• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.5
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• pp.566-574
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• 2016

Fiber metal laminates, which are hybrid materials consisting of metal sheets and composite layers, have contributed to aerospace and automotive industries due to their reduced weight and improved damage tolerance characteristics. In this study, the impact performance of the laminates, which are comprised of a self-reinforced polypropylene and two aluminum sheets, and the pure aluminum alloy sheet material were investigated experimentally via numerical simulation. In order to compare the impact performance, the laminates and aluminum alloy were examined by assessing the impact force, energy time histories, and specific energy absorption. ABAQUS is a commercial software that is used to simulate the actual drop-weight tests. Based on this study, it is noted that the impact performance of the laminates was superior to that of the aluminum alloy. In addition, a good agreement between the experimental and numerical results can be achieved when the impact force and energy time histories from the experiments and the numerical simulations are compared.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.4
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• pp.339-347
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• 2014

Floor impact sound in high-rise apartment building became one of social problems. A lot of civil complaints on floor impact sound occur continuously and the number of disputes between neighbors in small and aged apartment buildings is increasing. Interests on heavy-weight impact sound pressure level measurement and evaluation method is increased. Previous study reported that heavy-weight impact sound level was changed by the sound field condition of receiving reverberation chamber. In this study, heavy-weight impact sound pressure level change by the receiving sound field condition was measured in standard test facility and mock-up test room. These two experimental conditions were designed to simulate averaged living room of common apartment units. By the change of sound absorption power in receiving room, heavy-weight impact sound pressure level in most of frequency bands were changed in standard test facility and mock-up room. Normalized maximum sound pressure level regulated in ISO 16032 showed wider range of heavy/soft impact sound pressure level. Heavy/soft impact sound pressure level change was became smaller by the application of standardized maximum sound pressure level and ISO/CD 10140-3 Amd 2 method. In the case of standardized maximum sound pressure level, absolute sound pressure level changed. From these results, receiving sound field correction method regulated in ISO/CD 10140-3 Amd 2 is needed for the precision measurement and evaluation of heavy-weight impact sound.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.622-625
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• 2006

This study is a fundamental investigation for standardization of the heavy-weight floor impact measuring method by the impact ball. The distribution chrematistics of floor impact sound level and reverberation time in a receiving room of the testing building for floor impact sound were measured with variations of number and arrangement of the sound-absorbing materials. Total 8 cases were investigated. The distribution of the floor impact sound level($L_{i,\;Fmax}$) was measured at 30 points with same intervals. The absorption coefficient of the room is 0.10 in case of installation of 6 absorbing materials and 0.02 in case of non-installation. The distribution shape of the impact sound pressure level was similar to the result of the bang machine driving at the measured frequency range. However, the overall reduction of the impact sound level investigated in the 125 to 500 Hz shows that the sound absorption characteristics of the receiving room actually affects the result of the heavy-weight impact measurement.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.2
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• pp.144-150
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• 2008

In this study, the PVDF (polyvinylidene fluoride) piero-film sensor was applied to measure the internal quality of apple. The developed sensor detected the response signal through apple after mechanical impact on the surface of apple. The acoustical parameters at time domain such as rise time (RT), ring down count (RC), energy (EN), event duration (ED) and peak amplitude (PA) and acoustical parameter at frequency domain such as spectral density (SE) were analyzed. The size of waveform decreased as storage time of apple increased. The frequency at maximum magnitude was shifted to lower frequency band according to the storage time. The acoustical parameters showed strong relationship with storage time. The multiple linear regression equation was developed to estimate storage time of apple using the acoustical parameters at time domain and its coefficient of determination was 0.97. The internal quality of apple according to storage time is predictable using developed PVDF sensor and acoustical parameters defined in this study.

• 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.

• Korean Journal of Applied Biomechanics
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• v.20 no.1
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• pp.25-32
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• 2010

This study was performed to investigate the kinematic factors on the head hitting motion based on weight change of bamboo swords in kumdo. The kinematic factors, needed time per phase, COB displacement and velocity, angle(wrist, elbow, shoulder joint, hip joint, knee joint), were analyzed by the 3-D motion analysis method against 6 male middle school athletes. The results were as follows. 1. The needed time of head hitting motion based on weight change of bamboo swords was shorter when weight was heavier. 2. The COB displacement of left/right was bigger when weight was heavier. the displacement of right foot was higher at backswing phase and impact phase when weight was heavier and at impact time when weight was lighter. 3. The COB velocity was faster at impact time when weight was heavier, the velocity of sword tip was fastest for each event with bamboo sword weight of 440 g. 4. The angle of left elbow was smaller at top of backswing and impact when weight was heavier, the angle of left shoulder was bigger when weight was heavier, the right knee angle was biger at start when weight was heavier, at impact when weight was lighter.

