• 대한기계학회논문집A
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• 제24권12호
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• pp.2945-2951
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• 2000

Because of the inherent flexibility in their design for improved material properties, composites have wide applications in aerospace vehicles and automobiles. The purpose of this study is to investigate the energy absorption characteristics of CFRP( Carbon Fiber Reinforced Plastics); tubes on static and impact tests. Static compression tests have been carried out using the static testing machine(Shin-gang buckling testing machine)and impact compression tests have been carried out using the vertival crushing testing machine. When such tubes were subjected to crushing loads, the response is complex and depends on the interaction between the different mechanisms that control the crushing process. The collapse characteristics and energy absorption were examined. Trigger and interlaminar number affect energy absorption capability of CFRP tubes.

• Steel and Composite Structures
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• 제23권2호
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• pp.161-172
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• 2017

A new composite tube connection method called the pre-tightened teeth connection technique is proposed to improve the composite tube connection efficiency. This paper first introduces the manufacturing process of the proposed technique. It then outlines how the mechanical properties of this technology were tested using four test groups. The factors that influence the load-bearing capacity and damage model of the connection were analyzed, and finally, the transfer load mechanism was investigated. The following conclusions can be obtained from the research results. (1) The new technique improves the compressive connection efficiency by a maximum of 79%, with the efficiency exceeding that of adhesive connections of the same thickness. (2) Changing the depth of teeth results in two types of damage: local compressive damage and shear damage. The bearing capacity can be improved by increasing the depth, length, and number of teeth as well as the pre-tightening force. (3) The capacity of the technique to transfer high loads is a result of both the relatively high interlaminar shear strength of the pultruded composite and the interlaminar shear strength increase provided by the pre-tightening force. The proposed technique shows favorable mechanical properties, and therefore, it can be extensively applied in the engineering field.

• Carbon letters
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• 제5권1호
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• pp.1-5
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• 2004

The effects of fiber surface-treatment and sizing on the dynamic mechanical properties of unidirectional and 2-directional carbon fiber/nylon 6 composites by means of dynamic mechanical analysis have been investigated in the present study. The interlaminar shear strengths of 2-directional carbon/nylon 6 composites sized with various thermosetting and thermoplastic resins are also measured using a short-beam shear test method. The result suggests that different surface-treatment levels onto carbon fibers may influence the storage modulus and tan ${\delta}$ behavior of carbon/nylon 6 composites, reflecting somewhat change of the stiffness and the interfacial adhesion of the composites. Dynamic mechanical analysis and short-beam shear test results indicate that appropriate use of a sizing material upon carbon fiber composite processing may contribute to enhancing the interfacial and/or interlaminar properties of woven carbon fabric/nylon 6 composites, depending on their resin characteristics and processing temperature.

• 한국표면공학회지
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• 제46권5호
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• pp.223-228
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• 2013

In this work, the grow of carbon nanotube (CNT) on carbon fiber was introduced on PAN-based carbon fibers for the enhancement of mechanical interfacial strength of carbon fibers-reinforced composites. The surface properties of carbon fibers were determined by scanning electron microscopy (SEM) and mechanical interfacial properties of the composites were studied by interlaminar shear strength (ILSS). From the results, it was found that the mechanical interfacial properties of CNT-carbon fibers-reinforced composites (CNT-CFRPs) enhanced with decreasing the CNT content. The excessive CNT content can lead the failure due to the interfacial separation between fibers and matrices in this system. In conclusion, the optimum CNT content on carbon fiber surfaces can be a key factor to determine the mechanical interfacial properties of the CNT-CFRPs.

• Composites Research
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• 제32권2호
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• pp.102-107
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• 2019

Several studies related to reinforce composites structures in the through thickness direction have been developed along the years. As follows, in this study a new reinforced process is proposed based on previous experimental results using a novel stitching process in T-joints and one-stitched specimens. It was established the need to perform more analysis under standard test methods to obtain a better understanding. FEM analysis were compared after performed mode I interlaminar fracture toughness test, using different stitching patterns to analyze the through thickness strength with reference laminates without stitching. The stitching patterns were defined in $2{\times}2$ and $3{\times}3$, where the upper and lower head of the non-continuous stitching process (I-Fiber) has proven to influence in a higher through thickness strength of the laminate. In order to design the numerical model, cohesive parameters were required to define the surface to surface bonding elements using the cohesive zone method (CZM) and simulate the crack opening behavior from the double cantilever beam (DCB) test.

