• Geomechanics and Engineering
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• v.16 no.2
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• pp.205-215
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• 2018

Strain-based criteria are known as a direct method in determining the stability of the geomechanical structures. In spite of the widely use of Sakurai critical strain criterion, it is so conservative to make use of them in rocks with initial plastic deformation on account of the considerable difference between the failure and critical strains. In this study, a new criterion has been developed on the basis of the failure strain to attain more reasonable results in determining the stability status of the tunnels excavated in the rocks mostly characterized by plastic-elastic/plastic behavior. Firstly, the stress-strain curve was obtained having conducted uniaxial compression strength tests on 91 samples of eight rock types. Then, the initial plastic deformation was omitted making use of axis translation technique and the criterion was presented allowing for the modified secant modulus and by use of the failure strain. The results depicted that the use of failure strain criterion in such rocks not only decreases the conservativeness of the critical strain criterion up to 42%, but also it determines the stability status of the tunnel more accurately.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.10 s.253
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• pp.1219-1226
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• 2006

The ASTM test standard recommends the use of the compact tension specimen for creep crack growth rates measurement. In the creep crack growth rate test, the displacement rate due to creep is obtained by subtracting the contribution of elastic and plastic components from the total load line displacement rate based on displacement partitioning method fur determining $C^*-integral$, which involves Ramberg-Osgood (R-O) fitting procedures. This paper investigates the effect of the R-O fitting procedures on plastic displacement rate estimates in creep crack growth testing, via detailed two-dimensional and three-dimensional finite element analyses of the standard compact tension specimen. Four different R-O fitting procedures are considered; (i) fitting the entire true stress-strain data up to the ultimate tensile strength, (ii) fitting the true stress-strain data from 0.1% strain to 0.8 of the true ultimate strain, (iii) fitting the true stress-strain data only up to 5% strain, and (iv) fitting the engineering stress-strain data. It is found that the last two procedures provide reasonably accurate plastic displacement rates and thus should be recommended in creep crack growth testing. Moreover, several advantages of fitting the engineering stress-strain data over fitting the true stress-strain data only up to 5% strain are discussed.

• Computers and Concrete
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• v.19 no.6
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• pp.609-615
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• 2017

In this paper, the effects of elevated temperatures on the strength and compressive stress-strain curve (SSC) of recycled coarse aggregate concrete with different replacement percentages are presented. 90 recycled coarse aggregate concrete prisms are heated up to 20, 200, 400, 600, $800^{\circ}C$. The results show that the compressive strength, split tensile strength, elastic modulus of recycled aggregate concrete specimens decline significantly as the temperature rise. While the peak strain increase of recycled aggregate concrete specimens as the temperature rise. Compared to the experimental curves, the proposed stress-strain relations for recycled aggregate concrete after exposure elevated temperatures can be used in practical engineering applications.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.191-194
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• 2003

The results from a systematic study of the response of a Ti-6Al-4V alloy under quasi-static and dynamic loading at different strain rates and temperatures are presented. It has been shown that the work-hardening rate decreased as the strain rate and the strain increased. The correlations and predictions using modified KHL (Khan-Huang-Liang) viscoplastic constitutive model are compared with those from JC (Johnson-Cook) model and experimental observations. Overall, KHL model correlations and predictions compared much more favorably than the corresponding JC model predictions and correlations.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.31 no.5
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• pp.73-85
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• 1999

Yield and fracture are separated in the tensile failure of paper. Failure in the machine direction of photocopy paper is contrasted with failure in the cross-machine direction . The ratios of distortion (shape change) to dilatation (volume change) for individual elements at yield and fracture are described. The ratios of distortion to dilatation are measured and compared to predicted values of the strain energy density theory. To evaluate the effect of the angle from the principal material direction on the strain energy density theory. To evaluate the effect of the angle from the principal material direction on the strain energy density factor, samples are prepared from machine direction to cross-machine direction in 15 degree intervals. the strain energy density of individual elements are obtained by the integration of stress from finite element analysis with elastic plus plastic strain energy density theory. Poison's ratio and the angle from the principal material direction have a great effect ion the ratio fo distortion to dilatation in paper. During the yield condition, distortion prevails over dilatation . At fracture, dilatation is at a maximum.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.12
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• pp.1357-1365
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• 2009

