• Journal of the Korean GEO-environmental Society
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• v.15 no.5
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• pp.67-74
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• 2014

In this study, a constant rate of strain test (CRS) and oedometer test was performed in order to study the consolidation characteristics to the liquid limit using a re-shaped clay which was preconsolidated at a constant pressure. Consolidation samples were made of kaolinite which was mixed with bentonite of 6 %, 9 %, 12 % and 15 % of it by weight and the test value of liquid limit of samples were appeared in 77 %, 84 %, 88 % and 91 % respectively. And then consolidation samples which were agitated sufficiently adding distilled water 2 times of liquid limit were preconsolidated in the condition of a constant pressure of 0.2 MPa. The oedometer test which is commonly used recently and the consolidation test of constant rate of strain which were applied in 0.001 %/min, 0.004 %/min, 0.01 %/min rate of strain according to ASTM, D4186-82 were performed and the preconsolidation pressures were compared and analyzed at 0.2 MPa preconsolidated pressure. As a result, in the case of low value of liquid limit, preconsolidation pressure was appeared same as 0.2 MPa preconsolidated pressure at the high speed strain rate, and in the case of high value of liquid limit, preconsolidation pressure was appeared same as 0.2 MPa preconsolidated pressure at the low speed strain rate.

• Journal of Korean Society of Steel Construction
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• v.16 no.3 s.70
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• pp.315-324
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• 2004

This study performs a yield line analysis of welded T-joints in cold-formed Square Hollow Sections (SHS) with the branch in axial compression. The existing yield line models proposed by Koto, Packer, Zhao, and CIDECT and the proposed yield line model of the previous study are compared, using the existing test results of welded T-joints in cold-formed SHS. The yield line model suggested in the previous paper, which is based on the simplified yield line analysis, is reviewed to evaluate its application limit on cold-formed SHS T-joints. In the proposed model, the round corner of the cold-formed SHS section and weld size are taken into account. Finally, the validity range of yield line analysis is determined by observing the actual failure modes and comparing the test value with the analysis value, set as ${\beta}^{\prime}{\leq}0.8$ where ${\beta}^{\prime}=0.8$, ${\beta}^{\prime}=b_1^{\prime}/b_0^{\prime}$, $b_1{^{\prime}}=b_1+t_0$ and $b_0{^{\prime}}=b_0-t_0$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.8 s.239
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• pp.1139-1145
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• 2005

Most failures of ductile materials in metal forming processes occurred due to material damage evolution - void nucleation, growth and coalescence. In this paper, the modified yield function of Liao et al in conjunction with the Hosford's yield criterion is studied to clarify the plastic deformation characteristic of voided anisotropic sheet metals. The void growth of an anisotropic sheet under biaxial tensile loading and damage effect of void growth on forming limits of sheet metals are investigated. Also the characteristic length defining the neck geometry is introduced in M-K model to incorporate the effect of triaxial stress in necked region on forming limits. The forming limits theoretically predicted are compared with experimental data. Satisfactory agreement was obtained between the predictions and experimental data.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.7 s.94
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• pp.1751-1760
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• 1993

The squeeze casting process is considered as an attractive way to form the primary product of near net shape metal matrix composites for wide use in automobile industry. To understand for infiltration limit in squeeze casting processes, the SAFFIL short fiber preform of volume fraction $10%{\sim}23%$ were fabricated by vaccum pumping and speed control press, and the optimal condition for fiber preform fabrication had been experimentally obtained. The composite materials were fabricated by forced infiltration of molten metals such as Al6061, Al7075, pure Al, AC8A, and Al2024. The infiltration distance and deformation of fiber preform are observed, and tensile strength were measured from at the room temperature.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.172-175
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• 2009

The purpose of this study is to predict the forming limit diagram (FLD) of strain-rate sensitive materials on the basis of the Marciniak and Kuczynski (M-K) theory. The strain-rate effect is taken into consideration in such a way that the stress-strain curves for various strain-rates are inputted into the formulation as point data, not as curve-fitted models such as power function. To solve the nonlinear system of equations derived from the equilibrium and constraints in the groove region and the safe zone, the Newton-Raphson method is used. The theoretical FLDs using four different yield criteria, that are von Mises, Hill (1948), Hill (1979), Logan and Hosford, are compared with the experimental, numerical (FEA) and other theoretical results. A new trial is made where a modified M-K model having n-step grooves is introduced to describe a real localized neck.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.17 no.5
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• pp.223-230
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• 2007

Plasticity of clay bodies containing bottom ashes(BA) and small portion of other wastes was investigated. Plasticity indices of clay bodies using Atterberg limits were measured. It was confirmed that the plasticity indices could be applicable in actual forming process by extrusion. The forming possible compositions were found by changing the contents of water, bottom ash, stone dust, and sewage sludge. The relationship between the plasticity and physical properties of the aggregate green body was also investigated. The compositions for extrusion forming can be expected by measured the plasticity indices and these results were confirmed by real extrusion process. There is also strong relationship between the plasticity indices and the property of aggregate green body.

