• Geomechanics and Engineering
• /
• v.20 no.6
• /
• pp.517-525
• /
• 2020

The long-term stability of rock engineering is significantly affected by the time-dependent deformation behavior of rock, which is an important mechanical property of rock for engineering design. Although the hard rocks show small creep deformation, it cannot be ignored under high-stress condition during deep excavation. The inner mechanism of creep is complicated, therefore, it is necessary to investigate the relationship between microscopic creep mechanism and the macro creep behavior of rock. Microscopic numerical modeling of sandstone creep was performed in the investigation. A numerical sandstone sample was generated and Parallel Bond contact and Burger's contact model were assigned to the contacts between particles in DEM simulation. Sensitivity analysis of the microscopic creep parameters was conducted to explore how microscopic parameters affect the macroscopic creep deformation. The results show that the microscopic creep parameters have linear correlations with the corresponding macroscopic creep parameters, whereas the friction coefficient shows power function with peak strength and Young's modulus, respectively. Moreover, the microscopic parameters were calibrated. The creep modeling curve is in good agreement with the verification test result. Finally, the creep curves under one-step loading and multi-step loading were compared. This investigation can act as a helpful reference for modeling rock creep behavior from a microscopic mechanism perspective.

• Journal of the Korean Wood Science and Technology
• /
• v.33 no.5 s.133
• /
• pp.7-12
• /
• 2005

The objective of this study is to estimate the mechanical behavior in bending and the anatomical changes of wood under several deflection rates. Sample specimens of water-saturated Japanese cedar (Cryptomeria japonica) were stressed to rupture under several deflection rates. Mechanical properties of wood such as modulus of elasticity, modulus of rupture and stress at proportional limit, and anatomical changes affected by deflection rates were estimated. Microscopic observations on compression side of the test specimens when the specimen was loaded to rupture were carried out by the SEM (scanning electron microscopy). The results are summarized as follows: 1. The mechanical properties of wood were affected by variations of the deflection rates. The modulus of elasticity (MOE), modulus of rupture (MOR) and stress at proportional limit were in proportion to the logarithm of deflection rates. 2. The deflection of wood at rupture in bending increased as deflection rates decreased. 3. The variations of the microscopic deformations of sample specimens were closely related to the deflection of wood at rupture. In case of largely deflected wood by maximum bending load, severe and abundant microscopic deformations were observed.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1998.04b
• /
• pp.677-682
• /
• 1998

Concrete is an inhomogeneous material consisting of larger aggregates and sand embedded in a cement paste matrix. In this study, an acoustic emission technique has been used to clarify the microscope failure mechanisms of concrete under three point bending test. AE source location has also been done to monitor the activities of internal damage and the progress of microscopic failure path during the loading. The relationship between AE characteristic and microscopic and microscopic failure mechanism is discussed.

• Magazine of the Korea Concrete Institute
• /
• v.10 no.6
• /
• pp.203-211
• /
• 1998

It is well recognized recently that acoustic emission, which is an elastic wave generated from rapid release of elastic energy in steressed solids, is very useful tool for on-line monitoring of microscopic behavior of deformation of material. In this study, three point bend test was performed to evaluate the microscopic damage progress during the loading and failure mechanism of mortar beam by monitoring the characteristic of AE signal. The relationship between AE characteristic and microscopic failure mechanism is discussed. In addition 2 dimensional AE source location based on triangular method was also done to monitor the intiation and propagation of micro crack around notch tip of mortar beam. It was shown that AE source location was very effective to predict the growth behavior of micro crack in mortar beam specimen.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1996.03b
• /
• pp.55-61
• /
• 1996

Finite element calculations are performed for crystalline solids subjected to plane strain tensile loading. Using Asaro's double slop model, shearband developments in single crystals are analyzed. The effect of various rate sensitivities and latent hardening parameters on microscopic plastic behavior was clarified. Moreover the deformation behavior of polycystals which have grain boundaries was compared to that of single crystals.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.19 no.1
• /
• pp.25-33
• /
• 1999

Since concrete is an inhomogeneous material consisting of larger aggregates and sand embedded in a cement paste matrix, it relatively shows a complex failure mechanism. In order to assure the reliability of concrete structure. microscopic fracture behavior and internal damage progress of concrete under the loading should be fully understood. In this study, an acoustic emission(AE) technique has been used to clarify microscopic failure mechanism and their corresponding AE signal characteristics of concrete under three-point bending test. In addition 2-dimensional AE source location has been performed to monitor the progress of an internal damage and the successive crack growth behavior during the loading. The relationship between AE signal characteristics and microscopic fracture mechanism is discussed.

