• Journal of the Korean Society of Safety
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• v.14 no.3
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• pp.12-17
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• 1999

In this study, a drop-weight impact tester was manufactured to assess the strength of CFRP laminate plates. The tests were conducted on several laminates of different ply orientation. A system for the impact strength of CFRP laminates was made considering stress wave propagation theory using drop-weight impact tester as one of impact test. Results indicate that absorbed energy of quasi-isotropic specimen, haying four interfaces is higher than that of orthotropic laminates with two interfaces. Absorbed energy in the specimen that ply number, interface number and fiber stacking sequences is same but having hybrid is higher than that of orthotropic laminates without hybrid.

• Composites Research
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• v.12 no.5
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• pp.54-64
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• 1999

This study investigated the impact behaviors of the stitched sandwich composites under the low energy impact by the use of drop weight impact tester. These sandwich composites condidted of the glass fabric faces with a urethane foam core. The upper face and the lower face were stitched to combinr through the core thickness direction using the polyester reinforcements. Four types of the stitched sandwich composites, each having a different core thickness, were tested to determine the effects of the core thickness. The impact conditions were changes with the variations of the mass and drop height of the impact tup. The test results showed that the core thickness and the impact condidtions such as the drop height and the mass of the impact tup affected the impact force, the contact time, and the strain behaviors of the stitched sandwich composites. The stitched sandwich composites are able to avert the damage and also maintain the structural integrity even thouth the presence of the damage owing to the through-the-thickness reinforcements. However, it is important to improve the wetting ability of the stitched reinforcements so that the conventional structures are substituted for the stitched sandwich composites effectively.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.7
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• pp.658-664
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• 2010

A control element drive mechanism(CEDM) is a reactor regulating system, which inserts, withdraws or maintains a control rod containing a neutron absorbing material within a reactor core to control the reactivity of the core. The ball-screw type CEDM for the integral reactor has a spring-damper system to reduce the impact force due to the scram of the CEDM. This paper describes the experimental results to obtain the drop and damping characteristics of the CEDM. The drop tests are performed by using a drop test rig and a facility. A drop time and a displacement after an impact are measured using a LVDT. The influences of the rod weight, the drop height and the flow area of hydraulic damper on the drop and damping behavior are also estimated on the basis of test results. The drop time of the control element is within 4.5s to meet the design requirement, and the maximum displacement is measured as 15.6 mm. It is also found that the damping system using a spring-hydraulic damper plays a good damper role in the CEDM.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.710-713
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• 2005

Many impact or drop test researches of home appliances are published, but those of toys cannot be found easily. External impacts are the primary causes of fracture of toys. For impact proof design, the finished product should pass an impact test after molding design. There are several international toy safety standards or requirements such as US CPSC(Consumer Product Safety Commission), ASTM F963-96a, EN71 and so on. The puppy robot which patrols around the house, namely, the watchdog was selected to investigate toy safety because it has considerable weight and outer panels are made of plastics. First the model of watchdog robot was obtained by 3 dimensional scan. Surface data can be generated from 3D polygon data of the watchdog. A reliable drop simulation method for the watchdog was established using Pam-crash program according to Korean toy safety standards. When there is a low impact allowance value, the molding design should be reinforced or changed. It was found that the maximum impact stress reaches the ultimate stress of panel material.

• International Journal of Ocean System Engineering
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• v.2 no.3
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• pp.151-159
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• 2012

The characteristics of an impact load and pressure were experimentally investigated. Drop tests were carried out using a modified Wigley with CB = 0.56. The vertical force, pressures, and vertical accelerations were measured. A 6-component load cell was used to measure the forces, piezo-electric sensors were used to capture the impact pressure, and strain-gauge type accelerometers were used to measure the vertical accelerations. A 50-kHz sampling rate was applied to capture the peak values. The repeatability of the measured data was confirmed and the basic characteristics of the impact load and pressure such as the linearity to the falling height were observed for all of the measurements. A simple formula was derived to extract the physical impact load from the measured force based on a simple mass-sensor-mass diagram, which was validated by comparing impact forces with existing data using the mathematical model of Faltinsen and Chezhian (2005). The effects of the elasticity of the model and change in acceleration during the water entry were investigated. It is interesting to observe that the impact loads occurred and reached peak values at the same time duration after water entry for all drop heights.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.12 s.177
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• pp.117-123
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• 2005

This paper deals with the finite element model of the monitor fur the simulation of directional free drop tests such as the backward and vertex free drop as well as the associated free-drop experiment. The model was made for an unconditional stable solution fur the explicit integration algorithm. It was found through the comparison between simulation and experimental results that the general behaviors at the time of impact were observed to well correlate with each other in terms of acceleration, displacement, contact force and stress of monitor components.

