• 콘크리트학회논문집
• /
• 제11권3호
• /
• pp.69-80
• /
• 1999

The strengthening of reinforced concrete structures by externally bonded GFRP has become increasingly common in resent years. However the analysis and design method for GFRP plate strengthening of RC beams is not well established yet. The purpose of present paper is, therefore, to define the failure mechanism and failure behavior of strengthened RC beam using GFRP and then to propose a resonable method for the calculation of interface debonding load for those beams. From the experimental results of beams strengthened by GFRP, the influence of length and thickness, width of plate on the interfacial debonding failure behavior of beam is studied and, on the basis of test results, the semi-empirical equation to predict debonding load is developed. The proposed theory based on nonlinear analysis and critical flexural crack width, predicts relatively well the debonding failure load of test beams and may be efficiently used in the analysis and design of strengthened RC beams using GFRP.

• 터널과지하공간
• /
• 제18권6호
• /
• pp.447-456
• /
• 2008

노천광산에서 사면설계는 안정성과 경제성 측면에서 동시에 접근하여 결정해야 한다. 또한 일반 도로나 철도 연변의 사면과는 달리 대부분 지보나 보강없이 굴착해야 하기 때문에 사면각도가 가장 중요한 설계 변수이다. 본 연구에서는 인도네시아 파시르에 위치한 노천채광방식의 대규모 석탄광산 사면에 대하여 안정성 측면에서의 사면 각도 및 한계사면높이를 결정하였으며 이러한 설계가 가지고 있는 불확실성을 보완할 수 있는 계측 및 계측자료 해석을 수행하였다. 연구 결과, 사면각도(Overall Elope angle) $30^{\circ}$를 유지하는 경우 안전율 1.5를 확보하는 최대개발심도는 $353{\sim}438m$로 계산되었으나 강도정수에 대한 민감도분석결과를 고려할 때 사면높이는 300m를 초과하지 않는 것이 바람직하다. 또한 변위계측자료에 대한 역변위속도 분석 결과가 현장사면 사례와 잘 일치하여 이 방법을 통해 사면의 불안정성 및 파괴시기를 대략적으로 예측할 수 있을 것으로 판단된다.

• Tribology and Lubricants
• /
• 제33권4호
• /
• pp.127-133
• /
• 2017

In order to characterize the adhesive properties and failure mechanisms of diamond-like carbon (DLC) films of two different thicknesses (130 nm and $1.2{\mu}m$), deposited by plasma-enhanced chemical vapor deposition on a Si substrate, scratch testing with a micro-indenter ($12.5{\mu}m$ tip radius) was performed under a linearly increasing load. These scratch tests were conducted under the same test conditions for both films. The critical load of each film was estimated from the scratch test results, based on a sharp increase in the coefficient of friction and a clear distinction of failure modes. The critical load was the basis for evaluating the adhesion strength of the films, and the $1.2{\mu}m-thick$ DLC film had superior adhesion strength. For better understanding of the failure modes, the following analyses were conducted: friction behavior and scratch tracks analysis using scanning electron microscopy, energy-dispersive spectroscopy, and 3-D profilometry. The scratch test results showed that failure modes were related to the thickness of the films. The 130 nm-thick DLC film underwent cohesive failure modes (cracks and chipping) before reaching to a gross failure stage. On the other hand, the thicker DLC film ($1.2{\mu}m-thick$) did not exhibit micro cracks before a sudden gross failure of the film together with the evidence of cracking and chipping of the Si substrate.

• 한국해양공학회지
• /
• 제25권3호
• /
• pp.53-65
• /
• 2011

This is the third of several companion papers dealing with the derivation of material constants for ductile failure criteria under hydrostatic stress. It was observed that the ultimate engineering stresses and elongations at fracture from tensile tests for round specimens with various notch radii tended to increase and decrease, respectively, because of the stress triaxiality. The engineering stress curves from tests are compared with numerical simulation results, and it is proved that the curves from the two approaches very closely coincide. Failure strains are obtained from the equivalent plastic strain histories from numerical simulations at the time when the experimental engineering stress drops suddenly. After introducing the new concept of average stress triaxiality and accumulated average strain energy, the material constants of the Johnson-Cook failure criterion for critical energies of 100%, 50%, and 15% are presented. The experimental results obtained for EH-36 steel were in relatively good agreement with the 100% critical energy, whereas the literature states that aluminum fits with a 15% critical energy. Therefore, it is expected that a unified failure criterion for critical energy, which is available for most kinds of ductile materials, can be provided according to the used materials.

