최적 피닝조건을 적용한 A6061-T6 합금의 피로특성 및 Fractography에 관한 연구

이동선(Dong-Sun Lee),정성균(Seong-Kyun Cheong) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5

As the industrial society develops rapidly, the weight reduction and high strength are gradually demanded . In case of the welded joint for the rolling stock which receives the repeated load, the fracture can be easily occurred. However, the durability and fatigue characteristics can be improved if the shot peening technique is applied. The optimal peening process should be applied to the metal surface because the over peening can lower the durability of parts. Thus, the fatigue characteristics and Fractography of welded A6061-T6 alloy for a rolling stock were studied in the paper. The optimal peening condition and Fractography were examined. The experimental result show that over peening can lower fatigue life caused by micro crack, fold and incrustation. The fatigue life of welded A6061-T6 was tremendously improved.

Mechanical Properties of W-X (X=Cu, Ag or BAg-8) Composites

Hanado H.,Hiraoka Y.,Inoue T.,Akiyoshi N. 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

Bend tests were performed at temperatures between 77 and 473K for W-19vol%Cu, W-22vol%Ag and W-19vol%(BAg-8) composites. Yield and maximum strengths and ductility of the composite were discussed in terms of microstructure and fractography. Results are summarized as follows. (1) Almost no difference was recognized in yield strength between the composites. In contrast, a large difference was recognized in maximum strength and ductility between the composites. (2) Inferior mechanical properties of W-Ag composite to W-Cu composite are attributed to heterogeneous distribution of Ag-phases, whilst inferior mechanical properties of W-(BAg-8) composite to W-Cu composite are attributed to large pores at grain boundaries.

소성유동층을 갖는 마찰압접 계면의 회전굽힘응력 파괴거동

김대열(Dae Yeul Kim),오환섭(Hwan Sup Oh) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11

Friction Welding(FW) Technology is about Mechanical Connection in Solid state. When one material which is rotating(Rotation Part) approaches another material which is fixed(Fixed Part), Temperature in Connection Interface is going up to recrystallization degree in the material. That means Friction Welding has Elastic Flow. In this study, I can study the evidence of Elastic Flow in Friction Welding using the Carbon Steel, Stainless Steel, Aluminum that are widely used in industry. In first step, Similar material and dissimilar material Friction Welding are processed in the factory, depending on each mechanical property. In second step, I will try to test Tension Strength and Fatigue Strength with Universal testing machine and Rotary bending machine. Finally I can look for the evidence in Elastic Flow and Spiral Deformation with Scanning Electron Microscope(SEM) in Fractography.

고온 부품용 Ti-6Al-4V 합금의 미세조직과 고온 인장 특성과의 상관관계

이정섭(Jungsub Lee),송전영(Jeon Young Song),한정민(Jung Min Han),구지호(Ji Ho Gu),마영화(Young Wha Ma) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11

AM(Additive Manufacturing) has columnar prior beta grain with α’-martensite due to vertical direction temperature gradient and rapid cooling rate (10³~10⁴ K/s), and most AMed part performs the heat treatment to remove the crystallographic texture. After heat treatment of AMed Ti-6Al-4V alloy, α’-martensite transform to α+β mixture phase that reduce the anisotropy and maintain the strength stability at elevated temperature. However, Ti-6Al-4V alloy occurs degradation of tensile properties above 300 °C. It is necessary to study on life prediction at elevated temperature and build the database of AMed Ti-6Al-4V alloy to apply low-pressure and compressor turbine blades. In this study, horizontal and vertical specimen manufacture by L-PBF and elevated temperature tensile test conducted at 25~700 °C with analysis of microstructure and fractography. Tensile properties are decreased with increasing testing temperature. In fractographs, V series specimen has larger dimple size that indicates decreasing of strength due to Hall-Petch relationship. However, V series specimen has similar axis of tensile load and columnar grain that result in higher elongation at elevated temperature.

Zr-기 벌크 아몰퍼스 금속의 파괴거동에 미치는 부하속도와 노치 형상의 영향

신형섭(Hyung-Seop Shin),고동균(Dong-Kyun Ko),정영진(Young-Jin Jung),오상엽(Sang-Yeob Oh) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.8

In order to investigate the mechanical behavior of newly developed materials such as BAMs or BMGs, the evaluation of mechanical properties using small-size specimen is essential. An instrumented impact testing apparatus which provides the load-displacement curve under impact loading without oscillations was used. The influences of loading rate, notch shape on the fracture behavior of the Zr-based bulk amorphous metal(BAM) were examined. In addition, throughout the 3 dimensional topology analysis of fracture surfaces after testing, fracture characteristics of BAMs under different conditions were investigated. The absorbed impact energy in the Zr-based BAM was largely consumed in the process for crack initiation not for crack propagation. The absorbed impact energy increased with increasing of the radius of notch tip. The Zr-based BAM showed a significant notch sensitivity. Fracture surface under impact loading condition was more smooth than that under quasi-static loading condition. Depending on the appearance and distribution of shear bands developed, the absorbed energy appeared differently. It can be found that the resulting toughening of the Zr-based BAM was closely related with the development of shear bands and the fractography.

