• Interaction and multiscale mechanics
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• 제2권1호
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• pp.31-44
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• 2009

While the classical theory of Griffith is the foundation of modern understanding of brittle fracture, it has a number of significant shortcomings: Griffith theory does not predict crack initiation and path and it suffers from the presence of unphysical stress singularities. In 1998, Francfort and Marigo presented an energy functional minimization method, where the crack (or its absence) as well as its path are part of the problem's solution. The energy functionals act on spaces of functions of bounded variations, where the cracks are related to the discontinuity sets of such functions. The new model presented here uses modified energy functionals to account for molecular interactions in the vicinity of crack tips, resulting in Barenblatt cohesive forces, such that the model becomes free of stress singularities. This is done in a physically consistent way using recently published concepts of Sinclair. Here, for the consistency of the model, it becomes necessary to allow for crack reversibility and to consider local minimizers of the energy functionals. The latter is achieved by introducing different time scales. The model is solved in its global as well as in its local version for a simple one-dimensional example, showing that local minimization is necessary to yield a physically reasonable result.

• Computers and Concrete
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• 제1권1호
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• pp.47-60
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• 2004

The influence of the fracture process zone (FPZ) on the fracture properties is one of the hottest topics in the field of fracture mechanics for cementitious materials. Within the FPZ in front of a traction free crack, cohesive forces are distributed in accordance with the softening stress-separation constitutive relation of the material. Therefore, further crack propagation necessitates energy dissipation, which is the work done by the cohesive forces. In this paper $g_f$, the local fracture energy characterizing the energy consumption due to the cohesive forces, is discussed. The computational expression of $g_f$ in the FPZ can be obtained for any stage during the material fracture process regarding the variation of FPZ, whether in terms of its length or width. $G_{fa}$, the average energy consumption along the crack extension region, has also been computed and discussed in this paper. The experimental results obtained from the wedge splitting tests on specimens with different initial notch ratios are employed to investigate the property of the local fracture energy $g_f$ and the average value $G_{fa}$ over the crack extension length. These results can be used to indicate the influence of the FPZ. Additionally, changes in the length of the FPZ during the fracture process are also studied.

• Journal of Pharmaceutical Investigation
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• 제15권2호
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• pp.45-52
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• 1985

For the model tablets using mannitol and Avicel PH 101 as excipients, the patterns of disintegration and dissolution from the differences of physical properties were investigated. It was found that the patterns in the dissolution and binding forces in the interaction of materials by estimates of solid-solid or liquid surface free energy due to cohesive or adhesive properties of materials, and solid surface free energy in binding forces of tablet should be considered as an important factor in dissolution processes.

• 한국지반공학회지:지반
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• 제5권3호
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• pp.29-38
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• 1989

도시내 지하굴착공사에 저진동, 저소음의 장점이 있어 많이 사용될 수 있는 주열식 흙막이벽편 말뚝의 설계법이 제안되며, 그 실용성이 설계례를 통하여 검토된다. 먼저 점성토지반 속에 설치된 주렬식 흙막이말뚝의 저항력 산정식이 굴착 저면을 기준으로 상부와 하부지반에 대하여 각카 제시 된다. 이 산정식의 특징은 지반특성과 말뚝의 설치간격을 합리적으로 고려할 수 있자는 점이다. 이 저항력 산정식을 활용하여 흙막이 말뚝의 안정해절법이 확립된다. 흙막이 말뚝의 설계는 말뚝의 안 정성과 지반의 안정성을 동시에 만족시키는 범위에서 책시되며, 지반의 안정성 검토시에는 굴착 저 부에서의 정토지반 융기현상에 대한 안전검토도 실시된다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 봄 학술발표회 논문집
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• pp.58-76
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• 2000

An analytical solution method capable of determining the geometric configuration and developed tensile forces of mooring lines associated with fixed plate/pile or drag anchors is presented. The solution method, satisfying complete equilibrium conditions, is capable of analyzing multi-segmented mooring lines that can consist of either chains, cables, or wires embedded in layered seafloor soils. Centrifuge model tests and full -scale field tests were used to calibrate and validate the analytical solution.

