Papers by Keyword: Weld Joint

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Authors: Yong Yun Nam, Seung Ho Han, Jeong Woo Han, Byung Chun Shin
Abstract: The hot spot stress or the notch strain alleviates the welding detail dependency of S-N curve to some extent. This paper suggests a new stress model which alleviates the dependency further, thus the fatigue strengths of several welding details of same material can be evaluated with the S-N curve of the base material. A stress at the hot spot of a weld joint is decomposed into two components; linear rising one, and rapid rising one which is inversely proportional to the distance from the hot spot. For the stress decomposition, a formula is proposed with which the configuration of stress distribution near a hot spot is fitted exactly. The new stress model makes use of a geometric characteristic of the stress distribution curve by the formula. The stress model is applied to five different weld joints. As the result, the experimental fatigue data are plotted very closely to the S-N curve of the base material
Authors: Sheng Sheng Zhang, Y.H. Cheng, L. Cheng
Abstract: The effects of work-piece heating temperature, holding time, and vacuity upon the quality of soldered fittings, when welding stainless heat exchanger (0cr17Ni12Mo2 plate) by vacuum brazing, are discussed in this paper. It also presents an optimized brazing procedure of welding heat exchanger. The processing property of soldered corrosion-resistant plate handled by the brazing procedure are discussed and optimized. Based on the analysis of samples taken from different sections of the welding seams, the paper studies the joint structure of brazing stainless steel.
Authors: Masahito Mochizuki, Gyu Baek An, Masao Toyoda
Authors: C.M. Sonsino, D. Radaj, W. Fricke
Abstract: Some recently developed variants of local concepts for assessing the fatigue strength and structural durability of welded joints are reviewed. These comprise structural stress, notch stress or strain and fracture mechanics concepts. New variants of the structural stress concept are Dong’s gradient stress approach and Xiao-Yamada’s ‘one millimetre stress’ approach. FE meshing rules have been developed for welded joints in thin sheet structures. The concept of fictitious notch rounding is now better substantiated for aluminium alloys. The small-size notch concept is applicable to thin sheet lap joints. The new notch stress intensity factor concept is based on the singular stresses at the sharp weld toe notch. Advanced fracture mechanics concepts combine crack initiation at the seam weld root or nugget edge and crack propagation over the plate thickness resulting in endurable FK values as function of cycles per unit thickness, N/t.
Authors: Byeong Choon Goo
Abstract: A structural steel should satisfy various properties under varied conditions. Fatigue strength is one of them. When structural steels are used in the form of welded joints, fatigue strength is one of the key characteristics that should be considered. In this study, comprehensive fatigue tests of a structural steel with yielding strength of about 350 MPa and tensile strength of about 520 MPa were carried out. First, a lot of specimens: parent material plates, butt welded specimens with reinforcement removed, as-welded plates, plates with weld toe ground, load-carrying cruciform, non load-carrying cruciform, plates with transverse fillet welded rib, etc were prepared and tested. S-N curves for the above specimens were compared and analyzed. Secondly, some life-size rectangular beams were fabricated by welding and tested. It is found that annealing is detrimental to fatigue strength rather than beneficial. The experimental data and results may be used usefully by engineers.
Authors: Jeong K. Hong, Ping Sha Dong
Abstract: Solder fatigue is one of the major product reliability concerns in electric packaging design. In this paper, the application of a mesh-insensitive structural stress method, previously developed by the authors, is demonstrated for characterizing fatigue of solder joints under thermal fatigue and mechanical fatigue conditions. Three sets of experimental data from literature are analyzed to demonstrate the effectiveness of the structural stress method in its ability to correlate test data over different packaging designs, test methods, etc. As evidenced in this study, the meshinsensitive structural stress method offers a simple but effective means to correlate the fatigue behavior of solder joints among various test conditions. The results show that the structural stress method can be used as an effective alternative to existing methods in the literature, in reliability design of electronic packaging.
