• Structural Engineering and Mechanics
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• 제41권5호
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• pp.591-604
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• 2012

This paper provides an iteration approach for the solution of multiple notch problem, which is based on the complex variable boundary integral equation (CVBIE). The contours of notches are applied by some loadings. The source points are assumed on the boundary of individual notch and the displacements along the boundaries become unknowns to be investigated. After discretization of the BIE, many influence matrices are obtained. One does not need to assemble many influence matrices into a larger matrix. This will considerably reduce the work in the program. The displacements along the many boundaries can be obtained from an iteration. There is no limitation for the configuration of notches. Several numerical examples are provided to prove the efficiency of the suggested approach.

• 대한치과보철학회지
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• 제18권1호
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• pp.15-35
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• 1980

The purpose of this study was to investigate stresses in the various components of fixed partial dentures restoring the posterior teeth of the lower jaw, and to measure quantitatively the effects of certain modifications in structural design on the stresses in the restorations using two-dimensional photoelasticity. Two-dimensional photoelastic methods were used in this study. Several models of fixed partial dentures were constructed. Shoulder less margins and anatomic occlusal reduction were incorporated in Model 1. Rounded shoulders and flat occlusal reduction were incorporated in Model 2, while Model 3 was a cantilever fixed partial denture. Other similar fixed partial dentures were constructed with V and U notches deliverately included in the region of the fixed joints for comparative reasons. The birefringent materials used in this study were PSM-1 and PSM-5 in standard sheets. PSM-1 was used for constructing the substructure, and PSM-5 was used in making the components of the fixed partial dentures. The two materials were used in the construction of composite photoelastic models. Improved artificial stone was used to represent dental cement in luting the composite photoelastic models. Static loading procedures were used at preplanned sites to represent occlusal loads in the mouth. 35 mm color and B/W film were used to record isochromatics in accordance with photoelastic procedures. Data reduction was performed using the grid method, which helped in, the mathematical integration procedure (Shear difference method) to separate the principal stresses. The results were as follows. 1. Fixed partial dentures do not function in bending as a symmetrical beam. Alternate areas of tension and compression were demonstrated when multiple contact loading was used. 2. The weakest part in posterior fixed partial dentures is the fixed joint. 3. (1) Models I and modified Model I were loaded on the pontic using a 50 pound vertical static load. The shear stress near the posterior fixed joint in Model 1 (U notches) was+129.4 p.s.i., and at the same fixed joint in modified Model 1 (V notches) was+239.4 p.s.i. The concentration of stress in fixed joint was reduced by 50% when U notches replaced the V notches. (2) Modified Model 2 was loaded using a multiple contact loader at a total load of 125 pounds. The difference between the principal stresses (${\sigma}_1-{\sigma}_2$), shear stress, at the V notches was+600 p.s.i., and at the U notches was+3l7 p.s.i. The shear stress was reduced by 50% when U notches replaced the V notches. V-grooves at the fixed joints should be avoided, and should be replaced by regular shaped U-grooves. 4. Cantilever fixed partial dentures had much higher stresses at the fixed joint than fixed partial dentures that were attached at both ends.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제54권6호
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• pp.293-297
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• 2005

Linearity is an important property of optical devices for analog communications. In this paper, we study the 3rd-order interrnodulation distortion (IMD3) of an Inp/InGaAsP multiple-quantum-well (MQW) traveling-wave type electroabsorption modulator (TW-EAM). We observe abnormal notches in the IMD3 results those were different from notches by general transfer curve of electroabsorption modulators (EAMs). We analyze the phenomena through absorption coefficients according to wavelengths and bias voltages to verify appearance of the abnormal notchs, where it can be known to result from Stark-shift and broadening. We propose the method to enhance linearity of MQW-EAMs by using these effects.

• Journal of Magnetics
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• 제20권3호
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• pp.312-316
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• 2015

Unlike conventional Eddy Current Test (ECT), Pulsed Eddy Current (PEC) uses a multiple-frequency current pulse through the excitation coil. In the present study, the detection of subsurface cracks using a specially designed probe that allows the detection of a deeper crack with a relatively small current density has been attempted using the PEC technique. The tested sample is a piece of 304 stainless steel (SS304) with a thickness of 30mm. Small electrical discharge machining (EDM) notches were put in the test sample at different depths from the surface to simulate the subsurface cracks in a pipe. The designed PEC probe consists of an excitation coil and a Hall sensor and can detect a subsurface crack as narrow and shallow as 0.2 mm wide and 2 mm deep. The maximum distance between the probe and the defect is 28 mm. The peak amplitude of the detected pulse is used to evaluate the cracks under the sample surface. In time domain analysis, the greater the crack depth the greater the peak amplitude of the detected pulse. The experimental results indicated that the proposed system has the potential to detect the subsurface cracks in stainless steel plates.

• Composites Research
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• 제31권4호
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• pp.145-150
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• 2018

항공우주산업에서 구조물의 수명연장과 경제적 측면에서의 효율적인 운용을 위해 다양한 구조건전성모니터링(Structural Health Monitoring, SHM) 기법들이 제시되어왔다. 금속재 구조물의 경우, 수분이나 염분 등에 의한 부식이나 쉽게 응력집중이 발생하는 타공, 노치, 볼트 등과 같은 위치에서의 균열이 주된 관심사였으나, 항공우주산업에서의 복합재 사용비율이 증가함에 따라 손상 메커니즘이 더욱 복잡한 복합재 구조물에 적용이 가능한 고도화된 SHM 시스템의 필요성이 강조되고 있다. 본 논문에서는 Q-switched 레이저와 다수의 압전센서를 이용한 복합재에서의 AE(Acoustic emission) 위치탐지 기법을 제시한다. 제시되는 기법은 10 mm 이내의 거리오차로 방출위치 탐지를 목표로 하며 복합재 구조에서 수행된 AE 모사실험 및 위치탐지 시도 결과를 제시하여 기법이 유효함을 증명한다.