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

Effects of non-proportional loading paths on the multiaxial low-cycle fatigue
crack growth of hull cracked plate
Ruitao Lu1, Junlin. Deng1*, Dawei Dong1, Shenglin Qiu1.

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

ABSTRACTexperimental studies on fatigue crack expansion behavior of ductile
materials, and the results proved that the research method can wellconform to the fatigue crack expansion as well as life prediction ofductile materials. Among which (Dong Qin, 2018) carried out cyclicloading AH32 steel CT specimens with low-cycle fatigue crack growthexperiments, and the low-cycle fatigue crack growth rate calculation
model described by CTOD can well predict the low-cycle fatigue crack
growth behavior of cyclically loaded crack-containing samples. In thefield of uniaxial fatigue, a relatively well-developed theoretical model
is available for evaluating the low-cycle fatigue crack propagation
behavior.

In this paper, multiaxial non-proportional low-cycle fatigue crack
propagation of hull crack plate are studied under the loading paths withthe different phase differences about 0° ， 45° ， 90° and 180°
respectively. Mainly, the stress-strain field, accumulative plasticity andthe crack propagation rate at the crack tip of the cruciform hull plate
specimen with Q345 steel material under different loading paths isexplored by ABAQUS finite elements analysis software. It provides abasis for the correct evaluation of the effect of low-cycle fatigue crack
growth of the hull crack plate under the multiaxial non-proportionalloading paths.

A large number of studies have shown that the traditional uniaxial
theory cannot be better applied to multiaxial fatigue. While mostengineering structures, especially ship structures, are in long-term
multi-axial fatigue and fracture failure under working conditions.
Therefore, the study of multi-axial fatigue has become an urgent
problem for ship structures. In the past years, (Mall and Perel, 2015,
Meng et al, 2020, Lee and Taylor, 2011, Wolf et al, 2019) studied thecrack growth behavior of biaxial fatigue under different phasedifferences. The fatigue damage section of the specimen shows a
combination of KⅠ and KⅡ cracks. The crack growth rate and path wereaffected by the phase difference.

KEY WORDS: the multiaxial non-proportional load; low-cycle
fatigue crack growth; loading paths; phase differences.
INTRODUCTION
Since the last decade, the share of Chinese shipbuilding in the global
market has increased significantly, and China has become one of theimportant shipbuilding centers in the world. However, throughout the
global shipbuilding enterprises there are still ships that have structural
fracture failures during their service life cycle leading to overall ship
fracture maritime accidents, resulting in huge economic losses,
environmental damages and casualties. (Deng et al, 2016) pointed outthat with the development of the shipbuilding industry, the main scaleof the ship is increasing and the ship structure is mainly subjected tomulti-axial, high stress and low-cycle alternating load under its seastate, the problem of low-cycle fatigue damage of the ship is more
prominent.

Some studies have also been done on multiaxial fatigue behavior of thedifferent loading paths. (Li et al, 2014) proposed a new multiaxial
fatigue damage model based on the path correlation factor F in thecritical plane. (Neerukatti et al, 2018) investigated the fatigue damage
characteristics of aluminum alloys under complex biaxial loading withhomogeneous and heterogeneous phases and different biaxiality ratios.
Significant differences in crack sprouting and extension behavior wereobserved when phase differences were applied. (Feng et al, 2006)
conducted crack extension experiments on 1070 steel under axialtorsional loading paths and showed that crack extension was closely
related to the loading path. They found that neither theory could predict
the observed loading path-related crack extension behavior. (Reis et al,2005) investigated the effect of loading path on crack orientation. And

Therefore, the study of low-cycle fatigue fracture failure of ship
structure can effectively improve the safety and survivability of ship
structure and avoid such maritime accidents. Scholars at home andabroad have conducted a lot of research on uniaxial fatigue aspects,(Fatoba and Akid, 2018, Qian Yi and Cui Weicheng, 2012) conducted2964