• Explosives and Blasting
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• v.35 no.3
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• pp.15-20
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• 2017

In order to obtain the dynamic response behavior of the rock subjected to blasting loading, a shock-proof high sensitivity impact sensor which can measure high frequency dynamic force and strain events should be adopted. Because the impact sensors which uses quartz and piezoelectric element are costly, generally the strain measurement-based impact (SMI) sensors are applied to high speed loading devices. In this study, dynamic Brazilian tension tests of granitic rocks was conducted using the Nonex Rock Cracker (NRC) reaction driven-high speed loading device which adopts SMI sensors. The dynamic response of the granite specimens were monitored and the intermediate strain rate dependency of Brazilian tensile strengths was discussed.

• Journal of Welding and Joining
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• v.5 no.2
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• pp.1-8
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• 1987

MSR 처리를 실제구조물에 적용하기 위해서 잔류응력과 기계적성질에 대하여 조사해 본 결과 다음의 결론을 얻었다. (1) MSR 처리는 소성변형을 유발시켜 높은 인장잔류응력을 감소시키는데 유효하며, 잔류응력이 낮은 부위에 대해서는 잔류응력 재배치에 따른 응력치의 변화가 수반된다. (2) 잔류응력 감소량은 MSR 하중에 비례하여 증가 한다. (3) 모재의 항복응력보다 낮은 하중으로 MSR 처리를 하면 충격치의 감소는 무시할 정도이지만 모재의 항복응력보다 높은 하중으로 행하면 응착금속에서 충격치의 감소가 현저하다. (4) MSR 처리를 하게되면 항복응력이 높아지고, 잔류응력이 감소해서 선형의 응력-스트레인의 관계를 가지는 범위가 넓어져서 구조적으로 안전한 상태가 된다.

• Journal of the Korea Concrete Institute
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• v.28 no.4
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• pp.455-462
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• 2016

This experimental study aims to evaluate the impact performance of UHPC exterior panels through high velocity impact tests. The impact performance of UHPC was compared with that of granite in terms of panel thickness, and strain histories were recoded on the rear face of panel specimens. The UHPC turned out to be a good exterior facade material, because the appearance of UHPC is natural enough and impact performance was superior to granite. After colliding, compression pulse reached to the rear face but that pulse was reflected in tension pulse with respect to the free point outside the rear face of the panel. This tension pulse caused the scabbing from the rear side, as the strain histories on the rear face showed three different regions as compression region, steady region and tension region. The shear plug deformation by shear force also was one of the primary reasons for the scabbing based on the observation. Therefore, the scabbing seemed to be affected by both tension and shear forces.

• Tunnel and Underground Space
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• v.20 no.5
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• pp.318-324
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• 2010

Dynamic properties of materials by shock loads such as rock blasting and earthquake are recently attracted in the design of aboveground and underground structures. The advance of measuring devices enables to obtain the whole histories of stress and strain in rock specimen of which the failure is completed in several hundred microseconds. The SHPB has been a popular and promising technique to study the dynamic behavior of rock. And the dynamic compressive, tensile and other test with this experiment system are planned to be Suggested Methods of ISRM. This technical paper is to introduced one study article which focuses the design of 3S (special shaped striker) to produce the half-sine wave to eliminate the problems of the rectangular wave. This article is also describing the advantage of half-sine incident wave and size effect of rock dynamic strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.159-160
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• 2010

Due to the characteristics of high toughness, FRP is a valuable material to apply to the structures that have to withstand the blast or impact loads. FEM analyses for the concrete beams flexurally strengthened in tension part with FRP sheets were performed to improve the low-velocity impact resistance.

• Journal of Bio-Environment Control
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• v.5 no.1
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• pp.23-33
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• 1996

