• Journal of Welding and Joining
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• 제23권2호
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• pp.81-89
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• 2005

A numerical model for multiple reflection effects of a polarized beam on laser grooving has been developed. The surface of the treated material is assumed to reflect laser irradiation in a fully specular fashion. Combining electromagnetic wave theory with Fresnel's relation, the reflective behavior of a groove surface can be obtained as well as the change of the polarization status in the reflected wave field. The material surface is divided into a number of rectangular patches using a bicubic surface representation method. The net radiative flux far these patch elements is obtained by standard ray tracing methods. The changing state of polarization of the electric field after reflection was included in the ray tracing method. The resulting radiative flux is combined with a set of three-dimensional conduction equations governing conduction losses into the medium, and the resulting groove shape and depth are found through iterative procedures. It is observed that reflections of a polarized beam play an important role not only in increasing the material removal rate but also in forming different final groove shapes. Comparison with available experimental results for silicon nitride shows good agreement for the qualitative trends of the dependence of groove shapes on the electric field vector orientation.

• 한국방사선학회논문지
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• 제9권4호
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• pp.239-247
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• 2015

의료용 선형가속기의 헤드 구성요소인 표적물질과 일차 콜리메이터는 선속특징을 결정짓는데 가장 큰 영향을 미치며 이로 인해 발생하는 후방산란은 구조물 차폐와 장비 관리 관점에서 고려하여야 할 요소이다. 이에 본 연구에서는 몬테카를로 시뮬레이션 중 하나인 Geant4를 통해 선형가속기를 모델링하고 헤드 구성요소의 변화에 따른 후방산란 양상을 살펴보았다. 산란되어 발생한 전자의 경우, 표적물질이 위치한 일차 콜리메이터의 내부 반경에 대부분의 분포를 보였으며 이와 반대로 산란된 광자의 경우, 바깥쪽 영역에서 상대적으로 높은 에너지의 산란이 많음을 알 수 있었다. 산란된 양전자는 약 0.03%로 미미한 발생을 보였다. 일차 콜리메이터의 내부 반경이 달라짐에 따라 세 산란입자(전자, 광자, 양전자) 모두 반경 내부 쪽에서의 변화가 컸으며, 전체 반경의 변화에 따른 후방산란은 60 mm 이상에서부터 어느 정도의 영향을 보인다는 것을 알 수 있었다. 표적물질 두께의 변화에는 큰 영향을 받지 않는 것으로 나타났다. 이를 통하여 가속시킨 초기 전자에 대한 후방 쪽으로의 산란도 무시할 수 없음을 알 수 있었으며 주변 구성요소의 기하학적인 형태나 크기에 의해서도 후방산란의 양상이 달라질 수 있음을 알 수 있었다. 따라서 산란된 입자들의 에너지 분포를 통해 장비 관리의 관점에서도 고려하여야 할 결과라고 사료된다.

• 한국정밀공학회지
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• 제12권4호
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• pp.67-77
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• 1995

In modern industry the requirement of automation of manufacturing process increases so that unmanned system has been popular as an ultimate goal of modern manufacturing process. In unmanned manufacturing process the tool fracture is a very serious problem because it results in the damage of workpieces and can stop the operation of whole manufa- turing system. In this study, image processing technique is used to detect the fracture of insert tip of face milling using multi-point-tool. In order to acquire the image information of fracture shape of rotation insert tip. We set up the optical system using a light beam chopper. In this system we can reduce the image degradation generated from stopped image of rotating insert tip using image restoration technique. We calculated the mean square error to diagnose the condition of tool fracture, and determind the criteria of tool fracture using experimental and staticstical method. From the results of this study we've developed non- contact detection technique of tool fracture using image processing method and proposed the fracture direction of automation and unmanned system considering the optimal time of tool change milling.