• Transactions of the Society of Information Storage Systems
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• v.9 no.2
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• pp.56-61
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• 2013

The recent increased use of mobile phone has resulted in a technical focusing on reliability issues related to drop performance. Since mobile phone may be dropped several times during their use, it is required to survive common drop accidents. The plastic injection parts such as base stopper and carrier in the encoder type actuator can be broken easily in the actual reliability test of 1.5m free drop. So, we analyzed the shock resistance characteristics of auto focus actuator with variables in the material properties using finite element method. By applying the new resin materials, we can decrease the breakage of plastic injection parts and improve the reliability of mobile phone.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.3
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• pp.65-69
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• 2010

In this study, we investigated the effects of UBM(Under Bump Metallization) and solder composition on the drop impact reliability of wafer level packaging. Fan-in type WLP chips were prepared with different solder ball composition (Sn3.0Ag0.5Cu, and Sn1.0Ag0.5Cu) and UBM (Cu 10 ${\mu}m$, Cu 5 ${\mu}m$\Ni 3 ${\mu}m$). Drop test was performed up to 200 cycles with 1500G acceleration according to JESD22-B111. Cu\Ni UBM showed better drop performance than Cu UBM, which could be attributed to suppression of IMC formation by Ni diffusion barrier. SAC105 was slightly better than SAC305 in terms of MTTF. Drop failure occurred at board side for Cu UBM and chip side for Cu\Ni UBM, independent of solder composition. Corner and center chip position on the board were found to have the shortest drop lifetime due to stress waves generated from impact.

• Nuclear Engineering and Technology
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• v.53 no.8
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• pp.2682-2695
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• 2021

This paper aims to evaluate the structural dynamic responses and damage/failure of the nuclear fuel reprocessing plant under the free drop impact of spent fuel cask (SFC) and fuel assembly (FA) during the on-site transportation. At the present Part I of this paper, the large-scale SFC model free drop test and the corresponding numerical simulations are performed. Firstly, a composite target which is composed of the protective structure, i.e., a thin RC plate (representing the inverted U-shaped slab in the loading shaft) and/or an autoclaved aerated concrete (AAC) blocks sacrificial layer, as well as a thick RC plate (representing the bottom slab in the loading shaft) is designed and fabricated. Then, based on the large dropping tower, the free drop test of large-scale SFC model with the mass of 3 t is carried out from the height of 7 m-11 m. It indicates that the bottom slab in the loading shaft could not resist the free drop impact of SFC. The composite protective structure can effectively reduce the damage and vibrations of the bottom slab, and the inverted U-shaped slab could relieve the damage of the AAC blocks layer dramatically. Furthermore, based on the finite element (FE) program LS-DYNA, the corresponding refined numerical simulations are performed. By comparing the experimental and numerical damage and vibration accelerations of the composite structures, the present adopted numerical algorithms, constitutive models and parameters are validated, which will be applied in the further assessment of drop impact effects of full-scale SFC and FA on prototype nuclear fuel reprocessing plant in the next Part II of this paper.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.4
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• pp.321-328
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• 2009

Shock absorption performances of various rubbers were investigated by using drop impact test. Several types of rubber such as NR, NBR, EPDM, SR and PUR with three respective levels of shore hardness were used for the test. As in the cases, the absorbed impact energies in rubbers were measured under seven different loads against impact energy between 5-80J. The impact absorption efficiencies of the rubbers then were evaluated by means of both single impact energy condition and summation of all impact energy applied condition. As shown in the results, PUR and EPDM have better shock absorption performances than other rubbers. Further analysis was extended to determine a shear modulus of SR through the finite element implementation with Blatz-Ko model. As can be seen, relatively higher level of absorption energy results in a decreasing shear modulus.