• Journal of the Korean Society of Safety
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• v.5 no.2
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• pp.58-65
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• 1990

The purpose of this study is to consider the effects of strain rate on the stress-strain behavior of sheet metal at instability. The results and conclusions obtained as follows ： 1. As the strain rate increases, the fracture pressure increases and the polar height at fracture decreases. 2. The effect of strain rate on forming limit diagram produces a general lowering of the diagram with increasing strain rate but changes according to materials and strain paths. 3. The forming limit diagram predicted by swift instability theory is comparatively inconsistent with the experimental result at high strain rates, because there is inevitable gap between them.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2002.05a
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• pp.154-158
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• 2002

The mechanical properties of Al 6061 excluded bar were deformed in high temperature with the variable deformation conditions and characterized by the tensile test. Three types of different strain rate were experimentally performed by using hydraulic press, crank press and hammer and two types of the nominal strain 0.5 and 0.8 were achieved. To decide optimum forging process, the relationship among the strain rate, strain and mechanical properties was explained by analyzing the microstructures of the forged and heat heated parts. The strength was deeply related with the strain rate due to the dynamic recrystallization (DRX) in hot forging, and the best forging condition was presented in Al 6061 alloy.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.1
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• pp.48-53
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• 2006

A methodology is described for predicting the fatigue life of the resistance spot weldment including strain rate effect. Because it is difficult to perform a physical failure test with high strain rate, an analytical method is necessary to get the mechanical properties of various strain rate, To this end, quasi-static tensile-shear tests at several strain rate were performed on spot weldments of SPC. These test provided the empirical data with the strain rate. With these results, we formulated the function of fatigue life prediction using the lethargy coefficient which is the global material property from tensile test. And, we predicted the fatigue life of spot weldment at dynamic strain rate. To confirm this method for fatigue life prediction, analytical results were compared with the experimental fatigue data.

• Journal of Aquaculture
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• v.9 no.3
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• pp.195-203
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• 1996

Six strains (OKK, MOK, CHA, WON, 505 & PUA) of Korean rotifer, Brachionus plicatilis (S-type) were isolated from salt pond, and the resting egg production of these strains was investigated with the different salinities (10, 20, 30 put), Rotifer were cultured at $28^{\circ}C$ and 2,000 lux in 20 ml test tube with feeding Nannoohloris oculata. The maximum rotifer density was 2,050 inds./ml at 10 ppt for OKK strain, and MOK strain showed the highest specific growth rate (1.028) at 10 ppt. Mixis rate of CHA and WON strains increased with the lower salinity, while MOK strain increased the rate with salinity. PUA strain did not show the mixis rate even at the high rotifer density, and OKK strain showed the very low mixis rate ranging from 1.1 to $3.0\%$. Fertilization rate of CHA, MOK, SOS and WON strains was ranged from 10.4 to $68.8\%$, and OKK strain did not showed any fertilization rate. The highest production of resting egg in 20 ml test tube was 4,065 eggs at 10 ppt for WON strain. The results may suggest that the selection of rotifer strain and salinity are important factors for the mass production of resting egg.

• Structural Engineering and Mechanics
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• v.58 no.4
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• pp.719-729
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• 2016

The main objective of the present paper is to study the effect of the yield criterion on the magnitude of the strain rate and plastic work rate intensity factors in axisymmetric flow of isotropic incompressible rigid perfectly plastic material by means of a problem permitting a closed-form solution. The boundary value problem consisting of the axisymmetric deformation of a plastic tube is solved. The outer surface of the tube contracts. The radius of the inner surface does not change. The material of the tube obeys quite a general yield criterion and its associated flow rule. The maximum friction law is assumed at the inner surface of the tube. Therefore, the velocity field is singular near this surface. In particular, the strain rate and plastic work rate intensity factors are derived from the solution. It is shown that the strain rate intensity factor does not depend on the yield criterion but the plastic work rate intensity factor does.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.5
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• pp.206-214
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• 1996

