A Smart Health Monitoring System with Application to Welded Structures using Piezoceramic and Fiber Optic Transducers

Sage Publications 2006 Journal of intelligent material systems and struct Vol.17 No.1

<P>Large welded structures, including ships and offshore structures, are normally in operation under cyclic fatigue loadings. These structures include many geometric as well as material discontinuities due to weld joints, and the fatigue strength at these hot spots is of critical importance for the structural performance. In the past, various Non-Destructive Evaluation (NDE) techniques have been developed to detect fatigue cracks and to estimate their location and size. However, important limitations of most of the existing NDE methods are that they are off-line; the normal operation of the structure has to be interrupted and the device often has to be disassembled. In this context, a new impedance-based structural health monitoring system employing piezoceramic transducers is developed with a special interest in applying the technique for welded structural members in ship and offshore structures. In particular, the impedance-based structural health monitoring technique that employs the coupling effect of piezoceramic (PZT) materials and structures is investigated. Moreover, a preliminary study of using fiber Bragg grating (FBG) type optical fiber sensors for the stress measurement of a typical weld structure is investigated. The final goal is to extend the fiber optic sensor technique for the global and local stress measurements of ship or offshore structures.</P>

On the Estimation and Control of Welding Distortion of Guide Blade Carrier for a 660 MW Turbine by Using Inherent Strain Method

A. Vishvesha, C. Pandey,M. M. Mahapatra,R. S. Mulik 한국강구조학회 2017 International Journal of Steel Structures Vol.17 No.1

While predicting the welding distortion for a complex welded structure like the guide blade carrier assembly of power generation turbine, the traditional thermo-mechanical models commonly utilized for geometrically simple welded butt and T joints may not be adequate. For large and complex welded structures,the thermo-mechanical elasto-plastic analysis can be computationally prohibitive. Other than simplistic butt and T joints, the aforementioned distortion prediction technique is not so suitable to provide reliable results when applied to large complex 3-D welded structures. Hence, inherent strain method is proposed here to predict distortion in an outer ringof GBC (Guide Blade Carrier) of a steam turbine. Such welded outer rings of GBC are large welded structures having many welded joints of different weld geometries at several planes. In the present study, inherent strain based technique was utilized for the aforementioned welded structure in elastic finite element analysis for the accurate prediction of 3-D distortion patterns with reduced computational time. The predicted and measured values of 3- D distortions of GBC were observed to be in good agreement with the ones provided from the shop floor, indicating the adequacy of inherent strain based method for the prediction of welding distortion in large and complex welded structures. As part of this investigation, a suitable welding fixture was also designed and welding sequence was modified, which were verified through inherent stain method to aid in minimizing the distortion of welded GBC.

Design of a Laser Welded Thin Metal Tube Structure Incorporating Welding Distortion and Residual Stress

김재웅,김충기 한국정밀공학회 2010 International Journal of Precision Engineering and Vol. No.

The welding process, incorporating rapid heating and cooling, generates distortion and residual stress in the welded structures. In the design of a high quality welded structures, the weld distortion and residual stress have to be considered in advance. Especially, for the thin metal welded structures, the thermal distortion and residual stress have a severe effect on the structure’s precision, fatigue strength, buckling strength and so on. This study aims to analyze the design candidates of a laser welded thin metal tube structure in the view point of welding distortion and residual stress. Three design candidates were fabricated, and then the distortion was measured. And the residual stress distributions were calculated by using a commercial FEM package. The analysis results show that the distortion and residual stress were affected according to the position of weld line and the design of structure. By using the analyses the best one among the three design candidates was selected finally.

유한요소해석을 이용하여 파이버 레이저 용접으로 T형 구조물 용접 시 최적 조건 도출을 위한 연구

표창민,김재웅 한국기계기술학회 2022 한국기계기술학회지 Vol.24 No.6

Welding is a representative processing technology applied in many industrial sites due to its quality and convenience. In particular, fiber laser welding can be welded at a faster speed compared to arc welding, and there is an advantage in welding distortion, which is the most significant disadvantage of welding. In this study, the weldable thickness was predicted, and the optimal welding angle was estimated using simulations during the welding of the T-shape structure. The multi-layer heat source model proposed in the previous author's study was used, and the study was conducted using the proposed welding heat source under specific conditions of 4kw and 1.0m/min. As a result, it was predicted that high-quality welding would be possible when the thickness was 3mm or 4mm, and it was also confirmed that welding should be performed at an angle of 82.5° or more when welding a 3mm thick structure. As a follow-up study, we plan to build a welding heat source model under various conditions and conduct a study to derive welding conditions at various thicknesses.

Novel welding distortion analysis method for large welded structures using orthotropic thermal expansion coefficients

Seo Hyun-Duk,Lee Jae Min 한국CDE학회 2021 Journal of computational design and engineering Vol.8 No.4

This paper proposes an effective numerical method to predict welding distortion for large welded structures. To predict welding distortions, inherent strain-based methods are computationally efficient and widely used in engineering fields. However, there are some drawbacks such as the generation of undesirable longitudinal forces and the use of vector-type input variables. Equivalent loads are derived through finite element formulation considering orthotropic thermal expansion conditions. Unlike previous methods, the proposed method predicts transverse shrinkage and angular distortion accurately, removing the undesirable longitudinal forces. In addition, scalar-type input variables are employed, which results in a convenient design procedure. The performance of the proposed method is verified through various examples including complex and large welded structures.