• Steel and Composite Structures
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• 제44권4호
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• pp.519-529
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• 2022

Sandwich structures with the superior mechanical properties such as high stiffness and strength-to-weight ratio, good thermal insulation, and high energy absorption capacity are used today in aerospace, automotive, marine, and civil engineering industries. These structures are composed of moderately stiff, thin face sheets that withstand the majority of transverse and in-plane loads, separated by a thick, lightweight core that resists shear forces. In this research, the finite element technique is used to simulate a sandwich panel with a truss core under axial compressive stress using ABAQUS software. A review of past experimental studies shows that the bondline between the core and face sheets plays a vital role in the critical failure load. Therefore, this modeling analyzes the damage initiation modes and debonding between face sheet and core by cohesive surface contact with traction-separation model. According to the results obtained from the modeling, it can be observed that the adhesive stiffness has a significant influence on the critical failure load of the specimens. To achieve the full strength of the structure as a continuum, a lower limit is obtained for the adhesive stiffness. By providing this limit stiffness between the core and the panel face sheets, sudden failure of the structure can be prevented.

• Structural Engineering and Mechanics
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• 제73권5호
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• pp.585-598
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• 2020

We develop design model within which nucleation and propagation of crack in a fibrous composite is described. It is assumed that under loading, crack initiation and fracture of material happens in the composite. The problem of equilibrium of a composite with embryonic crack is reduced to the solution of the system of nonlinear singular integral equations with the Cauchy type kernel. Normal and tangential forces in the crack nucleation zone are determined from the solution of this system of equations. The crack appearance conditions in the composite are formed with regard to criterion of ultimate stretching of the material's bonds. We study the case when near the fiber, the binder has several arbitrary arranged rectilinear prefracture zones and a crack with interfacial bonds. The proposed computational model allows one to obtain the size and location of the zones of damages (prefracture zones) depending on geometric and mechanical characteristics of the fibrous composite and applied external load. Based on the suggested design model that takes into account the existence of damages (the zones of weakened interparticle bonds of the material) and cracks with end zones in the composite, we worked out a method for calculating the parameters of the composite, at which crack nucleation and crack growth occurs.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2009년도 정기 학술대회
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• pp.38-41
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• 2009

Debonding behavior of symmetric tilt bicrystal interfaces with <100> misorientation axis is investigated through molecular dynamics simulations. FCC single crystal copper is considered in each grain and the model is idealized as a grain boundary under mechanical loading. Embedded-Atom Method potential is chosen to calculate the interatomic forces between atoms. Constrained tensile deformations are applied to a variety of misorientation angles in order to estimate the effect of grain boundary angle on local peak stress. A new parameter of symmetric grain-boundary structure is introduced and refines the correlation between grain boundary angle and local peak stress.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1999년도 가을 학술발표회 논문집
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• pp.193-200
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• 1999

Since Broms and Bennermark(1967) suggested the face stability criterion based on laboratory extrusion tests and field observations, the face stability of a tunnel driven in cohesive material has been studied by several authors. And recently, more general solution for the tunnel front is given by Leca and Panet(1988). They adopted a limit state design concept to evaluate the face stability of a shallow tunnel driven into cohesionless material and showed that the calculated upper bound solution represented the actual behavior reasonably well. In this study, two factors are simultaneously considered for assessing tunnel face stability: One is the effective stress acting on the tunnel front calculated by upper bound solution; and the other is the seepage force calculated by numerical analysis under the condition of steady state ground water flow. The model tests were performed to evaluate the seepage force acting on the tunnel front and these results were compared with results of numerical analysis. Consequently, the methodology to evaluate the stability of a tunnel face including limit analysis and seepage analysis is suggested under the condition of steady state ground water flow.

• Geomechanics and Engineering
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• 제16권2호
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• pp.151-157
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• 2018

The constrained conditions of roof and floor for the coal pillar affect the strength of coal pillar very seriously. To analyze the influence of rock mass for the roof and floor on the stability of coal pillar comprehensively, one method based on the mechanical method for the composite rock mass was proposed. In this method, the three rock layers of roof, floor and coal pillar are taken as the bedded composite rock mass. And the influence of rock mass for the roof and floor on the elastic core of coal pillar has been analyzed. This method can obtain not only the derived stress by the cohesive constraining forces for the coal pillar, but also the derived stress for the rock mass of the roof and floor. Moreover, the effect of different mechanical parameters for the roof and floor on the stability of coal pillar have been analyzed systematically. This method can not only analyze the stability of strip coal pillar, but also analyze the stability of other mining pillars whose stress distribution is similar with that of the strip coal pillar.