변후(變厚)용접판재에서의 피로균열성장거동에 미치는 잔류응력의 영향에 관한 파괴역학적 연구

차용훈 한국산업안전학회 1993 한국안전학회지 Vol.8 No.1

The welding implementation used widely in the industrial field is gradually increasing due to weight reduction unlimited material thickness simplified structure design, and 1 manufacturing time and cost reduction. The most significant factor that influences the fatigue crack growth rate is the residual stress generated during the welding process. Many researchers have studied the effect of the residual stress on crack growth behavior. Through a fatigue test in a various-thickness welded specimen redistributed residual stress is measured as the crack is developed. Then, by superposing the measured residual stress on the K value obtained by the finite element method.

용접판재의 피로강도에 미치는 잔류응력 평가

차용훈,김덕중,이연신,채경수,성백섭,박회식 조선대학교 동력자원연구소 1997 動力資源硏究所誌 Vol.19 No.1

The objective of this thesis is to investigate the influence of the initial residual stress on the fatigue crack growth after the distribution of the initial residual stress is measured when the crack is growing from the compressive residual stress to the tensile residual stress field. In the case of as welded material, respective of load ratio, the span of the fatigue is the shortest in base metal, while in weld metal and HAZ, the crack growth was retarded due to the effect of the compressive residual stress at the crack tip as well as the span of the crack is longer than base metal. In region II that is in stable growth state of the fatigue crack, da/dN=C(ΔK)^m of power law was satisfied. Also, it was considered that the value of m is not affected by residual stress. Superimposing welding residual stress intensity factor K_res on ΔK, the value of ΔK_eff calculated was lower than ΔK in the same value of da/dN, while the ΔK_eff is almost the same at the high ΔK.

SUS 304 Stainless Steel의 F.C.C.에 關한 硏究

車龍勳 조선대학교 동력자원연구소 1988 動力資源硏究所誌 Vol.10 No.2

Crack growth behavior of SUS 304 Stainless steel in boiling MgCl_2 solution was investigated under low frequency cyclic loading. The results obtained are sumarized as follows ; 1) In the case of low stress level applied to the specimen, fatigue effects are significant on crack propagation at the beginning of fracture, but corrosion effects are significant on crack propagation during the long stable period of crack propagation. 2) Crack propagation rate is high at the crack initiation, and remains long stable period of crack propagation, and then finally becomes unstable fracture. 3) In case that K_max as well as R values increase, expression of equation da/dn=C(ΔK)^m is possible in the range of 27<K<37.

點 熔接部의 變形率 測定 및 影響 評價

차용훈,김덕중,성백섭 한국공작기계학회 1997 한국생산제조학회지 Vol.6 No.3

Electronic Speckle Pattern Interferometry(ESPI) using the Model 95 Ar. laser, a video system and an image processor was applied to the in-plane displacement measurements. Unlike traditional strain gauges or Moire method, ESPI method requires no special surface preparation or attachments and can be measured in-plane displacement with no contact and real time. In this experiment specimen was loaded in parallel with a loadcell. The specimen was the cold rolled steel sheet of 2mm thickness, which was attached strain gauges. The study provides an example of how ESPI have been used to measure strain displacement in this specimen. The results measured by ESPI compare with the data which was measured by strain gauge method in tensile testing.

鎔接材에서의 修正係數를 考慮한 疲勞龜裂成長擧動에 관한 硏究

차용훈,윤성운,김덕중 조선대학교 생산기술연구소 1995 生産技術硏究 Vol.17 No.1

In the present paper, based on the results obtaind from 2-dimensional F.E.M. and fatigue test, an empirical equation for the stress intensity factor for CT type plates having discontinuous thickness interfaced is presented. For the β=1 specimen with constant thickness crack growth rate is smoothly increasing in the a-N curve. On the other hand for the β=2 specimen with various thickness, the inflection point observed in crack growth rate near the thickness interface da/dN before compared to the β=1 specimen the inflection point is increased and da/dN after the point is decreased, da/dN near the thickness interface is approached zero. the descending point was preserved earlier as β increased. Considering the relation between da/dN, the crack propagation rates for the case of β=1 increased almost linearly, however the crack propagation rates for β= 2, 3 decreased more rapidly near the thickness interface Additionally, the decreased point in da/dN for β=3 is farther from the thickness interface than the case for β=2.