Authors: Liang Yun Lan, Chun Lin Qiu, De Wen Zhao
Abstract: Nanoindentation technique was employed to study the hardness and elastic modulus for different regions in the welded joint of high strength steel. And the variation in mechanical behavior at micro scales was analyzed combined with microstructure observation. Experimental results showed that both maximum hardness (4.11GPa) and maximum elastic modulus (210.3GPa) were obtained in the coarse grained HAZ and the corresponding microstructure was granular bainite. While the weld metal and fine grained HAZ had similar values of hardness and elastic modulus, and corresponding microstructures were acicular ferrite and polygonal ferrite respectively.
Authors: Ivica Čamagić, Nemanja Vasić, Zijah Burzić, Aleksandar Sedmak
Abstract: The problem of fracture toughness, KIc, determination at a crack tip localized in a welded joint is placed in principle because fracture mechanics assumes homogenous material, not only around the crack tip but on a distance from it, in order to maintain valid theoretical assumptions and importance of the fracture toughness as the property measured by some of the fracture mechanics methods. Welded joint, as an integral part of a structure, represents inhomogeneity by microstructure and mechanical properties, often by geometrical form, and by the stress field as well, which are affected by various factors as well as residual stresses after welding [1]. However, these general difficulties did not disenable experimental determination of the fracture toughness under plane strain, KIc, in certain critical areas of a welded joint, or welded joint as a whole, but rather there are difficulties in interpreting the meaning of the measured values. Specimens for the fracture mechanics parameters determination are specimens with cracks, and cracks appears in welded joints as the most critical defects.
Authors: Shu Wei Leng, Zhang Mu Miao, Fu Xiang Qiu, Li Na Niu, Ting Miao
Abstract: Several tests including CTOD and Charpy impact have been performed on the weld joints of high strength low alloy steel S335G10+N to identify the toughness. The fracture surface and microstructure of samples extracted from the weld joints are characterized using scanning electron microscopy. Based on all data obtained some relationships between toughness and microstructure has been detected. (1) The tendency of Charpy impact energy distribution with the position of notch is similar to the CTOD values in WP and FL but different in FL+2.CTOD values of FL+2 are greater than those of FL, but the Charpy impact energy has an opposite tendency. (2) The appearance of Pearlite and upper bainite found in WP sample S3554 is regarded as one of the reasons for the lowest CTOD values. The cavity and quasi-cleavage in S35510 fracture surface indicate an inferior toughness compared with some dimples and ripple morphology of slip separation in S3552. (3)Grains close to the fracture surface in the 35511 (Stable crack growth) of FL +2 were elongated owing to plastic deformation caused by crack growth. (4)Hardness of the HAZ is equal to fusion zone and lower than base metal or weld position in S35511. Hardness of fusion zone increases with the depth. (5)A big difference of Average Grain Size is found in microstructure close to the fracture surface among S3557, S3556 and S3559.The greater the Average Grain Size is, the lower the CTOD value will appear.
Authors: Gab Chul Jang, Kyong Ho Chang
Abstract: During welding process to make joints, residual stress is inevitably produced and weld metal should be used. These influence the static and dynamic behavior of steel structures with welded joints, such as steel piles. In steel structures, dynamic mechanical behavior is different to static mechanical behavior. Therefore, to accurately predict the behavior of steel piles with a welded joint under static-dynamic loading, the research on influence of a welded joint on the static and dynamic behavior of steel piles is necessary. For that purpose, a rate-dependent plasticity model was used, considering strain rate hardening and temperature rise. In this paper, the distribution of welding residual stress in a welded joint was computed by using three-dimensional heat conduction analysis and three-dimensional thermal elastic-plastic analysis. The behavior of steel piles with a welded joint under axial static and dynamic loading was investigated by using three-dimensional elastic-plastic finite element analysis, which employed a rate-dependent plasticity model and included residual stress and mechanical properties of weld metal in a welded joint. The rate-dependent plasticity model used in this paper is proposed by the authors based on the static-dynamic loading tests. Numerical analysis results of steel piles with a welded joint were compared to those without a welded joint. In comparison, the characteristics of static and dynamic behavior of steel piles with a welded joint were investigated.
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