• Steel and Composite Structures
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• 제42권5호
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• pp.685-697
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• 2022

In this paper, a vibration-based method using the change ratios of modal data and the experience-based learning algorithm is presented for quantifying the position, size, and interface layer of delamination in laminated composites. Three types of objective functions are examined and compared, including the ones using frequency changes only, mode shape changes only, and their combination. A fine three-dimensional FE model with constraint equations is utilized to extract modal data. A series of numerical experiments is carried out on an eight-layer quasi-isotropic symmetric (0/-45/45/90)s composited beam for investigating the influence of the objective function, the number of modal data, the noise level, and the optimization algorithms. Numerical results confirm that the frequency-and-mode-shape-changes-based technique yields excellent results in all the three delamination variables of the composites and the addition of mode shape information greatly improves the accuracy of interface layer prediction. Moreover, the EBL outperforms the other three state-of-the-art optimization algorithms for vibration-based delamination detection of composites. A laboratory test on six CFRP beams validates the frequency-and-mode-shape-changes-based technique and confirms again its superiority for delamination detection of composites.

• 항공우주시스템공학회지
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• 제17권6호
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• pp.82-93
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• 2023

본 논문에서는 층간분리 현상을 고려한 복합재 미사일 핀의 비선형 천음속 플러터 해석을 수행하였다. 층간분리 효과를 고려한 유한요소 진동해석 기법은 시험 결과와 비교 및 검증하였다. 비선형 천음속 플러터 해석은 자체 개발한 천음속 미소교란 방정식 기반의 시간영역 플러터 해석 프로그램을 개선하여 복합재 날개의 층간분리 효과까지 고려할 수 있도록 확장하여 활용하였다. 복합재 미사일 핀 모델에 대해 층간분리 영역에 따른 아음속, 천음속 및 초음속 플러터 해석을 수행하고 층간분리 영향에 따른 공력탄성학적 특성을 고찰하였다.

• 복합신소재구조학회 논문집
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• 제3권1호
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• pp.1-7
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• 2012

본 연구에서는 고체요소를 사용하여 내재된 층간분리의 크기 및 위치 변화에 대한 복합소재 적층구조의 자유진동 특성을 분석한다. 본 연구에서 제시하는 3차원 유한요소 모델은 기존의 접근 방법에 비하여 정확성 뿐만 아니라 전체 진동 모드를 보여준다는 점에서 장점을 갖는다. ABAQUS가 적용된 유한요소 모델은 다양한 내재된 층간분리를 포함하는 적층구조의 자유진동을 분석하기 위하여 사용되었다. 도출된 수치해석 결과는 기존의 연구결과와 비교하여 잘 일치함을 보였다. 특히, 본 연구에서 제시한 결과는 층간분리의 크기, 길이-두께의 비율, 그리고 층간분리의 위치변화에 대하여 국부 진동 모드에 미치는 중요한 영향들에 대하여 초점을 둔다.

• 한국구조물진단유지관리공학회 논문집
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• 제7권2호
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• pp.177-184
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• 2003

비파괴 검사에 널리 쓰이는 Ground Penetrating Radar (GPR)의 콘크리트내 공동 탐사 성능을 알아보기 위해, 일련의 실험을 실시하였다. 공동 탐사는 사용하는 안테나의 주파수에 가장 큰 영향을 받으며, 실험에서는 900 MHz, 1 GHz, 1.5 GHz 3개의 안테나를 사용하였다. 콘크리트 기본시편의 크기는 1,000 mm (길이) ${\times}$ 600 mm (폭) ${\times}$ 140 mm (두께)이고, 공동은 200 mm (길이) ${\times}$ 600 mm (폭) ${\times}$ 50 mm (두께)의 크기를 갖고 있다. 공동의 매립 깊이를 20 mm, 30 mm, 60 mm, 70 mm 4개고 달리한 결과, 모든 경우에서 공동을 성공적으로 탐사하였으며, 각 안테나 주파수에서의 특성을 파악하였다. 또한 상업용 레이더 시스템의 영상 처리 결과를 향상시킨 결과를 논문에서 다루었다.

• 대한기계학회논문집A
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• 제28권2호
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• pp.174-180
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• 2004

If Fiber Reinforced Metal Laminates(FRMLs) were delaminated, the decrease of stiffness and fiber bridging effect would result in the sudden aggravation of fatigue characteristics. It was reported that the delamination of FRMLs resulted from the crack of metal layers and that it depended on the crack growth. While cracks were made in FRMLs containing a saw-cuts under fatigue loading, cracks could be produced or not in FRMLs with circular holes under the same condition. When the FRMLs with the circular holes produce not the crack but the delamination, it is not possible to analyze it by the conventional fracture parameters expressed as the function of the crack. And so, this research suggests a new analytical model of the delamination to make the comparison of the delamination behavior possible whenever the cracks occur or not. Therefore, a new analytical model called Pseudo Crack Model(PCM) was suggested to compare the delaminations whether cracks were made or not. The relationship between the crack energy consumption rate( $E_{crack}$) and the delamination energy consumption rate( $E_{del}$) was discussed and it was also known that the effect of $E_{del}$ was larger than that of $E_{crack}$.