Because of the wide variety of the composite materials, inherent variability in properties, and complex temperature and strain rate dependence, large strain behavior of these materials has not been well characterized. Large strain behavior under uniaxial tension is characterized over a range of temperatures and strain rates, and a modified simple linear viscoelastic model is fit to the observed data. Of particular importance is the strain rate and temperature dependence of these composites, and it is the primary focus of this study. The strain rate and temperature dependence is then used to predict limiting tensile strains, based on Marciniak imperfection theory. Excellent correlation was obtained between model and experiment and the results are summarized in maps of forming limit as a function of strain rate and temperature.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.275-278
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• 2005

INCONEL 718, nickel based superalloy, has good formability, high strength, excellent corrosion resistance and mechanical properties at high temperature. Owing to theses attractive properties, it finds use in applications such as combustion system, turbine engines and nuclear reactors. In such applications, components are typically required to be tolerant of high stress impact loading. This may cause material degradation and lead to catastrophic failure during service operation. In order to design optimal structural parts made of INCONEL 718, accurate understanding of material's mechanical properties, dynamic behavior and fracture characteristic as a function of strain rates are required. This paper concerned with the dynamic material properties of the INCONEL 718 for the various strain rates. The dynamic response of the INCONEL 718 at intermediate strain rate is obtained from the high speed tensile test machine test and at the high strain rate is from the split Hopkinson pressure bar test. Based on the experimental results, the effects of strain rate on dynamic flow stress, work hardening characteristics, strain rate sensitivity and elongation to the failure are evaluated. Experimental results from both quasi-static and high strain rate up to the 5000/sec are interpolated in order to construct the Johnson-Cook model as the constitutive relation that should be applied to simulate and design the structural parts made of INCONEL 718.

• Transactions of Materials Processing
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• v.14 no.6 s.78
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• pp.559-564
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• 2005

INCONEL 718, nickel based superalloy, has good formability, high strength, excellent corrosion resistance and mechanical properties at high temperature. Owing to theses attractive properties, it is utilized in applications such as combustion system, turbine engines and nuclear reactors. In such applications, components are typically required to be tolerant of high stress impact loading. This may cause material degradation and lead to catastrophic failure during service operation. Accurate understanding of material's mechanical properties with various strain rates is required in order to guarantee the reliability of structural parts made of INCONEL 718. This paper is concerned with the dynamic material properties of the INCONEL 718 at various strain rates. The dynamic response of the INCONEL 718 at the intermediate strain rate is obtained from the high speed tensile test and at the high strain rate is from the split Hopkinson pressure bar test. The effect of the strain rate on dynamic flow stress, work hardening characteristics, strain rate sensitivity and elongation to the failure is evaluated with the experimental results. Experimental results from both the quasi-static and the high strain rate up to 5000/sec are interpolated in order to construct the Johnson-Cook model as the constitutive relation that should be applied to simulate and design the structural parts made of rNCONEL 718.

• 한국연소학회:학술대회논문집
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• 2006.10a
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• pp.65-72
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• 2006

Experiments in methane-air low strain rate counterflow diffusion flames diluted with nitrogen have been conducted to study the behavior of flame extinction and edge flame oscillation in which flame length is less than the burner diameter and thus lateral conduction heat loss in addition to radiative heat loss could be remarkable at low global strain rates. Critical mole fraction at flame extinction is examined with velocity ratio and global strain rate. Onset conditions of edge flame oscillation and flame oscillation modes are also provided with global strain rate and added nitrogen mole fraction to fuel stream (fuel Lewis number). It is seen that flame length is closely relevant to lateral heat loss, and this affects flame extinction and edge flame oscillation considerably. Edge flame oscillations in low strain rate flames are experimentally described well and are categorized into three: a growing oscillation mode, a decaying oscillation mode, and a harmonic oscillation mode. The regime of flame oscillation is also provided at low strain rate flames. Important contribution of lateral heat loss even to edge flame oscillation is clarified.

• Steel and Composite Structures
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• v.36 no.6
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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.