• Journal of the Korea Concrete Institute
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• v.27 no.4
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• pp.363-375
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• 2015

This research investigated the effects of diameter and material of energy frame on the impact velocity or strain rate of Strain Energy Frame Impact Machine (SEFIM). The impact speed of SEFIM have been clearly affected by changing the diameter and material of the energy frame. The reduced diameter of the energy frame clearly increased the impact velocity owing to the higher strain at the moment of coupler breakage. And, titanium alloy energy frame produced the fastest speed of impact among three materials including steel, aluminum and titanium alloys because titanium alloy has faster wave velocity than steel. But, aluminium energy frame was broken during impact tests. In addition, the tensile stress versus strain response of high performance fiber reinforced cementitious composites at higher and wider strain rates between 10 and 72 /sec was successfully obtained by using four different energy frames.

• Composites Research
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• v.31 no.5
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• pp.221-226
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• 2018

The Split Hopkinson Pressure Bar(SHPB) has been the most widely used apparatus to characterize dynamic mechanical behavior of materials at high strain rates between $100s^{-1}$ and $10,000s^{-1}$. The SHPB test is based on the wave propagation theory which was developed to give the stress, strain and strain rate in the specimen using the strains measured in the incident and transmission bars. In this study, the SHPB was directly designed and fabricated for the dynamic mechanical properties of fiber reinforced plastic (FRP) composites. In addition, this apparatus was verified for the validity by comparing the strain data obtained through the high speed camera and Digital Image Correlation(DIC) during the high strain rate compression test of the self-reinforced polypropylene composite (SRPP) specimen.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.5
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• pp.1563-1571
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• 1991

본 연구에서는 가상일 원리로 부터 유한 요소 수식화를 updated-Lagrangian 형태로 유도하였으며, 유도된 수식화를 연속체 유한 요소로 유한 근사화 하였다. 이 때 초소성 재료의 거동은 비압축성, 비선형 점성 유ㄷ옹으로 묘사하였다. 유한 요소 프로그램은 성형 기구 해석과 하중 압력을 제어하는 기법으로 구성되어 있으며 하중 압력의 제어는 성형 시간이 최소가 되게 하기 위하여 변형률 속도 민감 계수가 최대가 되고, 국부 변형에 의한 두께 감소를 방지하며 변형률 속도는 일정하게 유지되면서 성 형이 될 수 있도록 하였다. 즉 하중 압력 제어는 상당 변형률 속도가 최대가 되게하 여 성형 시간을 최소화하게 구성하였다.개발된 유한 요소 프로그램은 정수압 벌징 가공에 적용하였으며 최적 압력 시간 선도, 성형 형상, 두께 및 두께 변형률 분포, 상 당 변형률 분포 등을 구하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.11
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• pp.1369-1375
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• 2011

Shot ball impacts to materials cause residual compressive stress on their surfaces. Improving the fatigue strength of a material that has this residual compress stress is the purpose of the shot peening process. A numerical study was performed to evaluate the effect of the strain rate sensitivity and hardness of the shot ball on the residual compressive stress. We calculated the residual compressive stress due to multiple impact shot peening using ABAQUS 6.9-1. AISI 4340 steel was the material used in this study. We compared the effects of high strain rate sensitivities and low strain rate sensitivities and found that when the material's sensitivity to the strain rate increased, the residual compressive stress decreased. In addition, the residual compressive stress of low-hardness material is higher than that of high-hardness material.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.2
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• pp.470-474
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• 2008

The rate-dependent constitutive model and the rate-independent model were analyzed for comparing with the piezocone penetration test and dissipation test. The mathematical expressions of the rate-dependent constitutive model were introduced, and the predictions using the both models were compared with the experimental results of in-situ field test. The rate-dependent model analysis gave better results than the rate-independent model analysis, that is appreciated since the process of the piezocone penetration and dissipation depends on the strain rate. Therefore, it is recommended the concept of the rate-dependent model for the prediction of soil behaviors using the field penetration test.

• Journal of the Korean Geotechnical Society
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• v.19 no.3
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• pp.15-22
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• 2003

The appropriate description of the stress-anisotropy and time-dependent behavior of cohesive soils is very important in representing the real soil behavior. In this study, two constitutive relations have been incorporated based on the generalized viscous theory: one is the plastic constitutive relation adopted to capture the stress-anisotropy with a few model parameters; the other is the rate-dependent constitutive relation adopted to describe the strain rate-dependent behavior, an important time-dependent behavior in cohesive soils. The incorporated and proposed constitutive model has relatively a few model parameters and their values need not to be re-evaluated at different strain rates. The proposed model has been verified and investigated with the anisotropic triaxial test results obtained by using the artificial homogeneous specimens.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.4
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• pp.431-438
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• 2012

The mechanical behavior of the polymeric material, HDPE depends on both time and temperature. The study of the tensile behavior at different strain rates is important in engineering design of the orthopedics device such as X-band plate. The mechanical properties and deformation mechanisms of HDPE are strongly dependent on the applied strain rate. Generally, the deformation behavior of HDPE based on the stress-strain curve is complex because of the highly inhomogeneous nature of plastic deformation, particularly that of necking. Therefore, we attempted to determine the mechanical behavior of HDPE in this study. Normally, tensile testing under various strain rates of the HDPE has been used to determine the mechanical behavior. We performed tensile tests at various strain rates (1 to 500 %/min) to analyze the viscoelastic behavior on increasing the strain rate. A tensile stress-strain curve was plotted from the data, and the point of transition was marked to calculate the transition stress, strain, and modulus.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.2
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• pp.129-134
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• 2010

The influence of the strain-rate on the thermomechanical characteristics of shape memory alloys (SMAs) is numerically investigated. The three-dimensional SMA constitutive equations of strain-rate effect is developed. The strain-rate effect is taken into account by introducing a coupling equation between the production rate of martensite and the temperature change. For the numerical results, the SMA algorithm is implemented into the ABAQUS finite element program. Numerical simulation shows that the pseudoelasticity of SMA may significantly be changed by considering the strain-rate due to the temperature change.

• Journal of the Korean Geotechnical Society
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• v.21 no.6
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• pp.127-135
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• 2005

In order to analyze effects of strain rate on consolidation characteristics of Busan clay, a series of constant rate of strain (CRS) consolidation tests with different strain rate and incremental loading tests (ILT) were performed. From experimental test results on Busan clay, it was found that the preconsolidation pressure was dependent on the corresponding strain rate occurring during consolidation process. Also, consolidation curves normalized with respect to preconsolidation pressure gave a unique stress-strain curve. Coefficient of consolidation and permeability estimated from CRS test had a tendency to converge to a certain value at normally consolidated range regardless of strain rate. An increase in excess pore pressure was observed after the end of loading without change of total stress on the incremental loading test, which phenomenon is called Mandel-Cryer effect. It was also found that rapid generation of excess pore pressure took place due to collapse of soil structure as effective stress approached to preconsolidation pressure.

• Composites Research
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• v.35 no.1
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• pp.38-41
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• 2022

In this study, the strain rate dependent tensile and compressive properties of PP-LGF and TPO was investigated under the high strain rate by using the Split Hopkinson Pressure Bar (SHPB). The SHPB is the most widely used apparatus to characterize dynamic mechanical behavior of materials at high strain rates between 100 s^-1 and 10,000 s^-1. The SHPB test is based on the wave propagation theory which was developed to give the stress, strain and strain rate in the specimen using the strains measured in the incident and transmission bars. In addition, to verify the strain data obtained from SHPB, the specimen was photographed with a high-speed camera and compared with the strain data obtained through the Digital Image Correlation (DIC).