In this study, we enhance the numerical approach of Lee et al.$^{(1)}$ to spherical indentation technique for property evaluation of hyper-elastic rubber. We first determine the friction coefficient between rubber and indenter in a practical viewpoint. We perform finite element numerical simulations for deeper indentation depth. An optimal data acquisition spot is selected, which features sufficiently large strain energy density and negligible frictional effect. We then improve two normalized functions mapping an indentation load vs. deflection curve into a strain energy density vs. first invariant curve, the latter of which in turn gives the Yeoh-model constants. The enhanced spherical indentation approach produces the rubber material properties with an average error of less than 3%.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.194-199
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• 2000

The creep rate is affected by the temperature and in fact. if the temperature above $T_M/2(T_M:melting\;point)$. The aim of the present investigation is to study the relationship of static creep and cyclic creep behavior of pure copper and the formulation of these phenomena with the special attention to the instantaneous strain. strain rate from time and number of cycles have the same inclination Steady state creep rate depend upon maximum stress and can be expressed as linear function according to Power law creep equations Creep rupture time has relation with creep rate. and it make a group represented as the same direct line regardless of max stress, stress ratio and the temperature. Initial strain effect on continuous creep deformation. and have guantitative relationship between elastic and Plastic strain. LMP have similar tendency than OSDP and MHP according to temperature

• Geotechnical Engineering
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• v.2 no.1
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• pp.7-14
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• 1986

The structure of the collapsible soils, such as decomposed granite soil and loess, were examined by the odeometer test, SEM & XES analysis and static & cyclic triaxial test, and hove this structure have influences upon the collapsible behaviour under static and cyclic load was investigated. The study results obtained are as follows; 1. The macropores space of decomposed granite soil (rd=1.50g/cm3) and loess (rd=1.43g/cm3) used in this test were well developed, and showed the behaviour of collapsible soil. 2. Collapsible soil has high resistance on the strain under natural moisture content, however, the resistance on the strain was sharply decreased by the absorption and increasing load since its special structure was destructed. 3. Under the static load, the strain of collapsible soil was high by the viscous flow of the cyclic bonds with time lapse, but Infer the cyclic load, the strain of collapsible soil was low since the tinge needed to destruct the bonding force of clay was not enough. 4. The understanding about the cyclic behaviour of collapsible soil may be helpful to predict the elastic & residual strain of the foundations by the earthquake together with the damage by the additional failure.

• Proceedings of the KSR Conference
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• 2003.10c
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• pp.73-78
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• 2003

The residual stresses and. distortions of structures by welding exert negative effect on the safety of railroad structures. This investigation performs a thermal elasto-plastic analysis using finite element techniques to evaluate residual stresses in butted-welded joint. Considering this initial residual stresses, local stress and strain at the critical location (weld toe) during the loading were analyzed by elastic plastic finite element analysis. Fatigue crack initiation life and fatigue crack propagation life of butt-welded specimen were predicted by local strain approach and Neuber's role and Paris law. It is demonstrated that fatigue life estimates by local strain approach closely approximate the experimental results.

• Tunnel and Underground Space
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• v.27 no.5
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• pp.253-262
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• 2017

The purpose of this paper is to analyze the crack characteristics by performing the compression test of the rock and concrete specimens. The experiments are carried out by using strain sensors which can measure length change and the AE sensor which can detect the elastic wave from the crack. The crack volumetric strain calculated from measured strain is shown in different shape on the rock and the concrete specimens. This is because the specimens have a different degree of brittleness. However, the crack volumetric strain associated with the fracture and damage was similar to accumulated AE energy of the two specimens. This means that the AE sensor can assess damage in real time without damaging the structure.