• Journal of Biosystems Engineering
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• v.14 no.3
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• pp.207-214
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• 1989

In this study, impact force and angular displacement of the pendulum were measured by the load cell and potentiometer. Mechanical behavior of rough rice under impact loading was able to analyze precisely and efficiently, because measured data were accumulated and handled by the automatic data acquisition system making use of microcomputer system. Impact force and angular displacement were measured with a resolutiln of 1/1500 seconds in time. Mechanical behavior such as force and energy at rupture point of Japonica type and Indica type rough rice were measured with this system. After impact loading, the damage of rough rice was examined with the microphotograph and an allowable impact force was measured. The results obtained in this study are summarized as follows. 1. Machanical behavior of rough rice under impact loading was analyzed precisely and efficiently because measured data were accumulated and handled by this data acquisition system. 2. Rupture force and rupture energy of rough rice were appeared to be the lowest value in the range of 16 to 18 % moisture content, and rupture force and rupture energy of Japonica type were higher than those of Indica type in each level of moisture content. 3. From the result of the damage examined after the impact loading, allowable impact force was the lowest in the range of 16 to 18 % moisture content, and the value of the allowable impact force of Japonica type was higher than that of Indica type in each level of moisture content.

• Journal of Welding and Joining
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• v.13 no.2
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• pp.122-131
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• 1995

The effects of cooling rate on the microstructures, precipitation of Cu-cluster, .epsilon.-Cu and impact toughness of high strength low alloy(HSLA) steel were studied using hardness tester, impact tester, DSC(differential scanning calorimetry), AES(auger electron spectroscopy) and TEM(transmission electron microscopy). Not only the Cu-precipitates but also the segregation of Cu, As, Sb, P, S, N, Sn along grain boundary were not observed at the specimens heat treated from 800.deg. C to 300.deg. C with the cooling time of 12-125 sec. The Cu-cluster, .epsilon.-Cu are formed by introducing ageing after cooling and the effect of precipitates on hardening increase after cooling was the same in all cooling rate. The peak hardness was obtained at an ageing of 500.deg. C in all cooling conditions. The impact energy become higher as the cooling time increases. This fact can be explained to be due to the tempering effect applied on the cooling stage since the present alloy has a relatively high Ms temperature and the local high concentration of the retained austenite.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.4
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• pp.338-347
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• 2010

Heunginjimun designated as a Treasure No.1 is a two-story wooden structure with 5 bay and 2 bay in its front and side views, respectively. This paper presents an investigation on vibration characteristics of Heunginjimun through both ambient vibration and impact hammer tests. Ambient vibration test was performed to identify the natural frequency of Heunginjimun from the spectrum analysis of time history. Impact hammer test was undertaken to find the frequency of Heunginjimun which is affected by the surrounding traffics and to verify the reciprocal principle for the wooden structural system. Ambient vibration test results of Heunginjimun showed that the natural frequencies in two principal axes 1.5 Hz and 1.1 Hz, respectively. It was confirmed from impact hammer tests for a ground that the frequency of 4.2 Hz is caused by the traffics surrounding Heunginjimun. It was also observed that from the impact hammer test results between two locations in Heunginjimun that the transfer functions measured from two corresponding locations coincided well with each other. This result shows that the wooden structural system is globally linear, and the reciprocal principle is established.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.132-137
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• 2001

Miniaturized specimen technology is useful to characterize the mechanical behavior using a minimum volume of material, because it is almost impossible to sample the conventional specimen for the fracture toughness test without damage to equipment. Test material was 1Cr-1Mo-0.25V steel which was widely used for turbine rotor material. Two kinds of miniaturized impact specimens were prepared, i.e., miniaturized specimen with side groove and without side groove. The correlation between ductile brittle transition temperature(DBTT) of full size impact specimen and that of miniaturized impact specimen was made. The characteristics of miniaturized impact specimens technique as well as fracture stress were discussed. Finally, we concluded that the characteristics of fracture stress change on aging time were similar to that of DBTT.