• Geomechanics and Engineering
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• v.16 no.3
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• pp.273-284
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• 2018

A detailed understanding of the mechanical behaviors for crushed coal rocks after grouting is a key for construction in the broken zones of mining engineering. In this research, experiments of grouting into the crushed coal rock using independently developed test equipment for solving the problem of sampling of crushed coal rocks have been carried out. The application of uniaxial compression was used to approximately simulate the ground stress in real engineering. In combination with the analysis of crack evolution and failure modes for the grouted specimens, the influences of different crushed degrees of coal rock (CDCR) and solidified grout strength (SGS) on the mechanical behavior of grouted specimens under uniaxial compression were investigated. The research demonstrated that first, the UCS of grouted specimens decreased with the decrease in the CDCR at constant SGS (except for the SGS of 12.3 MPa). However, the UCS of grouted specimens for constant CDCR increased when the SGS increased; optimum solidification strengths for grouts between 19.3 and 23.0 MPa were obtained. The elastic moduli of the grouted specimens with different CDCR generally increased with increasing SGS, and the peak axial strain showed a slightly nonlinear decrease with increasing SGS. The supporting effect of the skeleton structure produced by the solidified grouts was increasingly obvious with increasing CDCR and SGS. The possible evolution of internal cracks for the grouted specimens was classified into three stages: (1) cracks initiating along the interfaces between the coal blocks and solidified grouts; (2) cracks initiating and propagating in coal blocks; and (3) cracks continually propagating successively in the interfaces, the coal blocks, and the solidified grouts near the coal blocks. Finally, after the propagation and coalescence of internal cracks through the entire specimens, there were two main failure modes for the failed grouted specimens. These modes included the inclined shear failure occurring in the more crushed coal rock and the splitting failure occurring in the less crushed coal rock. Both modes were different from the single failure mode along the fissure for the fractured coal rock after grouting solidification. However, compared to the brittle failure of intact coal rock, grouting into the different crushed degree coal rocks resulted in ductile deformation after the peak strength for the grouted specimens was attained.

• Steel and Composite Structures
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• v.46 no.1
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• pp.53-73
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• 2023

Man-made structure materials like concrete usually contain inclusions. These inclusions affect the mechanical properties of concrete. In this investigation, the influence of inclusion length and inclination angle on three-dimensional failure mechanism of concrete under uniaxial compression were performed using experimental test and numerical simulation. Approach of acoustic emission were jointly used to analyze the damage and fracture process. Besides, by combining the stress-strain behavior, quantitative determination of the thresholds of crack stress were done. concrete specimens with dimensions of 120 mm × 150 mm × 100 mm were provided. One and two holes filled by gypsum are incorporated in concrete samples. To build the inclusion, firstly cylinder steel tube was pre-inserting into the concrete and removing them after the initial hardening of the specimen. Secondly, the gypsum was poured into the holes. Tensile strengths of concrete and gypsum were 2.45 MPa and 1.5 MPa, respectively. The angle bertween inclusions and axial loadind ary from 0 to 90 with increases of 30. The length of inclusion vary from 25 mm to 100 mm with increases of 25 mm. Diameter of the hole was 20 mm. Entirely 20 various models were examined under uniaxial test. Simultaneous with experimental tests, numerical simulation (Particle flow code in two dimension) were carried out on the numerical models containing the inclusions. The numerical model were calibrated firstly by experimental outputs and then failure behavior of models containing inclusions have been investigated. The angle bertween inclusions and axial loadind vary from 0 to 90 with increases of 15. The length of inclusion vary from 25 mm to 100 mm with increases of 25 mm. Entirely 32 various models were examined under uniaxial test. Loading rate was 0.05 mm/sec. The results indicated that when inclusion has occupied 100% of sample thickness, two tensile cracks originated from boundaries of sample and spread parallel to the loading direction until being integrated together. When inclusion has occupied 75% of sample thickness, four tensile cracks originated from boundaries of sample and spread parallel to the loading direction until being integrated together. When inclusions have occupied 50% and 25% of sample thickness, four tensile cracks originated from boundaries of sample and spread parallel to the loading direction until being integrated together. Also the inclusion was failed by one tensile crack. The compressive strength of samples decease with the decreases of the inclusions length, and inclusion angle had some effects on that. Failure of concrete is mostly due to the tensile crack. The behavior of crack, was affected by the inclusion length and inclusion number.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.4
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• pp.353-362
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• 2016

An accurate hysteresis model of an elastomer is important for quantifying viscoelastic energy loss. We suggest a highly nonlinear hyper-viscoelastic constitutive model of elastomers. The model captures a nonlinear viscoelastic characteristic by combining Yeoh's hyperelastic model and Hoofatt's hysteresis model used Neo-Hookean hyperelastic model. Analytical and numerical models were generated from uniaxial cyclic tests of an elastomer under a sinusoidal load with a mean strain of 150%, amplitudes of 20~80%, and frequencies of 0.02~0.2Hz. The viscoelastic model can highly capture the viscoelastic energy loss up to a strain of 230%.

• 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.

• Magazine of the Korea Concrete Institute
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• v.5 no.2
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• pp.181-188
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• 1993

In this study, a numerical method for the material nonlinear analysis of reinforced concrete shell structures including the time dependent effects due to creep and shrinkage is developed. Degenerate shell elements with the layered approach are used. The perfect or strain hardening plasticity model in compression and the linearly elastic model in tension until cracking for concrete are employed. The reinforcing bars are considered as a steel layer of equivalent thickness. Each :steel layer has an uniaxial behaviour resisting only the axial force in the bar direction. A bilinear idealization is adopted to model elasto-plastic stress-strain relationships. For the nonlinear anaysis, incremental load method combined with unbalanced load iterations for each load increment is used. To include time dependent effects of concrete, time domain is divided into several time steps which may have different length. Some numerical examples are presented to study the validity and applicability of the present method. The results are compared with experimental and numerical results obtained by other investigator.

