• 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.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.15 no.2
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• pp.109-116
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• 2022

In this paper, we propose a band rejection filter (BRF) with a state variable filter (SVF) structure to effectively remove the influence of 60 Hz line frequency noise introduced into the sensor system. The conventional BRF of the SVF structure uses an additional operational amplifier (OPAMP) to add a low pass filter (LPF) output and a high pass filter (HPF) output or an input signal and a band pass filter. Therefore, the notch frequency and the notch depth that determine the signal attenuation of the BRF greatly depend on the tolerance of the resistors used to obtain the sum or difference of the signals. On the other hand, in the proposed BRF, since the BRF output is formed naturally within the SVF structure, there is no need for a combination between each port. The notch frequency of the proposed BRF is 59.99 Hz, and it can be confirmed that it is not affected at all by the tolerance of the resistor through the Monte Carlo simulation results. The notch depth also has an average of -42.54dB and a standard deviation of 0.63dB, confirming that normal operation as a BRF is possible. Also, with the proposed BRF, noise filtering was applied to the electrocardiogram (ECG) signal that interfered with 60 Hz noise, and it was confirmed that the 60 Hz noise was appropriately suppressed.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.5
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• pp.405-414
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• 2009

This paper proposed a methodology based on ultrasonic diffraction technique to inspect the depth of a crack initiated from a notch of CT specimen by fatigue test, and its usefulness was verified by experiments. Especially, in order to identify accurately the diffractive waves from the crack tip in the situation where there are extra diffractive elements such as a notch, we have tried imaging by transducer scan and analyzed the propagation path of diffracted wave. Two specimens with and without a crack were experimented. Higher frequency and larger refractive angle of transducer showed a tendency to decrease the error in the measurements, and the measured crack depth showed an error less than 0.38 mm in case of 4 MHz $60^{\circ}-60^{\circ}$. The proposed methodology is applicable to weak diffractive sources, and so that it would be useful to inspect micro cracks and for their depth sizing.

• Computers and Concrete
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• v.22 no.1
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• pp.39-51
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• 2018

This study introduces a new algorithm to determine size independent values of fracture energy, fracture toughness, and fracture process zone length in three-point bending specimens with shallow to deep notches. By using the exact beam theory, a concept of equivalent notch length is introduced for specimens with no notches in order to predict the peak loads with acceptable precisions. Moreover, the method considers the variations of fracture process zone length and effects of higher order terms of stress field in each specimen size. In this paper, it was demonstrated that the use of some recently developed size effect laws raises some concerns due to the use of nonlinear regression analysis. By using a comprehensive fracture test data, provided by Hoover and Bazant, the algorithm has been assessed. It could be concluded that the proposed algorithm can facilitate a powerful tool for size effect study of three-point bending specimens with different notch lengths.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.6
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• pp.916-922
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• 1986

This paper presents the preliminary results of an experimental study on surface crack growth under fatigue loadings. The objective of this paper is to assess the effect of the initial crack size on crack propagation behaviors. Transparent PMMA plate speciments with shallow circular arc notch were used. Crack growth behaviors were observed and measured in two directions by travelling microscopes. The fatigue crack initiated at the deepest part on the initial arc shaped notch and then propagated to depth direction as well as spreading gradually along the notch tip. A considerable number of cycles was needed until the depth crack spreaded to the surface notch tip. When the fatigue crack reached the surface notch tip the crack front became an approximate semi-ellipse, primary semi-elliptical crack. Test results suggest that the relationships between fatigue crack growth rate and stress intensity factor range in both directions can be expressed by power law (Paris) and that relationship in width direction depends upon the crack ratios a$_{1}$/b$_{1}$, of the primary semi-elliptical crack. The relationship between the nondimensional crack lengths in both directions can be represented as the formula: (a/t)$^{n}$ =B(2b/W+A) where n and A are constants and B is seems to be depended upon the crack ratio a$_{1}$/b$_{1}$.

• 제어로봇시스템학회:학술대회논문집
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• 1992.10a
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• pp.776-779
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• 1992

This paper describes the auto-depth control system with depth control tank for low speed submersible vehicle that can be used for both near surface and deeply submerged keeping operations. The PDA control algorithm is used to design controller and adaptive notch filter is designed to eliminate the dominant frequency of seaway. The computer simulations demonstrate the excellent depth keeping performance of the controller under seaway effects.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.335-340
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• 2002

By the recently, Environmental pollution is serious by the highly economic growth and expansion of lively country basic industry. Especially, in case of industrial waste and life waste leaped into a pollution source. Also, research for processing of waste and recycling countermeasure is a pressing question on national dimension because it is prohibited an ocean disposal and reclamation. In this study, it looked for fracture characteristic value of recycling a coal ash to decrease environmental pollution by picky and exhaustion of natural resources and to reduce self-weight to prepare for a tall building and earthquake. So a coal ash examined to be possible to do as construction material. It achieved compressive strength test and three points bending test with initial notch depth rate and age for variables to show a basic research data. From the basis of the three points bending test, the fracture parameters - notch sensitivity, fracture energy, initial compliance were experimentally proposed. From the results of the compressive strength test, the elastic modulus was experimentally proposed. Also on the basis of the three points bending test, the fracture parameters - notch sensitivity, fracture energy, initial compliance were experimentally proposed. The results that the strength and fracture energy value are lower than concrete or mortar is described in this paper. Also, it shows that the deflection at fracture decreases as the age increases and the notch sensitivity decrease. However, it is judged to be available to construction material if research is continuously gone forward.

• Journal of Magnetics
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• v.13 no.4
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• pp.136-139
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• 2008

A simplified equation of depinning fields from notches of ferromagnetic Permalloy nanowires is presented. The derived equation is given in the form of an explicit function of nanowire width and thickness, and notch depth and angle. The equation agrees with all micromagnetic simulation results to an accuracy of ${\pm}$ 0.5 mT.

• Journal of the Korean Society for Nondestructive Testing
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• v.9 no.1
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• pp.8-21
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• 1989

This paper presents the ultrasonic characteristics of weldment and detectability of defects of weldment in Austenitic Stainless Steel Type 304 that is composed of mostly coolant piping system in nuclear power plants. The results of this experient show as follows: 1. When the ultrasonic beam detects the defects on the side of base metal and on the opposite side of weldment, the indications which was detected on the screen show different amplitude and different metal path each. 2. The ultrasonically estimated notch depth is generally oversized than actual notch depth. 3. It is easy for the false indication to show up on the screen because of columnar structure of weldment in austenitic stainless steel. 4. The higher frequencies of transducer have more difficulties to detect the defects of the opposite side of weldment because of ultrasonic attenuation in weldment and the longitudinal transmitter-receiver transducer is the most effective in detecting the opposite side defects of weldment.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.185-190
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• 2000

The effect of specimen thickness and notch's depth and the validity of J-integral analysis were studied on the fracture behavior of concrete. Through the 3-point bending test, the stress-deformation curves were experimentally measured. Concrete fracture toughness is calculated from stress-displacement curves. Concrete fracture toughness decreases when notch's depth is longer. So, Gf is less sensitive than JIc and Gf is more useful factor as concrete fracture toughness parameter. The values of J-integral and fracture energy increase when the breadth of concrete specimen get longer from 75mm to 150mm. Therefore, the breadth effect of specimen has to be considered in determining the concrete fracture toughness.