• Geomechanics and Engineering
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• v.22 no.5
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• pp.461-473
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• 2020

Natural rock mass contains defects of different shapes, usually filled with inclusions such as clay or gravel. The presence of inclusions affects the failure characteristics and mechanical properties of rock mass. In this study, the strength and failure characteristics of rock with inclusions were studied using the particle flow code under uniaxial compression. The results show that the presence of inclusions not only improves the mechanical properties of rock with defects but also increases the bearing capacity of rock. Circular inclusion has the most obvious effect on improving model strength. The inclusions affect the stress distribution, development of initial crack, change in crack propagation characteristics, and failure mode of rock. In defect models, concentration area of the maximum tensile stress is generated at the top and bottom of defect, and the maximum compressive stress is distributed on the left and right sides of defect. In filled models, the tensile stress and compressive stress are uniformly distributed. Failing mode of defect models is mainly tensile failure, while that of filled models is mainly shear failure.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.6
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• pp.663-668
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• 2012

Fly ash erosion is a leading cause of boiler tube failure in PC boilers. Therefore, shields or baffle plates are installed in specific areas to mitigate fly ash erosion and prevent boiler tube failure. However, the tube failure problems caused by fly ash erosion cannot be eliminated with this solution alone, because each PC boiler has a different flue-gas flow pattern and erosion can become severe in unexpected zones. This problem is caused by an asymmetric internal flow velocity and local growth of the flue gas velocity. For these reasons, clearly defining the flow pattern in PC boilers is important for solving the problem of tube failure caused by fly ash erosion. For this purpose, the cold air velocity technique (CAVT) can be applied to the fly ash erosion problem. In this study, CAVT was carried out on the Hadong #2 PC boiler and the feasibility of application of CAVT to conventional PC boilers was validated.

• Journal of computational fluids engineering
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• v.10 no.1
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• pp.51-55
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• 2005

For proper installation, operation and performance of axial flow jet engines in aircrafts, the impacts and effects of inlet flow distortion in axial compressors have to be understood. Inlet distortion conditions may cause component-mismatch and instability problems known as rotating stall, and severe oscillations of mass flow rate called surge or a combination of both. Typical effects of this phenomenon include stresses and wear on the compressor blading, destruction of entire jet engines due to the failure of airfoil and mechanical failure or interruption of the combustion process. Therefore, it is important to study inlet flow distortion and its propagation effects to minimize and hence to prevent the occurrence of such calamity. The current novel integral method with parametric analysis signifies its validity to this field of research and offers much potential for further improvements. The present effort further indicates that this simple method may be flourishing in the problems of strongly distorted flow and propagating stall in axial compressor. It is therefore believe that using a more realistic and flexible velocity and pressure profiles could develop this approach further.

• Computers and Concrete
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• v.31 no.5
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• pp.443-455
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• 2023

This is a research analyses on the bearing capacity at a pile tip embedded in rock. The aim is to propose a shape coefficient for an analytical solution and to investigate the influence of the plastic flow law on the problem. For this purpose, the finite difference method is used to analyze the bearing capacity of various types and states of rock masses, assuming the Hoek & Brown failure criterion, by considering both plane strain and an axisymmetric model. Different geometrical configurations were adopted for this analysis. First, the axisymmetric numerical results were compared with those obtained from the plane strain analytical solution. Then the pile shape influence on the bearing capacity was studied. A shape factor is now proposed. Furthermore, an evaluation was done on the influence of the plastic flow law on the pile tip bearing capacity. Associative flow and non-associative flow with null dilatancy were considered, resulting in a proposed correlation. A total of 324 cases were simulated, performing a sensitivity analysis on the results and using the graphic output of vertical displacement and maximum principal stress to understand how the failure mechanism occurs in the numerical model.

• 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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.7 s.238
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• pp.947-954
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• 2005

The purpose of this study is to develop failure pressure evaluation models, which are applicable to straight pipes and elbows containing an internally wall thinning defect induced by flow-accelerated-corrosion (FAC). In this study, thus, three dimensional finite element (FE) analyses are performed to investigate the dependences of failure pressure of internally wall thinned pipe on the defect shape, the pipe geometry, and the defect location and bend radius of elbow. Also, the existing failure pressure assessment models for externally wall thinned pipes are examined. Based on these, the new models for assessing failure pressure of piping components with an internally wall thinning defect are proposed. Comparison of failure pressure, predicted by proposed models, with FE analysis result shows good agreement regardless of pipe type, defect shape, and defect location and bend radius.

• Journal of Chest Surgery
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• v.31 no.4
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• pp.402-408
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• 1998

A 56-year old female underwent total aortic arch replacement March 1995, because of an expanding chronic Debakey type I aortic dissection. This aortic dissection had an intimal tear at the origin of the right carotid artery. Retrograde and antegrade propagation of dissection resulted in aortic arch blood flow separation and expanding pseudolumen to the abdominal aorta. Sudden anuria(ARF) developed 3 hours later postoperatively and renal doppler ultrasonography and aortography showed diminished blood flow of renal arteries. We performed balloon aortic dilatation but failed. She could be restored good renal flow after intimal flap fenestration resection and thrombectomy of the abdominal aorta. This patient could be discharged in a state of mild CRF after 2 months of ICU care for respiratory and renal failure.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.125.2-125.2
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• 2005

• 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 Materials Processing
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• v.12 no.2
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• pp.134-140
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• 2003

Polymers such as polypropylene or polyethylene offer a unique feature of producing an integral hinge, which can flex over a million times without causing a failure. With such advantage manufacturing, time and cost required at the assembly stage can be eliminated by injecting the whole part as one piece. However, due to increased fluidity resistance at hinges during molding, several defects such as short shot or premature hinge failure can occur with the improper selection of gate locations. Therefore, it is necessary to optimize flow balancer in injection molding of part with hinges before actually producing molds. In this paper, resin flow patterns depending on several gate positions were investigated by numerical analyses of a simple strip part with a hinge. As a result, we found that the properly determined gate location leads to better resin flow and shorter hesitation time. Finally, injection molding tryouts using a mold that was designed one of the proposed gate systems were conducted using polypropylene that contained 20% talc. The experiment showed that hinges without defects could be produced by using the designed gate location.