Elsevier

Structures

Volume 29, February 2021, Pages 2094-2105
Structures

Direct measurements, numerical predictions and simple formula estimations of welding-induced biaxial residual stresses in a full-scale steel stiffened plate structure

https://doi.org/10.1016/j.istruc.2020.05.030Get rights and content

Abstract

As a sequel to another paper of the authors on welding-induced initial deformations [1], this paper aimed to obtain a direct measurement database of welding-induced biaxial residual stresses in a full-scale steel stiffened plate structure and also to study the applicability of computational models to predict them. A full-scale steel stiffened plate structure in association with plate panels in bottom structures of an as-built containership carrying 1900 TEU was fabricated using exactly the same welding technology as used in today’s shipbuilding industry. The X-ray diffraction method was employed to measure the biaxial residual stress distributions in the plating. In addition to simple formula estimations, computational models using the three-dimensional thermo-elastic-plastic finite element method were applied to predict the biaxial residual stress distributions. A comparison between full-scale measurements, numerical predictions and simple formula estimations was made. Details of the full-scale measurements are documented as they can be useful to validate the computational models formulated by other researchers.

Introduction

Stiffened panels are used in naval, offshore, mechanical and civil engineering structures as primary strength parts of ships, ship-shaped offshore installations and bridges which should sustain external forces with tolerance arising from operational and environmental conditions, as shown in Fig. 1. Support members (longitudinal stiffeners and transverse frames) are attached to plating by fillet welding, and pieces of plate sheets are connected by butt welding. Stresses occurred in the process of heating and cooling of welding do not disappear even after fabrication is completed, where tensile residual stress block develops around weld line (heat-affected zone) and compressive residual stress block appears in the remaining part of plating so as to keep an equilibrium condition between tensile and compressive stresses, as shown in Fig. 2 [2]. It is important to realize that welding-induced residual stresses develop in both the length and breadth directions of plating as welding is applied to attach both longitudinal stiffeners and transverse frames, as shown in Fig. 3 [3].

Welding-induced residual stresses affect buckling and ultimate strength of plate panels which is primary strength criteria for structural analysis and design. Thin-plated structures (e.g., accommodation structures and deck houses of ships or offshore platforms) sometimes buckle with significant distortions during fabrication which require costly fairing works. This is often recognized as thermal plate buckling phenomenon and it can be prevented or controlled if the welding-induced residual stresses can be predicted quickly and accurately [4].

During past several decades, the importance of characterizing welding-induced residual stresses in plate panels has been well recognized, and a large number of studies in numerical predictions and direct measurements are available in the literature. Studies of numerical predictions on welding-induced residual stresses of steel- and aluminum-plated structures include Masubuchi [5], Smith et al. [6], Paik and Pedersen [7], Ueda [2], Paik et al. [8], [9], [10], [11], Paik [12], [13], [14], [15], Vhanmane and Bhattacharya [16], Luís et al. [17], Bruno et al. [18], Khan and Zhang [19], Eggert et al. [20], Gannon et al. [21], [22], [23], Khedmati et al. [24], Teresa and Craig [25], Iranmanesh et al. [26], Farajkhah et al. [27], Fu et al. [28], Lillemäe et al. [29] and Chen et al. [30]. Studies of direct measurements include Masubuchi [5], Matsui [31], Smith et al. [6], Cheng et al. [32], Ueda [2], and Kenno et al. [33], [34].

Despite that the importance of direct measurements has been realized, the databases of direct measurements are still lacking in the literature, and moreover most of them have been obtained on small-scale structure models which cannot be directly related to full-scale structures because adequate scaling laws are unavailable. It is therefore needed to develop measurement database of welding-induced residual stresses on full-scale stiffened plate structures which can minimize unwanted uncertainties due to scale effects.

The aim of the present paper is to contribute to developing measurement data of welding-induced residual stresses in both the plate length and breadth directions of a full-scale steel stiffened plate structure. This paper is associated with a series of full-scale physical tests on the ultimate strength under lateral patch loading in fires without passive fire protection in transverse frames [35], under lateral patch loading in fires with passive fire protection in transverse frames [36], under cyclic axial-compressive loading [37], at cryogenic condition with a temperature of –160 °C [38], and at a temperature of –80 °C [39]. The data of direct measurements for welding-induced initial deformations in the same test structure was also obtained and reported in a separate paper [1].

Computational models for predicting welding-induced residual stresses in the test structure were developed using three-dimensional thermo-elastic-plastic finite element method, and simple formulations were also used to estimate them. A comparison between direct measurements, numerical predictions and simple formula estimations was made. Details of direct measurements are documented in a tabulated form, which will be useful to validate computational models developed by other researchers.

Section snippets

Design and fabrication of a full-scale steel stiffened plate structure

Bottom plate panels of an as-built containership carrying 1900 TEU were selected for the present study as shown in Fig. 4. Dimensions of the structure are presented in Fig. 5. With the nomenclature of structural scantlings shown in Fig. 6, Table 1 lists its dimensions in detail.

The material is high tensile steel with grade AH32. After material procurement, tensile coupon test specimens were extracted from the steel sheet as per ASTM E8 specifications [40], as shown in Fig. 7(a). The tensile

Measurements of welding-induced biaxial residual stresses

A non-destructive technique, the X-ray diffraction (XRD) method was used to measure welding-induced residual stresses in the structure. Table 4 indicates the details of the measuring tool called Xstress3000™ [42]. Fig. 11 shows the measurement of welding-induced residual stresses using the XRD tool.

Measuring (monitoring) points can be defined at locations of interest as shown in Fig. 12. As welding-residual stresses develop in both the plate length and breadth directions, the measuring points

Numerical predictions of welding-induced biaxial residual stresses

Three-dimensional thermo-elastic-plastic finite element method was applied to predict the welding-induced residual stress distributions. Details of the computational models and approaches are described in a separate paper of the authors [43]. Here only the results of computational models together with computed values are presented.

Fig. 15 shows the finite element method model for a quarter of the structure with symmetric conditions. The structure was modeled using 8-node 3D brick

Simple formula estimations of welding-induced biaxial residual stresses

Simple formulations are useful to quickly estimate welding-induced residual stresses in steel stiffened plate structures. For that purpose, empirical formulations [3], [4] were used.

The distribution of welding-induced residual stresses in both directions was modeled with rectangular type of tensile and compressive residual stress blocks as shown in Fig. 3. It is noted that buckling and ultimate compressive strength of plate elements is directly affected by compressive residual stresses rather

Concluding remarks

The aim of the paper was to obtain measurement data of welding-induced biaxial residual stresses in a full-scale steel stiffened plate structure. Computational models for their numerical predictions together with simple formula estimations were also presented. Based on the studies, the following conclusions can be drawn.

  • (1)

    A full-scale steel stiffened plate structure associated with bottom plate panels of an as-built containership carrying 1900 TEU was successfully designed and fabricated in a

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was conducted at the International Centre for Advanced Safety Studies/the Korea Ship and Offshore Research Institute (www.icass.center) which has been a Lloyd’s Register Foundation Research Centre of Excellence since 2008.

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