• 한국소음진동공학회논문집
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• 제22권2호
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• pp.179-186
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• 2012

The potential hazards resulting from a low-velocity impact(bird-strike, tool drop, runway debris, etc.) on aircraft structures, such as engine nacelle or leading edges has been a long-term concern to the aircraft industry. Certification authorities require that exposed aircraft components must be tested to prove their capability to withstand low-velocity impact without suffering critical damage. In most of the past research studies unloaded specimens have been used for impact tests, however, in reality it is much more likely that a composite structure is exposed to a certain stress state when it is being impacted, which can have a significant effect on the impact performance. And the radiated impact sound induced by impact is analyzed for the damage detection evaluation. In this study, an investigation was undertaken to evaluate the effect in-plane loading on the impact force and sound of composite laminates numerically.

• 대한조선학회논문집
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• 제57권4호
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• pp.182-190
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• 2020

This study reports a series of drop impact tests performed to generate denting damages on stiffened plates and their residual ultimate strength tests under axial compression. The models were fabricated of general structural steel, and each model has six longitudinal stiffeners and two transverse frames. Among six fabricated models, four were damaged, and two were left intact for reference. To investigate the effects of collision velocity and impact location on the extent of damage, the drop height and the impact location were changed in each impact test. After performing the collision tests, the ultimate axial compression tests were conducted to investigate the residual strengths of the damaged stiffened plates. Finite element analyses were also carried out using a commercial package Abaqus/Explicit. The material properties obtained from a quasi-static tensile tests were used, and the strain-rate sensitivity was considered. After importing the collision simulation results, the ultimate strength calculations were carried out and their results were compared with the test data for the validation of the finite element analysis method.

• Advanced Composite Materials
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• 제16권1호
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• pp.45-61
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• 2007

This paper describes a damage accumulation mechanism in cross-ply CFRP laminates $[0_2/90_2]_{2S}$ subjected to out-of-plane loading. Drop-weight impact and static indentation tests were carried out, and induced damage was observed by ultrasonic C-scan and an optical microscope. Both tests gave essentially the same results for damage modes, sizes, and load-deformation history. First, a crack occurred in the bottom $0^{\circ}$ layer accompanying some delamination along the crack caused by bending stress. Then, transverse cracks occurred in the middle $90^{\circ}$ layer with decreasing contact force between the specimen and the indenter. Measured local strains near the impact point showed that the stress state changed from a bending dominant state to an in-plane tensile dominant state. A cohesive interface element was used to simulate the propagation of multiple delaminations and transverse cracks under static indentation. Two types of analytical models are considered, one with multiple delaminations and the other with both multiple delaminations and transverse cracks. The damage obtained for the model with only multiple delaminations was quite different from that obtained from the experiment. However, the results obtained from the model with both delaminations and transverse cracks well explain the characteristics of the damage obtained in the experiment. The existence of the transverse cracks is essential to form the characteristic impact damage.

• Steel and Composite Structures
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• 제27권3호
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• pp.273-283
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• 2018

Nonlinear low velocity impact response of sandwich beam with laminated composite face sheets and soft core is studied based on Extended High Order Sandwich Panel Theory (EHSAPT). The face sheets follow the Third order shear deformation beam theory (TSDT) that has hitherto not reported in conventional EHSAPT. Besides, the two dimensional elasticity is used for the core. The nonlinear Von Karman type relations for strains of face sheets and the core are adopted. Contact force between the impactor and the beam is obtained using the modified Hertz law. The field equations are derived via the Ritz based applied to the total energy of the system. The solution is obtained in the time domain by implementing the well-known Runge-Kutta method. The effects of boundary conditions, core-to-face sheet thickness ratio, initial velocity of the impactor, the impactor mass and position of the impactor are studied in detail. It is found that each of these parameters have significant effect on the impact characteristics which should be considered. Finally, some low velocity impact tests have been carried out by Drop Hammer Testing Machine. The contact force histories predicted by EHSAPT are in good agreement with that obtained by experimental results.

