Interaction of surface cracks on an egg-shaped pressure shell
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T E C H N I C A L N OT E S
Yongmei Zhu · Rujun Li · Wenjing Fang · Xilu Zhao · Wenxian Tang · Baoji Yin · Jian Zhang
Interaction of surface cracks on an egg-shaped pressure shell
Received: 25 March 2020 / Accepted: 17 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract This paper is focused on the interaction of surface cracks of an egg-shaped pressure shell of manned deep-sea submersibles. The surface cracks of the egg-shaped shell were subjected to the combined action of uniform external pressure and welding residual stress. The stress intensity factors were calculated using the M-integral method as an important parameter to characterize the stress and displacement fields in the vicinity of crack tips. The study is to evaluate the influence degree of the disturbing crack on the main crack and investigate the interaction between multiple cracks. The results provide references for optimizing the design and manufacture of egg-shaped pressure shells. Keywords Egg-shaped pressure shell · Surface crack · Stress intensity factor · Single crack · Double cracks 1 Introduction Fatigue cracks are easy to initiate at welding seams of pressure shell, and the corrosion will accelerate the crack propagation and increase the risk of damage to the shell structure. The SIF is an important parameter to characterize the stress and displacement fields in the vicinity of crack tips. Using the finite element method (FEM) to calculate SIF has strong adaptability and high accuracy [1–4]. Many investigators simulated surface crack propagations at the welding node of a plate with Franc3D software [5–8] and verified the correctness and efficiency of FRANC3D to calculate the stress intensity factor. As one of the non-spherical shells with positive Gaussian curvature, the egg-shaped shell was found to have better overall strength, stability, and space utilization, as well as lower sensitivity to geometric imperfection than the spherical shell [9–11]. It is formed by welding together two shells at the equator [9]. Whether it is welding molding or opening holes in the shell, residual stress will be generated at the welding toe. Small cracks are often generated around the welding toe and may open due to concentrated tensile stress. The meridional curvature is determined using the N-R function [12], which is expressed as follows: 2 2n y = ± L n+1 x n+1 − x 2 (1) n = 1.057(L/B)2.372 The curve obtained from equation is the yellow curve in Fig. 1b. We set up a finite element model of the shell structure that had semi-elliptical surface cracks added to the welding toe in Fig. 1a. In this work, the SIFs were analyzed theoretically and numerically by M-integral in FRANC3D [13]. Y. Zhu (B) · R. Li · W. Fang · W. Tang · B. Yin · J. Zhang School of Mechanical Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, China E-mail: [email protected] X. Zhao College of Mechanical Engineering, Saitama Institute of Technology, Saitama 369-0293, Japan
Y. Zhu et al.
Table 1 Geometric parameters of the egg-shape
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