• Proceedings of the Korean Geotechical Society Conference
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• 2000.02a
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• pp.32-41
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• 2000

Sand drain as a vertical drainage is widely used in soft ground improvement Recently, sand, the principal source of sand drain, is running out. The laboratory model tests were carried out to utilize gravel as a substitute for sand. Though which the characteristics of gravel are compared to those of sand for engineering purpose. Two cylindrical containers for the model test were filled with marine clayey soil from the west coast of Korea with a column in the center, one with sand, the other with gravel. Vibrating wire type piezometers were installed at the distance of 1.0D, 1.5D and 2.0D from the center of the column. The characteristics of consolidation were studied with data obtained from the measuring instrument place on the surface of the container. The parameter study was performed on the marine clayey soil before and after the test in order to verify the effectiveness of the improvement. The clogging effect was checked at various depth in gravel column after the test. In-situ tests area was divided into two areas by material used. One is Sand Drain(SD) and Sand Compaction Pile(SCP) area, the other is Gravel Drain(GD) and Gravel Compaction Pile(GCP) area. Both areas were monitored to obtain the information on settlement, pore water pressure and bearing capacity by measuring instruments for stage loading caused by embankment. The results of measurements were analyzed. According to the test results, the settlement was found to be smaller in gravel drain than in sand drain. The increase in bearing capacity by gravel pile explains the result. The clogging effect was not found in gravel column. It is assumed that gravel is relatively acceptable as a drainage material. Gravel is considered to be a better material than sand for bearing capacity, and it is found that bearing capacity is larger when gravel is used as a gravel compaction pile than as a gravel drain.

• Computers and Concrete
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• v.2 no.3
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• pp.203-214
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• 2005

In the Part 1 paper (Gawin, et al. 2005) some experimental results concerning micro-structural tests, permeability measurements and stress-strain tests of four types of High Performance Concrete, exposed to elevated temperatures (up to $700^{\circ}C$) are presented and discussed. On the basis of these experimental results parameters of the constitutive relationships describing influence of damage and temperature upon material intrinsic permeability at high temperature were determined. In this paper the effects of various formulations of damage-permeability coupling on results of computer simulations are analysed and compared with the results obtained by means of the previously proposed approach, that does not take into account the thermo-chemical concrete damage directly. Numerical solutions are obtained using the recently developed fully coupled model of hygro-thermal and damage phenomena in concrete at elevated temperatures. High temperature effects are considered by means of temperature and pressure dependence of several material parameters. Based on the mathematical model, the computer code HITECOSP was developed. Material parameters of the model were measured by several European laboratories, which participated in the "HITECO" research project. A model problem, concerning hygro-thermal behaviour and degradation of a HPC structure during fire, is solved. The influence of two different constitutive descriptions of the concrete permeability changes at high temperature, including thermo-chemical and mechanical damage effects, upon the results of computer simulations is analysed and discussed.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.6
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• pp.104-112
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• 2014

Generally, numerical approaches of evaluation for vehicle seat comfort have been studied without considering time-dependent characteristics and the only seating moment have been considered in seat design. However, the comfort not only at the seating moment but also in the long-term should be evaluated because the passengers are sitting repeatedly on the seat to drive the vehicle for hours. So, the aim of this paper is to carry out a quantitative evaluation of the time-dependent mechanical characteristics of seat foams and to suggest a process for predicting the viscoelastic deformation of seat foam in response to long-term driving. To characterize the seat materials, uniaxial compression and tension tests were carried out for the seat foam and stress relaxation tests were performed for evaluating the viscoelastic behavior of the seat foam. A unit solid element model was used to verify the reliability of the material model with respect to the compression behavior of the seat foam. It is not straightforward to evaluate the time-dependent compression of foams using the explicit solver because the viscoelastic material model is limited. To use the explicit solver, the material model must be modified using stress-degradation data. Normalized stress relaxation moduli were added to the stress-strain curves obtained under static conditions to achieve a time-dependent set of stress-strain relations that were compatible with the implicit solver. There was good agreement between the analysis results and experimental data.

