• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.1
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• pp.42-48
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• 2001

Over two decades, many researchers have performed studies on strength size effects in composite laminates under tensile and flexural loads. It is well known that there is a tendency for the strength of fibre-reinforced composites to decrease with increasing specimen size. Under compressive load, however, little work has been done on the effect of specimen size to failure strength. This is due to the fact that compressive testing of composite is very difficult. In this paper, the effect of the test specimen size on the compressive strength of composites containing open hole was considered using T300/924C, $>[45/-45/0/90]_{3S}$. For sizing test specimens, the in-plane scaling method is used i.e., the change of two- dimensional specimen area in specimen width and gauge length. The results clearly show that there is a hole size effect in the finite width plates. In addition, the specimens which have the same a/W(hole diameter/specimen width) exhibit a tendency of size effect. In contrast, test results of the unnotched specimens did not show a clear strength size effect.

• Structural Engineering and Mechanics
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• v.17 no.1
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• pp.51-68
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• 2004

Since the linear elastic fracture analysis has been proved to be insufficient in predicting the failure of strain hardening materials, a number of fracture concepts have been studied which remain applicable in the presence of plasticity near a crack tip. This work thereby presents a new finite element model to predict the elastic-plastic crack-tip field and fatigue life of center-cracked panels(CCP) with ductile fracture under large-scale yielding conditions. Also, this study has been carried out to investigate the path-dependence of J-integral within the plastic zone for elastic-perfectly plastic, bilinear elastic-plastic, and nonlinear elastic-plastic materials. Based on the incremental theory of plasticity, the p-version finite element is employed to account for the accurate values of J-integral, the most dominant fracture parameter, and the shape of plastic zone near a crack tip by using the J-integral method. To predict the fatigue life, the conventional Paris law has been modified by substituting the range of J-value denoted by ${\Delta}J$ for ${\Delta}K$. The experimental fatigue test is conducted with five CCP specimens to validate the accuracy of the proposed model. It is noted that the relationship between the crack length a and ${\Delta}K$ in LEFM analysis shows a strong linearity, on the other hand, the nonlinear relationship between a and ${\Delta}J$ is detected in EPFM analysis. Therefore, this trend will be depended especially in the case of large scale yielding. The numerical results by the proposed model are compared with the theoretical solutions in literatures, experimental results, and the numerical solutions by the conventional h-version of the finite element method.

• Fire Science and Engineering
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• v.28 no.5
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• pp.52-57
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• 2014

When structural elements of steel framed structures are exposed to fire situations, the structural stability begins to decrease due to dislocation of substantial. The increase of the beam length causes an additional stress and deflection. These can be serious factors to cause a severe failure of structures. To improve the fire resistance of beams, prevention of the heat from a fire by coating with fire protection material is essential for beams. The FR 490 was developed to enhance fire resistance compared with SM 490 steel. However, the fire resistance of FR 490 H-beams has not been evaluated by analysis method since it was developed. In this paper, materials properties in high temperature and a heat transfer and thermal stress theory were used in the evaluation of the fire resistance of FR490 H-beams. The fire resistance of FR490 steel beams was compared with that of SM490 beams. The comparison verified that the structural stability of FR490 beams at high temperature was superior to that of SM490 beams.

• Journal of the Korea Concrete Institute
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• v.17 no.2 s.86
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• pp.213-220
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• 2005

Carbon fiber reinforced polymer (CFRP) sheets are becoming increasingly popular for strengthening deteriorated concrete bridges due to their excellent strength and stiffness-to-weight ratio, corrosion resistance, and convenience of construction work. The purpose of this study is to compare the performance of CFRP-strengthened reinforced concrete (RC) beams and to develop a new design formula. Simple beams with 3 m span length were tested to investigate the effect of reinforcing steel ratio and CFRP-reinforcing ratio on the flexural behavior of strengthened RC beams. The test results were analyzed with the special emphasis on the failure mode, the maximum load, and the strain distribution in the section. It is shown that the strain of the strengthened beams is not linearly distributed in the section. A new design formula based on the non-linear distribution of the strain has been derived and showed that it has a good agreement with the various domestic and foreign test results.