This study was performed to induce a quality improvement and standardization of materials used for greenhouse. For this purpose, physical and mechanical properties of agricultural films for greenhouse were measured by kinds and thickness of the films. The properties are composed of impact, tensile, tear propagation strength and light transmittance. The results were summarized as follows. 1. At the impact test result of the falling dart, the thicker the film, the greater the impact strength of soft film. The impact weight at 50 percents is from 158g to 213g and the strength of low density polyethylene(LDPE) film is higher than the rest of any other films. 2. Seeing the leveling of the impact rupture, maximum impact weight which was ruptured very little ranges from 62g to 192g. The impact strength of 0.1mm films was higher than that of 0.05mm as from 1.8 to 3.2 times. 3. Tensile weight covers from 0.95kg to 2.22kg in the test materials, and the weight of lengthwise film is larger than that of width. LDPE film has high value of tensile weight. Elongation range is from 345 to 102 percent and lengthwise elongation is greater than width as much as from 1.4 to 2.7 times. 4. Tea. propagation strength ranges from 80.5kg/cm to 121.7kg/cm, and unlike which of LDPE film has high value, EVA film has low value in the films tested. The width strength is higher than the lengthwise. 5. The light transmittance of the soft film is about 78-92 percent in the range of ultraviolet ray, but has high value in the visible ray range.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.7 s.94
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• pp.1772-1782
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• 1993

The characteristics of metal matrix composite under dynamic tension at high strain rates up to the order of $10^3/sec$ is studied by using newly developed apparatus. The composite material processed in this research is aluminum-alumina metal matrix composites, arid fabricated by compocasting with the fiber volume fraction from 5 to 20%. The whisker and matrix material used in this paper were ${\delta}-Al_2O_3$ and Al-6061, respectively. The mechanical tests performed in this research are low and high strain rate tensile test. At low strain-rate tensile test, the modulus of elasticity and the ultimate tensile strength of the composites were improved about 77 pct. and 55 pct., respectively comparing with the unreinforced materials. At strain-rate from $10^{-3}\;to\;10^3/s$, the effect of strain-rate on the modulus, ultimate strength, flow stress is determined. Also the effect of strain rate on the modulus, ultimate tensile strength, flow stress and elongation to failures were investigated.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.3
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• pp.349-355
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• 2020

The purpose of this study is to investigate the effects of types and amounts of fibers on the compressive strength and tensile behavior high strength fiber-reinforced composites under a static load and impact resistance properties of composites under a high-velocity projectile impact load. Three kinds of mixtures were designed and specimens were manufactured. compressive strength, uniaxial tension, and high velocity projectile impact load tests were performed. Test results showed that the amount of fiber has a greater effect on the tensile strength an d tensile strain capacity than the compressive strength, an d the tensile strain capacity was improved by using hybrid fibers. It was also found that the amount of steel fiber had a great influence on the impact resistance capacity of panels. Although the impact resistance capacity of panels could be improved by using hybrid fibers, the difference of impact resistance capacity between specimens was found to be larger than the case of use of single fiber.

• Composites Research
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• v.21 no.3
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• pp.9-17
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• 2008

In this paper, the low velocity impact characteristics of filament winding CFRP pressure vessel was investigated using numerical and experimental methods. The cylinder part of CFRP vessel was impacted using triangular shape impactor which simulated the sharp edge of dropping tools and impact response behavior of CFRP was reviewed. The mechanical behavior, such as deformation and stress distribution, were also predicted by explicit finite element method and the validity of the model was investigated. For the quantitative evaluation of the residual strength of the pressure vessel after impact, a series of the ring specimens was cut from the impacted vessel and its burst pressure was measured by hydraulic pressure hoop tension test. As the results, the relationship between the residual strength degradation and the impact energy was successively obtained and a useful methodology to evaluate quantitatively the impact damage tolerance of CFRP pressure vessel was established.

• Journal of the Society of Naval Architects of Korea
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• v.32 no.1
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• pp.118-131
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• 1995

The shock fracture analysis for the structures of navy vessels subject to underwater explosions or of high speed vessels frequently subject to impact loads has been carried out in two steps such as the global or macro analysis and the fine or micro analysis. In the macro analysis, Doubly Asymptotic Approximation(DAA) has been applied. The three main failure modes of structure members subject to strong shock loading are late time fracture mode such as plastic large deformation mainly due to dynamic plastic buckling, and the early time fracture mode such as tensile tearing failure or transverse shear failure. In this paper, the tensile tearing failure mode is numerically analyzed for the micro analysis by calculating the dynamic stress intensity factor $K_I(t)$, which shows the relation between stress wave and crack propagation on the longitudinal stiffener of the model. Especially, in calculating this factor, the numerical caustic method developed from shadow optical method of caustic well known as experimental method is used. The fully submerged vessel is adopted for the macro analysis at first, of which the longitudinal stiffener, subject to early shock pressure time history calculated in macro analysis, is adopted for the micro analysis.