• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.23 no.2
• /
• pp.61-65
• /
• 1987

In this study, the characteristics of TRC (tensile restraint crack) critical stress in the gravity type underwater wet welding process and in the in-air welding have been investigated for Y, y and 45$^{\circ}$r grooves using the KR Grade A-3 steel plates and the E4303 covered electrodes. The following results were obtained: (1) In the TRC tests, the initial critical stress of Y groove is higher than those of the 45$^{\circ}$r single bebel grooves in both in-air and underwater weldings, and the cold fracture sensitivity is higher in the underwater welding than in the in-air welding. (2) The hardness of underwater weld metal is the highest in heat affected zone is about Hk 365 in the in-air weld but Hk 670 in the underwater weld which is higher for cooling speed is more rapid, resulting in the lower critical stress by increase of fracture sensitivity. (3) The diffusible hydrogen quantity for 48 hours is about 18cc/100g-weld-metal in the in-air welding but 48cc/100g-weld-metal in the underwater welding. So that, in the case of underwater welding the diffusible hydrogen penetrates about 3 times more than that in the in-air welding.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.23 no.2
• /
• pp.15-15
• /
• 1987

In this study, the characteristics of TRC (tensile restraint crack) critical stress in the gravity type underwater wet welding process and in the in-air welding have been investigated for Y, y and 45°r grooves using the KR Grade A-3 steel plates and the E4303 covered electrodes. The following results were obtained: (1) In the TRC tests, the initial critical stress of Y groove is higher than those of the 45°r single bebel grooves in both in-air and underwater weldings, and the cold fracture sensitivity is higher in the underwater welding than in the in-air welding. (2) The hardness of underwater weld metal is the highest in heat affected zone is about Hk 365 in the in-air weld but Hk 670 in the underwater weld which is higher for cooling speed is more rapid, resulting in the lower critical stress by increase of fracture sensitivity. (3) The diffusible hydrogen quantity for 48 hours is about 18cc/100g-weld-metal in the in-air welding but 48cc/100g-weld-metal in the underwater welding. So that, in the case of underwater welding the diffusible hydrogen penetrates about 3 times more than that in the in-air welding.

• Proceedings of the KAIS Fall Conference
• /
• 2012.05b
• /
• pp.759-761
• /
• 2012

초음파는 정보 측정분야와 에너지를 이용한 용접 및 가동 등에서 널리 사용되고 있으며 최근에는 이 종금속 접합방법에 있어 초음파 에너지를 이용한 용접이 사용되고 있다. 진공유리 최종공정인 배기공정에 있어 연납과 유리의 접합에 초음파 에너지를 사용하고 있는데 초음파 접합기 하단부의 O링이 열에 의해 변형이 되어 기밀이 유지되지 않게 된다. 본 연구에서는 혼 하단부와 O링의 온도를 최적으로 유지하기 위해 냉각유로를 설치하여 O링의 온도에 미치는 영향에 대해 고찰하였다.

• Proceedings of the KSME Conference
• /
• 2001.06a
• /
• pp.483-488
• /
• 2001

Until now, the tensile properties of materials can be obtained just in accordance with conventional tensile testing methods which are described in several standards such as ASTM (American Society for Testing and Materials) standard and BS (British Standard). For some cases including on-service facility materials, however, the standard testing methods cannot be applicable due to the destructive testing procedure and specimen size requirement. Therefore, simple, non-destructive and advanced indentation technique was proposed. This test measures indentation load-depth curve during indentation and analyzes the mechanical properties related to deformation and fracture. In this paper, the research trend of non-destructive evaluation of tensile properties using AIS (advanced indentation system) and its application fields are reviewed and discussed.

• Journal of Welding and Joining
• /
• v.11 no.1
• /
• pp.42-51
• /
• 1993

In this study, investigations were conducted in calculating parameters of elastic-plastic fracture mechanics using single specimen. The validity of these testing methods was judged by the confirmation of multiple specimen method of stop block test. The results were as follows: In order to measure a fracture toughness using the instrumented impact test, two general requirement must be considered; One, setting up proper impact velocity considered the effect of loading and the other, the necessity of low blow test for obtaining true energy by the compliance correction. It was possible to detect a crack initiation point by calculating the compliance changing rate from a load-defection curve. Criterion of a stable crack growth, $T_{mat}$ could be estimated by using key-curve method for a base metal. and combining Kaiser's rebound compliance with Paris-Hutchison's $T_{appl}$ equation for the brittled zone of welding heat affected.at affected.d.