• Journal of the Korean Society of Safety
• /
• v.34 no.2
• /
• pp.7-14
• /
• 2019

A palladium can adsorb hydrogen and detect leaking hydrogen through changes in color and electrical resistance. This study is to evaluate the structural behavior of carbon fiber adding palladium composite materials used in the hydrogen storage vessel. A multi-scale analysis technique was used to analyze accurately the behavior of each material in relation to the microscopic composition. The multi-scale analysis is more proper and precise for composite materials because of considering the individual microscopic structure and properties of each material for composite materials. Also the crack evaluation was performed by XFEM analysis to confirm the reinforcement performance of aluminum as a liner of the hydrogen vessel. The results show that the addition of the palladium material increased the macroscopic stress, but microscopically the carbon fiber stress was reduced. It means the performance improvement of the palladium added carbon fiber/Al composite.

• Advances in materials Research
• /
• v.3 no.1
• /
• pp.283-295
• /
• 2014

In this paper, the microstructure, hardness, tensile deformation and fracture behavior of high strength alloy steel X2M is presented anddiscussed. The influence of both composition and processing on microstructure of the as-provided material and resultant influence of microstructure, as a function of orientation, on hardness, tensile properties and final fracture behavior is highlighted. The macroscopic mode and intrinsic microscopic features that result from fracture of the steel specimens machined from the two orientations, longitudinal and transverse is discussed. The intrinsic microscopic mechanisms governing quasi-static deformation and final fracture behavior of this high strength steel are outlined in light of the effects oftest specimen orientation, intrinsic microstructural effects and nature of loading.

• KCI Concrete Journal
• /
• v.11 no.3
• /
• pp.127-140
• /
• 1999

In this paper, a microscopic analysis of prefinitelv strained cement paste specimen was carried out. The microscopic behavior of concrete under triaxial stress must be fully understood in order to explain the additional ductilitv that comes from lateral confinement and to get microstructural information in large deformed and large strained concrete. The so-called "tube-squash" test was applied to achieve enormously high shear and deviatoric strain of concrete under extremly high pressure without fracture. Then, microscopic analyses by focusing on hydration and microstructure of Prefinitely strained cement paste were carried out on cored-out deformed and virgin (undeformed) cement paste specimens : the first specimen being 40 days old, the second one being one year old. The microscopic analysis bv Field Emission Scanning Electronic Microscope (FESEM) was carried out for comparison between the specimens after 40 days and those arter one year. For one year old specimens, X-Ray Diffractometer (XRD) analysis, Energy Dispersive x-rav Spectrometer (EDS) analysis, and Differential Thermal Analysis/Thermo-Gravitv (DTA/TG) analysis were also carried out to study the hydration and the microstructures of prefinitely strained cement paste specimen by focusing on the methodologies of their microscopic analyses. analyses.

• Journal of the Korean Wood Science and Technology
• /
• v.40 no.5
• /
• pp.352-362
• /
• 2012

Mass transfer behavior in wood was estimated through its microscopic structure. The diffusion coefficients which were decided by theoretical equations are influenced by different anatomical properties of wood. From the experiment, the moisture flux was linear to the square root of time. The diffusion coefficients had a regular tendency during the time elapse. During the modeling, it is necessary to understand the limitation of parameters and consider the particular situation to be simulated. In hardwood, because the apertures were not considered, tangential mass transfer simulation was totally different from experiment. As a result, a hardwood model design should consider the apertures which are even on the fiber walls.