• Journal of the Korean Society for Heat Treatment
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• v.31 no.4
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• pp.180-186
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• 2018

High temperature flow behaviors of Fe-Cr-Mo-V-W-C tool steel were investigated using isothermal compression tests on a Gleeble simulator. The compressive test temperature was varied from 850 to $1,150^{\circ}C$ with the strain rate ranges of 0.05 and $10s^{-1}$. The maximum height reduction was 45%. The dynamic softening related to the dynamic recrystallization was observed during hot deformation. The constitutive model based on Arrhenius-typed equation with the Zener-Hollomon parameter was proposed to simulate the hot deformation behavior of Fe-Cr-Mo-V-W-C steel. An artificial neural network (ANN) model was also developed to compare with the constitutive model. It was concluded that the ANN model showed more accurate prediction compared with the constitutive model for describing the hot compressive behavior of Fe-Cr-Mo-V-W-C steel.

• Geomechanics and Engineering
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• v.11 no.5
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• pp.657-670
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• 2016

The energy dissipation of coal under dynamic loads is a major issue in geomechanics and arising extensive concerns recently. In this study, dynamic loading tests of coal were conducted using a split Hopkinson pressure bar (SHPB) system, the characteristics of dynamic behavior and energy dissipation of coal were analyzed, and the mechanism of energy dissipation was discussed based on the fracture processes of coal under dynamic loads. Experimental results indicate that the energy dissipation of coal under dynamic loads has a positive linear correlation with both incident energy and dynamic compressive strength, and the correlation coefficients between incident energy, dynamic compressive strength and the energy dissipation rate are 0.74 and 0.98, respectively. Theoretical analysis demonstrates that higher level of stress leads to greater energy released during unstable crack propagation, thus resulting in larger energy dissipation rate of coal under dynamic loads. At last, a semi-empirical energy dissipation model is proposed for describing the positive relationship between dissipated energy and stress.

• Journal of Korea Foundry Society
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• v.22 no.1
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• pp.11-16
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• 2002

Hot deformation behavior of GCD-50 cast iron has been investigated by employing the compressive test. Phenomenological deformation behaviors, which were modeled based on the dynamic materials model and the kinetic model, have been correlated with the microstructural change taken place during compression. Microstructural investigation revealed that the adiabatic shear band caused by the locallized deformation was taken place in low temperature and high strain rate. On the other hand, the wavy and curved grain boundaries, which repersent the occurrence of dynamic microstructure change such as dynamic recovery and dynamic recrystallization, were observed in high temperature and low strain rate. Deformation model based on hyperbolic sine law has also been suggested.

• Computers and Concrete
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• v.22 no.3
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• pp.291-303
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• 2018

As the concept of "sponge city" is proposed, the pervious concrete for permeable pavement has been widely used in pavement construction. This paper aims at investigating the dynamic behavior and energy evolution of pervious concrete under impact loading. The dynamic compression and split tests are performed on pervious concrete by using split Hopkinson pressure bar equipment. The failure criterion on the basis of incubation time concept is used to analyze the dynamic failure. It is demonstrated that the pervious concrete is of a strain rate sensitive material. Under high strain rate loading, the dynamic strength increases while the time to failure approximately decreases linearly as the strain rate increases. The predicted dynamic compressive and split tensile strengths based on the failure criterion are in accordance with the experimental results. The total damage energy is found to increase with the increasing of strain rate, which means that more energy is needed to produce irreversible damage as loading rate increases. The fractal dimensions are observed increases with the increasing of impact loading rate.

