• Steel and Composite Structures
• /
• v.2 no.1
• /
• pp.35-50
• /
• 2002

A series of tests on simple-welded plate specimens (SWPS) and T-stub tension specimens simulating some of the joint details in moment frame connections were conducted in this investigation. The effects of weld strength mismatch and weld metal toughness on structural behavior of these specimens were considered under both static and dynamic loading conditions. Finite element analyses were performed by taking into account typical weld residual stress distributions and weld metal strength mismatch conditions to facilitate the interpretation of the test results. The major findings are as follows: (a) Sufficient specimen size requirements are essential in simulating both load transfer and constraint conditions that are relevant to moment frame connections, (b) Weld residual stresses can significantly elevate stress triaxiality in addition to structural constraint effects, both of which can significantly reduce the plastic deformation capacity in moment frame connections, (c) Based on the test results, dynamic loading within a loading rate of 0.02 in/in/sec, as used in this study, premature brittle fractures were not seen, although a significant elevation of the yield strength can be clearly observed. However, brittle fracture features can be clearly identified in T-stub specimens in which severe constraint effects (stress triaxiality) are considered as the primary cause, (d) Based on both the test and FEA results, T-stub specimens provide a reasonable representation of the joint conditions in moment frame connections in simulating both complex load transfer mode and constraint conditions.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.35 no.10
• /
• pp.1179-1185
• /
• 2011

Cold and hot-rolled carbon steel sheets are commonly used in railroad cars or commercial vehicles such as the automobile. The sheets used in these applications are mainly fabricated by spot welding, which is a type of electric resistance welding. However, the fatigue strength of a spot-welded joint is lower than that of the base metal because of high stress concentration at the nugget edge of the spot-welded part. In particular, the fatigue strength of the joint is influenced by not only geometrical and mechanical factors but also the welding conditions for the spot-welded joint. Therefore, there is a need for establishing a reasonable criterion for a long-life design for spot-welded structures. In this thesis, ${\Delta}P-N_f$ relation curves have been used to determine a long-life fatigue-design criterion for thin-sheet structures. However, as these curves vary under the influence of welding conditions, mechanical conditions, geometrical factors, etc. It is very difficult to systematically determine a fatigue-design criterion on the basis of these curves. Therefore, in order to eliminate such problems, the welding residual stresses generated during welding and the stress distributions around the weld generated by external forces were numerically and experimentally analyzed on the basis of the results, reassessed fatigue strength of gas welded joints.

• Journal of Welding and Joining
• /
• v.27 no.5
• /
• pp.49-54
• /
• 2009

Recently, a demand of ferritic STS is increasing rapidly in automobile exhaust system. Exhaust manifolds are the part nearest to the engine so that the material is exposed to high temperature exhaust gas. Excellent heat resistant properties, especially high temperature strength, thermal fatigue resistance and high corrosion resistance are necessary for these parts. STS429L contains 15 weight percent of Cr and low Mo, so has good price competitive. And it has excellent high temperature strength and corrosion resistance, so receives attentions as material that applying to exhaust manifold. In tensile test of lap joint welded STS 429L, most of specimens are failed in base metal, but occurs brittle fracture in weld metals at some specimens in the face of good welding conditions. In the process of tensile test, lap joint welded STS429L specimens are transformed locally. The brittle fracture occurs that local transforming area exists in weld metals. But, butt welding specimens made by same materials showed ductile fracture in tensile test and bending test. In this study, suppose the reason of brittle fracture is in the combined local transform and tensile stress, through analysis of bead geometry, evaluate geometrical factor of brittle fracture in lap joint welded STS429L.

• Journal of Welding and Joining
• /
• v.33 no.1
• /
• pp.35-40
• /
• 2015

Recently, there have been the increase of ship size and the development of oil and gas in arctic region. These trends have led to the requirements such as high strength, good toughness at low temperature and good weldability for prevent of brittle fracture at service temperature. There has been the key issue of crack arrestability in large size structure such as container ship. In this report for the first time, crack arrest toughness of thick steel plate welds was evaluated by large scale ESSO test for estimate of brittle crack arrestability in thick steel plate. For large structures using thick steel plates, fracture toughness of welded joint is an important factor to obtain structural integrity. In general, there are two kinds of design concepts based on fracture toughness: crack initiation and crack arrest. So far, when steel structures such as buildings, bridges and ships were manufactured using thick steel plates (max. 80~100mm in thickness), they had to be designed in order to avoid crack initiation, especially in welded joint. However, crack arrest design has been considered as a second line of defense and applied to limited industries like pipelines and nuclear power plants. Although welded joint is the weakest part to brittle fracture, there are few results to investigate crack arrest toughness of welded joint. In this study, brittle crack arrest designs were developed for hatch side coaming of large container ships using arrest weld, hole, and insert technology.

