• Tunnel and Underground Space
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• v.25 no.3
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• pp.284-292
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• 2015

The generalized Hoek-Brown failure criterion, the strength parameters of which are determined by using the GSI index, is an empirical nonlinear failure criterion of rock mass and has been widely employed in various rock engineering practices. Many rock engineering practitioners, however, are still familiar with the description of the strength of rock mass in terms of friction angle and cohesion. In addition, almost all rock mechanics softwares incorporate the simple linear Mohr-Coulomb function. Therefore, it is necessary to provide a tool to implement the Hoek-Brown function in the framework of the Mohr-Coulomb criterion. In this study, the use of upper-bound solution of limit analysis for bearing capacity of a strip footing resting on the ground surface is proposed for the estimation of the equivalent friction angle and cohesion of rock mass incorporating the generalized Hoek-Brown failure criterion. The upper-bound bearing capacity is expressed in terms of friction angle by use of the relationship between tangential friction angle and tangential cohesion implied in the generalized Hoek-Brown function. The friction angle minimizing the upper-bound bearing capacity is taken as the equivalent friction angle. Through the illustrative implementations of the proposed method, the influences of GSI, $m_i$ and D on the equivalent friction angle and cohesion are investigated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.8 s.227
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• pp.1229-1236
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• 2004

The specimen materials used in this research are isotropic epoxy resins. The static photoelastic experiment was applied to them. And then the specimens used in photoelastic experiment were fractured under static load. The static photoelastic experimental hybrid method was introduced and its validity had been assured. Crack propagation criterion used the stress components, which are considered the higher order terms, obtained from the static photoelastic experimental hybrid method was introduced and it was applied to the minimum strain energy density criterion, the maximum tangential stress criterion and mode mixity. Comparing the actual initial angle of crack propagation with the theoretical initial angle of crack propagation obtained from the above failure criterions, the validities of the above two criterions are assured and the optimal distance (r) from the crack-tip is 0.01mm in order to get the initial angle of crack propagation of isotropic epoxy resin.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.11
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• pp.1799-1806
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• 2004

The static photoelastic experiment was applied to orthotropic materials. And then the specimens used in photoelastic experiment were fractured under static load. The static photoelastic experimental hybrid method for orthotropic material was introduced and its validity had been assured. Crack propagation criterion used the stress components, which are considered the higher order terms, obtained from the static photoelastic experimental hybrid method was introduced and it was applied to the minimum strain energy density criterion, the maximum tangential stress criterion and mode mixity. Comparing the actual initial angle of crack propagation with the theoretical initial angle of crack propagation obtained from the above failure criterions, the validities of the above two criterions are assured and the optimal distance (${\gamma}$) from the crack-tip is 0.01mm in order to get the initial angle of crack propagation of orthotropic material(C.F.E.C.).

• Journal of Korean Society for Quality Management
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• v.25 no.3
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• pp.51-61
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• 1997

We introduce a method of estimating an unknown failure rate function based on sample data. We estimate failure rate function by a function s from a space of cubic splines constrained to be linear (or constant) in tails using maximum likelihood estimation. The number of knots are determined by Bayesian Information Criterion(BIC). Examples using simulated data are used to illustrate the performance of this method.

• Steel and Composite Structures
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• v.19 no.5
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• pp.1095-1113
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• 2015

In order to determine the mechanical behavior of the curved laminates in practical applications, three right-angled composite brackets with different lay-ups were investigated both experimentally and numerically. In the experimental, quasi-static tests on both unidirectional and multidirectional curved composite brackets were conducted to study the progressive failure and failure modes of the curved laminates. In the numerical modeling, three-dimensional finite element analysis was used to simulate the mechanical behavior of the laminates. Here, a strength-based failure criterion, namely the Ye criterion, was used to predict the delamination failure in the composite curved laminates. The mechanical responses of the laminate subjected to off-axis tensile loading were analyzed, which include the progressive failure, the failure locations, the load-displacement relationships, the load-strain relationships, and the stress distribution around the curved region of the angled bracket. Subsequently, the effects of stacking sequence and thickness on the load carrying capacity and the stiffness of the laminates were discussed in detail. Through the experimental observation and analysis, it was found that the failure mode of all the specimens is delamination, which is initiated abruptly and develops unstably on the symmetric plane, close to the inner surface, and about $29^{\circ}$ along the circumferential direction. It was also found that the stacking sequence and the thickness have significant influences on both the load carrying capacity and the stiffness of the laminates. However, the thickness effect is less than that on the curved aluminum plate.