• Composites Research
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• 제31권5호
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• pp.215-220
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• 2018

본 연구에서는 적층 패턴이 다른 5가지 섬유금속적층판(Fiber Metal Laminates, FMLs)에 대한 유한요소해석을 수행하여 선행 연구로 수행한 낙추충격시험과의 유사성을 검증하였고, 효과적인 저속 충격 해석 모델을 개발하였다. 또한 동일한 두께를 가지는 연강(mild steel)과 에너지흡수율을 비교하여 Carbon-Steel 섬유금속적층판의 내충격성을 확인하였다. Carbon-Steel 섬유금속적층판은 동일한 두께를 가지는 연강에 비하여 우수한 충격흡수율을 보였으며, 모든 적층 패턴에서 96% 이상의 높은 에너지흡수율 갖는 것을 확인하였다. 본 연구에서 제시한 저속 충격 해석 모델은 복합형상 및 자동차 구조체 연구에 효과적으로 적용할 수 있을 것으로 판단된다.

• 치위생과학회지
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• 제10권2호
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• pp.109-116
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• 2010

본 연구는 2006년과 2007년 경상북도 성주군과 영양군 내에 거주하는 만 65세 이상 노인들을 대상으로 노인들의 인구사회학적 특성에 구강건강과 관련된 삶의 질 증진에 관여하는 요인들을 분석하고자 하였다. 이를 위하여 경상북도 지역 내 2개군 지역을 선정하여 지역 내 만 65세 이상 노인들을 대상으로 구강건강영향지수(Oral Health Impact Profile: OHIP-14)를 활용하여 구강건강과 관련된 삶의 질을 설문조사하였다. 최종 수합된 546명의 자료를 분석한 결과 다음과 같은 결론을 얻었다. 1. 조사대상자의 구강건강과 관련된 삶의 질의 각 세부요인 중 사회적 능력저하는 평균 4.61점, 정신적 능력저하는 평균 4.53점, 신체적 능력저하는 평균 3.99점, 정신적 불편감은 평균 3.98점, 사회적 불리는 평균 3.82점, 신체적 동통은 평균 3.77점, 그리고 기능적 제한은 평균 3.44점으로 조사되었다. 2. 구강건강과 관련된 삶의 질 중 기능적 제한은 조사된 특성 중 성별, 교육수준 및 직업유무에 따라 통계적으로 유의한 차이가 있었고 신체적 동통은 조사된 특성 중 성별, 교육수준, 동거가족에 따라 통계적으로 유의하였으며, 정신적 불편감은 조사된 특성 중 성별, 교육수준, 직업유무 따라 통계적으로 유의한 차이가 있었고, 신체적 능력저하는 조사된 특성 중 성별, 교육수준, 월수입에 따른 차이가 통계적으로 유의하였다. 또한 정신적 능력저하는 조사된 특성 중 성별, 교육수준에 따라 통계적으로 유의한 차이가 있었고, 사회적 능력저하는 조사된 특성 중 교육수준, 직업유무, 월수입에 따른 차이가 통계적으로 유의하였으며, 사회적 불리는 조사된 특성 중 연령, 직업유무, 월수입에 따라 통계적으로 유의한 차이가 있었다. 3. 조사대상자의 구강건강과 관련된 삶의 질 총합은 조사된 특성 중 성별, 교육수준, 직업유무에 따른 차이가 통계적으로 유의하였다. 따라서 본 연구에서는 우리나라 일부 농촌노인들의 구강건강 영향지수를 측정하고 각 세부항목에 영향을 주는 요인들을 조사하였다. 구강건강 영향지수에 대한 세부요인 별 관련성을 볼 때, 구강건강과 삶의 질은 밀접한 관련이 있는 것으로 나타났다. 이에 노인들의 구강건강관련 삶의 질 향상을 위해서는 다양한 측면에서 노인들의 복지정책과 효과적인 노인건강 관리가 이루어져야한다고 본다. 또한 구강건강 영향지수와 관련된 다양한 연구가 지속적으로 필요하리라 사료된다.

