• KCI Concrete Journal
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• 제13권1호
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• pp.61-67
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• 2001

For the design of shear connection for the composite precast concrete slabs. it is necessary to investigate its strength, stiffness, slip capacity and fatigue endurance. For theme purposes, push-out tests were performed with variations of the stud shank diameter and the compressive strength of the mortar. From the experimental studies, it could be observed that the deformation of the shear studs in a full-depth precast concrete slabs were greater than those in a cast-in-place slabs. The static strength of the shear connections obtained agree approximately with those evaluated from the tensile strength of the stud shear connectors owing to the effect of the bedding layer between the slabs and the beams. An empirical equation for the initial shear stiffness of a shear connection was also proposed. On the basis of the push-out tests, a full-scale composite beams with 8.0m span was designed and fatigue tests were carried out to study the behaviour of the stud shear connection and its effects on the flexural behaviour of the beam. The bonding arid friction between the concrete slab and the steel beam considerably increased the fatigue endurance of the shear connection.

• 대한조선학회논문집
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• 제38권4호
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• pp.75-82
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• 2001

건조 후 수행하는 수압시험 또는 화물의 적재 등과 같은 정하중은 파랑변동하중에 비하여 선체구조물에 상당히 큰 응력을 유발한다. 이러한 정하중이력에 의하여, 선체구조물의 응력집중으로 인해 피로강도가 문제되는 용접이음부에서는, 재료의 탄소성 거동에 의하여 초기용접잔류응력이 상당히 이완될 것으로 예상된다. 따라서, 이러한 용접이음부의 피로강도를 평가할 때에는 이완된 잔류응력의 영향을 고려하는 것이 보다 합리적이다. 본 연구에서는 선체구조물의 여러 가지 용접형태 중 Padding plate가 용접된 형태에 대하여 정하중이력($0.5{\sigma}Y,\;0.85{\sigma}Y$)에 의한 초기 용접잔류응력의 변화를 측정하며, 잔류응력의 변화가 피로강도에 미치는 영향을 검토한다.

• 대한기계학회논문집A
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• 제22권3호
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• pp.554-561
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• 1998

Vehicle body structures are formed by thousands of spot welds and fatigue failure of vehicle structures occur near the spot welds after driving a long way at a durability test road. It is necessary to know accurately the reason of the fatigue failure of the spot weld in the developing stage in order to reinforce it. Many investigations have been done regarding the strength of spot welded joints, contributing to understand its fatigue strength. In developing process, a fatigue failed spot welded area can be repaired by $CO_2$ welding or another method to continue the test. To know the effect of reinforcing these welds, several methods of welding were analyzed and compared to spot welding. With the results of this test, the appropriate repair method can be used instead of spot welding during the development of new car and best design guide can be given for the strength. In this study, fatigue and static tensile tests are made and microstructure is investigated for the purpose of estimating the strength of welded joints by using spot welded and $CO_2$ plug welded specimens. The tested specimens are of two types : Tensile-shear type(TS) and L-tension type(LT).

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.447-452
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• 2004

Vacuum interrupters in order to be used in various switch-gear components such as circuit breakers, distribution switches, contactors, etc. spread the arc uniformly over the surface of the contacts. The electrodes of vacuum interrupters are made of sinter-forged Cu-Cr materials for good electrical and mechanical characteristics. Since the closing velocity is 1-2m/s and impact deformation of the electrode depends on the strain rate at that velocity, the dynamic behavior of the sinter-forged Cu-Cr is a key to investigate the impact characteristics of the electrodes. The dynamic response of the material at intermediate strain rate is obtained from the high speed tensile test machine test and at the high strain rate is obtained from the split Hopkinson pressure bar test. Experimental results from both quasi-static and dynamic compressive tests are interpolated to construct the Johnson-Cook model as the constitutive relation that should be applied to simulation of the dynamic behavior of the electrodes. The impact characteristics of a vacuum interrupter are investigated with computer simulations by changing the amount of chromium content.

• Journal of Welding and Joining
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• 제11권3호
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• pp.48-60
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• 1993

The cause of corrosion failure found in structures or various components operating in severe corrosive environments has been attributed to stress corrosion cracking(SCC)which is resulting from the combined effects of corrosive environments and static tensile stress. Slow strain rate test (SSRT) provides a rapid reliable method to determine SCC susceptibility of metals and alloys for a broad range of application. The chief advantage of SSRT procedures is that it is much more aggressive in producing SCC than conventional constant strain or constant load tests, so that the testing time is considerably reduced. Therefore, in this paper, the combined effects of material properties and strain rate on the tensile ductility and fracture morphology of parents and weldment for SM45C, SCM440 and SM20C steels were examined and discussed in synthetic sea water. The susceptibility of SCC was the most severe under the strain rate of $1.0{\times}10^{-6} sec^{-1}$, and R.O.A. can be used for parent and maximum load for weldment to evaluate the parameter for SCC susceptibility.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.746-749
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• 2004

