• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.48-53
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• 2007

The objective of this paper is to investigate the influence of impact conditions on the impact characteristics of the stainless sheet for the case of the fixed boundary conditions. In order to examine impact characteristics of the sheet, three-dimensional finite element analyses and impact tests have been performed. High speed tensile tests have been carried out to obtain strain-stress relationships including the effects of the strain rate. In order to improve an accuracy of the FE analysis, the hyper-elastic model and the damping factor have been introduced. The results of the FE analyses and the impact tests have been shown that the diameter of the impact head does not affect the absorption energy of the stainless sheet. In addition, it has been shown that the absorption rate of energy maintains almost $82.5\;\sim\;83.5\;%$ irrespective of the impact energy level and the diameter of the impact head. From the results of FE analyses, the variation of stress and strain energy in the stainless sheet has been quantitatively examined.

• 콘크리트학회논문집
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• 제27권4호
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• pp.363-375
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• 2015

본 연구에서는 탄성변형 에너지를 이용하는 충격실험장치인 변형에너지 충격시험장치(SEFIM)의 변형률 속도를 증가시키기 위하여, 탄성변형 에너지가 저장되는 에너지 프레임의 직경 및 재질을 다르게 하여 그 영향을 조사하였다. 현재 강재를 에너지 프레임의 재질로 사용한 SEFIM의 발현 가능한 변형률 속도범위는 10-40 /sec까지이지만, 에너지 프레임의 재질과 직경을 다르게 하여 충격 시 변형률 속도가 72 /sec까지 증가되었다. 충격실험에 사용된 HPFRCCs는 장섬유 1%와 단섬유 1%를 함께 초고강도 콘크리트에 혼입하였다. 정적 변형률 속도에서 뿐만 아니라, 네 가지 종류의 에너지 프레임을 사용한 높은 변형률 속도(14-72 /sec)에서도 변형경화 거동을 나타내었다. 에너지 프레임의 직경을 기존의 35 mm에서 25 mm로 작게 변경함에 따라서 변형률 속도가 증가하였으며, 에너지 프레임 재질을 강재, 알루미늄 그리고 티타늄으로 변경함에 따라, 강재보다 높은 탄성파 속도를 가지고 많은 크기의 탄성변형 에너지를 저장할 수 있는 티타늄 합금을 사용한 경우 더욱 높은 변형률 속도(72 /sec)를 생성하였다. 알루미늄 재질의 에너지 프레임의 경우 충격실험 시 작용되었던 응력으로 인해 탄성영역을 벗어나 소성변형을 일으켜 파단되어 본래 가지고 있던 성질을 발현하지 못하였다.

• 화약ㆍ발파
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• 제29권1호
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• pp.41-47
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• 2011

발파에 의한 암반손상영역을 평가하고 암반 파쇄도를 제어하기 위해서는 장약실 내 발생하는 폭발압력에 관한 정보는 중요하다. 이를 위하여 본 연구에서는 철, 알루미늄, 아크릴 재질의 센서에 대한 낙추 충격 시험으로부터 동적 변형률 신호를 측정하여 센서의 동적 응답 특성을 분석하였다. 철재 센서의 경우 충격하중에 가장 적은 변형률 출력 값을 보였으며 센서길이에 대한 출력 값의 변화는 적게 나타났다. 철제 센서를 뇌관의 충격하중 측정에 적용하였다.

• 한국군사과학기술학회지
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• 제6권3호
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• pp.62-73
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• 2003

The characteristics of constitutive equations, for hydrocodes, were Investigated by the comparison between the smoothed particle hydrodynamcis simulation and the experiment of rod impact test which resulted in a deformation history of impacting front where high strain and high strain rate dominate. The constitutive equations used in the simulation Is J-C(Johnson-Cook) model, Z-A(Zerilli-Armstrong) model, and S-C-G(Steinberg-Cochran-Guinan) model. The modification of Z-A model, based on the increased effect of strain-rate hardening, showed better correlation with expriment.

• Steel and Composite Structures
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• 재36권6호
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• pp.703-710
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• 2020

This paper presents numerical and theoretical investigations on the strain rate in steel-concrete composite (SC) panels under low-velocity impact of a hemispherical rigid body. Finite element analyses were performed on five specimens with different loading rates. The impact energy was kept constant to eliminate its influence by simultaneously altering the velocity and mass of the projectile. Results show that the strain rate in most parts of the specimens was low and its influence on bearing capacity and energy dissipation was limited in an average sense of space and time. Therefore, the strain rate effect can be ignored for the analyses of global deformation. However, the strain rate effect should be considered in local contact problems. Equations of the local strain and strain rate were theoretically derived.