• 한국기계가공학회지
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• 제21권4호
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• pp.1-13
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• 2022

Household refrigerator cabinets must undergo cyclic testing at -20 ℃ and 65 ℃ for quality control (QC) after their production is complete. These cabinets were assembled from different materials, including acrylonitrile butadiene styrene (ABS), polyurethane (PU) foam, and steel plates. However, different thermal expansion values could be observed owing to differences in the mechanical properties of the materials. In this study, a technique to predict delamination on a refrigerator wall caused by thermal deformation was developed. The mechanical properties of ABS and PU foams were tested, theload factors causing delamination were analyzed, delamination was observed using a high-speed camera, and comparison and verification in terms of stress and strain were performed using a finite element model (FEM). The results indicated that the delamination phenomenon of a refrigerator wall can be defined in two cases. A method for predicting and evaluating delamination was established and applied in an actual refrigerator. To determine the effect of temperature changes on the refrigerator, strain measurements were performed at the weak point and the stress was calculated. The results showed that the proposed FEM prediction technique can be used as a basis for virtual testing to replace future QC testing, thus saving time and cost.

• Advances in materials Research
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• 제11권4호
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• pp.375-390
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• 2022

Carbon Fiber Reinforced Polymer (CFRP) composite provides outstanding mechanical capabilities and is therefore popular in the automotive and aerospace industries. Drilling is a common final production technique for composite laminates however, drilling high-strength composite laminates is extremely complex and challenging. The delamination of composites during the drilling at the entry and exit of the hole has a severe impact on the results of the holes surface and the material properties. The major goal of this research is to investigate contemporary industry solutions for drilling CFRP composites: enhanced edge geometries of cutting tools. This study examined the occurrence of delamination at the entry and exit of the hole during the drilling. For each of the 80°, 90°, and 118°point angle uncoated Brad point, Dagger, and Twist solid carbide drills, Taguchi design of experiments were undertaken. Cutting parameters included three variable cutting speeds (100-125-150 m/min) and feed rates (0.1-0.2-0.3 mm/rev). Brad point drills induced less delamination than dagger and twist drills, according to the research, and the best cutting parameters were found to be a combination of maximum cutting speed, minimum feed rate, and low drill point angle (V:150 m/min, f: 0.1 mm/rev, θ: 80°). The feed rate was determined to be the most efficient factor in preventing hole entry and exit delamination using analysis of variance (ANOVA). Regression analysis was used to create first-degree mathematical models for each cutting tool's entrance and exit delamination components. The results of optimization, mathematical modelling, and experimental tests are thought to be reasonably coherent based on the information obtained.

• 대한기계학회논문집A
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• 제22권3호
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• pp.611-623
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• 1998

The delamination fracture of multidirectional carbon-fiber/epoxy laminates under the Mode I condition has been studied using the modified beam analysis for a fracture mechanics approach. It was found that the variation of fracture energy $G_IC$ with increasing length of the propagating crack exhibited a minimum for the pure interlaminar fracture and a maximum for the intraply fracture,i.e. a rising "R-curve", which was strongly affected by the degree of fiber bridging and crack-tip splitting arising in the global delamination. The maximum $G_IC$ value was significantly dependent on such types of delamination as no crack jumping, crack jumping into the adjacent ply and edge-delamination. It was shown also that the value of "effective flexural modulus" estimated from the modified beam analysis increased much with the development of fiber bridging behind the crack tip.ehind the crack tip.

• 대한기계학회논문집
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• 제18권8호
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• pp.2139-2157
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• 1994

In order to understand the delamination between leadframe and epoxy molding compound in an electronic packaging of surface mounting type, the stress intensity factor, T-stress and J-integral in fracture mechanics are obtained. The effects of geometry, material properties and molding process temperature on the delamination are investigated taking into account the temperature dependence of the material properties, which simulates as more realistic condition. As the crack length increases the J-integral increases, which suggest that the crack propagates if it starts growing from the small size. The effects of the material properties and molding process temperature on stress intensity factor, T-stress is and J-integral are less significant than the chip size for the practical cases considered here. The T-stress is negative in all eases, which is in agreement with observation that interfacial crack is not kinked until the crack approaches the edge of the leadframe.

• 대한기계학회논문집A
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• 제24권6호
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• pp.1491-1498
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• 2000

In recent years, CFRP composite materials have been increasingly used in various fields of engineering because of a high specific strength and stiffness properties. Drilling is one of the most impo rtant cutting processes that are generally carried out on CFRP materials owing to the need for the structural integration. However, delamination are often occurred as one of the drilling damages. Therefore, there are needs studying for the relationships between CFRP drilling and delamination in order to avoid low strength of the structures and inaccuracies of the integration. In this study, AE signals and thrust forces were used for the evaluations of the delamination from a drilling process in [0/900]s CFRP materials. And the drilling damage processes were observed and measured by a real time monitoring technique with a video camera. From the results, we found that the relationships between the delamination from drilling and AE characteristics and drill thrust forces for [0/900]s CFRP composites. Also, we proposed the monitoring method for a visual analysis of drilling damages.