Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Crack closure effect of Three-dimensional surface cracked plate in Marine structures
under low-cycle fatigue
Shenglin Qiu1, Junlin Deng1, Ruitao Lu1, Dawei Dong1

1. School of Mechanical and Marine Engineering,Beibu Gulf University
Qinzhou, Guangxi, China

ABSTRACT
Three-dimensional complex cracks and other defects often exist in thestructural components of offshore engineering, which lead to stressconcentration, strength decline and catastrophic fracture accidents. Inpractice, the fracture failure of Marine structural components is usuallycaused by the propagation of three-dimensional curved cracks which do
not penetrate the plate thickness, and the ideal two-dimensional cracks
almost do not exist. In order to solve the fracture problem inengineering practice, it is very important to study the fracture
characteristics of three-dimensional non-penetration cracks. In theservice process of Marine structure, it is inevitable to encounter bad sea
conditions, which makes local materials into plastic state. The plasticinduced closure effect is widely used in the analysis of low cycle
fatigue propagation of plastic materials. In order to study the crackclosure effect in the process of low-cycle fatigue crack propagation of
three-dimensional surface cracked slabs in Marine structures, based on
the theory of elastic-plastic fracture mechanics and crack closure theory,the finite element numerical simulation of ABAQUS was used toobtain the stress-strain field at the crack tip of 3d surface cracked plates
made of Q345 steel. The relationship between three-dimensionalsurface crack cumulative plasticity and crack closure effect under
different stress ratio and crack length was investigated. It provides a
new reliable basis for further evaluation of low-cycle fatigue crack
propagation fracture characteristics of three-dimensional surface
cracked slabs in marine structures.

KEY WORDS: Marine structure, Three-dimensional surface cracked
plate, Low-cycle fatigue, Crack closure effect, Accumulative plastic.

INTRODUCTION
With the rapid development of economy and trade, in order to improvetransportation efficiency, the demand of large ship transportation isincreasing. The development of large-scale ships has significantly
improved the economy, but at the same time, the marine accidents

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caused by ships have also increased. The accidents in the operation oflarge-scale ships have brought more serious loss of life, property andenvironmental damage than before. And among these marine accidents,
a considerable part is caused by the fracture of the ship structure causedby the fatigue failure of the ship hull. According to the research, theoverall failure of ship structure is usually the result of the coupling
effect of low-cycle fatigue failure and accumulative plastic
failure(Huang Z Q,1993; Huang Z Q, 1999). In practice, the fracture
failure of Marine structural components is usually caused by thepropagation of impenetrable three-dimensional curved cracks, and theideal two-dimensional cracks almost do not exist. Under the action ofhigh stress, due to the inevitable three-dimensional cracks in the marinestructure itself, serious stress concentration will appear in the region of
the crack tip. When the stress reaches the yield limit that the material
can withstand, irreversible plastic strain will be generated in the crack
tip area and gradually accumulate leading to accumulative plastic. In
order to solve the fracture problem in practical engineering, it isparticularly important to study the fracture characteristics of threedimensional non-penetrating curve cracks. Crack closure often occurs
during crack propagation. Crack closure is one of the important factors
in the process of crack propagation, which affects the stress intensityfactor at the crack tip and thus affects the crack growth rate. At present,
the closure mechanisms recognized by the public are divided into four
categories : plastic closure, roughness closure, oxidation closure andphase transition closure.
A large number of studies have shown that the crack closure caused byplasticity has been widely accepted as one of the main closure
mechanisms affecting the fatigue crack growth rate (De Matos, P. F. P.,& Nowell, D. 2008; Cochran K B et al, 2011). Plasticity-induced crackclosure effect (PICC) is widely used to analyze the low-cycle fatigue
growth of plastic materials.
Newman et al. (1988) believed that when the load was unloaded, theelastic zone near the crack tip rebounded due to the recovery of
deformation, while the plastic zone could not recover the deformation.
Thus, the residual compressive stress causes the upper and lower
surfaces of the crack tip to contact before the load is unloaded to zero,