• Journal of The Korean Dental Society of Anesthesiology
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• v.3 no.1 s.4
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• pp.28-33
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• 2003

Background: The fundamental responsibility of an anesthesiologist is to maintain adequate gas exchange. Failure to maintain a patent airway can result in brain damage or death. Generally, in patients with mandibular prognathism, who have the protruded mandible, the mask ventilation was thought to be not easy. The purpose of this study was to observe the degree of the difficulty of airway management in mandibular prognathism using some anatomic criteria for defining and grading difficulty of airway and difficulty of endotracheal intubation with direct laryngoscope. Methods: The observations and measurements are done to the 54 patients with mandibular prognathism, who were scheduled for corrective esthetic surgery. The case study is done to the 30 patients with normal mandible for control group. In all patients, mouth opening distance (MOD), mouse opening angle (MOA), mandibular length (ML), mandibular depth (MD), thyromental distance (TMD), thyromental area (TMA), Mallampati grades, and Cormack and Lehane grades are measured. T-test and Chi-square test are done (P < 0.05). Results: In the mandibular prognathism cases, the measurements of MD, TMD and TMA are more greater than those of controls (P < 0.05). Mallampati grades with tongue thrust are higher in the female mandibular prognathism cases than those of female controls. Most of the grades of the mandibular prognathism cases with Cormack and Lehane grading system are I or II being easy intubation cases (P < 0.05) Conclusions: In the patients of mandibular prognathism, the intubation with laryngoscope will be easer than that of normal mandible in general. It is for that their laryngeal aperture can be easily visible when the laryngoscope are used.

• Restorative Dentistry and Endodontics
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• v.42 no.3
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• pp.224-231
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• 2017

Objectives: To determine the actual revolutions per minute (rpm) values and compare the cyclic fatigue life of Reciproc (RPC, VDW GmbH), WaveOne (WO, Dentsply Maillefer), and TF Adaptive (TFA, Axis/SybronEndo) nickel-titanium (NiTi) file systems using high-speed camera. Materials and Methods: Twenty RPC R25 (25/0.08), 20 WO Primary (25/0.08), and 20 TFA ML 1 (25/0.08) files were employed in the present study. The cyclic fatigue tests were performed using a dynamic cyclic fatigue testing device, which has an artificial stainless steel canal with a $60^{\circ}$ angle of curvature and a 5-mm radius of curvature. The files were divided into 3 groups (group 1, RPC R25 [RPC]; group 2, WO Primary [WO]; group 3, TF Adaptive ML 1 [TFA]). All the instruments were rotated until fracture during the cyclic fatigue test and slow-motion videos were captured using high-speed camera. The number of cycles to failure (NCF) was calculated. The data were analyzed statistically using one-way analysis of variance (ANOVA, p < 0.05). Results: The slow-motion videos were indicated that rpm values of the RPC, WO, and TFA groups were 180, 210, and 425, respectively. RPC ($3,464.45{\pm}487.58$) and WO ($3,257.63{\pm}556.39$) groups had significantly longer cyclic fatigue life compared with TFA ($1,634.46{\pm}300.03$) group (p < 0.05). There was no significant difference in the mean length of the fractured fragments. Conclusions: Within the limitation of the present study, RPC and WO NiTi files showed significantly longer cyclic fatigue life than TFA NiTi file.

• Tunnel and Underground Space
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• v.30 no.1
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• pp.87-97
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• 2020

Fracture toughness of rock is a constant that can indicate the initiation and propagation of cracks due to blasting, excavation, etc. Scaled model tests have been applied to the behavior of tunnels and the stability of limestone mines. Through the scaled model, damaged zone evaluation due to blasting is also carried out, and the scale factor is not applied to the failure-related factors. In this study, DCT (diametral compression test) and finite element method ATENA2D numerical analysis results were compared to determine whether the scale factor could be applied to the fracture toughness of rock. The theoretical values of the scale factor applied to the fracture toughness of the rock and the DCT test results and the numerical results are 0.21~0.46, 0.40, and 0.99MPa ${\sqrt{m}}$ respectively, so these three values should be considered when determining scale factor. It is necessary to derive a suitable scale factor in consideration of the length, time, and mass to which the scale factor is applied, as well as the values of the scale factor of major design factors such as uniaxial compressive strength and density.