• Geotechnical Engineering
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• v.13 no.3
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• pp.63-76
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• 1997

To investigate the engineering characteristics of crushed rockfill material, the large-scaled triaxial tests have been carried out, The rpckfill is made from the greywacke, and the 3 parallel gradations with different maximum particle size(dmu=38.1mm, 25.4mm and 19.1mm) were designed for the test. The dimension of the specimen is 300mm in diameter and 600mm in height, and the applied confining stress varied from 5t/$51.6^{\circ}$ to 60t/$51.6^{\circ}$. The test results show that the influence of the maximum particle size on the stress -strain r$51.6^{\circ}\; to\; 40.5^{\circ}$ when the confining stress increases from 5t/$51.6^{\circ}$ to 60t/$51.6^{\circ}$ The hyperbolic parameter values estimated from the test result for rockfill are much different from the recommended values by Duncan et. at(1980) for GW and GP material, especially in the $\phi$ ad K-values.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.1
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• pp.94-101
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• 2003

The pressure tubes made of cold-worked Zr-2.5Nb alloy are subjected to creep deformation during service period resulting in changes to their geometry such as longitudinal elongation, diameter increase and sagging. To evaluate integrity of them, information on the material creep property of the serviced tubes is essential. As one of the methods with which the creep property is directly measured from the serviced components, small punch(SP) creep testing has been considered as a substitute for the conventional uniaxial creep testing. In this study, applicability of the SP creep testing to Zr-2.5Nb pressure tube alloy was studied particularly by measuring the power law creep constants, A, n. The SP creep test has been successfully applied fur other high temperature materials which have isotropic behavior. Since the Zr-2.5Nb alloy has anisotropic property, applicability of the SP creep testing can be limited. Uniaxial creep tests and small punch creep tests were conducted with Zr-2.5Nb pressure tube alloy along with finite element analyses. Creep constants obtained by each test method are compared. It was argued that the SP creep test result gave results reflecting material properties of both directions. But the equations derived in the previous study for isotropic materials need to be modified. Discussions were made fur future research directions for application of the SP creep testing to Zr-2.5Nb tube alloy.

• Journal of Korea Foundry Society
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• v.35 no.4
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• pp.80-87
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• 2015

The Al die casting process has been widely used in the manufacturing of automotive parts when the process requires near-net shape casting and a high productive rate. However, porosity arises in the casting process, and this hampers the wider use of this method for the creation of high-durability automotive components. The porosity can be controlled by the shot condition, but, it is critical to set the shot condition in the sleeve, and it remains difficult to optimize the shot condition to avoid air entrapment efficiently. In this study, the 4.5 mm, 2.0 mm plate die castings were fabricated under various shot conditions, such as plunger velocities of 0.7 m/s ~ 3.0 m/s and fast shot set points of the cavity of -25%, 0%, 25%, and 50%. The mold filling behavior of Al melts in the cavity was analyzed by a numerical method. Also, according to the shot conditions, the results of numerical analyses were compared to those of die-casting experiments. The porosity levels of the plate castings were analyzed by X-ray CT images and by density and microstructural analyses. The effects of the porosity on the mechanical properties were analyzed by tensile tests and hardness tests. The simulation results are in good general agreements with the die-casting experimental results. When plunger velocity and fast shot set point are 1.0 m/s and cavity 25% position, castings had optimum condition for good mechanical properties and a low level of porosity.

