• 한국세라믹학회지
• /
• 제29권10호
• /
• pp.806-814
• /
• 1992

The aim of this study was to investigate the change in compressive strength, freacture behavior and degradation of piezoelectric properties with compressive cyclic loading in Pb(Zr, Ti)O3 of tetragonal, morphotropic phase boundary and rhombohedral composition. The highest compressive strength was found in rhombohedral composition. After poling treatment the strength increased by 8.4% and 6.5% in tetragonal and morphotropic phase boundary compositions respectively while changed little in rhombohedral. The increase of compressive strength after poling treatment is believed to be due to the internal stress around grain boundary by domain alginment toward electric field direction in the microstructures having tetragonality and the occurrence of domain switching to the direction perpendicular to electrical field during fracture. Fracture mode relatively change from transgranular to intergranular was observed in the large grain sized tetragonal and morphotropic phase boundary compositions before and after poling but the transgranular fracture mode always remained in the rhombohedral composition. From the X-ray diffractometer analysis the domains parallel to the electric field direction is known to undergo rearrangement during the cyclic loading into random direction that is responsible for the degradation of piezoelectric property.

• Structural Engineering and Mechanics
• /
• 제55권1호
• /
• pp.205-228
• /
• 2015

The results of a numerical investigation pertaining to the hysteretic behaviour of concrete filled steel tubular (CFT) column to I-beam connections are discussed in detail. Following the verification of the numerical results against the available experimental tests, the nonlinear finite element (FE) analysis was implemented to evaluate the effects of different parameters including the column axial load, beam lateral support, shape and arrangement of stiffeners, stiffness of T-stiffeners, and the number of shear stiffeners. Pursuing this objective, an external CFT column to beam connection, tested previously, was selected as the case-study. The lateral forces on the structure were simulated, albeit approximately, using an incremental cyclic loading reversal applied at the beam tip. The results were compared in terms of hysteretic load-displacement curves, stress distributions in connection, strength, rotation, and energy dissipation capacity. It was shown that external T-stiffeners combined with internal shear stiffeners play an important role in the hysteretic performance of CFT columns to I-beam connections.

• Wind and Structures
• /
• 제13권3호
• /
• pp.257-273
• /
• 2010

The aerodynamic and aero-elastic model tests of the China''s highest cooling tower has been carried out in the TJ-3 Boundary Layer Wind Tunnel of Tongji University. By adopting a scanivalve system, the external wind pressure is firstly measured on $12{\times}36$ taps for a single tower, two and four grouped towers under the condition of both smooth flow and the boundary layer due to surrounding geographic and building topography. The measurements of internal wind pressure distribution of $6{\times}36$ taps are taken for a single tower under the various ventilation ratios ranging from 0% to 100% of stuffing layers located at the bottom of the tower. In the last stage, the wind tunnel tests with an aero-elastic model are carefully conducted to determine wind-induced displacements at six levels (each with eight points) with laser displacement sensors. According to the measurement results of wind pressure or vibration response, the extreme aerodynamic loading values of the single or grouped towers are accordingly analyzed based on probability correlation technique.

• 대한치과기공학회지
• /
• 제35권4호
• /
• pp.281-286
• /
• 2013

Purpose: Surface modification is important techniques in modern dental and orthopedic implants. This study was performed to try embedding of bioactive materials in porous Ti implants. Methods: Porous Ti implant samples were fabricated by sintering of spherical Ti powders in a high vacuum furnace. It's diameter and height were 4mm and 20mm. Embedding process was used to suction and vacuum chamber. Loading properties of porous Ti implants were evaluated by scanning electron microscope(SEM), confocal laser scanning microscope(CLSM), and UV-Vis-NIR spectrophotometer. Results: Internal pore structure was formed fully open pore. Average pore size and porosity were $10.253{\mu}m$ and 17.506%. Conclusion: Porous Ti implant was fabricated successfully by sintering method. Particles are necking strongly each other and others portions were vacancy. This porous structure can be embedded to bioactive materials. Therefore bioactive materials will be able to embedding to porous Ti implants. Bioactive materials embedding in the porous Ti implant will induced new bone faster.

• 한국윤활학회:학술대회논문집
• /
• 한국윤활학회 2001년도 제33회 춘계학술대회 개최
• /
• pp.265-270
• /
• 2001

Hip joint simulator which Is an essential device for evaluating the wear of biomaterials (ultrahigh molecular weight polyethylene, Co-Cr alloy, alumina, etc.) used in total hip joint replacement was developed. This hip joint simulator mimics the joint motion and joint loading of human gait by adapting the 4 degree of freedom in kinematic motion (flexing/extension, adduction/abduction, Internal rotation/external rotation) and axial loading, Four stations are operated by 8 servo-motors and harmony drives. Joint leading was imposed by displacement control from a ball screw, LM guide, and spring system. Each kinematic link system operates separately or coupled modes. A heater and a thermocouple were installed for keeping the body temperature in each station.