자동차 차체 다점용접부의 면외변위측정에 관한 연구

차용훈,성백섭,이연신,박영문,김충환 朝鮮大學校 機械技術硏究所 2002 機械技術硏究 Vol.5 No.1

The very few non-contact method are still in the early stage. One of the non-contact methods is by the use of the laser that has high-level of the accuracy for the measurement, and this laser also has excellent characteristics on which many studies for its applications are focused throughout the many fields. The dissertation is on the measurement of the strain caused by the characteristics of the spot welded zone which is used with 3-D ESPI system that is functionally modified through the laser ESPI(Electronic Speckle Pattern Interferometry) system. This system employed the SGCC 1.2t which are mainly used for the steel plate such as automobile, structure, electronics instrument, building material and electronic appliances.

Photo Stress를 이용한 압력용기 용접부의 잔류응력 측정

차용훈,김덕중,장훈 朝鮮大學校 機械技術硏究所 2004 機械技術硏究 Vol.7 No.1

Recently, studies on the deformation and residual stresses measurement in pressure vessel welded zone have been obtained from strain gaging method which had directly attached the gage on the surface of the material. But the non-contact method are not still general. In this paper, we will study effect on residual stress at the pressure vessel welded zone under the high pressure. The strain and residual stresses are measured by the photo-stress and hole drilling method. The material of Butt weld specimens are A516 GR70 steel for pressure vessel.

ESPI法을 利用한 點 熔接部의 面內變位 測定에 關한 硏究

차용훈,김덕중,이연신,채경수,성백섭 조선대학교 생산기술연구소 1997 生産技術硏究 Vol.19 No.1

Electronic Speckle Pattern Interferometry(ESPI) using the Model 95 Ar laser, a video system and an Image processor was applied to the in-plane displacement measurements. Unlike traditional strain gauges or Moire method, ESPI method requires no special surface preparation or attachments and can be measured in-plane displacement with no contact and real time. In this experiment specimen was loaded in parallel with a loadcell. The specimen was the cold rolled steel sheet of 2mm thickness. which was attached strain gauges. The study provides an example of how ESPI have been used to measure strain displacement in this specimen. The results measured by ESPI compare with the data which was measured by strain gauge method in tensile testing.

알루미늄合金 熔接部의 疲勞破壞擧動에 關한 硏究

車龍勳 조선대학교 동력자원연구소 1990 動力資源硏究所誌 Vol.12 No.1

This study practices the fatigue test of base metal, weld metal and HAZ specimen using 5052-H38-aluminum alloy welded by the GTA welding method and investigates the effect of initial residual stress which influences the fatigue crack growth rate. The results of this experimentation are summarized as follows ; 1. This experimentation confirms that the number of repeated cycle from each specimen to the last rupture is the most in the HAZ specimen and is in the order of weld metal specimen and base metal specimen. 2. The condition of crack growth retardation is occured by the effect of compressive residual stress from edge and HAZ specimen is greater than the weld metal specimen of the initial crack growth. 3. In the stable growth region of each specimen, m values are showed that m value of HAZ specimen is the greatest as 2.3, weld metal specimen is 2.2 and base metal specimen is 1.8. 4. Crack growth retardation by the compressive residual stress can be interpreted as superposition technique of kres.

알루미늄 合金 熔接材의 疲勞破壞에 미치는 殘留應力의 影響에 關한 硏究

차용훈,김하식,김덕중 한국공작기계학회 1995 한국생산제조학회지 Vol.4 No.4

This study is to inspect the influence of the initial residual stress on fatigue crack growth behavior after the distribution of the initial residual stress is measured when the crack is growing from the compressive residual stress field to the tensile residual stress field. Also, the influence of the variation of residual stress distribution on fatigue crack growth behavior at the crack tip is studied when the initial crack occurs on weld metal, bead interface and HAZ (Heat Affected Zone), respectively. For this purpose, CT-type specimen that crack parallel to the welding bead were manufactured by butt welding on the Al. Alloy 1100-O plate.