• 한국정밀공학회지
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• 제25권8호
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• pp.80-87
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• 2008

This paper investigated into the impact characteristics of the stainless sheet with thickness of 0.7 mm on the stretching boundary condition through three-dimensional finite element analysis. High speed tensile tests were carried out to obtain strain-stress relationships with the effects of the strain rate. The FE analysis was performed by the ABAQUS explicit code. In order to improve an accuracy of the FE analysis, the hyper-elastic model and the damping factor were introduced. Through the comparison of the results of the FE analyses and those of the impact tests, a proper FE model was obtained. The results of the FE analyses showed that the absorption rate of energy maintains almost 82.5-83.5% irrespective of the impact energy level and the diameter of the impact head. From the results of FE analyses, variations of stress, strain, dissipation energy, strain energy density, and local deformation characteristics in the stainless sheet during the collision and the rebound of the impact head were quantitatively examined. In addition, it was shown that the fracture of the specimen occurs when the plastic strain is 0.42 and the maximum value of the plastic dissipation energy of the specimen is nearly 1.83 J.

• Nuclear Engineering and Technology
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• 제54권10호
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• pp.3766-3777
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• 2022

It is essential to ensure the safety of spent nuclear fuel (SNF) transport cask in drop situation that is included in transport accident scenarios. The safety of the drop situation is affected by the impact absorption performance of impact limiters. Therefore, when designing an impact limiter, the uncertainty in the material properties that affect the impact absorption performance must be considered. In this study, the material properties of the wood inside the impact limiter were selected as the variables for a parametric study. The sensitivity analysis of the drop response of the SNF transport cask with impact limiter was performed. The minimum wood strength required to prevent a direct collision between the cask and floor was derived from the analysis results. In addition, the plastic strain response was analyzed and strain-based evaluation was performed. Based on this result, the critical values of wood properties that change the impact dynamic characteristics were investigated. Finally, the optimal material properties of wood were obtained to secure the structural safety of the SNF transport cask. The results of this study can contribute to the development of SNF transport cask, thereby ensuring safety in transport accident conditions.

• 한국안전학회지
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• 제27권6호
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• pp.7-13
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• 2012

A lack of study on the dynamic tensile strengths of Sn-based solder joints at high strain rates was the motivation for the present study. A modified miniature Charpy impact testing machine instrumented with an impact sensor was built to quantitatively evaluate the dynamic impact strength of a solder joint under tensile impact loading. This study evaluated the tensile strength of lead-free solder ball joints at strain rates from $1.8{\times}10^3s^{-1}$ and $8.5{\times}10^3s^{-1}$. The maximum tensile strength of the solder ball joint decreases as the load speed increases in the testing range. This tensile strength represented that of the interface because of the interfacial fracture site. The tensile strengths of solder joints between Sn-3.0Ag-0.5Cu and copper substrate were between 21.7 MPa and 8.6 MPa in the high strain range.

• 동력기계공학회지
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• 제21권5호
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• pp.29-34
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• 2017

Many household appliances, including vacuum cleaners, are being subjected to various of impact damages, and made of plastic. However, researches on the damage of appliances materials by repetitive impacts have been rarely conducted. the mechanical stress exerted upon impact-modified polycarbonate (PC) has a great influence not only on the quality of the product but also on the life span. The purpose of this research was to quantify the effects of repetitive impact on the polycarbonate. Second, it was to design the repetitive impact tester for controlling the impact energy. The mechanical properties of tensile strength, yielding stress and strain on the specimens subjected to cyclic impacts were discussed. Tensile strength was sharply declined at the beginning of the impact cycles, while the strain gradually decreased during impact cycles.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 추계학술발표대회 논문집
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• pp.174-178
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• 2001

The piezoelectric thin film sensor can be used to interpret variations in structural and material properties, e.g. for structural integrity monitoring and assessment. To illustrate one of this potential benefit, PVDF film sensors are used for monitoring impact damage initiation in Gr/Ep composite panel. Both PVDF film sensors and strain gages are surface mounted to the Gr/Ep specimens. A series of impact test at various impact energy by changing impact mass and height is performed on the instrumented drop weight impact tester. The sensor responses are carefully examined to predict the onset of impact damage such as matrix cracking, delamination, and fiber breakage, etc. Test results show that the particular waveforms of sensor signals implying the damage initiation and development are detected above the damage initiation impact energy. As expected, the PVDF film sensor is found to be more sensitive to impact damage initiation event than the strain gage.