• Structural Engineering and Mechanics
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• v.83 no.5
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• pp.609-615
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• 2022

A numerical approach for dynamic stability analysis of sandwich plates has been provided using Chebyshev-Ritz-Bolotin approach. The sandwich plate with porous core has been formulated according to a higher-order plate. All of material properties are assumed to be dependent of porosity factor which determines the amount or volume of pores. The sandwich plate has also been assumed to be under periodic in-plane loading of compressive type. It will be shown that stability boundaries of the sandwich plate are dependent on static and dynamical load factors, porosity factor, porosity variation and core thickness.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.5
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• pp.437-445
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• 2016

Recently, polyurethane foam has been used in various industry fields to preserve temperature environment of structures, and a wide range of loads from the static to the dynamic are imposed on the material during a life period. The biggest characteristic of polyurethane foam is porosity as being polymeric material, and it is generally known that insulation performance of the material strongly depends on internal void size. In addition, polyurethane foam's mechanical behavior has high dependence on strain rate and temperature as well as being highly non-linear ductile for compression. In the non-linear compressive behavior, volume fraction of voids and elastic modulus decrease as strain increases. Therefore, in this study, temperature-dependent viscoplastic-damage constitutive model was developed to describe the non-linear compressive behavior with the aforementioned features of polyurethane foam.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.4
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• pp.87-96
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• 2004

As a special concrete, which is a mixture of soil, cement and water, has strength like regular concrete for pavement, soil cement has been used in various field such as pavement and soft soil improvement. The objective of this study was to investigate the characteristic of unconfined compressive strength and time dependent behavior of soil cement that is made from decomposed granite soil or coluvial and inorganic solidification liquid. The results showed that the unconfined compressive strength appears to increase as the amount of cement and curing time increase In addition, the strength seems to decrease with increase of the potion of fine particles(No 200 sieve). The result of XRD indicated that there is Vermiculite, the product of reaction, in the soil cement. The dynamic properties of material, such as shear complex compliance, shear complex modulus, and phase angle could be calculated from the hysteresis loop obtained from the Haversine Creep Tests. Finally, creep behavior was able to be predicted from these dynamic properties.

• Journal of the Korea institute for structural maintenance and inspection
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• v.4 no.3
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• pp.137-144
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• 2000

Judging from the occasional occurrences of minor and major earthquakes in Korean peninsula, it is generally considered that Korean peninsula is not located in safe zone from earthquake any more. The worldwide damages from earthquake in public buildings such as bridges are also urging the necessity for an appropriate earthquake proof action. The elastomeric bearings have been used in seismic isolation design of bridges. and elastomeric bearings are quite ideal ones which allow movement and rotation in all directions without restraining superstruture. Within the limits of this study on dynamic behavior of the LBR for seismic isolation design, the reaearch results revealed that the Laminated Rubber Bearing(LRB) is useful in bridges for seismic isolation design. In addition, the relationship between the shape factor and compressive strength is linear. It was also found that the compressive strength gets higher as the shape factor increases.

• Journal of The Korean Society of Agricultural Engineers
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• v.46 no.1
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• pp.61-71
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• 2004

The performance evaluation and deflection of 3 spans concrete simplicity slab bridge analyzed by non-destructive and loading test. Compressive strength of slab and pier appeared in the range of each 353∼366 kgf/$cm^2$ and 152∼215 kgf/$cm^2$ in rebound number test. Also, it appeared that concrete quality of slab was good after performance improvement. The average compressive strength of slab by core picking appeared 229 kg/$cm^2$. In reinforcing bar arrangement test of span and member, it appeared that horizontal and vertical reinforcing bar was arranged to fixed interval. The value of calculation deflection that carried structural analysis with deflection analysis wave in static loading test appeared higher than that of experimental deflection and it appeared that hardness of this bridge was good. Maximum impact factor that estimated from deflection by running speed in dynamic loading test appeared by 0.216 in 10 km/hr running speed.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.4
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• pp.64-69
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• 2018

This paper investigates the compressive deformation behavior of direct metal tooling (DMT), processing titanium alloy (Ti-6Al-4V) parts under high strain loading conditions. Split Hopkinson Pressure Bar (SHPB) experiments were performed to determine the flow stress and the coefficients of the Johnson-Cook model. This model is described as a function of strain, strain rate, and temperature. SHPB experiments were performed to characterize the deformation behavior of specimens made with 3D printers, using Ti-6Al-4V material under high temperature and dynamic loading.