• Journal of Powder Materials
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• v.11 no.2
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• pp.179-185
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• 2004

통상적인 금속분말의 성형은 분말야금 공정으로 이루어지기 때문에 복잡한 형상의 부품을 구현하는 데는 제약이 있다. 하지만, 1970년대 후반 이래 새로운 금속분말의 성형기술로 크게 각광을 받으며 연구되고 있는 금속분말사출성형(Metal Powder Injection Molding, MIM) 기술을 이용하면 다양한 형태의 부품을 성형할 수 있다 최근에는 이러한 MIM 기술을 이용하여 다양한 산업분야에 응용될 수 있는 마이크로 부품을 제조하고자 하는 연구개발이 주목받고 있다./sup 1)/ 현재까지는 마이크로 부품을 제조하는 원천기술이 반도체 공정기술이나 마이크로 기계가공기술에 크게 의존하고 있다./sup 2,3)/ 특히, 경제적 효용성이라는 관점에서 수 마이크로 이하의 극미세 구조물은 반도체 공정기술을 이용하여 성형하는 것이 유리하며, 1㎜의 치수를 갖는 미세 구조물은 마이크로 기계가공기술로 제조하는 것이 적합하다(그림 1). 하지만, 수십 마이크로에서 수백 마이크로의 치수를 갖는 구조물 제조에 있어서 앞선 두 공정기술은 응용 재료의 종류와 복합한 형상의 대량생산에 한계가 있다. 비록 반도체 공정기술에서 박막 증착과 전기화학적 도금기술을 이용한 표면미세가공 기술에 의해 수십 마이크로 이내의 치수를 갖는 미세 구조물을 정밀하게 성형하지만,/sup 4,5,)/ 수백 마이크로 크기의 치수를 반도체공정기술로 구현하기는 곤란하다. 또한, 마이크로 기계가공기술도 높은 가공 정밀도를 유지하며 수백 마이크로 크기의 구조물을 가공할 수 있지만 복잡한 모양의 형태를 대량생산하기에는 적합하지 않다.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.378-382
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• 2008

Since the sheet metal forming of Mg alloy is perform at elevated temperature, the effect of strain rates related with the forming temperature and forming speed and R-value is very important factor for formability and forming limits and deep drawing. It is investigated that the effect of material properties such as various temperature, forming speed and strain rates on formability and R-value of Mg alloy sheet in round cup deep drawing. Therefore, the investigation for process variables is necessary to improve formability and forming limits and deep drawing. Also, the effects of strain rate and drawbility were studied by the experiment. The temperature, forming speed, and strain rates and R-value are investigated. Forming of Mg alloy takes consider into temperature, proper forming speed and strain-rate and R-value the formed parts were good without defects for forming limits and deep drawing.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.243-246
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• 2005

A tube hydroformability testing system was designed and manufactured to observe the forming steps and to provide arbitrary combination of internal pressure and axial feed. The forming limit diagram of an aluminum tube was obtained from the free bulge test and the T-shape forming test using this system, giving the criteria for predicting failure in the hydroforming process. The hydroformability of aluminum tube according to different conditions of a prebending process was discussed, based on the finite element analysis and the forming limit test. The effects of 2D and 3D prebending on the tube hydroforming process of an automotive failing arm were evaluated and compared with each other.

• Proceedings of the KAIS Fall Conference
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• 2010.05b
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• pp.1145-1148
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• 2010

우리 생활에서 큰 비중을 차지하고 있는 플라스틱은 그 사용 정도가 점점 증가하고 있는 추세이다. 그중에서도 플라스틱은 사출성형제품에서 가장 많이 사용한다. 사출성형의 제품은 높은 정밀도와 긴수명이 요구되며, 품질, 가격, 납기에 대해 사용자의 욕구를 충족시켜줄 수 있어야한다. 하지만 플라스틱은 열이나 하중 등 사용 환경에 따라 변하는 결점을 가지고 있으므로 일용잡화나 케이스류, 장식품 등의 일반적인 용도 이외에는 사용에 한계가 있다. 그러므로 설계자는 보다 과학적이고 합리적인 이론적 지식이 필요하다. 이에 사출성형 제품의 합리적인 설계를 위해 공리적 설계 기법을 이용하여 보다 좋은 설계를 수행하고 트리즈 기법을 활용함으로써 사출성형 제품의 문제들을 창의적으로 접근해봄으로써 문제 해결을 시도하려는 것이다.