 한계가 있음을 알 수 있었다. 따라서 아스팔트 혼합물의 균열 저항성을 보다 명확히 평가하기 위해서는 혼합물의 크리프 거동과 파괴 한계점을 동시에 고려하는 것이 필수적임을 알 수 있었다. 또한 수퍼페이브 간접 인장 강도 시험으로부터 구한 잔여 소멸 에너지는 비교적 손쉬운 실험을 통해 아스팔트 혼합물의 균열 저항성의 상대적인 차이를 보여줄 수 있는 유용한 물성치임을 알 수 있었으며, 장기 크리프 시험에서 얻어지는 파괴 변형률은 아스팔트 혼합물의 크리프 거동과 파괴 한계점을 동시에 고려함으로써 균열 저항성을 평가할 수 있는 유용한 물성치 임을 알 수 있었다.

• 한국해양공학회지
• /
• 제3권2호
• /
• pp.625-625
• /
• 1989

To check technical improvement in the soundness and strength of 12% Cr steel rotor, a 25 tons of rotor with 65 tons of ingot was made in real size and was cut to pieces to take test samples, and the various mechanical tests such as impact, tensile, creep, and fatigue were carried out. The strengths are compared with those of 1% Cr-Mo-V rotor of same size. Microstructures of the samples are examined and reviewed. The results can be summarized as follows. 1) Fracture appearance transition temperatures are 80.deg. C at the center part and 60.deg. C near surface of 12% Cr rotor, and 8.deg. C near surface of 1% Cr-Mo-V rotor. 2) Comparative rapid softening occurs at higher temperatures above 600.deg. C for 12% Cr steel and 550.deg. C for 1% Cr-Mo-V steel in tension tests. 3) Fatigue crack propagation rate of 12% Cr steel is almost same as that of 1% Cr-Mo-V steel at the same corresponding surface part of the rotors. The crack growth rate of center part of 12% Cr rotor is faster than near surface part of the rotor, and the crack growth rate at the load condition of R=0.04 is slower than that of the load condition of R=0.5 for both 12% Cr steel and 1% Cr-Mo-V steel. 4) Crack growth rate of radial direction near surface of 12% Cr rotor is faster than that of transverse direction at the same part because of the difference in residual stresses. 5) Both creep and fatigue strengths of 12% Cr steel are superior to those of 1% Cr-Mo-V steel and the difference is thought the effect of climb and glide controlled creep by solid solution of alloying elements and dispersion of carbides.