• 대한기계학회논문집A
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• 제20권7호
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• pp.2148-2158
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• 1996

Uncoupled, quasi-static and linear thermoviscoelastic problems are analyzed in time domain by the finite element approximation which is developed using the principle of virtual work and viscoelasticity matrices instead of shear and bulk relaxation functions as in usual formulations. The material is assumed to be isotropic, homegeneous and thermorheologically simple, which means that the temperature-time equivalence postulate is effective. The stress-strain laws are expressed by relaxation-type hereditary integrals. In spatial and time discritizations, isoparametric quadratic quadrilateral finite elements and linear time variations are adopted. For explicit derivations, the viscoelastic material is assumed to behave standard linear solid in shear and elastically in dilatation. Two-dimensional examples are solved under general temperature distributions T = T(x, t), and compared with other opproximate solutions to show the versatility of the presented analysis.

• Geomechanics and Engineering
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• 제32권6호
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• pp.639-652
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• 2023

Stepped earth slopes incorporated with anti-slide piles are widely utilized in landslide disaster preventions. Explicit consideration of the three-dimensional (3D) effect in the slope design warrants producing more realistic solutions. A 3D limit analysis of the stability of pile stabilized stepped slopes is performed in light of the kinematic limit analysis theorem. The influences of seismic excitation and surcharge load are both considered from a kinematic perspective. The upper bound solution to the factor of safety is optimized and compared with published solutions, demonstrating the capability and applicability of the proposed method. Comparative studies are performed with respect to the roles of 3D effect, pile location, pile spacing, seismic and surcharge loads in the safety assessments of stepped slopes. The results demonstrate that the stability of pile reinforced stepped slopes differ with that of single stage slopes dramatically. The optimum pile location lies in the upper portion of the slope around L_x/L = 0.9, but may also lies in the shoulder of the bench. The pile reinforcement reaches 10% universally for a looser pile spacing D_c/d_p = 5.0, and approaches 70% when the pile spacing reaches D_c/d_p = 2.0.

• 대한기계학회논문집A
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• 제21권12호
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• pp.2209-2219
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• 1997

A split hopkinson bar could be used for obtaining the high strain rate material properties of sheet metals for an autobody. In high speed tensile tests of sheet matals, a new design of a tension split Hopkinson bar apparatus is needed. The design of grips and an anvil length are numerically analyzed with ABAQUS/Explicit for the new apparatus of split Hopkinson bars. From the experiments with the new apparatus, the material properties of SPCEN in the high strain rate state have been acquired and compared with quasi-static experimental results. The material properties of SPCEN as well as other sheet metals in an autobody are indispensible for the analysis of crashworthness. Nevertheless the experiment of sheet metal in the high strain rate state has not been done or reported.

• Steel and Composite Structures
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• 제25권6호
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• pp.685-692
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• 2017

In this study, the effect of various adhesively bonded composite patches on mechanical properties of notched Al-Mg alloy plates was analyzed. For this purpose firstly, the un-notched and notched specimens were fabricated from 5086 Al-Mg alloys which have been used in armor-plated military vehicles. The surface notches as a flaw were machined with circular cutting tool to form notch aspect ratio a/c=0.15 and notch-to-thickness ratios a/t=0.5 in the radial direction on the test specimens. Then, various composite patches which reinforced by glass, carbon and Kevlar fibers were bonded adhesively at elliptically surface notches. Finally, experimental measurements conducted by applying tensile static loading. The experimental results showed that repairing with composite patches with order of carbon, glass and Kevlar fibers have remarkable effect on tensile strength of the notched plate. Also the finite element models were developed using Abaqus/Explicit code to predict the tensile strength and elongation of unrepaired notched specimen and specimen repaired by carbon fiber composite patch. The comparison between numerical and experimental results showed good agreement between them and proved the accuracy of numerical modeling.

• Geomechanics and Engineering
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• 제12권1호
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• pp.161-183
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• 2017

This paper investigates the damage identification of the concrete pile element through axial wave propagation technique using computational and experimental studies. Now-a-days, concrete pile foundations are often common in all engineering structures and their safety is significant for preventing the failure. Damage detection and estimation in a sub-structure is challenging as the visual picture of the sub-structure and its condition is not well known and the state of the structure or foundation can be inferred only through its static and dynamic response. The concept of wave propagation involves dynamic impedance and whenever a wave encounters a changing impedance (due to loss of stiffness), a reflecting wave is generated with the total strain energy forked as reflected as well as refracted portions. Among many frequency domain methods, the Spectral Finite Element method (SFEM) has been found suitable for analysis of wave propagation in real engineering structures as the formulation is based on dynamic equilibrium under harmonic steady state excitation. The feasibility of the axial wave propagation technique is studied through numerical simulations using Elementary rod theory and higher order Love rod theory under SFEM and ABAQUS dynamic explicit analysis with experimental validation exercise. Towards simulating the damage scenario in a pile element, dis-continuity (impedance mismatch) is induced by varying its cross-sectional area along its length. Both experimental and computational investigations are performed under pulse-echo and pitch-catch configuration methods. Analytical and experimental results are in good agreement.

