• Interaction and multiscale mechanics
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• v.5 no.2
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• pp.157-168
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• 2012

The dilatancy of granular materials has significant influence on its mechanical behaviors. The dilation angle is taken as a constant in conventional associated or non-associated flow rules based on Drucker-Prager yields theory. However, various experimental results show the dilatancy changes during progressive failure of granular materials. A non-associated flow rule with evolution of dilation angle is adopted in this study, and Cosserat continuum theory is used to describe the behaviors of granular materials for considering to some extent the its internal structure. Numerical examples focus on the bearing capacity and localization of granular materials, and results illustrate the capability and performance of the presented model in modeling the effect on failure behavior of granular materials.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2006.11a
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• pp.230-232
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• 2006

Failure behaviors of thin cylinder with corrosion are very important for the integrity of boiler and pressure vessel system. In this study, FEM with internal pressure are conducted on 1000 mm diameter (length 3000 mm and thickness, 5.9 mm) SS400 carbon steel. Failure behaviors of locally wall thinned cylinders were calculated by elasto-plastic analysis using finite element method. The elasto-plastic analysis was performed by FE code ANSYS. We simulated various types of local wall thinning that can be occurred at cylinder surface due to corrosion. Locally wall thinned shapes were machined to be different in size along the circumferential or axial direction of straight cylinder. In case of local wall thinned length 30 mm, internal pressure, when the crack initiation and the plastic collapse occur, didn't decrease dramatically even though local wall thinned depth was deep. In 400 mm, the more local wall thinned depth is deep, the more internal pressure decreased dramatically. In degraded materials, crack is easily initiation but plastic collapse was difficult.

• Structural Engineering and Mechanics
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• v.74 no.3
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• pp.407-423
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• 2020

The pre-peak cyclic shear mechanism of two-order asperity degradation of rock joints in the direct shear tests with static constant normal loads (CNL) are investigated using experimental and numerical methods. The laboratory testing rock specimens contains the idealized and regular two-order triangular-shaped asperities, which represent the specific geometrical conditions of natural and irregular waviness and unevenness of rock joint surfaces, in the pre-peak cyclic shear tests. Three different shear failure patterns of two-order triangular-shaped rock joints can be found in the experiments at constant horizontal shear velocity and various static constant normal loads in the direct and pre-peak cyclic shear tests. The discrete element method is adopted to simulate the pre-peak shear failure behaviors of rock joints with two-order triangular-shaped asperities. The rock joint interfaces are simulated using a modified smooth joint model, where microscopic scale slip surfaces are applied at contacts between discrete particles in the upper and lower rock blocks. Comparing the discrete numerical results with the experimental results, the microscopic bond particle model parameters are calibrated. Effects of cyclic shear loading amplitude, static constant normal loads and initial waviness asperity angles on the pre-peak cyclic shear failure behaviors of triangular-shaped rock joints are also numerically investigated.

• Structural Engineering and Mechanics
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• v.74 no.5
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• pp.657-670
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• 2020

Due to the high compressive and tensile strength of ultra-high performance concrete (UHPC), UHPC used in steel concrete composite structures provided thinner concrete layer compared to ordinary concrete. This leaded to the headed stud shear connectors embedded in UHPC had a low aspect ratio. In order to systematic investigate the effect of headed stud with low aspect ratio on the structural behaviors of steel UHPC composite structure s this paper firstly carried out a test program consisted of twelve push out specimens. The effects of stud height, aspect ratio and reinforcement bars in UHPC on the structural behaviors of headed studs were investigated. The push out test results shows that the increasing of stud height did not obviously influence the structural behaviors of headed studs and the aspect ratio of 2.16 was proved enough to take full advantage of the headed stud strength. Based on the test results, the equation considering the contribution of weld collar was modified to predict the shear strength of headed stud embedded in UHPC. The modified equation could accurately predict the shear strength of headed stud by comparing with the experimental results. On the basis of push out test results, bending tests consisted of three steel UHPC composite slabs were conducted to investigate the effect of shear connection degree on the structural behaviors of composite slabs. The bending test results revealed that the shear connection degree had a significantly influence on the failure modes and ultimate resistance of composite slabs and composite slab with connection degree of 96% in s hear span exhibited a ductile failure accompanied by the tensile yield of steel plate and crushing of UHPC. Finally, analytical model based on the failure mode of composite slabs was proposed to predict the ultimate resistance of steel UHPC composite slabs with different shear connection degrees at the interface.

• Structural Engineering and Mechanics
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• v.58 no.3
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• pp.577-596
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• 2016

FRP-concrete interfacial mechanical properties determine the strengthening effect of RC beams strengthened with FRP. In this paper, the model experiments were carried out with eight specimens to study the failure modes and the strengthening effect of RC beams strengthened with FRP. Then a theoretical model based on interfacial performances was proposed and interfacial mechanical behaviors were studied. Finite element analysis confirmed the theoretical results. The results showed that RC beams strengthened with FRP had three loading stages and that the FRP strengthening effects were mainly exerted in the Stage III after the yielding of steel bars, including the improvement of the bearing capacity, the decreased ultimate deformation due to the sudden failure of FRP and the improvement of stiffness in this stage. The mechanical formulae of the interfacial shear stress and FRP stress were established and the key influence factors included FRP length, interfacial bond-slip parameter, FRP thickness, etc. According to the theoretical analysis and experimental data, the calculation methods of interfacial shear stress at FRP end and FRP strain at midspan were proposed. When FRP bonding length was shorter, interfacial shear stress at FRP end was larger that led to concrete cover peeling failure. When FRP was longer, FRP reached the ultimate strain and the fracture failure of FRP occurred. The theoretical results were well consistent with the experimental data.

