• 한국재료학회지
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• 제26권10호
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• pp.535-541
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• 2016

The present study deals with the effects of micro-alloying elements such as Ni, V, and Ti on the recrystallization behavior of carbon steels at different strain rates. Eight steel specimens were fabricated by varying the chemical composition and reheating temperature; then, a high-temperature compressive deformation test was conducted in order to investigate the relationship of the microstructure and the recrystallization behavior. The specimens containing micro-alloying elements had smaller prior austenite grain sizes than those of the other specimens, presumably due to the pinning effect of the formation of carbonitrides and AlN precipitates at the austenite grain boundaries. The high-temperature compressive deformation test results indicate that dynamic recrystallization behavior was suppressed in the specimens with micro-alloying elements, particularly at increased strain rate, because of the pinning effect of precipitates, grain boundary dragging and lattice misfit effects of solute atoms, although the strength increased with increasing strain rate.

• Journal of Welding and Joining
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• 제29권4호
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• pp.54-60
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• 2011

Adhesive bonding is one of the most promising joining methods which may substitute for conventional metallurgical joining processes, such as welding, brazing and soldering. Curing behavior and mechanical properties of adhesive joint are largely dependent on the curing agent including hardener and catalyst. In this study, effects of curing system on the curing behavior and single-lap shear strength of epoxy adhesive joint are investigated. Dihydrazide, anhydride and dicyandiamide(DICY) were chosen as hardener and imidazole and triphenylphosphine(TPP) were chosen as catalyst. In curing behavior, TPP showed the delay of the curing rate for DICY and ADH at $160^{\circ}C$, compared to imidazole catalyst due to the high curing onset/peak temperature. DICY seemed to be most beneficial in the joint strength for both steel and Al adherends, although the type of adherends affected the shear strength of epoxy adhesive joint.

• 한국컴퓨터정보학회논문지
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• 제20권1호
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• pp.29-37
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• 2015

Nowadays, the user-centric application based web 2.0 has replaced the web 1.0. The users gain and provide information by interactive network applications. As a result, traditional approaches that only extract and analyze users' local document operating behavior and network browsing behavior to build the users' preference profile cannot fully reflect their interests. Therefore this paper proposed a preference analysis and indicating approach based on the users' communication information from MicroBlog, such as reading, forwarding and @ behavior, and using the improved PersonalRank method to analyze the importance of a user to other users in the network and based on the users' communication behavior to update the weight of the items in the user preference. Simulation result shows that our proposed method outperforms the ontology model, TREC model, and the category model in terms of 11SPR value.

• Structural Engineering and Mechanics
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• 제18권5호
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• pp.691-707
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• 2004

This paper presents the micro-mechanical modeling for predicting concrete behavior under compressive loading. The model is able to represent the heterogeneities in the microstructure up to three phases, i.e., aggregate particles, matrix and interfaces. The smeared crack concept based on non-linear fracture mechanics is implemented in order to formulate the constitutive relation for each component. The splitting tensile strength is considered as a fracture criterion for cracking in micro-level. The finite element method is employed to simulate the model based on plane stress condition by using quadratic triangular elements. The validation of the model is verified by comparing with the experimental results. The influence of tensile strength from both aggregate and matrix phases on the concrete compressive strength is demonstrated. In addition, a guideline on selecting appropriate tensile strength for each phase to obtain specified concrete compressive strength is also presented.

• Advances in aircraft and spacecraft science
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• 제5권3호
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• pp.295-318
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• 2018

This research studies thermo-elastic behavior of rotating micro discs that are employed in various micro devices such as micro gas turbines. It is assumed that material is functionally graded with a variable profile thickness, density, shear modulus and thermal expansion in terms of radius of micro disc and as a power law function. Boundary condition is considered fixed-free with uniform thermal loading and elastic field is symmetric. Using incompressible material's constitutive equation, we extract governing differential equation of four orders; to solution this equation, we utilize general differential quadrature (GDQ) method and the results are schematically pictured. The obtained result in a particular case is compared with another work and coincidence of results is shown. We will find out that surface effect tends to split micro disc's area to compressive and tensile while nonlocal parameter tries to converge different behaviors with each other; this convergence feature make FGIMs capable to resist in high temperature and so in terms of thermo-elastic behavior we can suggest, using FGIMs in micro devices such as micro turbines (under glass transition temperature).

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2007년도 춘계학술대회 논문집
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• pp.641-642
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• 2007

• 대한금속재료학회지
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• 제49권1호
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• pp.32-39
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• 2011

The present investigation was performed on the die compaction and sintering behavior of Fe micro-nano mixed powder with a mixed binder for powder injection molding. Warm die compaction of the feedstock for simulation of the static injection molding process was conducted using a cylindrical mold of 10 mm diameter at $100^{\circ}C$ under 4MPa. The die compaction of the micro-nanopowder feedstock underwent a uniform molding behavior showing a homogeneous distribution of nanopowders among the micropowders without porosity and distortion. After debinding, the powder compact maintained a uniform structure without crack and distortion, leading to a high green density of 64.2% corresponding to the initial powder loading of 65%. The sintering experiment showed that the micro-nanopowder compact underwent a near full and isotropic densification process during sintering. It was observed that the nanopowders effectively suppressed the growth of micropowder grains during densification process. Conclusively, the use of nanopowder for PIM feedstock might provide a new concept for processing a full density PIM parts with fine microstructure.

• Smart Structures and Systems
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• 제22권6호
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• pp.643-662
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• 2018

One of the methods for investigation of mechanical behavior of materials is numerical simulation. For simulation, its need to model behavior is close to real condition. PFC is one of the rock mechanics software that needs calibration for models simulation. The calibration was performed based on simulation of unconfined compression test and Brazilian test. Indeed the micro parameter of models change so that the UCS and Brazilian test results in numerical simulation be close to experimental one. In this paper, the effect of four micro parameters has been investigated on the uniaxial compression test and Brazilian test. These micro parameters are friction angle, Accumulation factor, expansion coefficient and disc distance. The results show that these micro parameters affect the failure pattern in UCS and Brazilian test. Also compressive strength and tensile strength are controlled by failure pattern.

• 콘크리트학회논문집
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• 제22권1호
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• pp.69-76
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• 2010

콘크리트의 수축으로 인한 균열가능성 평가에 있어서 대부분의 경우 콘크리트를 균질한 물질로 가정하는 방식으로 접근하고 있다. 그러나 이러한 방식으로 접근할 경우 불구속조건 하의 콘크리트에서 자기수축으로 인한 미세균열(micro-cracking) 현상을 평가하는 것이 불가능함과 동시에 콘크리트 내부의 균열 발생 현상을 이해하는데 한계가 있다. 이에 이 연구에서는 시멘트 모르타르 시험체를 가지고 실험적으로는 음향방출(acoustic emission) 장비를 사용하여 내부 균열 발생량을 측정 및 평가하였으며, 이론적인 접근방식의 일환으로 실제 모르타르 시험체로부터 구하여진 이차원 이미지를 사용하여 NIST에서 개발한 OOF code로 유한요소해석을 수행하였다. 실험 및 해석 결과, 모르타르의 내부에서 시멘트 페이스트상의 수축 및 골재의 내부구속으로 인하여 발생하는 미세균열 발생 현상을 보다 현실적으로 이해할 수 있었다.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2007년도 춘계학술발표대회 및 제12회 신소재 심포지엄
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• pp.11.1-11.1
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• 2007