• Geomechanics and Engineering
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• 제17권3호
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• pp.295-305
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• 2019

The bedding plane has a significant influence on the effect of blasting fragmentation and the overall performance of underground mining. This paper explores the effects of fragmentation of the bedding plane and different angles by using the numerical analysis. ANSYS/LS-DYNA code was used for the implementation of the models. The models include a dynamic compressive and tensile failure which is applied to simulate the fractures generated by the explosion. Firstly, the cracks propagation with the non-bedding plane in the coal with two boreholes detonated simultaneously is calculated and the particle velocity and maximum principal stress at different points from the borehole are also discussed. Secondly, different delay times between the two boreholes are calculated to explore its effects on the propagation of the fractures. The results indicate that the coal around the right borehole is broken more fully and the range of the cracks propagation expanded with the delay time increases. The peak particle velocity decreases first and then increases with the distance from the right borehole increasing. Thirdly, different angles between the bedding plane and the centerline of the two boreholes and the transmission coefficient of stress wave at a bedding plane are considered. The results indicated that with the angles increase, the number of the fractures decreases while the transmission coefficient increases.

• 대한조선학회논문집
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• 제42권5호
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• pp.466-471
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• 2005

The out-of-plane deformation in thin plate structure has been a serious qualify problem. It has been known that the out-of-plane deformation is caused by the angular deformation of welded joint. However, experimental results show that the conventional theory based on angular deformation is not appropriate for prediction of the out-of-plane deformation in thin plate structure. In this study, large deformation plate theory is introduced to clarify the effect of residual stress on the out-of-plane deformation. A simple equation is proposed to predict the out-of-plane deformation. The results by the proposed method show good agreement with the experimental results.

• Steel and Composite Structures
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• 제24권5호
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• pp.523-536
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• 2017

A layerwise (LW) formulation based on the Galerkin method is presented to investigate the three-dimensional stress state in long sandwich plate which is subjected to tension force and pure bending moment. Based on the Galerkin method and the LW discretization approach, the equilibrium equations of elasticity for the long plate are written in the weak form and discretized through the thickness of the plate. The discretized equations are written in terms of displacement components of the numerical layers. The governing equations of the plate are solved analytically for the free edge boundary conditions. The distribution of stress state especially the 3D stress state in the vicinity of the edges of the sandwich plate which is subjected to tension and pure bending is studied. In order to increase the accuracy, the out of plane stresses are obtained by integrating the equilibrium equations of elasticity. The convergence and accuracy of the predictions are studied and various numerical results are presented for distribution of the in-plane and out of plane stresses in symmetric and un-symmetric sandwich plates.

• Journal of Welding and Joining
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• 제17권4호
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• pp.76-84
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• 1999

The residual stress generated when the steel plates were produced, did not influence on the out-of-plane deformation and residual stress generated by welding. When the initial deflection shape was a concave(Type I), the out-of-plane deformation became the same shape as that of the initial deflection and its magnitude became small. When the initial deflection made a winding in the welding direction(Type III), the out-of-plane deformation became large in the plate width. The initial deflection shape did not influence on residual stress and plastic strain produced by welding.

• Structural Engineering and Mechanics
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• 제32권4호
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• pp.549-561
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• 2009

As it is known, laminated composite materials are increasingly used in many technological applications, and in some instance, cutouts must be made into laminated panels for practical reasons, changing the stress distribution. The present study deals with the determination of the stress concentration factor that holes of square shape cause in an orthotropic plate subjected to distributed in - plane loading. Square holes of rounded corners in a rectangular plate are considered, and the effect of different combinations of axial and tangential forces applied to its middle plane at the external edges, is studied. The mutually perpendicular axes, which define the principal axes of orthotropy, are assumed in many different directions referred to the sides of the plate. Numerical experiments by means of a finite element code is performed, evaluating the influence of the fiber orientation with respect to the edges of the plate and the characteristics of the orthotropic materials since such structures do not exhibit easily predictable behavior.

