• Proceedings of the Korean Fiber Society Conference
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• 2003.04a
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• pp.64-67
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• 2003

Poly(trimethylene terephthalate)(이하 PTT)는 1941년 Caligo Printing Ink사의 Whinfield와 Dickson에 의해 중합 방법이 보고[1]된 이후 상업화를 위한 많은 학문적 연구가 이어져왔다. 그럼에도 불구하고 아직 PET에 비하여 기초 연구가 미비하며 상업적으로 사용하기에는 많은 불안정한 요소들을 가지고 있다. 앞선 연구자들이 밝힌바와 같이 PTT의 결정구조는 2개의 단량체가 1개의 unit cell을 이루면서 결정격자 내에서 O-C $H_2$-C $H_2$-C $H_2$-O가 trans-gauche-gauche-trans형의 coiled spring처럼 형성되어 좋은 elastic recovery와 뛰어난 신축성, 염색성 등 우수한 물성을 가지며 전반적인 성질은 PET와 Nylon의 중간성질을 뛰고 있지만 [2,3] 유리전이온도 (Tg : dir 4$0^{\circ}C$)와 냉결정화오도 ( $T_{ c cold}$ : dir 55$^{\circ}C$)사이의 차이가 15$^{\circ}C$ 정도이므로 섬유상에 많은 경시변화가 일으켜 구조적 불안정성을 가지게 한다 [4]. (중략)

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.233-238
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• 2002

In this paper, the characteristics of fresh and hardened recycled concrete were experimentally compared to investigate the applicability of the recycled fine aggregates with the substitution ratio. Test results show that the workability of the recycled concrete decreases with the increment of substitution ratio of the recycled fine aggregates except for type-D case which has a lower absorption ratio. Also air content was increased with increasing substitution ratio. It was found that the compressive strength and elastic modulus of recycled concrete were decreased with increasing substitution ratio of the recycled fine aggregates. And, the superplasticizer was more effective on the workability recovery of the recycled concrete.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.113-116
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• 2003

Hem quality can be determined mainly by turn-down and roll-in. Turn-down, that is created by the elastic recovery, can't be easily detected and measured since it is usually as small as 0.03 m. This study is focused on the precise evaluation of the hemming defects through analytical and experimetal approaches, and on the investigation of the influence of process parameters on the final hem quality. Implicit finite element analysis of plane-strain hemming process is performed by using a commercial code ABAQUS/Standard. Experiment and measurement is also carried out for steel and aluminium sheet metals, and the results are compared with those of analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.7 s.250
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• pp.757-764
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• 2006

Isothermal cyclic stress-strain deformation and thermomechanical deformation (TMD) of 429EM stainless steel were analyzed using a rheological model employing a bi-linear model. The proposed model was composed of three parameters: elastic modulus, yield stress and tangent modulus. Monotonic stress-strain curves at various temperatures were used to construct the model. The yield stress in the model was nearly same as 0.2% offset yield stress. Hardening relation factor, m, was proposed to relate cyclic hardening to kinematic hardening. Isothermal cyclic stress-strain deformation could be described well by the proposed model. The model was extended to describe TMD. The results revealed that the hi-linear thermomechanical model overestimates the experimental data under both in-phase and out-of-phase conditions in the temperature range of $350-500^{\circ}C$ and it was due to the enhanced dynamic recovery effect.

• Proceedings of the Korean Fiber Society Conference
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• 2002.04a
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• pp.301-304
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• 2002

In the prior work,$\^$l)/ we introduced several chemical cross-linking agents in order to improve elastic recovery of copolyetheresters, but we are confronted by two difficulties. The first is that cross-linking agents interfere with crystal growth which acts as a physical interlocking. The second is that strain at breaking decreases with the amount of cross-linking agent. It is considered that the chemical interlocking parts couldn't be deformed like crystalline phase. (omitted)

• Transactions on Electrical and Electronic Materials
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• v.14 no.3
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• pp.116-120
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• 2013

This paper proposes a novel RF MEMS dc-contact switch with stiff membrane on a quartz substrate. The uniqueness of this work lies in the utilization of a seesaw mechanism to restore the movable part to its rest position. The switching action is done by using separate pull-down and pull-up electrodes, and hence operation of the switch does not rely on the elastic recovery force of the membrane. One of the main problems faced by electrostatically actuated MEMS switches is the high operational voltages, which results from bending of the membrane, due to internal stress gradient. This is resolved by using a stiff and thick membrane. This membrane consists of flexible meanders, for easy movement between the two states. The device operates with an actuation voltage of 6.43 V, an insertion loss of -0.047 dB and isolation of -51.82 dB at 2 GHz.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1511-1516
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• 2007

Because Seaming process of MPJ (Mechanical Press Joining) has various design factors such as thickness, bending radius, seaming width, caulking press width and the dynamic factor such as multistage plastic working, elastic recovery, residual stress, the optimum conditions can't be easily determined. Using a design of experiment based on the FEM, which has several advantages such as less computing, high accuracy performance and usefulness, this study was performed investigating the interaction effect between the various design factor as well as the main effect of the each design factor during drum MPJ and proposed optimum condition using center composition method among response surface derived from regression equation of simulation-based DOE.

• Journal of Pharmaceutical Investigation
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• v.35 no.4
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• pp.243-247
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• 2005

Although many scientists have used pectin, its feasibility in terms of tablet manufacturability with a high speed machine has never been evaluated. Therefore, compactibility of different pectin types for large scale tableting operation has been evaluated. The compactibility behavior of powder pectins was studied by a compaction simulator. It was found that pectin on its own does not produce tablets of acceptable quality even at a punch velocity as low as 20 rpm (e.g. low tensile strengths, capping and lamination irrespective of applied compression force). Thus, dwell time was introduced and more hard compact was produced as relaxation time in die increases. It was concluded that frequent structural failure observed in both pectin types was due to lack of plastic deformation, poor compactibility and high elastic recovery.

• Transactions of Materials Processing
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• v.21 no.6
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• pp.384-388
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• 2012

Sheet metal forming processes induce residual stress in the final product due to plastic deformation. The residual stress leads to elastic recovery of the formed part called springback, which causes shape errors in the final product. This error is a serious issue, especially for high strength steels, which are widely used in auto-body structures. Therefore, the evaluation of the amount of springback becomes critical for high strength steels. This paper investigates the springback behavior of DP780 steel sheets after the U-bending process using the geometry of the standard U-shape tool from the NUMISHEET'93 benchmark problem. The amounts of springback were measured as a function of the intrusion direction, forming speed and blank holding force.

• Journal of Chest Surgery
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• v.19 no.4
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• pp.688-694
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• 1986

Takayasu`s disease is an arteritis of unknown etiology involving larger elastic arteries such as aorta and its branches, pulmonary arteries and rarely coronary arteries. Especially, aortic root involvement with the valvular leaflets has been reported in several cases of Takayasu`s arteritis. Recently we have experienced one case of Takayasu`s arteritis involving left subclavian artery, descending aorta, left renal artery and multiple valvular leaflets. The patient was 33 year-old female and admitted with complaints of cough, dyspnea and general weakness. Aortogram revealed extensive type of arteritis showing dilatation of ascending aorta, segmental narrowing of thoracic aorta and Riolan`s anastomosis. Double valve replacement [mitral and aortic valve] and tricuspid valve annuloplasty were performed. The patient made an excellent postoperative recovery and has shown striking improvement in cardiac status, NYHA functional class II eight months after operation.