• The Korean Journal of Pain
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• 제27권4호
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• pp.353-359
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• 2014

Background: Epidural steroid injections are an accepted procedure for the conservative management of chronic backache caused by lumbar disc pathology. The purpose of this study was to evaluate the epidurographic findings for the midline, transforaminal and parasagittal approaches in lumbar epidural steroid injections, and correlating them with the clinical improvement. Methods: Sixty chronic lower back pain patients with unilateral radiculitis from a herniated/degenerated disc were enrolled. After screening the patients according to the exclusion criteria and randomly allocating them to 3 groups of 20 patients, fluoroscopic contrast enhanced epidural steroids were injected via midline (group 1), transforaminal (group 2) and parasagittal interlaminar (group 3) approaches at the level of the pathology. The fluoroscopic patterns of the three groups were studied and correlated with the clinical improvement measured by the VAS over the next 3 months; any incidences of complications were recorded. Results: The transforaminal group presented better results in terms of VAS reduction than the midline and parasagittal approach groups (P < 0.05). The epidurography showed a better ventral spread for both the transforaminal (P < 0.001) and the paramedian approaches (P < 0.05), as compared to the midline approach. The nerve root filling was greater in the transforaminal group (P < 0.001) than in the other two groups. The ventral spread of the contrast agent was associated with improvement in the VAS score and this difference was statistically significant in group 1 (P < 0.05), and highly significant in groups 2 and 3 (P < 0.001). In all the groups, any complications observed were transient and minor. Conclusions: The midline and paramedian approaches are technically easier and statistically comparable, but clinically less efficacious than the transforaminal approach. The incidence of ventral spread and nerve root delineation show a definite correlation with clinical improvement. However, an longer follow-up period is advisable for a better evaluation of the actual outcom.

• Composites Research
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• 제30권6호
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• pp.365-370
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• 2017

탄소섬유 강화 열가소성 수지 복합재료(Carbon fiber reinforced thermoplastic composites; CFRTPs)의 물성은 다양한 요인들에 영향을 받는다. 그 중에서도 탄소섬유 표면에 Sizing되어 있는 에폭시(Epoxy) 층은 열가소성 수지와 상호 작용(Interaction)이 없어 매우 취약한 계면을 형성하며, 열가소성 수지의 높은 용융 점도(Melting viscosity)는 탄소섬유 다발(Bundle) 사이로 함침(Impregnation)이 어려워 탄소섬유 강화 복합재료 내부에 기공(Void)를 형성한다. 이와 같이 탄소섬유와 열가소성 수지 간의 낮은 계면전단강도(Interfacial shear strength)은 탄소섬유강화 열가소성 복합재료(Carbon fiber reinforced thermoplastic composites; CFRTPs)의 기계적 물성을 저하시키는 가장 중요한 요인 중 하나이다. 따라서, 본 연구에서는 열가소성 수지와의 상호작용이 없는 탄소섬유 표면의 에폭시 층을 열풍을 통해 제거하고, 열가소성 수지의 점도를 낮춰 함침도를 향상시키기 위해서 용액형 열가소성 수지를 제조하여 탄소섬유 표면에 Sizing 처리 함으로써 CFRTPs의 물성을 향상시켰다. CFRTPs의 층간전단강도(Interlaminar shear strength; ILSS) 및 굽힘 강도(Flexural strength)를 통해 이를 검증하였으며, 수지의 함침도는 기공률(Void content)의 계산을 통해 분석하였다.