• Journal of the Korean Society of Safety
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• v.22 no.4
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• pp.7-12
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• 2007

In order to evaluate the integrity of Zr-2.5Nb pressure tubes, probabilistic fracture mechanics(PFM) approach was employed. Failure assessment diagram(FAD), plastic collapses, and critical crack lengths(CCL) were used for evaluating the failure probability as failure criteria. The Kr-FAD as failure assessment diagram was used because fracture of pressure tubes occurred in brittle manner due to hydrogen embrittlement of material by deuterium fluence. The probabilistic integrity evaluation observed AECL procedures and used fracture toughness parameters of EPRI and recently announced theory. In conclusion, the probabilistic approach using the Kr-FAD made it possible to determine major failure criterion in the pressure tube integrity evaluation.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.89-92
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• 2002

Traditionally unidirectional laminated composite which are characterized by high specific stiffness and strength were used for structural application. But theses composites are highly susceptible to impact damage because of lower transverse tensile strength. The main failure modes of laminated composite are fiber breakage, matrix cracking and delamination for low velocity impact. The modified failure criterions are implemented to predict these failure modes with finite element analysis. Failure behavior of the woven fabric laminated composite which is used in forehead part of subway to lighten weigh has been studied. The new failure criterions are in good agreement with experimental results and can predict the failure behavior of the woven fabric composite plate subjected to low velocity impact more accurately.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.1
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• pp.173-180
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• 2004

This paper presents the effect of varying boundary conditions such as ground subsidence, internal pressure and temperature variation for buried pipelines on failure prediction by using a failure probability model. The first order Taylor series expansion of the limit state function incorporating with von-Mises failure criteria is used in order to estimate the probability of failure mainly associated with three cases of ground subsidence. Using stresses on the buried pipelines, we estimate the probability of pipelines with von-Mises failure criterion. The effects of varying random variables such as pipe diameter, internal pressure, temperature, settlement width, load for unit length of pipelines, material yield stress and pipe thickness on the failure probability of the buried pipelines are systematically studied by using a failure probability model for the pipeline crossing ground subsidence regions which have different soil properties.

• International Journal of Precision Engineering and Manufacturing
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• v.1 no.2
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• pp.48-54
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• 2000

This paper presents the effect of shape of external corrosion in pipeline on failure prediction by using a numerical simulation. The numerical study for the pipeline failure analysis is based on the FEM(Finite Element Method)with an elastic-plstic and large-deformation analysis. Corrosion pits and narrow corrosion grooves in pressurized pipeline were analysed. A failure criterion, based on the local stress state at the corrosion and a plastic collapse failure mechanism, is proposed. The predicted failure stress assessed for the simulated corrosion defects having different corroded shapes along the pipeline axis compared with those by methods specified in ANSI/ASME B31G code and a modified B31G code. It is concluded the corrosion geometry significantly affects the failure behavior of corroded pipeline and categorisation of pipeline corrosion should be considered in the development of new guidance for integrity assessment.

• Steel and Composite Structures
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• v.15 no.2
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• pp.203-220
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• 2013

The study of the tensile strength of composite materials is far more complex than analysis of the properties of elasticity and plasticity. Indeed, during mechanical loading, micro-cracks in the matrix, the fibers break, debonding of the interfaces are created. The failure process of composites is of great diversity and cannot be described if even we know: the strength criterion of each individual component, the state of stress and strain in the material, the propagation phenomena cracks in the structure and nature of the interface between the matrix and the reinforcement. This information is only partially known and the obtained by the analysis of a stress limit beyond which there is destruction of the material is almost impossible. To partially process the issue, a solution lies in a mesoscopic approach of seeking a law to locate the ultimate strength of the material for a plane stress state. Tests on rectangular plates in bending PEEK/APC2 and T300/914 three were made and this in order to validate our approach, the calculation has been implemented in a nonlinear finite element code (Castem 2000), in order to make comparison with the numerical results. The results show good agreement between numerical simulation and the two materials; however, it would be interesting to consider other phenomena in the criterion.