• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
• /
• 2006.06a
• /
• pp.141-146
• /
• 2006

Mechanical fibres are commonly characterized by measuring their length distribution and freeness. These parameters, however, do not adequately characterize the influence of refining on their mechanical properties. In this work we conducted multiple compression on fibre mats prepared from different length fractions (Bauer McNet fractions) to generate stress-strain curves from which several quality parameters can be derived such as modulus, stress and toughness. We found that these characteristics of fibre are strongly influenced by the refining energy used to produce pulp; fibres of similar length exhibit different mechanical properties depending on the refining energy6 consumption.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1997.10a
• /
• pp.216-219
• /
• 1997

Hot workability of SiCp/AA2024 composites reinforced with different vol. % of SiCp reinforcements (0, 5, 10, 15, 20, and 30 vol. %) was investigated by hot torsion tests. Hot restoration of the composites was studied from the flow curves and deformed microstructures. Dynamic recrystallization (DRX) was occurred in all the composites during the hot deformation at 370-43$0^{\circ}C$ under a strain rate of 1.0/sec. Also, the flow stress of the composites increased with increasing the SiCp reinforcement vol. % and the difference of flow stress between the composites decreased with increasing the deformation temperature.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2001.04a
• /
• pp.197-204
• /
• 2001

The purpose of this paper is to develope the evaluation technique to find proper elastic constants that characterize the material nonlinearity of structural membrane. The stress-strain curves of membrane material show strong nonlinearity. But generally the analysis is carried out under the assumption on material linear and geometrical nonlinear method. Because, it is very difficult to evaluate proper tangential stiffness. This paper use multi-step-linear approximation method taking the concept of effective stress for the evaluation of stiffness of membrane material, and then compare the results between linear and nonlinear analysis. Also. it shows better results than linear method

• Proceedings of the Korean Geotechical Society Conference
• /
• 2002.10a
• /
• pp.259-264
• /
• 2002

In this study the shear strengths of a poorly grad ed rock material(d/sub max/≤50.8mm, C/sub u/=1.86) were determined by large direct shear test and large triaxial test. The obtained stress-strain curves by the above large shear tests for the rock materials are similar to the loose sand's or normally consolidated clay's curve, in which the peak strength does not appear obviously. And for the uniformly graded rock material the shear strength by large direct shear test may be overestimated around 1.54∼1.70 times that of large triaxial test.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09a
• /
• pp.81-82
• /
• 2006

This paper presents the influence of the compositions of sintered Ti-Ni alloys on their thermo-mechanical properties. The Ti-Ni alloys having various compositions from 50at%Ni to 51at%Ni were sintered using elemental Ti and Ni powders by a pulse-current pressure sintering equipment. The deformation resistance in stress-strain curves increased with an increase in Ni content. In the case of Ti-50at%Ni, tensile strength and elongation were more than 500 MPa and 7%, respectively. The increase in Ni content also makes the transformation temperatures lower. The deformation resistance at a test temperature change from 293K and 353K in isothermal tensile test increased with elevating test temperature.

• Structural Engineering and Mechanics
• /
• v.10 no.2
• /
• pp.165-180
• /
• 2000

An analytical model with tension softening for the prediction of the capacity of prestressed concrete beams under pure torsion and under torsion combined with shear and flexure is introduced. The proposed approach employs bilinear stress-strain relationship with post cracking tension softening branch for the concrete in tension and special failure criteria for biaxial stress states. Further, for the solution of the governing equations a special numerical scheme is adopted which can be applied to elements with practically any cross-section since it utilizes a numerical mapping. The proposed method is mainly applied to plain prestressed concrete elements, but is also applicable to prestressed concrete beams with light transverse reinforcement. The aim of the present work is twofold; first, the validation of the approach by comparison between experimental results and analytical predictions and second, a parametrical study of the influence of concentric and eccentric prestressing on the torsional capacity of concrete elements and the interaction between torsion and shear for various levels of prestressing. The results of this investigation presented in the form of interaction curves, are compared to experimental results and code provisions.

• Geomechanics and Engineering
• /
• v.17 no.5
• /
• pp.497-505
• /
• 2019

Biocementation based on the microbially induced calcite precipitation (MICP) process is a novel soil improvement method. Biocement can improve significantly the properties of soils by binding soil particles to increase the shear strength or filling in the pores to reduce the permeability of soil. In this paper, results of triaxial consolidated undrained (CU) tests and constant shear drained (CSD) tests on biocemented Ottawa sand are presented. In the CU tests, the biocemented sand had more dilative behaviour by showing a higher stress-strain curves and faster pore pressure reducing trends as compared with their untreated counterparts. In the CSD tests, the stress ratio q/p' at which biocemented sand became unstable was higher than that for untreated sands, implying that the biocementation will improve the stability of sand to water infiltration or liquefaction.

