• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2000년도 춘계학술대회논문집
• /
• pp.187-191
• /
• 2000

High temperature creep behaviour of Al-5 wt% Mg alloy reinforced with 7.5% BN flakes was studied. The composite specimens showed two main creep characteristics : (1) the value of the apparent stress exponent of the composite was high and varied with applied stress (2) the apparent activation energy for creep was much larger than that for self-diffusion in aluminum The true stress exponent of the composite was set equal to 5. Temperature dependence of the threshold stress of the composite was very strong. Which could not be rationalized by allowing for the temperature dependence of the elastic modulus change. AIN particles which were incorporated into the Al matrix during fabrication of the composite by the PRIMEXTM method were found to be effective barriers to dislocation motion and to give rise the threshold stress during creep of the composite

• 한국안전학회지
• /
• 제21권4호
• /
• pp.1-6
• /
• 2006

The lightness of components that was required in automobile and machinery industry requires high strength of components. In particular, manufacturing process and new materials development for solving the fatigue facture problem attendant upon high strength of suspension of automobile are actively advanced. In this paper, the effect of compressive residual stress of spring steel(JISG SUP-9)by shot-peening on fatigue crack growth characteristics in high temperature($100^{\circ}C,\;150^{\circ}C,\;180^{\circ}C$)was investigated with considering fracture mechanics. So, we can obtaint the followings. (1) Compressive residual stress is decreased with increasing the test temperature. (2) The effect of compressive residual stress on fatigue crack growth behavior in high temperature is increased below ${\Delta}K=17{\sim}19MPa{\sqrt{m}}$. (3) It was investigated by SEM that the constraint of compress residual stress for plastic zone of fatigue crack tip was decreased in high temperature as compared with room temperature.

• 한국해양공학회지
• /
• 제10권2호
• /
• pp.106-119
• /
• 1996

The ceramic has various high mechanical properties such as heat, abrasion, corrosion resistance and high temperature strength compared with metal. It also has low speciffic weight, low thermal expansibillity, low thermal conductivity. However, it could not be used as structural material since it is brittle and difficult for the machining. Therefore, there have been many researches to attempt to join ceramic with metal which is full of ductillity in order to compensate the weakness of ceramic.The problem is that residual stress develops around the joint area while the ceramic/metal joint material is cooled from high joining temperature to room temperature due to remarkable difference of thermal expansion coefficients between ceramic and metal. Especially, the residual stress at both edges of the specimen reduces the strngth of joint to a large amount by forming a singular stress field. In this study, two dimensional finite element method is attempted for the thermal elastic analysis. The joint residual stress of ceramic/metal developed in the cooling process is investigated and the change of joint residual stress resulted from the repetitive heat cycle is also examined. In addition, it is attempted to clarify the joint stress distribution of the case of tensile load and of the case of superposition of residual stress and actual loading stress.

• 대한기계학회논문집A
• /
• 제37권3호
• /
• pp.333-338
• /
• 2013

본 논문에서는 쇼트피닝 가공된 Alloy 600 재료의 고온환경하에서의 압축잔류응력 및 피로거동에 대해 연구하였다. 연구에 사용된 Alloy 600 재료는 원자력발전소에서 사용되는 주요부품 소재이며, 피닝가공으로 형성된 압축잔류응력은 응력부식균열(SCC; Stress Corrosion Cracking)의 발생을 크게 억제하는 것으로 알려져 있다. 현실성 있는 실험결과를 획득하기 위하여 실제 국내 원자력 발전소 주요부품의 사용온도를 포함한 고온 환경에서 피로특성 및 압축잔류응력을 평가하였다. 연구결과 약 $538^{\circ}C$이하에서는 피닝가공 효과가 존재하는 것으로 파악되었다. 피로수명은 $538^{\circ}C$ 까지 유지되는 것으로 분석되었으며, $538^{\circ}C$ 에서의 압축잔류응력은 상온에서의 값에 비하여 68.2%를 유지하였다. 본 연구결과는 원자력발전소의 안전 및 신뢰성 확보에 기초자료로 활용될 것으로 기대된다.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2001년도 춘계학술대회 논문집
• /
• pp.167-171
• /
• 2001

High temperature deformation behavior of Fe-28Al-5Cr alloy has been investigated known to show anomalous temperature dependence of yield strength. Specifically, the effect of Cr addition has been examined. A series of tensile and load relaxation tests have been carried out to obtain the flow behavior of Fe-28Al-5Cr alloy at the elevated temperatures. The flow curves have then been analyzed using the inelastic deformation theory recently proposed. Firstly, high temperature flow stress of iron aluminides can be resolved into internal stress and frictional stress. Secondly, the temperature corresponding to peak strength gets higher level at faster strain rate, which presumably due to the increased contribution of internal stress in observed flow stress. And thirdly, the alloying of Cr seems to cause solid-solution strengthening of frictional stress level and the elevation of 2nd order transition temperature. In this analogy, Fe-28Al-5Cr exhibits better strength especially at relatively higher temperature and lower strain rate than Fe-28Al.