• Tribology and Lubricants
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• v.30 no.4
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• pp.234-239
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• 2014

Magneto-rheological elastomer (MR elastomer) is a smart material, because it has mechanical properties that change under a magnetic field. An MR elastomer changes its stiffness characteristics when the inner particles (iron particles) align along the direction of a magnetic field. There has been much research to make use of this characteristic to control vibration issues in various mechanical systems, such as for mounting systems in the automotive field, home appliances, etc. Furthermore, the friction and wear properties of MR elastomer have been studied, as these relate to the durability of the material needed to meet engineering requirements. Rolling friction (or rolling resistance) is one of these friction properties, but has not yet been studied in the context of MR elastomers. In this study, an MR elastomer is fabricated in the shape of a hollow cylinder to evaluate the rolling friction characteristic under a magnetic field. The test apparatus is setup and a strain gauge is used to calculate the rolling resistance under test conditions. Permanent magnets are used to supply the magnetic field during tests. The load and rolling speed conditions are also considered for the tests. The test results show that rolling friction characteristic has a different trend under different magnetic field, load, and rolling speed conditions. It is assumed that the stiffness change of an MR elastomer under a magnetic field has an effect on the rolling friction characteristic of the MR elastomer. For the future work, the rolling friction characteristics of MR elastomers will be controlled by adjusting the strength of the magnetic field using electromagnets.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.15 no.4
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• pp.8-15
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• 2019

In order to design coaxial-type Ground Heat Exchangers (GHEXs) efficiently, the effect of components (i.e, heat exchange pipe and grouting material) on the thermal performance of coaxial-type GHEXs should be identified in advance. In this paper, three coaxial-type GHEXs with different configurations were constructed in a test bed. Then, the effect of heat exchange pipes and grouting materials on the thermal performance of coaxial-type GHEXs was investigated by performing in-situ thermal response tests (TRTs) and thermal performance tests (TPTs). In the TRTs, the effective thermal conductivities of the coaxial-type GHEXs with concrete grouting and STS pipes were improved by 6.15 and 22.7%, respectively compared to those of bentonite grouting and HDPE pipes. Additionally, in the TPTs, the use of concrete grouting and STS pipes in the coaxial-type GHEXs enhanced the in-situ thermal performance by 15 and 33.8%, respectively.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.2
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• pp.253-265
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• 1993

This paper presents a numerical method for implementing a nonlinear constitutive material model developed by Lade, into a finite element computer program. The techniques used are based on the displacement method for the solution of axial symmetric and plane strain nonlinear boundary value problems. Laboratory behaviour of Baekma river sand(#40-60) is used to illustrate the determination of the parameters and verification of the model. Computer procedure is developed to determine the material parameters for the nonlinear model from the raw laboratory test data. The model is verified by comparing its predictions with observed data used for the determination of the parameters and then with observed data not used for the determination. Three categories of tests are carried out in the back-prediction exercise; (1) A hydrostatic test including loading and unloading response, (2) Conventional triaxial drained compression tests at three different confining pressure and (3) A model strip footing test not including in the evaluation of material parameters. Pertinent observations are discussed based on the comparison of predicted response and experimental data.

• Geomechanics and Engineering
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• v.15 no.4
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• pp.1005-1016
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• 2018

This paper presents an investigation on the properties of two types of cement kiln dust (CKD)-stabilized dredged sediments, silt and clay with a comparison to hydrated lime stabilization. Unconfined compressive strength (UCS) and California bearing ratio (CBR) tests were conducted to examine the optimal stabilizer content and classify the type of highway material. A strength development model of treated dredged sediments was performed. The influences of various stabilizer types and sediment types on UCS were interpreted with the aid of microstructural observations, including X-ray diffraction and scanning electron microscopy analysis. The results of the tests revealed that 6% of lime by dry weight can be suggested as optimal content for the improvement of clay and silt as selected materials. For CKD-stabilized sediment as soil cement subbase material, the use of 8% CKD was suggested as optimal content for clay, whereas 6% CKD was recommended for silt; the overall CBR value agreed with the UCS test. The reaction products calcium silicate hydrate and ettringite are the controlling mechanisms for the mechanical performance of CKD-stabilized sediments, whereas calcium aluminate hydrate is the control for lime-stabilized sediments. These results will contribute to the use of CKD as a sustainable and novel stabilizer for lime in highway material applications.