• The Journal of Korean Physical Therapy
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• v.15 no.1
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• pp.155-170
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• 2003

Lumbar segmental instability is considered to represent a significant sub-group within the chronic low back pain population. This condition has a unique clinical presentation that displays its symptoms and movement dysfunction within the neutral zone of the motion segment. The loosening of the motion segment secondary to injury and associated dysfunction of the local muscle system renders it biomechanically vulnerable in the neutral zone. There in evidence of muscle dysfunction related to the control of the movement system. There is a clear link between reduced proprioceptive input, altered slow motor unit recruitment and the development of chronic pain states. Dysfunction in the global and local muscle systems in presented to support the development of a system of classification of muscle function and development of dysfunction related to musculoskeletal pain. The global muscles control range of movement and alignment, and evidence of dysfunction is presented in terms of imbalance in recruitment and length between the global stability muscles and the global mobility muscles. The local stability muscles demonstrate evidence of failure of aeequate segmental control in terms of allowing excessive uncontrolled translation or specific loss of cross-sectional area at the site of pathology Motor recruitment deficits present as altered timing and patterns of recruitment. The evidence of local and global dysfunction allows the development of an integrated model of movement dysfunction. The clinical diagnosis of this chronic low back pain condition is based on the report of pain and the observation of movement dysfunction within the neutral zone and the associated finding of excessive intervertebral motion at the symptomatic level. Four different clinical patterns are described based on the directional nature of the injury and the manifestation of the patient's symptoms and motor dysfunction. A specific stabilizing exercise intervention based on a motor learning model in proposed and evidence for the efficacy of the approach provided.

• Journal of Chest Surgery
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• v.27 no.2
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• pp.140-147
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• 1994

Reconstruction of the pharynx and cervical esophagus presents a tremendous challenges to surgeons. Over the past 2 years[1990, Dec.-1993, Jun], the free jejunal graft has been performed in 17 cases in Korea Cancer Center Hospital.The indications of this procedures were almost malignant neoplasms involving neck and upper aero-digestive tract; Hypopharyngeal cancer[12 cases, including 2 recurrent cases], laryngeal cancer[2 cases], thyroid cancer[2 cases, including 1 recurrent case], cervical esophageal cancer[1 case]. There were fifteen men and two women, and the mean age was 59.6 years. The anastomosis site of jejunal artery were common carotid artery[16 cases] or external carotid artery[1 case] and that of jejunal vein were internal jegular [15 cases] or facial[1 case] and superior thyroid vein[1 case]. The length of jejunal graft was from 9 cm to 17 cm[mean 13 cm] and the mean ischemic time was 68 minutes. There was one hospital mortality which was irrelevant to procedures[variceal bleeding] and one graft failure[1/16]. Other postoperative complications were neck bleeding or hematoma[3 cases], abdominal wound infection or disruption[5 cases], anastomosis site leakage[1 case], pneumonia[2 cases], graft vein thrombosis[1 case], and food aspiration[1 case]. The function of conduit was excellent and ingestion of food was possible in nearly all cases. Postoperative adjuvant radiation therapy was also applicable without problem in 7 cases. During follow-up periods, the anastomosis site stenosis developed in four patients, and the tracheal stoma was narrowed in one case but easily overcome with dilation. In conclusion, we think that the free jejunal graft is one of the excellent reconstruction methods of upper digestive tract, especially after radical resection of malignant neoplasm in neck with a high success rate and low mortality and morbidity rate.

• Journal of Trauma and Injury
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• v.21 no.2
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• pp.85-90
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• 2008

Purpose: Supraventricular arrhythmia is a well-known complication of cardiothoracic surgery, and is common in patients wirth underlying cardiovascular disease. Also, it's treatment and prognosis are well known. However the incidence, the contributing factors, and the prognosis for supraventricular arrhythmias in noncardiothoracic surgical patients are less well known. This study was undertaken to investigate the incidence, the clinical presentation, the prognosis, and the factors comtributing to the prognosis for supraventricular arrhythmia in the surgical intensive care unit. Methods: We performed a retrospective study of 34 patients with newly developed or aggravated supraventricular arrhythmias in the surgical intensive care unit between March 2004 and February 2005. The incidence, the risk factors, and the prognosis of supraventricular arrhythmias were analyzed. Results: During a 12month period, the incidence of supraventricular arrhythmia was 1.79% (34/1896). Most patients had pre-existing cardiovascular disease and sepsis. The mortality rate was 29.4%, and the most common cause of death was multiple organ failure due to septic shock. The mean value of the APACHE II score was 20.9, and the surgical intensive care unit and the hospital lengths of stay were 9.9 days and 25.8 days, respectively. The APACHE II score measured when the arrhythmia developed was a significant factor in predicting mortality, Conclusion: Supraventricular arrhythmias result in increased mortality and increased length of stay in both the surgical intensive care unit and the hospital. The arrhythmia itself did not cause death, but a high APACHE II score incicated a poor prognosis. This may reflect the severity of the illness rather than an independent contributor to mortality.