창의적 문제해결 이론을 이용한 소성역깊이 측정에 관한 연구

이동우(Dong-Woo Lee),주원식(Won-Sik Joo) 한국기계가공학회 2008 한국기계가공학회지 Vol.7 No.1

Machine parts subjected to fluctuating or cyclic loads induce repeated stresses that often result in failure by fatigue. In such cases, the fatigue failures unfortunately sometimes occur. These may arise from a lack of knowledge with regard to the design, fabrication and operation of the machines or structures. The failure analysis provides valuable information regarding the prevention of similar failures. Furthermore, this information will be useful to improve or to develop new products. Failure stress analysis is classified into X-ray fractography. X-ray fractography has the limited applications because of material crystal size, difficult measurement method, electrolytic polishing precision, and long test time. Therefore, this study proposed the new method to improve the measurement precision of plastic zone depth and test time using TRIZ.

초음파 파면해석에 의한 대차 프레임의 건전성 평가

윤인식(In-Sik Yun),권성태(Sung-Tae Kwon),선종성(Jong-Sung Sun),명노종(No-Jong Myung),정우현(Woo-Hyun Chung),손태순(Tai-Soon Son),김경국(Kyung-Kook Kim),김순철(Soon-Cheol Kim) 한국철도학회 2000 철도저널 Vol.3 No.2

This study proposes the integrity evaluation of the bogie frame using ultrasonic fractography analysis. Analysis objectives in this study are to investigate fracture planes of damaged zone by the A-scan method. The surface condition of fracture planes shows degree of degradation by the stress concentration. The detection of the natural defects in the bogie frame is performed using the characteristics of echodynamic pattern in ultrasonic signal. Results of ultrasonic testing agree fairly well with those of actual fracture plane. In quantitative fractography analysis, microstructures of actual fracture plane turned out to be intergranular and transgranular fracture. Proposed ultrasonic fractography analysis in this study can be used for the integrity evaluation of the bogie frame.

평생 능력 개발 : 금속재료의 재료시험법 교과내용 개선을 위한 Fractography 신개념 소개 및 도입에 대한 연구

오동준 ( Dong Joon Oh ) 한국실천공학교육학회 2010 실천공학교육논문지 Vol.2 No.1

Material Testing Method subject of Metal Materials, which is one of curriculum of engineering major high school, is not properly updated even though both science and technology are advancing rapidly. Especially, the need of fractographic technique, which can analyze the fracture surface with the advanced testing equipment and technique, is increasing. The importance and the analyzing method of Fractography are proved by the characteristic analysis of pressure tube fracture surface of HWPR. In the future, in order to increase the professional knowledge and their pride of engineering major high school student, these advanced subject should be included in the new crriculum of engineering major high school. This activity to involve the advanced subject should be carried out voluntary by the first line teacher before the responsible body.

신갈나무 정상재와 인장이상재의 전단 및 휨 파면해석

권성민 ( Sung Min Kwon ),권구중 ( Gu Joong Kwon ),장재혁 ( Jae Hyuk Jang ),김남훈 ( Nam Hun Kim ) 한국목재공학회 2011 목재공학 Vol.39 No.4

This study has been carried out to understand the fracture characteristics of the tension wood of Quercus mongolica under the shear and bending stress Macroscopically, the wood fluff in the shear surface appeared more frequently in tension wood than sound wood, and more coarse wood fluffs were observed in 30% than 10% moistured shear surface. In the fractured tension wood from bending stress, more thick and long wood fiber appeared than sound wood. The observation using scanning electron microscope indicated that both sound and tension wood samples from radial shear surface showed the intrawall dominated failure and the fracture surface of the ray parenchyma cell showed the transwall dominated failure. In tangential shear surface, wood fiber surface showed the intrawall failure and short and coarse wood fiber was observed in tension wood. Ray parenchyma cell of sound and tension wood samples showed the transwall failure. The surfaces of tension wood`s ray parenchyma cell were relatively clean. The fractured tension wood from bending stress showed unsharp and flat wood fiber compared with sound wood.

구조용 목질재료의 전단파괴기구 해명을 위한 파면해석적 연구

김남훈,홍순일,이성재 한국가구학회 1999 한국가구학회지 Vol.10 No.1

The ultrastructural characteristics of shear fracture surfaces of laminated wood prepared from major four Korea wood specimens were examined. Commercial urea and urethan resin were used as adhesives for laminated woods of both homospecies and heterospecies. The morphology of fracture surface was observed using an optical microscopy and scanning electron microscopy. Three anatomical failure types were recognized : intercell failure, intrawall failure and transwall failure. In dry specimen, failure occurred mainly in woods. Laminated woods of softwoods showed mostly intrawall failure and transwall failure of tracheids, and them of hardwoods indicated mainly intrawall failure and interwall failure. Laminated woods prepared with urethan resin showed coarse fracture surface, on the other hand, those prepared with an urea formaldehyde resin had clean surface. In wet specimen, failure occurred dominantly in glue line. Intrawall failure and flags were characterized in laminated wood prepared with urethan resin. In heterospecies laminated woods, failure was occurred mainly in softwood. Consequently, fracture morphology of laminated wood may be influenced by adhesives, moisture content, species and anatomical characteristics.