• 한국철도학회논문집
• /
• 제9권2호
• /
• pp.131-136
• /
• 2006

Most modern railways, especially the high speed railway tracks, use continuous welded rail(CWR) for the less maintenance. For the CWR track has very few expansion joints, track buckling has always been an unpredictable event and it happens mainly by high compressive stress in rail in summer period. Therefore, it is important to understand the variation of rail stress induced by thermal loads which has direct influence on the rail buckling and stability of railway track. This paper describes the experimental investigation of the variation of rail temperature and stress in a high speed railway track on bridge structure. Field measurement was performed to examine the correlation between the rail temperature and rail stress on the Korean High Speed Railway line. Regression functions were derived from measured data to determine the rail stress f3r an arbitrary rail temperature varies from 20 to 50 degree Celsius.

• Journal of Advanced Marine Engineering and Technology
• /
• 제25권5호
• /
• pp.1108-1114
• /
• 2001

The fatigue crack propagation behavior of the SA516-Grade 70 steel which is used for pressure vessels was experimentally examined under the condition of at room temperature, $150^{\circ}C$, $250^{\circ}C$ and $370^{\circ}C$ with stress ration of R=0.1 and 0.3. The fatigue crack propagation rate , da/dN, related with the stress intensity factor range, $\vartriangle$N, was influenced by the stress ration within the stable growth of fatigue crack(Region II) with an increase in $\vartriangle$N. The resistance to the fatigue crack growth at high temperature is higher in comparison with that at room temperature, and the resistance attributed to the extent of plasticity-induced by compressive residual stress according to the cyclic loads. Fractographic examinations revels that the differences of the fatigue crack growth characteristics between room and high temperatures are mainly explained by the crack and oxide-induced by high temperature.

• Steel and Composite Structures
• /
• 제46권6호
• /
• pp.805-821
• /
• 2023

This study developed an evaluation system to explore the effect of the environmental temperature on the stress redistribution produced by cable stress relaxation of structural members in a steel cable-stayed bridge. The generalized Maxwell model is used to estimate stress relaxation at different temperatures. The environmental temperature is represented using the thermal coefficients and temperature loads. The fmincon optimization function is used to determine the set of stress relaxation parameters at different temperatures for all cables. The ABAQUS software is employed to investigate the stress redistribution of the steel cable-stayed bridge caused by the cable stress relaxation and the environmental temperature. All of these steps are set up as an evaluation system to save time and ensure the accuracy of the study results. The developed evaluation system is then employed to investigate the effect of environmental temperature and cable type on stress redistribution. These studies' findings show that as environmental temperatures increased up to 40 ℃, the redistribution rate increased by up to 34.9% in some girders. The results also show that the cable type with low relaxation rates should be used in high environmental temperature areas to minimize the effect of cable stress relaxation.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2001년도 춘계학술대회 논문집
• /
• pp.332-337
• /
• 2001

The objective of research is to clarify the interaction between dislocations and precipitates during high temperature creep deformation behaviors of high Mn austenitic steels. After measuring the internal stress in minimum creep rate at 873K, a transmission electron microscope (TEM) observation was performed to investigate the interaction between dislocations and precipitates during high temperature creep deformation. The band width of effective stress and internal stress increased when the nitride precipitates distribute more densely. Fine nitrides disturbed the dislocation movement with pinning the dislocations and perfect dislocations were separated into Shockley partial dislocations by fine nitrides. Coarse nitrides disturbed the dislocation movement with climb mechanism.

• 대한기계학회논문집A
• /
• 제27권7호
• /
• pp.1152-1158
• /
• 2003

The mechanical behavior of a commercially pure titanium (CP-Ti) is investigated at high temperature Split Hopkinson Pressure Bar (SHPB) compression test with high strain-rate. Tests are performed over a temperature range from room temperature to 1000$^{\circ}C$ with interval of 200$^{\circ}C$ and a strain-rate range of 1900 ∼ 2000/sec. The true flow stress-true strain relations depending on temperature are achieved in these tests. For construction of constitutive equation from the true flow stress-true strain relation, parameters for the Johnson-Cook constitutive equation is determined. And the modified Johnson-Cook equation is used for investigation of behavior of flow stress in vicinity of recrystalization temperature. The Modified Johnson-Cook constitutive equation is more suitable in expressing the dynamic behavior of a CP-Ti at high temperature, i.e. about recrystalization temperature.