• Journal of Ocean Engineering and Technology
• /
• v.17 no.4
• /
• pp.31-36
• /
• 2003

In case of this thick rolling-steel for a multistory building, a large oil-drilling structure, a large vessel, a bridge and so on, Lamella Tearing around the welded joint zone is the most serious problems. In order to prevent Lamella Tearing, not only is choice of material important, but also the comprehensive investigation for the structural design and the construction. The Lamella Tearing that is a staircase-shape occurs due to the contraction stress to the thickness direction of the plate and has the character that the cracks progress along the elongated inclusion by rolling. In general, because cracks occur at the heat affected zone and around HAZ, it is necessary to establish the safety and the confidence of the welded structure to restrain the welding defect such as Lamella Tearing. The mechanical approaches are the easier and more economical than the approaches of the material and the construction method. In addition, the appropriate welding profile and the optimum welding condition contribute toward the improvement of the productivity and influence on the standardization of the manufacturing technology.

• Journal of Welding and Joining
• /
• v.15 no.1
• /
• pp.46-54
• /
• 1997

The object of this paper is to evaluate SCC(stress corrosion cracking) susceptibility for parent metal and bond line region of weld joints which have the various weld heat input condtions in TMCP(thermo-mechanical control process) steel by SP-SSRT(small punch-slow strain rate test) method. And the SCC test results of TMCP steel are compared with those of the conventional HT50 steel which has te almost same tensile strength level like TMCP steel. The loading rate used was $3\times10^{-4}$mm/min and the corrosive environment was synthetic sea water. According to the test results, in the case of parent metal, TMCP steel showed higher SCC susceptibility than HT50 steel because of the high plastic strain level of ferrite microstructure obtained by accelerated cooling. And in the case of bond line, the both TMCP steel and HT50 steel showed low load-displacement behaviors and higher SCC susceptibility above 0.6. These results may be caused by theembrittled martensite structure on HT50 steel and by the coarsened grain and the proeutectoid ferrite structure obtained by the impart of accelerated cooling effect on TMCP steel.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.15 no.3
• /
• pp.120-126
• /
• 2006

In this paper, we investigated the characteristics of fatigue fracture on TB(Tailored Blank) weldment by comparing the fatigue crack propagation characteristics of base metal with those of TB welded sheet used for vehicle body panels. We also investigated the influence of center crack on the fatigue characteristic of laser weld sheet of same thickness. We conducted an experiment on fatigue crack propagation on the base metal specimen of 1.2mm thickness of cold-rolled metal sheet(SPCSD) and 2.0mm thickness of hot-rolled metal sheet(SAPH440) and 1.2+2.0mm TB specimen. We also made an experiment on fatigue crack propagation on 2.0+2.0mm and 1.2+1.2mm thickness TB specimen which had center crack. The characteristics of fatigue crack growth on the base metal were different from those on 1.2+2.0mm thickness TB specimen. The fatigue crack growth rate of the TB welded specimens is slower in low stress intensity factor range$({\Delta}K)$ region and faster in high ${\Delta}K$ region than that of the base metal specimens.

• Journal of Welding and Joining
• /
• v.16 no.3
• /
• pp.64-73
• /
• 1998

This paper is concerned with defects detection and evaluation of heat affected zone (HAZ) in austenitic stainless steel type 304 by ultrasonic wave and neural network. In experiment, the reflected ultrasonic defect signals from artificial defects (side hole, vertical hole, notch) of HAZ appears as beam distance of prove-defect, distance of probe-surface, depth of defect-surface on CRT. For defect classification simulation, neural network system was organized using total results of ultrasonic experiment. The organized neural network system was learned with the accuracy of 99%. Also it could be classified with the accuracy of 80% in side hole, and 100% in vertical hole, 90% in notch about ultrasonic pattern recognition. Simulation results of neural network agree fairly well with results of ultrasonic experiment. Thus were think that the constructed system (ultrasonic wave - neural network) in this work is useful for defects dection and classification such as holes and notches in HAZ of austenitic stainless steel 304.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.41 no.6
• /
• pp.455-467
• /
• 2017

In this study, a finite element analysis of a cylindrical multi-pass weldment for dissimilar metals was performed. The effects of the heat input method and weld bead generation method were considered. We compared two heat input methods: the heat flux method and the temperature method. We also compared two weld bead generation methods: the element birth method and the quiet element method. Although the results of the thermal analysis show deviations between the two heat input methods, the welding residual stresses were similar. Because the areas exposed to high temperature were similar and the strength of the material was very low in high temperature (above the $1000^{\circ}C$), the effects of the weld bead temperature were insignificant. The distributions of the welding residual stress were similar to each other. However, gaps and overlaps occurred on the welding boundary surfaces when the element birth method was applied. The quiet element method is more suitable for a large deformation model in order to simulate a more accurate weld shape.