A new-type of FRP-concrete composite bridge deck system is proposed and its behaviors are experimentally studied. The new-typedeck consists of FRP as a permanent form and main tension resisting member and concrete as a compression resisting member. A suitable bonding method such as silica coating is applied to the interface between FRP and concrete to ensure composite behavior. The proposed deck system uses the box-shape FRP member, while a typical FRP-concrete composite deck uses the I-shape FRP member. Theproposed deck system has inherent advantages of a FRP-concrete composite deck like corrosion free and easy construction. The new-type deck shows the equal performances compared to a previous one, and has the advantage of reducing self-weight. In this study, the static tests on 3-span FRP-concrete decks in full scale are carried out, so that load-displacement relation, stress distribution, failure mode and design criteria are analyzed. The test results show that the deflection design criterion (L/800, L: span length) is satisfied at the service load state. No concrete tensile crack occurs in the negative moment region above the main girder, regardless of no tensile reinforcement at upper concrete portion.

• 대한기계학회논문집A
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• 제21권12호
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• pp.2209-2219
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• 1997

A split hopkinson bar could be used for obtaining the high strain rate material properties of sheet metals for an autobody. In high speed tensile tests of sheet matals, a new design of a tension split Hopkinson bar apparatus is needed. The design of grips and an anvil length are numerically analyzed with ABAQUS/Explicit for the new apparatus of split Hopkinson bars. From the experiments with the new apparatus, the material properties of SPCEN in the high strain rate state have been acquired and compared with quasi-static experimental results. The material properties of SPCEN as well as other sheet metals in an autobody are indispensible for the analysis of crashworthness. Nevertheless the experiment of sheet metal in the high strain rate state has not been done or reported.

• 대한금속재료학회지
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• 제46권9호
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• pp.563-571
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• 2008

The influence of annealing treatment on dynamic deformation behavior of ultra-fine grained aluminum alloys was investigated in this study. After equal-channel angular pressing at $200^{\circ}C$, most of the grains were considerably reduced to nearly equiaxed grains of $0.3{\mu}m$ in size. With an increment of various annealing treatments for 1 hour, resultant microstructures were found to be fairly stable at temperatures up to $200^{\circ}C$, suggesting that static recovery would be dominantly operative, whereas grain growth was pronounced above $250^{\circ}C$. The tensile test results showed that yield and ultimate tensile strengths decreased, but elongation-to-failure and strain hardening rate increased with increasing annealing temperature. The dynamic deformation behavior retrieved with a series of torsional tests was explored with respect to annealed microstructures. Such mechanical response was analyzed in relation to resultant microstructure and fracture mode.

• Advances in concrete construction
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• 제16권2호
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• pp.119-126
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• 2023

Steel fiber reinforced self-compacting concrete (SFRSCC) has good workability such as high flowability and good cohesiveness. The workability, compressive strength, splitting tensile strength, and anti-penetration characteristics of three kinds of SFRSCC were investigated in this paper. The fraction of steel fibers of the SFRSCC is 0.5%, 1.5% and 2.0% respectively. The results of the static tests show that the splitting tensile strength increases with the increase of fraction of steel fibers, while the compressive strength of 1.5% SFRSCC is lowest. It is demonstrated that the anti-penetration ability of 1.5% SFRSCC subjected to a velocity projectile (200-500 m/s) is better than 0.5% and 2.0% SFRSCC according to the experimental results. Considering the steel fiber effects, the existing formula is revised to predict penetration depth, and it is revealed that the revised predicted depth of penetration is in good agreement with the experimental results. The conclusion of this paper is helpful to the experimental investigations and engineering application.

• 터널과지하공간
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• 제22권5호
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• pp.339-345
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• 2012

동적하중 하에서 암석의 변형거동 및 파괴강도는 발파, 지진 또는 암반돌출의 지진동에 의한 지하구조물의 안정해석에 중요하다. 본 연구에서는 스플릿 홉킨슨 압력봉(SHPB) 충격실험시스템을 석회암시료의 일축압축시험과 압열인장시험에 적용하여 고변형률과 동적강도 평가를 수행하였다. 충격봉의 발사속도를 제어하여 파괴강도 이하 동적응력 상태에서의 석회암시료의 동적응력-변형거동을 분석하였다. 시료 내 파괴여부 및 파괴양상을 파악하기 위하여 Micro-focus X-ray 단층촬영을 수행하였다. 동적 압축강도 실험결과, 석회암시료의 동적압축강도는 변형율속도 의존성을 보였으며, 동적 압축파괴강도는 140 MPa 이상으로 평가되었다. 동적 압열 인장 실험결과, 석회암시료의 동적 압열인장강도는 21 MPa 이상으로 정적 압열인장강도보다 3배 이상 높은 것으로 평가되었다.