Welding sequence optimization using the strain direct boundary method based on the welding induced change in structural stiffness

노홍준,윤희찬,임헌봉,HyunIk Yang 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.12

The method proposed in this study is to determine the welding sequence to suppress welding de-formation using the strain directed as boundary (SDB) method. Welded joints are modeled by constructing tack welds and gaps as kinematic constraints in shell models. In addition, the SDB method considering the elastoplastic properties is used to evaluate the effect on the previous welding procedure. The results of the constructed analysis model are compared with the experimental results. The residual strain of each weld is calculated using the verified model, and joint stiffness is determined and compared by considering this together with the relationship between tensile stress and shrinkage strain of the weld. The optimal welding sequence is determined by comparing the stiffness of each welding joint, and this is compared and verified with the experimental results. In addition, it is confirmed that the determined welding sequence reduced the out-of-plane deformation by 2.01 % compared to the original welding sequence. The proposed method thus provides an analytical approach for welding sequence design.

Validation of Efficient Welding Technique to Reduce Welding Displacements of Ships using the Elastic Finite Element Method

Donghan Woo 해양환경안전학회 2020 해양환경안전학회지 Vol.26 No.3

Welding is the most convenient method for fabricating steel materials to build ships and offshore structures. However, welding using high heat processes inevitably produces welding displacements on welded structures. To mitigate these, heavy industries introduce various welding techniques such as back-step welding and skip-step welding. These techniques effect on the change of the distribution of high heat on welded structures, leading to a reduction of welding displacements. In the present study, various cases using different and newly introduced welding techniques are numerically simulated to ascertain the most efficient technique to minimize welding displacements. A numerical simulation using a finite element method based on the inherent strain, interface element and multi-point constraint function is introduced herein. Based on several simulation results, the optimal welding technique for minimizing welding displacements to build a general ship grillage structure is finally proposed.

용접 구조물 압축강도의 간이해석에 관한 연구

서승일 대한용접접합학회 2000 대한용접·접합학회지 Vol.18 No.4

Residual stresses and deformations due to welding have effects on the strength of structures. In this paper, the compressive strength of basic welded structures is studied and the effects of the residual stresses and deformations on the compressive strength of beams, plates and shells are investigated,. Theoretical analysis for the basic structures is carried out and simplified methods to calculate the compressive strength are proposed. The proposed methods yield simple formulas to calculate the compressive strength, of which results are much helpful. The accuracy of the proposed method is revealed by comparison with experimental results.

Fatigue Crack Detection Test of Weldments Using Piezoceramic Transducers

MYUNG HYUN KIM,SUNG WON KANG,CHUNG-YON KEUM 한국해양공학회 2005 韓國海洋工學會誌 Vol.19 No.4

Large welded structures, including ships and offshore structures, are normally in operation under cyclic fatigue loadings. These structures include many geometric discontinuities, as well as material discontinuities due to weld joints. The fatigue strength at these hot spots is very important for the structural performance. In the past, various Non Destructive Evaluation (NDE) techniques have been developed to detect fatigue cracks and to estimate their location and size. However, an important limitation of most of the existing NDE methods is that they are off line; the normal operation of the structure has to be interrupted, and the device often has to be disassembled. This study explores the development of a structural health monitoring system, with a special interest in applying the technique to welded structural members in ship and offshore structures. In particular, the impedance based structural health monitoring technique that employs the coupling effect of piezoceramic (PZT) materials and structures is investigated.

Welding Distortion Prediction for Multi-Seam Welded Pipe Structures using Equivalent Thermal Strain Method

Chunbiao Wu,Chao Wang,Jae-Woong Kim 대한용접·접합학회 2021 대한용접·접합학회지 Vol.39 No.4

Distortion prediction of a welded structure is an important way to improve work efficiency and ensure product quality during the fabrication process. Recently, the widely used approaches for evaluating residual deformation include the thermo-elastic-plastic finite element method (TEP-FEM) and the inherent strain method (ISM). The former can accurately simulate the entire welding process with excessive computational time, whereas the latter has great potential in the fast prediction of residual distortion in complex welded components. In this study, an equivalent thermal strain method based on inherent strain theory was proposed to predict residual deformation of the multi-seam welded pipe structures. Moreover, a full 3D TEP-FEM model was also developed to estimate the distributions of inherent strain in longitudinal (L-seam) and circumferential (C-seam) welds. To validate the accuracy of the proposed ISM, the welding distortion predicted by the proposed ISM is compared with the experimental data and TEP-FEM simulation results. It is discovered that the proposed ISM can be used to accurately predict welding-induced deformation in multi-seam welded pipe structures. Furthermore, compared with TEP-FEM simulation, the significant advantage of this approach is that the computing efficiency can be increased by about 50 times.