• Journal of Korean Society of Steel Construction
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• v.9 no.2 s.31
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• pp.193-204
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• 1997

In order to quantify the relationships of the important physical factors relating failure to strong earthquake loading, the plastic fatigue problems for structural components under repeated loading were reviewed first. A new concept of very low cycle fatigue failure for structural components under severe cyclic excitations as in strong earthquakes was represented. Also, an experimental study was made of the very low cycle fatigue failure of structural steel elements. It was attempted to realize the ultimate failure in the course of loading repetitions of the order of several to twenty. The test specimen had a form of rectangular plate, representing a thin-plated element in a steel member as wide-flange cross section. It was subjected to uniaxial loading repeatedly, until complete failure takes place after undergoing inelastic buckling, plastic elongation and/or their combination. It was seen as a result that the state of the ultimate failure is closely related to the maximum strain at the extreme fiber in the cross section.

• Journal of Biomedical Engineering Research
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• v.25 no.4
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• pp.309-314
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• 2004

in this study, hybrid bioreactor was used to apply physical stimuli in cell culture. Effect of the applied physical stimuli on the growth and differentiation of MC3T3-El cell in a three-dimensional Chitosan scaffold were studied by using the hybrid bioreactor. The hybrid bioreactor for physical stimulus was specially designed to apply uniaxial cyclic compressive and shear strain. Physical stimulus was applied over a period of 14 days with 150 cycles per day at a frequency of 0.5Hz. Strain magnitude was 2.5% of the scaffold size. Control group and physically stimulated group of the MC3T3-El tell were incubated and harvested at the indicated times (Day 6, 8, 10, 12, 14). The total amount of protein, which obtained information of cell growth, was determined by Lowey method. Alkaline phosphatase activity was examined by ELISA. Physically stimulated group using the hybrid bioreactor was increased in alkaline phosphatase activity comparing with control group. The nodule formation and calcium deposit of the physical stimuli group which resulted in cell differentiation was faster than that of control group.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.905-909
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• 2001

The significance of casting/forging process for reducing the production cost of large components is being noted in these days. This casting/forging process is a method of forging a workpiece preformed by casting into the final shape. In this study, the casting/forging process has been applied in manufacturing a large aluminum flange in order to determine the optimum forging condition of the aluminum flange. The optimum range of forging temperature of Al 5083 was from $420^{\circ}C$ to $450^{\circ}C$. The suitable strain rate was 1.5 $sec^{-1}$. The deformation amount of a preform in a forging process is key role in the mechanical properties of casting/forging products. In order to find the change of mechanical properties according to effective stain of cast aluminum billets, a hot upsetting test were performed with rectangular blocks and then a uniaxial tensile test was performed with specimens cut from the upsetted billets. The tensile strength and the elongation of cast/upsetted aluminum billets were increased largely until the effective strain was 0.7. FE analysis was performed to determine the configurations of cast preform and die for an aluminum flange. In the FE analysis, the forging load-limit was fixed 1500ton for the low equipment cost. The cast preform was designed so that the effective stain around the neck of a flange exceeds 0.7. In the forging experiment for an aluminum flange, it was confirmed that the optimal configuration of the cast preform predicted by FE analysis was very useful. The cast/forged products using designed preform were made perfectly without any defects.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.5
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• pp.530-537
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• 2008

Austenitic stainless steels(SUS 304, SUS 316), which are used for safety control valve of LNG carrier, are occasionally exposed in the cryogenic environment. In this regards, it is required to evaluate the mechanical characteristics under the low temperature environment. In this study, a series of uniaxial tensile test was carried out varying temperature for austenitic stainless steel. The phenomena of the strain-induced plasticity have been observed on the all temperature ranges. The critical value for threshold of 2nd hardening due to the phase transformation induced plasticity as well as the increase of hardening have been reported. The summarized experimental results would be used for the validation of numerical techniques applicable for the nonlinear hardening behavior of austenitic stainless steel under the cryogenic temperature environment.

• Advances in concrete construction
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• v.8 no.4
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• pp.285-294
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• 2019

In the present paper, the fiber theory has been employed to model the reinforced concrete (RC) deep beams (DBs) considering the reinforcing steel bar-concrete interaction. To simulate numerically the behavior of materials, the uniaxial materials' constitutive laws have been employed for reinforcements and concrete and the bond stress-slip between the reinforcing steel bars and surrounding concrete are taken into account. Because of the high sensitivity of DBs to shear deformations, the Timoshenko beam theory has been applied. The shear stress-strain (S-SS) relationship has been defined by the modified compression field theory (MCFT) model. By modeling about 300 RC panels and employing a produced numerical database, a study has been carried out to show the sensitivity of the MCFT model. This is performed based on the multiple linear regression (MLR) models. The results of this research also illustrate how different parameters such as characteristic compressive strength of concrete, yield strength of reinforcements and the percentages of reinforcements in different directions get involved in the shear behavior of RC panels without applying complex theories. Based on the results obtained from the analysis of the MCFT S-SS model, a relatively simplified numerical S-SS model has been proposed. Application of the proposed S-SS model in modeling and analyzing the considered samples indicates that there is a good agreement between the simulated and the experimental test results. The comparison between the proposed S-SS model and the MCFT model indicates that in addition to the advantage of better accuracy, the main advantage of the proposed method is simplicity in application.