• 대한기계학회논문집A
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• 제25권6호
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• pp.949-958
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• 2001

A semi-infinite interfacial crack propagated with constant velocity in two bonded anisotropic strips under out-of-plane clamped displacements is analyzed. Using Fourier integral transform the problem is formulated and the Wiener-Hopf equation is derived. By solving this equation the asymptotic stress and displacement fields near the crack tip are obtained, where the results get more general expressions applicable not only to isotropic/orthotropic materials but also to the extent of the anisotropic material having one plane of elastic symmetry for the interfacial crack. The dynamic stress intensity factor is obtained as a closed form, which is decreased as the velocity of crack propagation increases. The critical velocity where the stress intensity factor comes to zero is obtained, which agrees with the lower value between the critical values of parallel crack merged in the material 1 and 2 adjacent to the interface. Using the near tip fields of stresses and displacements, the dynamic energy release rate is also obtained as a form of the stress intensiy factor.

• 한국결정성장학회지
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• 제10권4호
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• pp.337-343
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• 2000

사파이어 ($\alpha$-Al$_2$O$_3$) 단결정에 있어 prism plane slip {11$\bar{2}$0}1/3{$\bar{1}$120} 전위속도를 에치-피트 방법으로 측정하였다. 전위속도 측정시 온도범위는 $1150^{\circ}C$에서 $1400^{\circ}C$까지 였으며, 응력범위는 140 MPa에서 250 MPa까지였다. 얻어진 전위속도의 온도 및 응력 의존성에 대해 검토하였다. 전위속도의 온도의존성을 이용하여 prism plane slip 전위속도를 위한 활성화에너지를 구하였으며, 그 값은 대략 4.2$\pm$0.4 eV이었다. 또한, 전위속도의 응력의존성을 나타내는 응력지수 m은 4.5$\pm$0.8이었다. 한편, 전위속도 측정을 통해 사파이어 단결정에서 basal 면이 3-fold 대칭을 가진다는 사실을 재확인하였다.

• Structural Engineering and Mechanics
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• 제43권6호
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• pp.739-759
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• 2012

The tailoring optimization technique recently developed by the author for improving structural response and energy absorption of composites is extended to sandwich shells using a previously developed zig-zag shell model with hierarchic representation of displacements. The in-plane variation of the stiffness properties of plies and the through-the thickness variation of the core properties are determined solving the Euler-Lagrange equations of an extremal problem in which the strain energy due to out-of-plane strains and stresses is minimised, while that due to their in-plane counterparts is maximised. In this way, the energy stored by unwanted out-of-plane modes involving weak properties is transferred to acceptable in-plane modes. As shown by the numerical applications, the critical interlaminar stress concentrations at the interfaces with the core are consistently reduced without any bending stiffness loss and the strength to debonding of faces from the core is improved. The structural model was recently developed by the author to accurately describe strain energy and interlaminar stresses from the constitutive equations. It a priori fulfills the displacement and stress contact conditions at the interfaces, considers a second order expansion of Lame's coefficients and a hierarchic representation that adapts to the variation of solutions. Its functional d.o.f. are the traditional mid-plane displacements and the shear rotations, so refinement implies no increase of the number of functional d.o.f. Sandwich shells are represented as multilayered shells made of layers with different thickness and material properties, the core being treated as a thick intermediate layer.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.117-122
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• 2000

In this paper the stress intensity factor under uniform pressure in the arbitrarily-shaped plane crack configuration transformed elliptic crack by Mobius mapping are determined. Using Dyson's formula Boussinesq-Papkovich potentials for mode I deformation are constructed. In the example the stress intensity factors are approximately calculated by least square method.

• Journal of Mechanical Science and Technology
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• 제14권9호
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• pp.920-927
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• 2000

A multi-layered orthotropic material with a center crack is subjected to an anti-plane shear loading. The problem is formulated as a mixed boundary value problem by using the Fourier integral transform method. This gives a Fredholm integral equation of the second kind. The integral equation is solved numerically and anti-plane shear stress intensity factors are analyzed in terms of the material orthotropy for each layer, number of layers, crack length to layer thickness and the order of the loading polynomial. Also, the case of monolithic and hybrid composites are investigated in terms of the local fiber volume fraction and the global fiber volume fraction.