• Journal of Welding and Joining
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• 제6권4호
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• pp.44-53
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• 1988

The mechanical strengths of buried lamellar tears located near the weld toe in the welded tee joints were evaluated in terms of the loss of load carrying capacity as a function of tear area. In static loading, the load carrying capacity was significantly reduced when tear intercepted over 10% of the cross-sectional area of the welded joints. However, the welded joints containing buried tears still failed at stresses over the yield strength of the base metal in the through-thickness direction in spite of the presence of tears up to 20-25% of the area. Fatigue strength of welded joints containing tears markedly reduced with increasing tear areas. Lehigh lamellar tearing test used in this study to produce speicmens was described in detail. The load carrying cpapacity in static loading was influenced by the reduction of supporting area whereas that in fatigue loading was influenced by the stress-concentration effects of lamellar tears and the reduction of supporting area. In bend tests, the pre-existing lamellar tears always grew up toward the weld toe. However, in fatigue loading, cracks grew up and down simultaneously form both the weld toe and the top of lamellar tears because of stress concentration. In fatigue loading, delaminations and decohesion of inclusion/matrix interface generated in multipass welds provided crack propagation paths and enhanced crack propagation because the tips of delaminations and deconhesios acted as stress raisers.

• Tribology and Lubricants
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• 제39권1호
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• pp.8-12
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• 2023

This study presents a molecular simulation of adhesion control between carbon nanotube (CNT) and Ag thin film deposited on silicon substrate. Rough and flat Ag thin film models were prepared to investigate the effect of surface roughness on adhesion force. Heat treatment was applied to the models to modify the adhesion characteristics of the Ag/CNT interface based on thermal wetting. Simulation results showed that the heat treatment altered the Ag thin film morphology by thermal wetting, causing an increase in contact area of Ag/CNT interface and the adhesion force for both the flat and rough models changed. Despite the increase in contact area, the adhesion force of flat Ag/CNT interface decreased after the heat treatment because of plastic deformation of the Ag thin film. The result suggests that internal stress of the CNT induced by the substrate deformation contributes in reduction of adhesion. Contrarily, heat treatment to the rough model increases adhesion force because of the expanded contact area. The contact area is speculated to be more influential to the adhesion force rather than the internal stress of the CNT on the rough Ag thin film, because the CNT on the rough model contains internal stress regardless of the heat treatment. Therefore, as demonstrated by simulation results, the heat treatment can prevent delamination or wear of CNT coating on a rough metallic substrate by thermal wetting phenomena.

• 비파괴검사학회지
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• 제33권1호
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• pp.40-45
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• 2013

위상잠금 적외선열화상기법을 이용하여 치과용 복합레진 수복재의 내부 홀 결함 크기에 따른 검출 가능성을 연구하였다 위상잠금 주파수 조건을 다르게 하며 진폭과 위상영상을 분석하였다. 진폭 이미지 분석을 통해 직경 2 mm 이상의 결함 검출이 가능함을 알았으며 0.05 Hz 부근에서 결함부의 구별이 뚜렷하고 선명한 이미지를 획득할 수 있었다. 진폭 대비차는 결함부의 직경 크기에 비례하였다. 위상 이미지 분석 결과 0.3-0.5 Hz 부근에서 최적의 대조 영상을 보였으며 0.006 Hz 에서는 반대 명암의 뚜렷한 이미지를 얻을 수 있었다. 진폭 분석보다 위상 분석에서 결함부 크기가 작은 시편의 검출 가능성이 더 높았다.

• Composites Research
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• 제18권3호
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• pp.7-13
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• 2005

본 논문에서는 하이브리드 복합재 철도차량차체에 적용되는 복합적층판에 대한 저속충격시험을 수행하였다. 이를 위해 2.4J, 2.7J 및 4.2J의 세 가지 충격에너지 조건에서 세 가지의 다른 적층구조를 갖는 적층판에 대한 저속충격시험을 수행하였다. 시험에 적용된 직조된 카본/에폭시 적층판의 크기는 $100mm\times100mm$ 이다. 충격시험 후 충격하중이력, 흡수된 에너지 및 손상면적 등이 각 충격에너지와 적층순서에 따라 고찰되었다. 손상면적은 육안검사와 C-scan을 이용하여 동시에 검사하였다. 시험결과 흡수된 에너지는 $[fill]_8$, 적층판이 가장 높았고 $[fill_2,/warp_2)_s$ 적층판이 가장 낮았다. 또한 손상면적은 $[fill]_8$, 적층판에서 가장 넓은데 이것은 상대적으로 흡수에너지가 높기 때문이다.

• Advances in aircraft and spacecraft science
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• 제4권6호
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• pp.679-699
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• 2017

The aim of this study is to perform a finite element analysis of the Von Mises stresses distribution in the adhesive layer and of the J-Integral for a damaged plate repaired by a composite patch. Firstly, we study the effect of the fiber orientation, especially the position of the layers that have orientation angle different of $0^{\circ}$ from the first layer which is in all cases of our study oriented at ($0^{\circ}$) on the J-Integral. Secondly, we evaluate the effects of the mechanical properties of the patch and the use of a hybrid patch on the reduction of stresses distribution and J-Integral. The results show clearly that the stacking sequence for the composite patch must be selected to absorb optimally the stresses from the damaged area and to position the various layers of the composite under the first layer whose fibers orientation will remain in all cases equal to $0^{\circ}$. The use of a hybrid composite reduces significantly the J-Integral and the stresses in both damaged plate and the adhesive layer.