• Smart Structures and Systems
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• v.30 no.1
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• pp.49-62
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• 2022

Experimental and discrete element methods were used to investigate the effects of triple joints lengths and triple joint angle on the failure behavior of rock mass under uniaxial compressive test. Concrete samples with dimension of 20 cm × 20 cm × 5 cm were prepared. Within the specimen, three imbedded joint were provided. The joint lengths were 2 cm, 4cm and 6 cm. In constant joint lengths, the angle between middle joint and other joints were 30°, 60°, 90°, 120° and 150°. Totally 15 different models were tested under compression test. The axial load rate on the model was 0.05 mm/min. Concurrent with experimental tests, the models containing triple joints, length and joint angle are similar to the experiments, were numerical by Particle flow code in two dimensions (PFC2D). Loading rate in numerical modelling was 0.05 mm/min. Tensile strength of material was 1 MPa. The results show that the failure behaviors of rock samples containing triple joints were governed by both of the angle and the length of the triple joints. The uniaxial compressive strengths (UCS) of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. Furthermore, it was shown that the compressive behavior of discontinuities is related to the number of the induced tensile cracks which are increased by decreasing the joint length. Along with the damage failure of the samples, the acoustic emission (AE) activities are excited. There were only a few AE hits in the initial stage of loading, then AE hits rapidly grow before the applied stress reached its peak. In addition, every stress drop was accompanied by a large number of AE hits. Finally, the failure pattern and failure strength are similar in both methods i.e., the experimental testing and the numerical simulation methods.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.5 no.2
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• pp.27-34
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• 2009

This paper proposes a simple numerical method to simulate ductile failure behaviors. The method is based on finite element analysis with a simple damage theory. To validate the proposed method, simulated results are compared with experimental data. Despite its simplicity, the proposed method well predicts experimental results systematic analyses are also performed to investigate the effect of the element size.

• Journal of Ocean Engineering and Technology
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• v.25 no.2
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• pp.92-100
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• 2011

The main goal of this paper is to provide the theoretical background for the fracture phenomena in marine structural steels. In this paper, various fracture criteria are theoretically investigated: shear failure criteria with constant failure strain and stress triaxiality-dependent failure strain (piecewise failure and Johnson-Cook criteria), forming limit curve failure criterion, micromechanical porosity failure criterion, and continuum damage mechanics failure criterion. It is obvious that stress triaxiality is a very important index to determine the failure phenomenon for ductile materials. Assuming a piecewise failure strain curve as a function of stress triaxiality, the numerical results coincide well with the test results for smooth and notched specimens, where low and high stress triaxialities are observed. Therefore, it is proved that a failure criterion with reliable material constants presents a plastic deformation process, as well as fracture initiation and evolution.

• Journal of Korean Clinical Nursing Research
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• v.22 no.1
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• pp.28-37
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• 2016

Purpose: This study was to investigate the relationships between among health literacy, knowledge and self-care behavior in elderly patients with heart failure(HF). Methods: 166 patients (age ${\geq}65$ years) with HF were recruited in a cardiovascular center of an university affiliated hospital. The structured questionnaire included Health literacy, Dutch Heart Failure Knowledge Scale, European Heart Failure Self-care Behavior, Self-Care of Heart Failure Index. Data were analyzed by descriptive statistics, Chi-test, Pearson correlation analysis, t-test and ANCOVA using SPSS/WIN version 21.0. Results: Participants with the high level of health literacy were more likely to be younger (p=.001), men (p=.001), with more education (p<.001), and have a job (p=.004), and with a higher economic status (p=.005). The positive correlations between the level of health literacy, knowledge, and self-care behavior were confirmed (p<.001). Participants with the high level of health literacy showed higher level of knowledge, more self-care behavior for health maintenance, and confidence. Conclusion: This study shows that the level of health literacy may influence knowledge and self-care behavior in elderly patients with HF. In order to improve self-care behaviors in elderly patients, a strategic nursing approach based on the level of patients' health literacy needs to be considered.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.525-530
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• 2002

This study is peformed to propose the slab deck for the composite bridge with two girders. Considering the characteristics of the long span and the construction conditions in korea, a cast-in-place PSC deck was proposed for that bridge. To examine structural behaviors and safety of the proposed PSC deck, two real scale partitions of deck(12m$\times$3.2m) were tested under the fatigue loading. In the test, the failure mode and behaviors of each specimen, and the ultimate load carrying capacity of the two-girder-bridge deck were identified. Generally, the failure of concrete bridge deck is caused by the local punching shear stress resulting from the moving wheel load. Even though its ultimate flexural capacity is sufficiently larger than the demand, it could be failed by the punching shear fatigue. Therefore, the fatigue safety of the proposed PSC deck should be checked.