• Composites Research
• /
• v.17 no.4
• /
• pp.53-60
• /
• 2004

This paper describes a method for a falling weight impact test to estimate the impact energy absorbing characteristics and impact strength of CFRP laminate plates based on considerations of stress wave propagation theory. The absorbed energy of T300 orthotropic composites is higher than that of quasi-isotropic specimen over impact energy 6.8J, but in case of using T700 fiber, much difference does not show. Also, absorbed energy of T300 orthotropic composites, which are composed of the same stacking number and orientation became more than that of T700 fiber specimen; however there was no big difference in case of quasi-isotropic specimens. The delamination areas of the impacted specimen were measured with the ultrasonic C-scanner to find correlation between impact energy and delamination area. The fracture surfaces were observed by using the SEM (scanning electron microscope) through a low-velocity impact test in order to confirm the fracture mechanism.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.40 no.7
• /
• pp.555-563
• /
• 2012

In earth orbit, a great number of orbital debris move around in extremely high velocity, and they become serious threats to satellites. In this study, smoothed particle hydrodynamics(SPH) is used to analyze the damage of a low earth orbit satellite due to the hypervelocity impact with orbital debris. The damage of honeycomb sandwich panel(HC/SP) used for walls of a satellite is analyzed with respect to impact velocities. For the additional analysis to examine the safety of interior components of the satellite, an attached electronic box and an offset electronic box are considered. As a result of the analysis considering the orbital debris having a probability of collision more than 2% at altitude of 685km, it is shown that the HC/SP can be perforated but only small craters are formed on both the attached electronic box and the offset electronic box.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.17 no.2
• /
• pp.81-88
• /
• 1997

Impact behavior of carbon fiber reinforced plastics (CFRP) laminates were evaluated with tension test and compact tension test. A steel ball launched by an air gun collides against CFRP laminates to generate impact damage of relatively low energy. The static tensile and fracture toughness tests were performed to evaluate the residual strength and the AE behavior of impact-damaged laminates. As a results, it was found that the static strength, the fracture toughness and the AE-event count were decreased with increasing of impact velocity and delamination area, and to have a different strength ratio and fracture toughness ratio for each stacking method. And also, it was confirmed that strength and fracture toughness of impact-damaged CFRP laminates could be evaluated and analyzed quantitatively by AE techniques.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.5 no.1
• /
• pp.141-148
• /
• 2001

Dynamic compaction is the ground improvement method by applying the impact energy. This impact energy can damage to adjacent structure in urban area. Therefore, if dynamic compaction method is applied, careful attention should be payed to surrounded structures. In this study, the method was performed in waste landfill and the frequency of vibrations were measured according to each distances, drop-heights, and vibrating directions. The measured data show that particle velocity bas low frequency and it is greatest in longitudinal direction. There was little differences between Maynes suggestion and measured data. Therefore, Maynes suggestion can be adopted if the range of vibration can be predicted. Also, It was found that minimum 45m distance is needed in order to satisfy the administrative code if dynamic compaction method is applied.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.37 no.7
• /
• pp.693-700
• /
• 2009

In this paper, conventional z-pinning technology which can be used to reinforce inter-laminar property of laminated composites is introduced and new z-pinning technique recently proposed by author is also introduced. On some trial specimens manufactured by the new z-pinning technique, the low-velocity impact test was performed and impact damage area was measured. Similar impact test was performed on normal composite laminate specimens and those test results were compared to each other. Consequently, it can be seen that the new z-pinning technique is more useful in applying to mass production of z-pinned composite laminate structures than the conventional techniques and some clear improvement on impact resistance of z-pinned composite laminates manufactured by the new z-pinning technique is observed.

• Composites Research
• /
• v.18 no.3
• /
• pp.38-46
• /
• 2005

In order to characterize the outstanding performance of three-dimensional (3D) composites, the low velocity impact test has been carried out. 3D fiber structures have been achieved by using the automated tape placement (ATP) process and a stitching method. Materials for the ATP and the stitching process were carbon/epoxy prepreg tapes and Kevlar fibers, respectively. Two-dimensional composites with the same stacking sequence as 3D counterparts have also been fabricated for the comparison of damage tolerance. For the assessment of damage after the impact loading, specimens were subjected to C-Scan nondestructive inspection. Compression after impact (CAI) tests were conducted to evaluate residual compressive strength. The damage area of 3D composites was greatly reduced $(30-40\%)$ compared with that of 2D composites. Although the CAI strength did not show drastic improvement for 3D composites, the ratio of retained strength was $5-10\%$ higher than 2D samples. The effect of stitching on the impact performance was negligible above the energy level of 35 Joules.