• Radiation Oncology Journal
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• 제11권2호
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• pp.421-430
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• 1993

The calculation of dose distribution in multiple arc stereotactic radiotherapy is a three-dimensional problem and, therefore, the three-dimensional dose calculation algorithm is important and the algorithm's accuracy and reliability should be confirmed experimentally. The aim of this study is to verify the dose distribution of stereotactic radiosurgery experimentally and to investigate the effect of the beam quality, the number of arcs of radiation, and the tertiary collimation on the resulting dose distribution. Film dosimetry with phantom measurements was done to get the three-dimensional orthogonal isodose distribution. All experiments were carried out with a 6 MV X-ray, except for the study of the effects of beam energy on dose distribution, which was done for X-ray energies of 6 and 15 MV. The irradiation technique was from 4 to 11 arcs at intervals of from 15 to 45 degrees between each arc with various field sizes with additional circular collimator. The dose distributions of square field with linear accelerator collimator compared with the dose distributions obtained using circular field with tertiary collimator. The parameters used for comparing the results were the shape of the isodose curve, dose fall-offs fom $90\%$ to $50\%$ and from $90\%\;to\;20\%$ isodose line for the steepest and shallowest profile, and $A=\frac{90\%\;isodose\;area}{50\%\;isodose\;area-90\%\;isodose\;area}$(modified from Chierego). This ratio may be considered as being proportional to the sparing of normal tissue around the target volume. The effect of beam energy in 6 and 15 MV X-ray indicated that the shapes of isodose curves were the same. The value of ratio A and the steepest and shallowest dose fall-offs for 6 MV X-ray was minimally better than that for 15 MV X-ray. These data illustrated that an increase in the dimensions of the field from 10 to 28 mm in diameter did not significantly change the isodose distribution. There was no significant difference in dose gradient and the shape of isodose curve regardless of the number of arcs for field sizes of 10, 21, and 32 mm in diameter. The shape of isodose curves was more circular in circular field and square in square field. And the dose gradient for the circular field was slightly better than that for the square field.

• 한국생산제조학회지
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• 제19권4호
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• pp.511-520
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• 2010

In general, spot welding is used at no welding rod or flux for the process, low welding point temperature compared to arc welding, short heating time, less damage to the parent material, and low deformation and residual stress, relatively. Also, because of the pressurization effect, better mechanical qualities of the welding parts are obtained. Therefore, in various fields of industry its rapid operation speed can make mass production possible such as motor industry. In FEM analysis for the spot welding process, it is effective to use simple modeling rather than complicated one because of its numerous number of spots and reduction of analysis time. Therefore, this study provides with not only simplification of modeling analysis by using beam component composition of structure without re-compositing the spot welding point mesh but also modeling analysis of which property of fracture strength is reflected. In addition complete spot welding model is examined at rectangular post shape (hat shape) by impact test, compared the results, and verified its validity. As a result, it is possible to optimize the welding position and to recognize the strength of structure and the proposed equal distance model shows the effect of welding point reduction and improvement of stiffness.

• 대한치과의사협회지
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• 제50권4호
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• pp.203-210
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• 2012

Objective: The aim of this study was to investigate the incidence of the C-shaped canal of permanent mandibular second molar (PMSM) in Korean sub-population using Cone-Beam CT (CBCT) data and analyze the types of C-shaped canal. Materials & Methods: The protocol for this study was approved by the Institutional Review Board at the Pusan National University Hospital (E-2011039). Among the CBCT images taken of patients who visited the St. Bennedict Dental Hospital (Busan, Korea) from May 2008 to April 2011 for implant surgery and surgical removal of impacted teeth, high-quality CBCTs from 705 patients (361 male and 342 female) were screened and 607 PMSMs of 383 patients were evaluated retrospectively. All PMSMs were anatomically analyzed in detail by using image viewer software (EasyDent; Vatech). PMSMs were evaluated in the axial plane to investigate the shape of root and canals. The C-shaped canals were classified into five types. The total incidence, gender ratio, bilateral and unilateral appearance. and the correlation between right-side and left-side occurrences of C-shaped PMSMs were computed and compared statistically using the chi-square test. Results: Among the 607 PMSMs of 383 CBCTs of 187 females and 196 males, 198 PMSMs(32.6%) had C-shaped root and 158 PMSMs(26.0%) had C-shaped canals. The shape of C-shaped root canals at the furcalion level did not have significant change at the level of mid root (P<0.0001). Female had more prevalence of C-shaped root canals than male (P<0.0001). The prevalence of bilateral occurrence of C-shaped root canals was higher than unilateral occurrence. Conclusions: The occurrence of C-shaped PMSMs among a Korean population was 32.6% and was higher than other countries and ethnicities. Understanding the prevalence of PMSMs with a C-shaped root and/or canal in a Korean population may be useful for successful endodontic treatments.

