저속충격에 의한 복합재료 적층판의 손상

안석환(SEOK-HWAN AHN),김진욱(JIN-WOOK KIM),도재윤(JAE-YOON DO),김현수(HYUN-SOO KIM),남기우(KI-WOO NAM) 한국해양공학회 2005 韓國海洋工學會誌 Vol.19 No.1

The study investigated the nondestructive characteristics of damage, caused by low-velocity impact, on symmetric cross-ply laminates, composed of [0o/90o]16s, 24s, 32s, 48s. The thickness of the laminates was 2, 3, 4 and 6 ㎜, respectively. The impact machine used, Model 8250 Dynatup Instron, was a drop-weight type that employed gravity. The impact velocities used in this experiment were 0.75, 0.90, 1.05, 1.20 and 1.35 m/sec, respectively. Both the load and the deformation increased when the impact velocity was increased. Further, when the load increased with the laminate thickness in the same impact velocity, the deformation still decreased. The extensional velocity was quick, as the laminate thickness increased in the same impact velocity and the impact velocity increased in the same laminate thickness. In the ultrasonic scans, the damaged area represented a dimmed zone. This is due to the fact that the wave, after the partial reflection by the deflects, does not have enough energy to touch the opposite side or to come back from it. The damaged laminate areas differed, according to the laminate thickness and the impact velocity. The extensional velocities are lower in the 0o direction and higher in the 900 direction, when the size of the defect increases. However, it was difficult to draw any conclusion for the extensional velocities in the 45o direction.

Experimental Investigation of Impact Behaviour of RC Slab with Different Reinforcement Ratios

Tolga Yılmaz,Nevzat Kıraç,Özgür ANIL,R. Tuğrul Erdem,Gökhan Kaçaran 대한토목학회 2020 KSCE Journal of Civil Engineering Vol.24 No.1

Reinforced concrete (RC) slabs may be exposed to the low-velocity impact load during their service periods. In low-velocity impact scenarios, the effect of strain rates has been remarkably higher than quasi-static loading because the loading duration is very short. Thus, structural responses and failure modes will be different. The present study aims to investigate dynamic response and failure modes of simply supported two-way RC slabs exposed to low-velocity impact load. In the experimental part of this study, nine RC slabs with the dimension of 1,000 × 1,000 × 80 mm were tested. The reinforcement ratio of RC slabs and the input impact energy applied to RC slabs were experimental variables investigated. A drop-weight test setup was utilized to apply impact load to RC slabs. By varying drop-height as 1,000, 1,250 and 1,500 mm, three different impact energies have been applied to RC slabs via a hammer of which weight is 84 kg. The time histories of the accelerations, displacements and impact loads were recorded. The dynamic responses obtained by tests and the failure modes observed has been interpreted in detail. Besides, a finite element model where explicit dynamic analysis is performed has been established for verification of the experimental results. There was observed good accordance between numerical and experimental results. Consequently, it is considered that the present finite element treatment can be used for the evaluation of the dynamic responses and failure modes of RC slabs exposed to low-velocity impact load.

The effects of stacking sequence on the penetration-resistant behaviors of T800 carbon fiber composite plates under low-velocity impact loading

Furqan Ahmad,Jung-Wuk Hong,Heung Soap Choi,Soo-Jin Park,Myung Kyun Park 한국탄소학회 2015 Carbon Letters Vol.16 No.2

Impact damages induced by a low-velocity impact load on carbon fiber reinforced polymer (CFRP) composite plates fabricated with various stacking sequences were studied experimentally. The impact responses of the CFRP composite plates were significantly affected by the laminate stacking sequences. Three types of specimens, specifically quasi-isotropic, unidirectional, and cross-ply, were tested by a constant impact carrying the same impact energy level. An impact load of 3.44 kg, corresponding to 23.62 J, was applied to the center of each plate supported at the boundaries. The unidirectional composite plate showed the worst impact resistance and broke completely into two parts; this was followed by the quasi-isotropic lay-up plate that was perforated by the impact. The cross-ply composite plate exhibited the best resistance to the low-velocity impact load; in this case, the impactor bounced back. Impact parameters such as the peak impact force and absorbed energy were evaluated and compared for the impact resistant characterization of the composites made by different stacking sequences.