• Composites Research
• /
• v.24 no.1
• /
• pp.24-30
• /
• 2011

Low-velocity impact can cause various damages which are mostly hidden inside the laminates or occur in the opposite side. Thus, these damages cannot be easily detected by visual inspection or conventional NDT systems. And if they occurred between the scheduled NDT periods, the possibilities of extensive damages or structural failure can be higher. Due to these reasons, the built-in NDT systems such as real-time impact monitoring system are required in the near future. In this paper, we studied the impact monitoring system consist of impact location detection and damage assessment techniques for composite flat and stiffened panel. In order to acquire the impact-induced acoustic signals, four multiplexed FBG sensors and high-speed FBG interrogator were used. And for development of the impact and damage occurrence detections, the neural networks and wavelet transforms were adopted. Finally, these algorithms were embodied using MATLAB and LabVIEW software for the user-friendly interface.

• Journal of the Korea Concrete Institute
• /
• v.24 no.3
• /
• pp.293-303
• /
• 2012

Recently, as construction technology improved, concrete structures not only became larger, taller and longer but were able to perform various functions. However, if extreme loads such as impact, blast, and fire are applied to those structures, it would cause severe property damages and human casualties. Especially, the structural responses from extreme loading are totally different than that from quasi-static loading, because large pressure is applied to structures from mass acceleration effect of impact and blast loads. Therefore, the strain rate effect and damage levels should be considered when concrete structure is designed. In this study, the low velocity impact loading test of steel fiber reinforced concrete (SFRC) slabs including 0%~1.5% (by volume) of steel fibers, and strengthened with two types of FRP sheets was performed to develop an impact resistant structural member. From the test results, the maximum impact load, dissipated energy and the number of drop to failure increased, whereas the maximum displacement and support rotation were reduced by strengthening SFRC slab with FRP sheets in tensile zone. The test results showed that the impact resistance of concrete slab can be substantially improved by externally strengthening using FRP sheets. This result can be used in designing of primary facilities exposed to such extreme loads. The dynamic responses of SFRC slab strengthened with FRP sheets under low velocity impact load were also analyzed using LS-DYNA, a finite element analysis program with an explicit time integration scheme. The comparison of test and analytical results showed that they were within 5% of error with respect to maximum displacements.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.38 no.6
• /
• pp.525-538
• /
• 2014

Safety of reactive systems is one of the most important research areas in the field of weapon development. A NoGo response or at least a low-order explosion should be ensured to prevent unexpected accidents when the reactive system is impacted by high-velocity projectile. We investigated the shock-induced detonation of cased reactive systems subject to a normal projectile impact to the cylindrical surface based on two-dimensional hydrodynamic simulations using the I&G chemical rate law. Two types of energetic materials, namely LX-17 and AP-based solid propellant, were considered to compare the dynamic responses of the reactive system when subjected to the threshold impact velocity. It was found that shock-to-detonation transition phenomena occurred in the cased LX-17, whereas no full reaction occurred in the propellant.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.17 no.4
• /
• pp.118-125
• /
• 2009

Bumper is designed to protect the automotive frame without damage at low velocity. Expanded polypropylene (EPP) foam is used in the bumper as an energy absorbing material. In order to exactly predict the energy absorbing performance of the foam material under impact loading condition, it is important to use high strain rate material properties. In this study, a new apparatus for dynamic compression tests was developed to investigate the high strain rate behavior of EPP foams. Three kinds of EPP foams which have different expansion ratios were tested to investigate the quasi-static and dynamic compression behavior. Quasi-static compressions were performed at low strain rates of 0.001/s, 0.1/s and 1/s. The dynamic compressions were carried out at high strain rates of 50/s and 100/s with the developed apparatus. It was observed that the EPP foam has significant strain rate effect as compared to quasi-static behavior.