• 한국콘텐츠학회논문지
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• 제13권2호
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• pp.1-7
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• 2013

본 연구는 골프 드라이버의 임팩트 위치에 따른 소리의 특성을 평가하고자 하였다. 일정한 임팩트 소리를 발생시키기 위하여 골프공 자유낙하 장치를 고안하여 사용하였다. 임팩트 소리의 시간에 따른 진폭과 주파수영역에서 파워의 피크값 분포가 드라이버 헤드면의 임팩트 위치에 따라 다르게 나타났으나 재현성이 부족하여 비교할 수 없었다. 드라이버의 임팩트 부위에 따른 소리를 구분하기 위하여 대안적인 방법으로 파워스펙트럼 누적합(cumsum)을 사용하였다. 파워스펙트럼 누적합의 20%, 40%, 60%, 80%에 해당하는 주파수를 비교한 결과 드라이버 면의 중앙(center)에서 발생하는 임팩트 소리의 40% 누적합주파수가 바깥쪽(toe)과 안쪽(heel)에서 발생하는 임팩트 소리에 비하여 유의하게 낮은 것을 관찰하였다. 이러한 결과는 드라이버 헤드면의 중앙이 바깥쪽 또는 안쪽에 비하여 임팩트 소리의 저주파수 성분 파워가 상대적으로 높다는 것을 시사하였다.

• 한국포장학회지
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• 제12권1호
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• pp.35-40
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• 2006

Cushioning systems, which are cushion material and its designed configuration, are important to protect fragile items since they act as buffers between the impact force and the fragile product. As cushioning materials, several plastic foams are commonly used in industry. However, the utilization of the plastic material has been causing a solid waste problem and pollution. Thus, as an alternative cushion material to the plastic foams, a corrugated cushion, which is considered environmentally friendly and cheap material, was put into drop tests and its impact shock attenuation was investigated. Flat and free drop data were recorded and compared to the dynamic shock of EPS cushion. In addition, the mathematical model of the shock attenuation of the corrugated cushion was developed. The result showed that the corrugated cushion gave an excellent protection for items that were subjected to the limited number of drops. There was no significant difference of the shock absorbing ability between the EPS and corrugated cushions. Energy density model of cushioning material successfully explained the mechanical behavior and fatigue of the corrugated cushions.

• 한국운동역학회지
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• 제22권2호
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• pp.237-242
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• 2012

The purpose of this study was (a) to develop carbon nanotube-based shock absorbers for reducing potentially harmful impact forces and excessive foot pronation, and (b) to briefly determine how the effects of carbon nanotube-based shock absorbers on biomechanical variance during drop landing. A university student(age: 24.0 yrs, height: 176.2 cm, weight: 679.5 N) who has no musculoskeletal disorder was recruited as the subject. Hardness, specific gravity, tensile strength, elongation, 100% modulus, tear strength, split tear strength, compression set, resilience, vertical GRF, and loading rate were determined for each material. For each dependent variable, a descriptive statistics was used for different conditions. The property test results showed that tensile strength, tear strength, split tear strength, compression set, and resilience in carbon nanotube-based shock absorbers were greater than general Ethylene Vinyl Acetate(EVA). These indicated that resistance against variable strength in developed carbon nanotube-based shock absorbers were greater than general EVA. In vertical GRF of CNTC was less than those of EVA during drop landing and loading rate of CNTC was greater than EVA. It seems that the use of CNT can be a effective way of reducing and controlling shock from impact.

• 한국포장학회지
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• 제23권2호
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• pp.103-108
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• 2017

The amount of delivered parcels have been increasing according to the change and expansion of consumption pattern through e-commerce, and they are required to minimize breakout or failure under the delivery. In this study, we measured and analyzed the distribution environment data (vibration and impact) occurred in the packaging, which were prepared with 5 types by the weight and dimension, distributed from Seoul to Busan in Korea by 2 parcel delivery service companies through e-commerce order. Date showed the parcels had 3-5 times of drop impact and 0.3-0.7 m of drop height on average, and 0.8 Grms of vibration acceleration from equivalent equation to the vertical direction. The significant gap in service quality was not found between 2 parcel delivery service companies. This study is expected to be useful for designing the suitable packaging in order to enhance safe transportation of the delivered packaging, and furthermore useful for developing Korean testing method for Field-to-Lab simulation.