Low-Velocity Impact Characterization of Composite Plate by Direct Numerical Simulation(DNS)

Kim, Seung-Jo,Ji, Kuk-Hyun 서울대학교 항공우주신기술연구소 2000 항공우주신기술연구소 연구보고 Vol.1 No.2

In this paper, the low-velocity impact behavior is analyzed by the Direct Numerical Simulation(DNS) approach. In DNS approach, we discretize the composite plates through separate modelling of fiber and matrix for the three dimensional analysis since we believe that the impact behavior, specially, damage due to low-velocity impact highly depend on the local microscopic arrangements of composite materials as mixture. A general explicit finite element code, LS/DYNA 3D installed in IBM SP2 of Seoul National University, is used for the DNS. The DNS simulation results of the impact event by low-velocity(10m/s) aluminuum projectile are compared with the ones by the homogenized model and the impact damages, fiber-breakage, matrix cracking and delamination etc. are examined in the microscopic sense.

Real-time estimation of delamination occurrence induced by low-velocity impact in composite plates using optical fiber sensing system

Jang, Byeong-Wook,Kim, Chun-Gon Elsevier 2018 Composite structures Vol.189 No.-

<P><B>Abstract</B></P> <P>Low-velocity impact is the one of the most critical events to reduce the reliability of composite structures, because it can generate hidden damages such as delamination inside the structures. In order to address this problem, impact monitoring systems have been suggested using various types of built-in sensors. Generally, such impact monitoring systems are consisted of impact localization and damage assessment. In this paper, a methodology of impact-induced delamination assessment was studied using fiber Bragg grating (FBG) sensors. Because of its multiplexing capability, FBG sensors are advantageous of monitoring large areas of target structures. However, it is hard to be applied in impact monitoring systems due to its low sensitivity and narrow bandwidth. In this study, a quantification method of delamination was examined with maintaining the merits of FBG sensors. For the acquisition of impact-generated acoustic emission (AE) signals, the commercial FBG system was adopted with a sampling frequency of 100 kHz. Then, the acquired AE signals during the low-velocity impact fracture tests were analyzed with the wavelet transform (WT) method for measuring the delamination areas due to different energies. Finally, it can be concluded that the quantities of WT detailed portions are linearly correlated with the delamination areas.</P>

NDE of Low-velocity Impact Damages in Composite Laminates using ESPI, Digital Shearography and Ultrasound C-scan Techniques

김기석,홍순성,장경영,김건희 한국정밀공학회 2012 International Journal of Precision Engineering and Vol. No.

In this paper, the low-velocity impact damage in composite laminates was investigated by three NDE (Non-destructive Evaluation) techniques, Electronic Speckle Pattern Interferometry (ESPI), digital shearography and ultrasound C-scan. The objective of this study is to evaluate the detection performance of each NDE technique against low-velocity impact damage in fiber glass composite laminates when the specimen was inspected from front surface (impact side) which may be available in depot level. Unidirection and crossply fiber glass composite laminates were impact damaged with four energy levels (5,10, 15, 18 J) by drop weight impact machine. The results showed that ESPI and digital shearography techniques were able to identify the barely visible low-velocity impact damage. However, some limitations for detection depth were found in ESPI and digital shearography because the impact damage on reverse side was rarely detected by them. Nonetheless, ESPI and digital shearography techniques were estimated as one of useful NDE methods embedded with improved post processings including image process and optimal calibration method for different excitations.

Real-time detection of low-velocity impact-induced delamination onset in composite laminates for efficient management of structural health

Jang, B.W.,Kim, C.G. Elsevier Science Ltd 2017 Composites Part B, Engineering Vol.123 No.-