• 대한의용생체공학회:의공학회지
• /
• 제22권1호
• /
• pp.109-117
• /
• 2001

본 연구는 요통재해를 일으킬 수 있는 위험요소를 많이 내포한 운수유통업의 인력운반방법(Manual Material Handing)에 대한 요통발병의 위험정도를 측정하였다. 운수유통업에서 이루어지고 있는 운반작업은 우리나라의 제반환경특성상 도구를 사용하지 않고 대부분 사람에 의해 이루어지고 있다. 운반방법도 짊어지는 형태인 등짐작업이 많이 이용되고 있다. 그러나 이에 대한 체계적인 연구가 수행되고 있지 않은 실정이다. 본 연구의 목적은 등짐자세로 물건을 운반할 때와 물건을 하역하여 정리하는 작업이 요추에 미치는 물리적 힘이 어느정도인지 규명하여 위험수준을 파악하는데 그 목적이 있다. 등짐운반과 정리작업(비대칭형 작업)에 대한 역학적인 연구를 수행하기 위하여 몸통근육에 미치는 internal force을 규명하여 정량화한 Han's (1991) model을 이용하여, 이들 작업에 대한 역학적인 분석을 실시하였다.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2006년도 하계학술발표대회 논문집
• /
• pp.436-441
• /
• 2006

In recent European telecommunication base transceiver stations(BTS) a membrane laminated air filter is reported to replace a heat exchanger in order to cool internal digital units of BTS. The concept of using the air filter is for the direct ambient cooling(DAC) of BTSs without heat loss generally found ill the heat exchanger type BTS. In the present study, a performance evaluation experiment was conducted to investigate the pressure drop characteristics with dust loading and the particle collection efficiency of the air filter for the DAC of BTS.

• International Journal of Internet, Broadcasting and Communication
• /
• 제14권3호
• /
• pp.258-269
• /
• 2022

In these days, innovative functions are required to unmanned parcel delivery lockers. As non-face-to-face transactions become the center due to the recent COVID-19 pandemic, many problem occurs in society such as theft crimes and lack of loading space. Therefore, New concept storage device is developed in korea. It has the functions that minimizes empty spaces by using the internal transport device to enable efficient space loading and refrigerate goods such as foods. In order to systematically approach the system design of the unmanned parcel delivery lockers which is the new function is applied, We applied model-based system engineering to improve the development efficiency and use a system modeling language to express the system. We conducted interworking research of CAD data including system modeling and design data. it is expected that this method will increase the effective development efficiency such as maintenance traceability and reduction of development period and cost.

• 한국초전도ㆍ저온공학회논문지
• /
• 제8권4호
• /
• pp.26-29
• /
• 2006

The study to be presented related on initial behavior of quench concerned with many considerations, such as epoxy impregnated coil, critical current density related on strain and temperature, winding effect and behavior of internal superconducting wire. Especially, the deformation behavior of coils under magnetic field and thermal contractions at cryogenic temperatures to be dealt with the analytical method related on Fracture Mechanics. From the results, we know that the strain by self weight contribute to epoxy cracking at the edge of deformed coils and the deformation behavior relate on epoxy cracking must be dealt with biaxial loading problem. Then, the epoxy crack on $r\theta-plane$ under biaxial loading have been propagated with inclined crack angle and joined superconducting wire. Also, we can explain transfer of epoxy crack propagation energy from epoxy resin to superconducting wire.

• Journal of Forest and Environmental Science
• /
• 제14권1호
• /
• pp.89-100
• /
• 1998

본 연구는 제지 원료의 효율적 이용 및 기능의 최적화를 위한 수단으로 사용되고 있는 다층구조화에 따른 종이의 내부응력 및 물성의 변화를 조사하기 위하여 수행되었다. 또한 최근 사용량이 급증되고 있는 재생섬유를 다층구조에 도입할 경우 수반되는 종이의 물성 변화도 조사되었다. 펄프의 고해처리는 단층지의 내부응력을 증가시켜준 반면 충전제의 사용은 내부응력을 감소시켰다. 종이의 다층구조화는 인열지수를 제외한 대부분의 종이물성과 내부응력을 감소시켰으며, 이러한 변화는 사용된 펄프의 종류, 고해수준, 원료의 배합 방법에 따라 다양하게 나타났다. 충전시에는 충전제를 외층 또는 내층에 사용함으로써 단층지보다 우수한 내부응력 및 종이물성을 얻을 수 있었다. 재생섬유를 사용할 때는 다층구조화를 통하여 투기도와 빳빳이의 개선이 가능하였으나, 파열지수가 감소되었다.