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

Stress-strain field at crack tip for low-cycle fatigue analysis of surface cracked plate in marine structures
Dawei Dong1, Junlin. Deng1*, Shenglin Qiu1, Ruitao Lu1.

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

ABSTRACTtime , people only seen one of many ways, not enough attention waspaid. Newman(1979) found that surface craks with relatively small
crack length were the approachest in all approximate solutions,particularly in the linear spring model solution and three-dimensional
finite element solution. So researchers began to pay attention to thismodel, the essence of this model is to transform a complex threedimensional surface crack problem into a two-dimensional penetratingcrack problem, and the dimension of the problem get reduced,
Guo(1999) introduce to the out-of-plane factor Tz , then, relate the outof-plane stress to the in-plane stress, Establish K-T-Tz three parameter theory to describing the three - dimensional crack tip field.
Yang(2003) discussed the three-dimensional elastic stress field near thefront of a penetrating crack in a plate of finite thickness, The stressintensity factors were obtained under different crack lengths anddifferent thickness plates. Four typical cracks are systematically studied
by three-dimensional finite element method, they obtained Semianalytical solutions of K, T and Tz for straight crack, 1/4 elliptic Angle
crack, semi-elliptic surface crack and embedded crack, then,theysummarize complete description of three parameters in various typicalcrack tip fields. (Zhao, 2007; Meng, 2006). In the 1990s, the study offracture mechanics gradually shifted from two-dimensional crack underplane stress and plane strain to three-dimensional crack under threedimensional stress state. In particular, domestic scholars have madeinnovative work on the higher order solution of two-dimensionalelastic-plastic stress field, three-dimensional constrained fracture theory,
creep multi-axial stress effect and so on(Tan, 2013; Yu, 2021).
Although the three-dimensional fracture problem has attracted theattention of many researchers, but the study on the elastic-plastic
fracture characteristics of three-dimensional unpenetrated cracks is still
very immature. How to accurately describe the stress-strain field of
three-dimensional crack tip and how to judge the propagation of threedimensional non-penetrating crack has not been solved yet. For
research method, the more used is numerical method and finite element
method, although numerical method makes the three-dimensional
problem down to two-dimensional, but must seek the basic solution ofthe problem. Up to now, numerical research based on finite element
method is still the main research means of this kind of problem, but theamount of modeling work, calculation time and space required is quiteamazing.

In this study, the constitutive model of semi-elliptical threedimensional surface cracked plate made of Q345 steel is established byused the nonlinear finite element software ABAQUS based on thethree-dimensional elastic-plastic theory. The effects of different stressamplitudes, stress ratios and elliptic shape factor on the stressstrain field and the accumulative plasticity at crack tip of the threedimensional surface cracked plate are analyzed. It provides a newreliable basis for further evaluation of low-cycle fatigue crack
propagation fracture characteristics of three-dimensional surface
cracked plate in marine structures .

KEY WORDS:

3D surface cracked plate; Low-cycle fatigue;
Accumulative plasticity; Stress and strain field.

INTRODUCTION
The three-dimensional complex cracks and other defects often exist in
the structural components of marine engineering, which cause stressconcentration and strength decline of components, and result incatastrophic fracture accidents. In fact, the fracture failure of marine
structural components is usually caused by the three-dimensional nonpenetrated curved cracks propagation. Meanwhile, there are not ideal
two-dimensional cracks in practice. In order to solve the fracture
problem better in practical engineering, it is particularly important tostudy stress-strain field of three-dimensional non-penetrating curved
crack tip in marine structures. In addition, in harsh sea conditions withcyclic loading , it will occur low cycle fatigue failure and accumulative
plastic failure.
The stress-strain field of crack is the basis for the study ofthe cumulative plasticity and crack propagation of crack tip,so scholars have never sto pped the researches . Copley andSanders(1969) gave the linear elastic solutions of cylindrical shells withaxial penetrating cracks under tensile and bending actions. Then, Yangand Freund(1985) gave a quasi-analytical solution of the crack tip fieldunder the assumption of thickness averaging for penetrating cracks inelastic thin plates. Rice and Levy(1972) proposed to solve the stressintensity factor problem of surface cracks on a flat plate with using
linear spring model. This is an analytical method base on model. At theFrom the above analysis, most of the current analysis of crack stressstrain field is focused on two-dimensional cracks, there are few studies2958