• Tuberculosis and Respiratory Diseases
• /
• 제65권4호
• /
• pp.292-300
• /
• 2008

연구배경: 호흡부전은 중환자실 치료가 필요한 흔한 원인 중 하나로, 호흡보조치료의 발전에도 불구하고 높은 사망률을 보이고 있다. 호흡부전환자에 대한 기존의 국내보고는, 특정질환만을 대상으로 하거나, 외과계 환자가 상당수 포함되어 있어, 내과계 호흡부전 환자들의 현황을 알기가 어렵다. 본 연구에서는 한 내과계 중환자실에서 기계환기치료를 시행 받은 성인환자들의 임상적 특성과 치료성적 및 예후와 관련된 인자를 알아보고자 하였다. 방 법: 한 3차 병원 내과계 중환자실에서 48시간 이상 기계환기치료를 받은 479명의 성인환자를 대상으로 의무기록을 후향적으로 분석하였다. 결 과: 대상환자의 평균연령은 $60.3{\pm}15.6$세였고, 34.0%가 여성이었다. 중환자실 입실시점의 APACHE III 점수의 평균값은 $72.3{\pm}25$점이었다. 호흡부전의 원인은 급성호흡부전(71.8%), 만성폐질환의 급성악화(20.9%), 혼수(5.6%), 신경근육계질환(1.7%)이었다. 초기 기계환기방식으로는 67.8%에서 압력조절환기법이 사용되었고, 초기 이탈방식으로는 압력보조환기법이 83.6%에서 사용되었다. 중환자실 사망률은 49.3%, 병원사망률은 55.4%였다. 주된 병원내 사망원인은 패혈성 쇼크(32.5%), 호흡부전(11.7%), 다발성 장기부전(10.2%)이었다. 남성, APACHE III 점수가 70점 이상, 호흡부전의 원인이 간질성폐질환, 혼수, 흡인, 폐렴, 패혈증, 객혈인 경우, 총 기계환기시간 및 병원 재원일이 사망과 독립적으로 관련되었다. 결 론: 호흡부전의 원인질환, 환자의 중증도, 성별에 따라 호흡부전환자의 예후에 차이가 있었다.

• Nuclear Engineering and Technology
• /
• 제55권12호
• /
• pp.4647-4658
• /
• 2023

In this paper, elastic-plastic fracture mechanics analysis is performed to determine the critical crack sizes of the multipurpose canister (MPC) manufactured using austenitic stainless steel under dynamic loading conditions that simulate drop accidents. Firstly, dynamic finite element (FE) analysis is performed using Abaqus v.2018 with the KORAD (Korea Radioactive Waste Agency)-21 model under two drop accident conditions. Through the FE analysis, critical locations and through-thickness stress distributions in the MPC are identified, where the maximum plastic strain occurs during impact loadings. Then, the evaluation using the failure assessment diagram (FAD) is performed by postulating an external surface crack at the critical location to determine the critical crack depth. It is found that, for the drop cases considered in this paper, the principal failure mechanism for the circumferential surface crack is found to be the plastic collapse due to dominant high bending axial stress in the thickness. For axial cracks, the plastic collapse is also the dominant failure mechanism due to high membrane hoop stress, followed by the ductile tearing analysis. When incorporating the strain rate effect on yield strength and fracture toughness, the critical crack depth increases from 10 to 20%.

• 한국해양공학회지
• /
• 제27권2호
• /
• pp.19-26
• /
• 2013

Stress triaxiality is recognized as one of the most important factors for predicting the failure strain of ductile metals. This study dealt with the effect of the average stress triaxiality on the failure strain of a typical low-temperature high-strength marine structural steel, EH36. Tensile tests were carried out on flat specimens with different notches, from relatively smooth to very sharp levels. Numerical simulations of each specimen were performed by using ABAQUS. The failure initiation points in numerical simulations were identified from a comparison of the engineering stress vs. strain curves obtained from experiments with simulated ones. The failure strain curves for various dimensionless critical energy levels were established in the average stress triaxiality domain and compared with the identified failure strain points. It was observed that most of the failure initiation points were approximated with a 100% dimensionless critical energy curve. It was concluded that the failure strains were well expressed as a function of the average stress triaxiality.

• Asian Journal of Innovation and Policy
• /
• 제3권1호
• /
• pp.25-49
• /
• 2014

We wanted to show the different group dynamics of factors for success and failure cases for technology commercialization in small technology-based firms. Existing studies are based on product level, project level, division level or firm level. We deal with technology level, and at small-technology-based firms. This is a longitudinal case study based on 8 cases from Korea. Our study on technology level is a first trial in success and failure studies unlike all existing studies. As a first step, we introduced new categories and factors such as technology attributes and CEO reflecting data, and especially a new concept of launch readiness level. Finally, we adopted correspondence analysis to show the group dynamics. The results are as follows; Technology factors are the most important factors. Second, resource-based factors are more critical in failure cases than success cases and technology factors are more critical to success.

• 수산해양기술연구
• /
• 제28권3호
• /
• pp.295-305
• /
• 1992

The critical strain energy release rate and the failure mechanisms of glass-carbon epoxy resin hybrid composites are investigated in the temperature range of the ambient temperature to 8$0^{\circ}C$. The direction of laminates and the volume fraction are [(+45, -45, 0, 0) sub(2) ] sub(s), 50%, respectively. The major failure mechanisms of these composites are studied using the scanning electron microscope for the fracture surface. Results are summarized as follows: 1) The critical strain energy release rate shows a maximum at ambient temperature and it tends to decrease as temperature goes up. 2) The critical strain energy release rate increases as the content of glass increases, and especially shows dramatic increase for the high glass fiber content specimens. 3) Major failure mechanisms can be classfied such as localized shear yielding, fiber-matrix debonding, matrix micro-cracking, and fiber pull-out and/or delamination.

• Tuberculosis and Respiratory Diseases
• /
• 제42권6호
• /
• pp.951-954
• /
• 1995

Diagnostic procedures in pregnant wowen is limited and is usually delayed, especially so if she is on mechanical ventilation. A 28-year-old pregnant woman with severe dyspnea was referred to our hospital under the impression of miliary tuberculosis. The respiratory failure was so severe that patient had to be managed with mechanical ventilator under clinical impression of overwhelming pneumonia or pulmonary tuberculosis. But the patient's conditions deteriorated. Bronchoscopy and blind transbronchial lung biopsy performed to determine the nature of the etiology, and to our surprise, revealed squamous cell carcinoma of the lung.