• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.10
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• pp.1890-1899
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• 1992

In bonded structures, there are V-notched cracks in dissimilar materials and the stress concentration of these V-notched cracks causes to occur interface cracks in dissimilar materials Therefore the strength evaluation of V-notched cracks in dissimliar materials seems to be important. The stress fields of a V-notched cracks is known as .sigma.$_{ij}$ .var. K $r_{p-1}$,where K is the stress intensity factor and p-1 is the stress singularity. When the distance, r, approaches to 0 at the stress fields of V-notched cracks, the stresses become infinites by two more stress singularities of p-1 and p-1 is no more -0.5. Stress singularities and stress intensity factors for V-notched cracks in dissimilar materials are treated and discussed. The Newton-Raphson method which is an efficient numerical method for solving a non-linear equation is used for solving stress sigularities. And stress intensity factors are solved by the collocation method using the Newton-Raphson and least squares method. The effects of stress intensity factors and stress singularities on stress fields of V-notched cracks in dissimilar materials are studied by using photoelasic isochromatic frings patterns obtained from computer graphics.s.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.4
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• pp.511-519
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• 2013

Switching controllers for active magnetic bearings are claimed to minimize the copper losses because they do not use bias currents. In this study, we compare the performances of the switching controller with those of the widely used proportional-derivative (PD) controller. The PD controller is combined with a synchronous notch filter to reduce the effect of the unbalance disturbance. For a fair and objective comparison, the PD controller is designed systematically. The switching controller is designed so that the dynamics of the two controllers are almost identical. A system model is developed. This model includes the flexible modes of the rotor and the dynamics of the sensors and amplifiers. The simulation results show that the switching controller indeed reduces the copper loss at lower speeds. However, it fails to operate around the speed close to the bending mode of the rotor.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.5
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• pp.418-424
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• 2014

We propose and experimentally demonstrate a photonic microwave notch filter with a negative coefficient. The negative coefficient is obtained by using cross gain modulation (XGM) in a reflective semiconductor optical amplifier (RSOA). When the RSOA is operated in saturated region, the signal carried on the pump wavelength is inversely copied to the probe wavelength by the XGM effect, showing a negative coefficient. Time delay between pump signal and probe signal is provided by single mode fiber (SMF) with wavelength dependent time delay. The proposed microwave notch filter shows notch dips of more than 35.1 dB and free spectral range (FSR) of about 380.6 MHz.

• Journal of the Korean Institute of Gas
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• v.12 no.1
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• pp.1-6
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• 2008

The notched Charpy impact test is one of the most prevalent techniques used to characterize the effect of high impulse loads on polymeric materials. In this study, a method of analysis in nylon plastic materials is suggested to evaluate the critical strain energy release rate for variation of notch angles from the Charpy impact energy measurement. Instrumented Charpy impact tester was used to extract ancillary information concerning fracture parameters in addition to total fracture properties and maximum critical load. The dynamic stress intensity factor of nylon plastic material was calculated for the ASTM Charpy specimen from the obtained maximum critical load. Also, the finite element model was developed to figure out the stress distributions for Charpy specimen with different notch angles subject to 3 point bending load which is equivalent to the load applied in the experiment.

• Journal of the Korea Convergence Society
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• v.9 no.2
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• pp.177-182
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• 2018

In this paper, the fracture behaviour at CFRP laminated structure due to the vertical falling impact of the fight drone frame composed of CFRP was investigated through the analytical study. As CFRP consists of fiber differently from the existing plastic material, the fracture behaviour becoms complex. So, the preceding study is important through the analytical study before this experiment. By comparing with the existing study model at the same condition as the result of this study, the applied stress value is shown to decrease greatly at the analysis model with the center notch hole of the laminated CFRP drone frame. On the basis of this study result, the esthetic sense can be shown as the foundation data about the notch hole of drone frame are grafted onto the convergence technique.