• 비파괴검사학회지
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• 제17권2호
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• pp.81-88
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• 1997

탄소섬유강화복합재료(CFRP) 적층판에 비교적 낮은 에너지의 충격을 주어, 충격에 의해서 손상된 적층판을 사용하여 인장강도, 파괴 인성 및 AE 신호 특성에 미치는 충격 손상의 영향에 대하여 검토하였다. 충격손상재의 인장강도, 파괴 인성 및 AE-event count는 충격 속도와 박리 면적의 증가에 따라서 감소함을 알 수 있었다. 그리고 충격시험시에 발생한 박리 면적은 충격 속도와 비례하였다. 또한 적층 방법에 따른 손상재의 강도비와 파괴 인성비가 달라짐이 확인되어 복합재료의 내충격 설계시 손상량과 손상재의 파괴 인성 및 강도에 대한 정량적 평가를 AE 신호로부터 해석할 수 있음이 확인되었다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
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• pp.89-92
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• 2001

Drop weight impact tests were performed to investigate the impact behavior of carbon fiber/epoxy composite laminates reinforced by short fibers and other interleaving materials. Characterization techniques, such as cross-sectional fractography and scanning acoustic microscopy, were employed quantitatively to assess the internal damage of some composite laminates. Scanning electron microscopy was used to observe impact damage and fracture modes on specimen fracture surfaces. The results show that composite laminates experience various types of fracture; delamination, intra-ply cracking, matrix cracking and fiber breakage depending on the interlayer materials. Among the composite laminates tested in this study, the composites reinforced by Zylon fibers showed very good impact damage resistance with medium level of damage, while the composites interleaved by poly(ethylene-co-acrylic acid) (PEEA) film is expected to deteriorate the bulk strength due to the reduction of fiber volume fraction, even though the damaged area is significantly reduced.

• Advanced Composite Materials
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• 제18권1호
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• pp.43-59
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• 2009

The current study assessed the effect of a bolt hole on tensile fatigue properties of CFRP laminates. Two specimens, i.e. $[(0/90)_3]S$, $[(0/45/90/-45)_2]_S$, were analyzed using a finite element method and were experimentally tested for cases, both with and without a hole, whose diameter corresponded to 0.12 times the specimen width. Delamination positions predicted by a 3-dimensional static finite element analysis were matched well to those observed by an ultrasonic imaging system in the middle of fatigue test. A hole whose diameter corresponds to 0.12 times the specimen width caused the fatigue strength to decrease by 9% and 11% under 5 Hz loading frequency, and by 22% and 25% under 10 Hz loading frequency for $[(0/90)_3]_S$ and $[(0/45/90/-45)_2]_S$, respectively. Because the decrease in sectional area due to the hole was normalized in calculation of the tensile strength, a stress concentration around the hole is believed to induce the strength degradation of fatigue specimens. From the finite element analyses, the stress concentration factor around a hole was expected as 8.8 and 9.5 for $[(0/90)_3]_S$ and $[(0/45/90/-45)_2]_S$, respectively.

• 비파괴검사학회지
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• 제27권3호
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• pp.268-279
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• 2007

The reliability of cold-bonding repair technique of carbon-fiber reinforced plastics (CFRP) laminates, often used as a temporary repair for the airplane maintenance, has been evaluated during cyclic loading and localized heating by nondestructive methods. Major concern was given to the evolution of damage after repair in the form of delaminations due to localized heating and cyclic loading combined. An area of interest both on the specimen repaired by cold-bonding and the specimen without repair where delaminations were induced by localized heating and cyclic loading was monitored by acoustic emission (AE) testing and further examined by pitch-catch low-frequency bond testing, and pulse-echo high-frequency ultrasonic testing. The results showed that the reliability of cold-bonding repair would be significantly reduced by the localized heating and cyclic loading combined rather than by the cyclic loading only. AE monitoring appeared to be an effective and reliable tool to monitor the integrity of temporarily repaired CFRP laminates in terms of the structural health monitoring (SHM) philosophy.

• 보존과학회지
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• 제35권5호
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• pp.494-507
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• 2019

A diagnostic investigation of the conservation state of damaged murals of the Payathonzu temple mainly indicated delamination, exfoliation, and contamination of the coloring layer; cracks and damage to the wall; and separation from gaps. In particular, vulnerabilities resulting from cracks in the wall and damage from gaps demand swift reinforcement measures. Ultrasonic testing uncovered damage caused by gaps between the base layer and plastered wall in several areas of the mural, vulnerable parts in the wall around the cracks, and considerable degradation of the physical properties where cracks and gaps were severe. Moisture measurements identified vast disparities in moisture depending on location even within a single area of the mural, and it was clear that these disparities were the result of environmental conditions such as humidity. Damage to the murals in monument 477 was the most severe, and a diagnostic of the physical properties uncovered severe physical damage to the upper part of the mural as well as to the corridor ceiling, thus presenting the need for conservation treatment utilizing scientific diagnosis as well as objective data.