• 대한토목학회논문집
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• 제33권2호
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• pp.409-422
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• 2013

부재간의 연결조건에 따른 다양하고 복잡한 강구조물의 P-${\Delta}$ 해석 및 좌굴 거동특성을 파악하기 위하여, 본 연구에서는 부재의 연결이 회전 및 이동스프링으로 구성된 부분강절(semi-rigid) 뼈대요소의 일반화된 접선강도 행렬을 유도하였고 이로부터 다시 Taylor 전개를 적용하여 탄성강도 행렬과 기하학적 강도행렬을 일반화된 형태로 제시하였다. 이를 위하여, 보-기둥부재의 좌굴조건을 만족시키는 처짐함수로부터 안정함수(stability function)를 유도하였고, 횡변위(sway)를 고려한 힘-변위관계와 적합조건을 고려하여 엄밀한 부분강절 뼈대요소의 접선강도행렬을 제시하였다. 다양한 수치해석 예제에 대해 타 연구자의 해석 결과 및 본 연구의 선형 및 비선형 해석이론을 통한 좌굴해석 결과를 비교하여 본 연구의 타당성과 부분강절 뼈대구조물의 좌굴거동 특성을 제시하였다.

• 대한조선학회논문집
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• 제57권4호
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• pp.182-190
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• 2020

This study reports a series of drop impact tests performed to generate denting damages on stiffened plates and their residual ultimate strength tests under axial compression. The models were fabricated of general structural steel, and each model has six longitudinal stiffeners and two transverse frames. Among six fabricated models, four were damaged, and two were left intact for reference. To investigate the effects of collision velocity and impact location on the extent of damage, the drop height and the impact location were changed in each impact test. After performing the collision tests, the ultimate axial compression tests were conducted to investigate the residual strengths of the damaged stiffened plates. Finite element analyses were also carried out using a commercial package Abaqus/Explicit. The material properties obtained from a quasi-static tensile tests were used, and the strain-rate sensitivity was considered. After importing the collision simulation results, the ultimate strength calculations were carried out and their results were compared with the test data for the validation of the finite element analysis method.

• Nuclear Engineering and Technology
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• 제55권4호
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• pp.1382-1399
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• 2023

Pressure relief valve (PRV) is one of the important control valves used in nuclear power plants, and its sealing performance is crucial to ensure the safety and function of the entire pressure system. For the sealing performance improving purpose, an explicit function that accounts for all design parameters and can accurately describe the relationship between the multi-design parameters and the seal performance is essential, which is also the challenge of the valve seal design and/or optimization work. On this basis, a surrogate model-based design optimization is carried out in this paper. To obtain the basic data required by the surrogate model, both the Finite Element Model (FEM) and the Computational Fluid Dynamics (CFD) based numerical models were successively established, and thereby both the contact stresses of valve static sealing and dynamic impact (between valve disk and nozzle) could be predicted. With these basic data, the polynomial chaos expansion (PCE) surrogate model which can not only be used for inputs-outputs relationship construction, but also produce the sensitivity of different design parameters were developed. Based on the PCE surrogate model, a new design scheme was obtained after optimization, in which the valve sealing stress is increased by 24.42% while keeping the maximum impact stress lower than 90% of the material allowable stress. The result confirms the ability and feasibility of the method proposed in this paper, and should also be suitable for performance design optimizations of control valves with similar structures.

• 한국강구조학회 논문집
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• 제22권1호
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• pp.33-42
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• 2010

막구조의 설계에서 막재료의 효율적인 사용을 위해서는 측지선에 의한 재단도 해석을 수행해야 한다. 막구조의 측지선 결정방법은 크게 측지요소(geodesic element)를 이용한 비선형 형상해석에 의한 방법과 임의의 곡면 형상에 대한 측지선 탐색에 의한 방법으로 나눌 수 있는데, 현재까지 이 두 가지 해석법은 모두 3절점요소에 대한 적용알고리즘 만이 제시되었고, 4절점 요소에 대한 해석법은 제시되지 않았다. 이는 막구조의 설계에서 4절점 요소의 적용을 어렵게 하는 가장 큰 요인이라고 할 수 있다. 본 연구에서는 3절점, 4절점 평면요소에 동시에 적용 가능한 측지선 결정알고리즘을 제시한다. 이를 위해 저자의 이전 연구를 발전시켜 명시적 비선형 해석법인 동적이완법을 비선형 측지선 형상해석에 적용하였다. 또한 3절점요소 뿐만 아니라 4절점요소에 대해서도 측지요소의 도입에 의한 형상해석이 가능하도록 하였으며, 4절점요소와 측지선요소에 의한 비선형 형상해석 및 재단도 해석예제를 통하여 본 연구에서 제시한 알고리즘의 정확성 및 효율성을 검증하였다. 따라서 본 연구에서 제안한 측지선 형상해석알고리즘은 형상해석, 응력해석, 재단도 해석과 관련된 일련의 해석과정에 대한 4절점요소의 적용성을 높일 수 있을 것으로 사료된다.