• Journal of Ocean Engineering and Technology
• /
• v.13 no.3 s.33
• /
• pp.68-76
• /
• 1999

The welding residual stresses produced by the welding frequently caused a crack and promote stress corrosion etc. in HAZ(heat affected zone) contained with external load and weakness of material. Therefore, PWHT(post welding heat treatment) is widely used to reduce wekdubg residuss, to relax hardening of heat affected zone and to get rid of impurity. In this study, in order to define the effect on shappes of T-welded joint, during the post welding heat treatment, we have carried out numerical analyses on the several test pieces by using computer program which was based on thermal-elasto-plato-plasto-creep theories for the study. The main results obtained form this study is as follows: 1) The mechanical difference for change the thickness of plate and groove angle did not appear. 2) The distribution modes of welding residual stresses are same on the all test specimens during the post welding heat treatment. 3) In a mecharical point of view, minimum groove groove angle($40^{circ}$) is more suitable than maximum groove angle($60^{circ}$). 4) Therefore, it is appropriate to minimize the size of groove shape in strength and safety.

• Journal of Welding and Joining
• /
• v.17 no.6
• /
• pp.53-61
• /
• 1999

The use of thick plate in increasing in recent years due to the rapid expansion of chemical plants, nuclear plants, ships and other industrial plants. Welding is the most popular joining techniques employed in manufacturing industrial machineries and structures. Normally, Groove shapes are prepared according to appropriate rules and regulations such as KS, JIS, AWS, LR, DNV and etc. for various thicknesses of plate. However those groove angles tend to be too large. As a result of large groove angle, residual stress, deformation of material and strength reduction is obtained. Therefore, the reliability and safety of structures and machinery tend to be decreasing. Therefore, in this paper, theoretical as well as experimental study are carried out to find optimum groove shapes for T-welded joint of mild steel. The test specimen are made in same condition with simulation model. Welding residual stresses measurement by sectional cutting method. ⅰ) The mechanical difference for change the thickness of plate and groove angle are not appeared. ⅱ) In a mechanical point of view minimum preparation angle(40°) is more suitable than maximum groove angle(60℃). ⅲ) The measurement value and distribution of welding residual stresses are not effected largely by groove angle. It is mechanical restraint that mainly affect welding residual stresses distribution. In mechanical point of view minimum groove angle is more suitable than maximum groove angle. Therefore, it is appropriate to minimize the size of groove shape in strength and safety.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.22 no.1
• /
• pp.129-136
• /
• 2018

The estimation of the fatigue design life for large welded structures is usually performed using the liner cumulative damage method such as Palmgren-Miner rule or the equivalent damage method. When a fatigue crack is detected in a welded steel structure, the residual service life has to be estimated base on S-N curve method and liner elastic fracture mechanics. In this study, to examine the 3D fatigue crack behavior and estimate the fatigue life of out-of-plane gusset fillet welded joint, the fatigue tests were carried out on the model specimens. Investigations of three-dimensional fatigue crack propagation on gusset welded joint was used the finite element analysis of FEMAP with NX NASTRAN and FRANC3D. Fatigue crack growth analysis was carried out to demonstrate the effects of aspect ratio, initial crack length and stress ratio on out-of-plane gusset welded joints. In addition, the crack behaviors of fatigue tests were compared with those of the 3D crack propagation analysis in terms of changes in crack length and aspect ratio. From this analysis result, SIFs behaviors and crack propagation rate of gusset welded joint were shown to be similar fatigue test results and the fatigue life can also be predicted.

• Journal of Welding and Joining
• /
• v.16 no.4
• /
• pp.47-54
• /
• 1998

Various equipments in plants are welded with two different materials and it is required to investigate the effects of fatigue crack propagation on the neighborhood of a welded portion. The characteristics of fatigue crack growth in the base metal of carbon and stainless steel, in the carbon and stainless steel sides located in the neighborhood of welded portion (carbon/stainless steel), respectively and welded portion, are investigated. The results show that the crack growth in the welded portion (carbon/stainless steel) is an average value of the crack growths in the carbon and stainless steel respectively located in the neighborhood of the welded portion. It is found that the crack growth in the welded portion is not significantly different from those in the carbon and stainless steel sides. Hence it can be concluded that the structure welded with two different materials wold not impede the integrity based on the fatigue crack growth.

• Proceedings of the KWS Conference
• /
• 1997.05a
• /
• pp.107-111
• /
• 1997

In this paper distribution of welding residual stress on the double fillet welded joint which exits and not exits root gap, i.e. full penetration and partial penetration is investigated by two dimensional cunduct and thermal elasto-plastic analysis. And stress distribution on notch-tip of the structure where welding residual stress regarded as initial stress and then external load is added is also investigated.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.6 no.4
• /
• pp.27-33
• /
• 1997

Spot welding has been used in the sheet metal jointing processes because of its high productivity and convenience. In this study, effects of welding conditions on the fatigue life and prediction methods of fatigue life of spot welded joint have been studded . Fatigue life was estimated by stress index parameter considering multiaxial stresses. Fatigue tests were conducted with the tensile-shear specimens using SPCC. Fatigue life of spot welded joint was influenced by welding currents and was predicted exactly with taking into account StageIII.