• Advanced Composite Materials
• /
• v.17 no.1
• /
• pp.57-73
• /
• 2008

The present paper focuses on experimental verification of the ply-by-ply basis inelastic analysis of multidirectional laminates. First of all, rate dependence of the tensile behavior of balanced symmetric cross-ply T800H/epoxy laminates with a $[0/90]_{3S}$ lay-up under off-axis loading conditions at $100^{\circ}C$ is examined. Uniaxial tension tests are performed on plain coupon specimens with various fiber orientations $[{\theta}/(90-{\theta})]_{3S}$ ($\theta$ = 0, 5, 15, 45 and $90^{\circ}C$) at two different strain rates (1.0 and 0.01%/min). The off-axis stress.strain curves exhibit marked nonlinearity for all the off-axis fiber orientations except for the on-axis fiber orientations $\theta$ = 0 and $90^{\circ}$, regardless of the strain rates. Strain rate has significant influences not only on the off-axis flow stress in the regime of nonlinear response but also on the apparent off-axis elastic modulus in the regime of initial linear response. A macromechanical constitutive model based on a ply viscoplasticity model and the classical laminated plate theory is applied to predictions of the rate-dependent off-axis nonlinear behavior of the cross-ply CFRP laminate. The material constants involved by the ply viscoplasticity model are identified on the basis of the experimental results on the unidirectional laminate of the same carbon/epoxy system. It is demonstrated that good agreements between the predicted and observed results are obtained by taking account of the fiber rotation induced by deformation as well as the rate dependence of the initial Young's moduli.

• Geomechanics and Engineering
• /
• v.37 no.1
• /
• pp.9-19
• /
• 2024

This study presents an energy analysis for large-strain cavity expansion problem based on the general strength criterion and energy theory. This study focuses on the energy dissipation problem during the cavity expansion process, dividing the soil mass around the cavity into an elastic region and a plastic region. Assuming compliance with the small deformation theory in the elastic region and the large deformation theory in the plastic region, combined with the general strength criterion of soil mass and energy theory, the energy dissipation solution for cavity expansion problem is derived. Firstly, from an energy perspective, the process of cavity expansion in soil mass is described as an energy conversion process. The energy dissipation mechanism is introduced into the traditional analysis of cavity expansion, and a general analytical solution for cavity expansion related to energy is derived. Subsequently, based on this general analytical solution of cavity expansion, the influence of different strength criterion, large-strain, expansion radius, cavity shape and characteristics of soil mass on the stress distribution, displacement field and energy evolution around the cavity is studied. Finally, the effectiveness and reliability of theoretical solution is verified by comparing the results of typical pressure-expansion curves with existing literature algorithms. The results indicate that different strength criterion have a relatively small impact on the displacement and strain field around the cavity, but a significant impact on the stress distribution and energy evolution around the cavity.

• Korean Journal of Materials Research
• /
• v.28 no.6
• /
• pp.317-323
• /
• 2018

Crystal structure of the $L1_2$ type $(Al,X)_3Ti$ alloy (X = Cr,Cu) is analyzed by X-ray diffractometry and the nonuniform strain behavior at high temperature is investigated. The lattice constants for the $L1_2$ type $(Al,X)_3Ti$ alloys decrease in the order of the atomic number of the substituted atom X, and the hardness tends to increase. In a compressive test at around 473K for $Al_{67.5}Ti_{25}Cr_{7.5}$, $Al_{65}Ti_{25}Cr_{10}$ and $Al_{62.5}Ti_{25}Cu_{12.5}$ alloys, it is found that the stress-strain curves showed serration, and deformation rate dependence appeared. It is assumed that the generation of serration is due to dynamic strain aging caused by the diffusion of solute atoms. As a result, activation energy of 60-95 kJ/mol is obtained. This process does not require direct involvement. In order to investigate the generation of serrations in detail, compression tests are carried out under various conditions. As a result, in the strain rate range of this experiment, serration is found to occur after 470K at a certain critical strain. The critical strain increases as the strain rate increases at constant temperature, and the critical strain tends to decrease as temperature rises under constant strain rate. This tendency is common to all alloys produced. In the case of this alloy system, the serration at around 473K corresponds to the case in which the dislocation velocity is faster than the diffusion rate of interstitial solute atoms at low temperature.