Carbon fiber reinforced polymer (CFRP) laminates have been becoming primary structures in the aerospace industry because of their high specific strength and stiffness. However, CFRP laminates have susceptibility to low-velocity impact events which can easily induce internal or hidden damages such as delamination. Such impacts frequently arise during maintenance, flight operation or in-service events. Thus, composite structures have to be irregularly inspected in addition to the periodic maintenance for ensuring the structural health. However, such irregular inspections can inherently incur the overall maintenance cost because it has to be performed in all suspicious cases of damages. For this reason, the methodology for accurately realizing the onset of delamination induced by low-velocity impact events is required for reducing the operating cost of composite structures. In this paper, the potential of using high speed fiber Bragg grating (FBG) sensing system for detecting the delamination onset was studied for thick CFRP laminates. Because FBG sensors can be simply multiplexed to capture the structural responses, the proposed method in this study can be quite attractive for an efficient impact monitoring system. To obtain the impact response signals and contact force histories, several low-velocity impact experiments were performed in a range of 1-30 J. From the signal processing of these experimental data, the meaningful damage index was introduced using the detail components of wavelet transformed sensor signals. Although this result is in the preliminary step, such damage index can be useful for applying an in-situ impact damage assessment system to the real composite structures in the near future.

NDE of Low-velocity Impact Damages in Composite Laminates using ESPI, Digital Shearography and Ultrasound C-scan Techniques

Kim, Ghi-Seok,Hong, Soon-Sung,Jhang, Kyung-Young,Kim, Geon-Hee 한국정밀공학회 2012 International Journal of Precision Engineering and Vol.13 No.6

In this paper, the low-velocity impact damage in composite laminates was investigated by three NDE (Non-destructive Evaluation) techniques, Electronic Speckle Pattern Interferometry (ESPI), digital shearography and ultrasound C-scan. The objective of this study is to evaluate the detection performance of each NDE technique against low-velocity impact damage in fiber glass composite laminates when the specimen was inspected from front surface (impact side) which may be available in depot level. Unidirection and crossply fiber glass composite laminates were impact damaged with four energy levels (5, 10, 15, 18 J) by drop weight impact machine. The results showed that ESPI and digital shearography techniques were able to identify the barely visible low-velocity impact damage. However, some limitations for detection depth were found in ESPI and digital shearography because the impact damage on reverse side was rarely detected by them. Nonetheless, ESPI and digital shearography techniques were estimated as one of useful NDE methods embedded with improved post processings including image process and optimal calibration method for different excitations.

SUS304 판재의 저속 충격 특성에 관한 연구

안동규(Dong-Gyu Ahn),문경제(Kyung-Je Moon),김진석(Jin-Suk Kim),한길영(Gil-Young Han),정창균(Chang-Gyun Jung),양동열(Dong-Yol Yang) 한국기계가공학회 2006 한국기계가공학회 춘추계학술대회 논문집 Vol.2006 No.-

The objective of this paper is to investigate into the influence of boundary condition of impact tests and diameters of impact head on low-velocity impact characteristics of SUS304 sheet. Several drop impact tests have been performed. Through the results of the experiments, the characteristics of the deformation, the energy absorption and the failure for the SUS304 sheet have been quantitatively examined. From the results of the experiments, it has been shown that the absorption mechanism of the impact energy is changed from the depression of the impact area to the mixed mode with the depression of the impact area and a successive wrinkle in the center line. In addition, it has been shown that the maximum absorption energy and the rate of energy absorption for drawing type impact tests increases with increasing diameters of the impact head, whereas that for stretching type impact tests maintains almost the same value irrespective of diameters of the impact head.

An Experimental Investigation on Low-Velocity Impact Responses of Sandwich Panels with the Changes of Impact Location and the Wall Partition Angle of Honeycomb Core

전광우,신광복 한국정밀공학회 2012 International Journal of Precision Engineering and Vol. No.

This paper describes an experimental investigation on low-velocity impact responses and damage modes of sandwich composites due to the changes of impact loading location and wall partition angle of honeycomb core. The sandwich panels were composed of a glass/epoxy laminated facesheet and an aluminum honeycomb core. Square samples of 100mm by 100mm sides were subjected to a low-velocity impact load using an instrumented testing machine at three different energy levels. Impact parameters such as maximum force, time to maximum force, deflection at maximum force, and absorbed energy were evaluated and compared. Sandwich specimens were cut to analyze damage modes after impact. The experimental results showed that low-velocity impact responses and damage mechanism of sandwich panels were affected significantly by the changes of wall partition angle of honeycomb core, and the energy absorption capacity of sandwich panels with wall partition angle of 45o was improved by about 25%.