• Structural Engineering and Mechanics
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• 제33권4호
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• pp.503-527
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• 2009

This paper presents experimental results on the behaviour and ultimate load of fifteen pipes and six roof panels made of ferrocement. Additional results from three roof panels, carried out by others, are also compared with this research results. OPC cement, natural sand and galvanised iron wire mesh were used for the construction of 20 mm thick specimens. The pipe length was 2 m and roof panel length was 2.1 m. The main variables studied were the number of wire mesh layers which were 1, 2, 3, 4 and 6 layers, the inner pipe diameter which were 105, 210 and 315 mm, cross sectional shape of the panel which were channel and box sections and the depth of the edge beam which were 95 mm and 50 mm. All specimens were simply supported and tested for pure bending with test span of 600 mm at mid-span. Tests revealed that increasing the number of wire mesh layers increases the flexural strength and stiffness. Increasing the pipe diameter or depth of edge beam of the panel increases the cracking and ultimate moments. The change in the pipe diameter led to larger effect on ultimate moment than the effect of change in the number of wire mesh layers. The box section showed behaviour and strength similar to that of the channel with same depth and number of wire mesh layers.

• 한국재료학회지
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• 제18권11호
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• pp.592-596
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• 2008

Spring constants (displacement per unit applied load) of MEMS socket pins of given structures were computed by theoretical analysis and confirmed by the finite element method (FEM). In the theoretical analysis, the displacement of pins was calculated based on the 2-dimensional bending theory of the curved beam. For the 3-dimensional modeling, CATIA was used. After modeling, the raw data were transferred to ANSYS, which was employed in the 3-dimensional analysis for the calculation of the stress and strain and loaddisplacement The theoretical analysis and the FEM results were found to agree, with each showing the spring constants as 63.4 N/m within a reasonable load range. These results show that spring constants can be easily obtained through theoretical calculation without resorting to experiments and FEM analysis for simple and symmetric structures. For the some change of shape and structural stiffness, this theoretical analysis can be applied to MEMS socket pins.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.116-119
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• 2004

The use of higher strength materials frequently requires the change of design provisions. Following to the previous researches, high strength reinforcing bars have a weak point about the development and splice length. Based on the previous research about high relative rib area, bond strength between reinforcing bars and concrete can be improved by the control of rib height and spacing. But, the code provisions do not include these specific shape of reinforcing bars. So, the purpose of this paper is to determine the effect of relative rib area to the bond strength. This paper describes the experiment and analysis of 5 beam-spliced specimens containing D25 with relative rib areas ranging from 0.073 to 0.17. The test results are also analyzed to make a design formula about the calculation of splice length on the consideration of relative rib area.

• Structural Engineering and Mechanics
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• 제26권2호
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• pp.179-190
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• 2007

Damage detection based on measured vibration data has received intensive studies recently. Frequently, the damage to a structure may be reflected by a change of some system parameters, such as a degradation of the stiffness. In this paper, we apply a method to nondestructively locate and estimate the severity of damage in corrosion pipeline for which a few natural frequencies or mode shapes are available. The method is based on the strain modal sensitivity ratio (SMSR) and the orthogonality conditions sensitivities (OCS) applied to vibration features identified during the monitoring of the pipeline. The advantage of these methods is that it only requires measuring few modal parameters. The SMSR-based and OCS-based damage detection methods are illustrated using computer-simulated and laboratory testing data. The results show that the current method provides a precise indication of both the location and the extent of corrosion pipeline.