• Journal of Korean Society of Steel Construction
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• v.22 no.6
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• pp.589-597
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• 2010

Steel structures have a higher probability of being damaged by fatigue than by other causes of deterioration. As such, their maintenance to prevent fatigue damage is essential to sustain their safety and performance during their service period. In their maintenance, the current state of their fatigue cracks must be assessed to determine appropriate reinforcement methods and the suitable time intervals of periodic inspections when fatigue cracks are detected. Determining the crack growth rate is a successful method of predicting fractures, but it requires technical knowledge on fracture mechanics and experience in numerical methods and software for finite element analysis. In this study, a fatigue crack growth test on through-thickness cracked steel plates was conducted to assess the crack growth rate without superior technical knowledge and experience. The relationship between the Crack Opening Displacement (COD) and the crack growth rate was found in relatively long fatigue cracks.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.2
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• pp.331-341
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• 1993

The propagating crack problems under dynamic antiplane mode in orthotropic material is studied in this paper. To analyze the dynamic fracture problems by theoretical method or experimental method in orthotropic material, it is important to know the dynamic stress intensity factor in the vicinity of crack tip. Therefore the dynamic stress field and dynamic displacement field with dynamic stress intensity factor of orthotropic material in mode III were derived. When the crack propagation speed approachs to zero, the dynamic stress components and dynamic displacement components derived in this paper are identical to the those of static state. In addition, the relationships between dynamic stress intensity factor and dynamic energy release rate are determined by using the concept of crack closure energy with the dynamic stresses and dynamic displacements derived in this paper. Finally, the characteristics of crack propagation are studied with the properties of orthotropic material and crack speed. The variation of angle .alpha. between fiber direction and crack propagating direction and crack propagation speed fairly effect on stress component and displacement component in crack tip. The influence of crack propagation speed on the speed on the stress and displacement is greater in the case of .alpha.=90.deg. than in the case of .alpha.=0.deg. and the faster the crack propagation speed, the greater the stress value and displacement value.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.731-734
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• 2002

There have been no obvious design criteria of high efficient displacement pump using a dimensionless parameter which can represent many physical aspect of displacement pump could be very useful to estimate displacement pump performance. Many dimensionless analysis methods have been developed in fluid dynamics, machine design and so on. In this study a new dimensionless parameter is developed for estimate displacement pump performance and efficiency, until now to evaluate the performance of displacement pumps which are widely used in industry field, primarily experimental methods have been used. The dimensionless parameter contains many physical information about pump design. For example, they are the relation between flow rate and power, displacement operation displacement and size, inlet and outlet valve size. And the developed dimensionless functions are induced from numerical method.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.15-16
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• 2006

In-process surface roughness prediction is studied in this research. To implement in-process prediction, spindle displacement is introduced. Machined surface's roughness is assumed to be expressed in terms of spindle displacement. In-process measurement of spindle displacement is conducted using CCDS (cylindrical capacitive displacement sensor). Two prediction models are developed. One is simple linear model between measured surface roughness and values by spindle displacement. The other is multiple regression model including machining parameters like spindle speed, fee rate and radial depth of cut. Relation between machined surface roughness and roughness by spindle displacement are verified.

• Geomechanics and Engineering
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• v.9 no.5
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• pp.585-599
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• 2015

Laboratory model tests were conducted to investigate the effect of surcharge loading rate on the magnitude of lateral displacement of prefabricated vertical drains (PVDs) improved deposit. The test results indicate that under the condition that the system had sufficient factor of safety (FS) ($FS{\geq}1.2$), for the similar model ground under the same total applied surcharge load, the lateral displacement increases with the increase of loading rate. The test results have been used to check the validity of a previously proposed method for predicting the maximum lateral displacement, and it shows that the data points are around the middle line of the predicted range, which supports the usefulness of the proposed method. The basic idea of the prediction method is an empirical relationship between the normalized lateral displacement (NLD) and a ration of load to the undrained shear strength of the deposit (RLS). The model test results offer some modifications of the NLD-RLS relationship: (1) instead of a bilinear relationship, NLD-RLS relationship may be entirely nonlinear; (2) the upper bound value of RLS for the proposed method can be used may be limited to 2.1 instead of the originally proposed value of 3.0.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.2
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• pp.291-295
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• 2006

Recently, greenhouse effect by $CO_2$ gas emitted by use of fossil fuel causes earth environmental problem. As a countermeasure of the global warming. micro hydropower under 100kW becomes the focus of attention for its clean and renewable energy sources. Newly developed micro positive displacement hydraulic turbine shows high efficiency and good applicability for the micro hydropoewer. The purpose of this study is to clarify the influence of leakage loss and effective head on the performance of the positive displacement hydraulic turbine for the further improvement of the turbine performance. The results show that the turbine. with a smaller side clearance. has much higher efficiency than that with bigger side clearance and it can sustain the high efficiency under the wider range of operation conditions. The turbine torque is proportional to the effective head and independent of the flow rate. The leakage is also dependent on the effective head but nearly independent of the flow rate.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.4
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• pp.149-157
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• 2000

Computer simulations of the mechanical behavior of a three point bend specimen with a quarter notch under impact load are performed. The case with a load application point at the side is considered. An elastic-plastic von Mises material model is chosen. Three phases such as impact bouncing and bending phases are found to be identified during the period from the moment of impact to the estimated time for crack initiation. It is clearly shown that no plastic deformation near the crack tip is appeared at the impact phase. However it is confirmed that the plastic zone near the crack tip emerges in the second phase and the plastic hinge has been formed in the third phase. Gap opening displacement crack tip opening displacement and strain rate are compared with rate dependent material(visco-plastic material). The stability during various dynamic load can be seen by using the simulation of this study.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.35 no.4
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• pp.410-420
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• 1999

The value of the mode I interlamina fracture toughness, GIC, is calculated by experimental compliance method, modified compliance method and beam theory. The value of the mode II interlamina fracture toughness, GIC, is evaluated by beam method, theory beam theory and compliance method. This paper describes the effect of load pint displacement rate and speicimen geometries for mode I and II interlaminar fracture toughness of glass fiber reinforced plastic composites by using double cantilever beam (DCB) and end notched flexure (ENF) specimen. For the load point displacement rate of increases whereas the value of 2,6 and 10 mm/min the value of GIC decrease as load point displacement rate increases whereas the value of GIC is found to be no significant effect. The value of GIC decreases as initial crack length increases. The fractured surface of the DCB and ENF samples are examined by scanning electron microscopy (SEM).

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.3
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• pp.34-38
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• 2018

Recently, the turbo charger has become an important part because it yields little displacement and high power while downsizing the engine's fuel ratio for environmental purposes. In this study, flow analysis was conducted to form the basis of data regarding the best efficiency. The axial displacement was changed from none to 25 mm by controlling the configuration of the turbo charger and the flow analyses were compared with each other. The maximum rate of the outlet of model 1 was 46.36 m/s and the maximum pressure of model 4 was 0.761946 Pa. The maximum flow rate of model 4 was 0.000187650 kg/s. This study's result should aid in the effective design of a turbo charger with high performance.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.10a
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• pp.131-136
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• 2003

Five expensive sensors are necessary to control a magnetic bearing system. The sensor price rate of magnetic bearing system is high. So it is necessary that cheap and good sensor is developed. The optical fiber displacement sensor is adaptive to satisfy this condition. We can design magnetically suspended spindle based on static characteristic of optical fiber displacement sensor developed. The controller can be designed by decoupled feedback PD. Therefore, it is simpler than any other controller comparatively.