• 공업화학
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• 제23권3호
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• pp.313-319
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• 2012

본 연구에서는 Polyacrylonitrile (PAN)계 탄소섬유 표면에 구리도금 표면처리가 탄소섬유 강화 복합재료의 기계적 계면 특성에 미치는 영향에 관하여 관찰하였다. 탄소섬유 표면특성은 주사전자현미경, X-선 광전자 분광법, X-선 회절분석기, 접촉각 측정기로 측정하였고, 탄소섬유 강화 복합재료의 기계적 계면 물성은 층간전단강도(interlaminar shear strength, ILSS)와 파괴인성(critical stress intensity factor, $K_{IC}$)측정을 통하여 알아보았다. 실험결과로부터, 기계적 계면물성은 탄소섬유 표면에 COOH group과 도금된 구리함량이 증가됨에 따라 순차적으로 증가되는 것이 확인되었으나, 도금시간을 길게 하여 과량의 구리가 도입되었을 경우 기계적 계면 물성을 도리어 감소시키는 것으로 확인되었다. 결론적으로 구리함량이 탄소섬유 복합재료의 기계적 계면물성을 결정하는 중요 요소라 판단되나, 최적의 함량이상에서는 계면분리에 의한 물성저하의 원인이 될 수 있다.

• 공업화학
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• 제27권5호
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• pp.472-477
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• 2016

본 연구에서는 전류밀도 변화에 따른 탄소섬유의 양극산화 처리가 탄소섬유 표면과 탄소섬유 강화 복합재료의 기계적 계면결합력에 미치는 영향을 고찰하였다. 양극산화 처리된 탄소섬유 표면 특성은 원자간력 현미경(Atomic force microscope, AFM)과 전계방사형 주사전자현미경(Field emission-scanning electron microscope, FE-SEM), 적외선 분광법(Fourier transform infrared spectroscopy, FT-IR) 및 X선 광전자 분광법(X-ray Photoelectron Spectroscopy, XPS)으로 분석하였으며, Short beam 전단시험을 통해 표면처리에 따른 탄소섬유 강화 복합재료의 계면 전단강도를 측정하였다. 실험 결과 전류밀도가 증가함에 따라 탄소섬유 표면의 거칠기와 산소관능기의 함량의 증가와, 탄소섬유 강화 복합재료의 층간전단강도(Interlaminar shear strength, ILSS)의 향상 및 페놀릭 하이드록실 그룹과의 비례관계를 확인하였다. CF-2.0 시편의 층간전단강도는 87.9 MPa로 CF-AS 시편에 비해 약 4% 증가하였는데, 이러한 결과는 양극산화 처리가 산소관능기와 탄소섬유 표면 거칠기의 증가를 유도하여 탄소섬유와 수지의 계면 결합력이 증가된 것으로 판단된다. 그중 층간전단강도와 비례관계인 페놀릭 하이드록실 그룹은 탄소섬유 강화 복합재료의 계면결합력을 향상시키는 중요한 요소라 판단된다.

• 대한약침학회지
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• 제18권1호
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• pp.79-85
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• 2015

Objectives: A vertebral compression fracture (VCF) is characterized by back pain and fracture of a vertebral body on spinal radiography. VCFs of the thoraco lumbar spine are common in the elderly. In general, appropriate analgesics should be prescribed to reduce pain and, thus, promote early mobilization. The ideal treatment approach for VCFs has not been determined. In Korea, acupuncture and herbal medication have been used to treat VCFs for many years. There is empirical evidence that acupuncture might benefit patients with a VCF. However, no randomized, controlled, clinical trials evaluating the efficacy and the safety of acupuncture for treating a VCF have been published. Therefore, we designed a randomized, controlled, pilot, clinical trial to obtain information for the design of a further full scale trial. Methods: A five week protocol for a randomized, controlled, pilot, clinical trial is presented. Fourteen patients will be recruited and randomly allocated to two groups: a control group receiving interlaminar epidural steroid injections once a week for three weeks, and an experimental group receiving interlaminar epidural steroid injections plus acupuncture treatment (three acupuncture sessions per week for three weeks, nine sessions in total). The primary outcomes will be the pain intensity (visual analogue scale and PainVision$^{TM}$ system). The secondary outcome measurements will be the answers on the short form McGill pain questionnaire and the oswestry disability index. Assessments will be made at baseline and at one, three, and five weeks. The last assessment (week five) will take place two weeks after treatment cessation. This study will provide both an indication of feasibility and a clinical foundation for a future large scale trial. The outcomes will provide additional resources for incorporating acupuncture into existing treatments, such as nonsteroidal anti-inflammatory medications, narcotics and vertebral augmentation. This article describes the protocol.