• Journal of the Korea Concrete Institute
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• v.17 no.2 s.86
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• pp.255-261
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• 2005

Immense quantities of coal combustion by-products are produced every year, and only a small fraction of them are currently utilized. The purpose of this study is to investigate reused techniques of coal ash in the construction field, which may contribute to the savings of building materials and conservation of environment. From the results of the compressive strength test, the elastic modulus was experimentally proposed. Also, based on the three- point-bending test, the fracture parameters - notch sensitivity, fracture energy, and initial compliance were experimentally proposed. As a result, the strength and fracture characteristics were lower than those of concrete or mortar. Also, the study showed that the deflection at a fracture decreased as the age increased and as the notch depth rate decreased. However, it was judged that its use as a building material could be expected if further research is carried out.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.12 s.243
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• pp.1605-1614
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• 2005

For the last four decades, tension test of notched bars has been performed to investigate the effect of stress triaxiality on ductile fracture. To quantify the effect of the notch radius on stress triaxiality, the Bridgman equation is typically used. However, recent works based on detailed finite element analysis have shown that the Bridgman equation is not correct, possibly due to his assumption that strain is constant in the necked ligament. Up to present, no systematic work has been performed on fully plastic stress fields for notched bars in tension. This paper presents fully plastic results for tension of notched bars and plates in plane strain, via finite element limit analysis. The notch radius is systematically varied, covering both un-cracked and cracked cases. Comparison of plastic limit loads with existing solutions shows that existing solutions are accurate for notched plates, but not for notched bars. Accordingly new limit load solutions are given for notched bars. Variations of stress triaxiality with the notch radius and depth are also given, which again indicates that the Bridgman solution for notched bars is not correct and inaccuracy depends on the notch radius and depth.

• Composites Research
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• v.18 no.2
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• pp.1-12
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• 2005

Fracture behaviors of single-edge-notched monolithic aluminum plates and glass fiber/aluminum laminates under tensile loadings have been studied using acoustic emission(AE) monitoring. AE signals from monolithic aluminum could beclassified into two different types. For glass fiber/aluminum laminates, AE signals with high amplitude and long duration were additionally confirmed on FFT frequency analysis, which corresponded to macrocrack propagation and/or delamination. AE source location determined by signal arrival time showed the zone of fracture. On the basis of the above AE analysis and fracture observation, characteristic features of fracture processes of single-edge-notched glass fiber/aluminum laminates were elucidated according to different fiber ply orientations and fiber/aluminum lay-up ratios.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.706-711
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• 2007

Numerical studies were performed to examine the effects of notch location of impact specimens on the failure behavior of HAZ (heat affected zone) when Charpy V-notch impact test were made at a low temperature ($1^{\circ}C$). Carbon steel plate (SA-516 Gr. 70) with thickness of 25mm for pressure vessel was welded by SMAW (shielded metal-arc welding) and specimens were fabricated from the welded plate. Charpy tests were then performed with specimens having different notch positions of specimens varying from the fusion line through HAZ to base metal. A series of finite element analysis which simulates the Charpy test and crack propagation initiating at the tip of V-notch was carried out as well. The finite element analysis takes into account the irregular fusion line and non-homogenous material properties due to the notch location of the specimen in HAZ. Results reveals that the energies absorbed during impact test depend significantly on the notch location and direction of specimen. Finite element analysis also demonstrates that the notch location of specimens, to a great extent, influences the reliability and consistency of the test.

• Journal of Advanced Navigation Technology
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• v.13 no.3
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• pp.412-418
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• 2009

This study aims to develop a system that enables 20 to 25 wafers to be automatically aligned at the position of the corresponding serial number and facilitates the checkout of wafer processing by sensing them before and after semiconductor processing. It also suggests compensation algorithm and stepper motor control algorithm that carefully align notches. This study minimizes the rate of occurrence by adopting materials of which the surface has proper coefficient of friction when wafers are rotating and that do not rarely produce particles. This study completed the development of a slip resistance apparatus and carried out performance tests through mathematical verification. This system is expected to improve semiconductor yield due to anti-pollution technology in semiconductor processing and can be selectively applied to a large size wafer over 450mm in the future.