Solution to the problem of low sensitivity of crack closure models to material properties

0580722 - ÚFM 2025 RIV NL eng J - Journal Article
Kubíček, Radek - Vojtek, Tomáš - Jambor, Michal - Pokorný, Pavel - Náhlík, Luboš - Pokluda, J. - Hutař, Pavel
Solution to the problem of low sensitivity of crack closure models to material properties.
Theoretical and Applied Fracture Mechanics. Roč. 130, APR (2024), č. článku 104243. ISSN 0167-8442. E-ISSN 1872-7638
R&D Projects: GA ČR(CZ) GA22-28283S
Institutional support: RVO:68081723
Keywords : Load ratio * Crack closure * Cyclic softening * Strip-yield model * Steel
OECD category: Materials engineering
Impact factor: 5.3, year: 2022
Method of publishing: Limited access
https://www.sciencedirect.com/science/article/pii/S0167844223005062?via%3Dihub

The paper focuses on differences between crack closure obtained by numerical models and by experimental
fatigue crack growth rates, namely for three different steels (bainitic steel, predominantly pearlitic steel and
additively manufactured austenitic stainless steel). The experimental data revealed a load ratio effect different
from that predicted by the most used plasticity-induced crack closure (PICC) models. The term “irreversibility of
plastic deformation” was proposed in this work to be used as a material property to estimate how strong the PICC
effect would be in a material. Two basic phenomena, which are usually omitted in other models, were considered
in the explanation: (i) cyclic softening/hardening, (ii) brittle microcracking at the maximum load. The strip-yield
model has the ability of conducting fast and accurate simulations under the variable-amplitude loading. It was
demonstrated that the results of this model are practically independent of the material properties. This is caused
by the consideration of only monotonic elastic–plastic material properties. To simulate real load ratio effects, the
parameter β in the strip-yield model (constraint factor in compression) is proposed to be used as a variable. It
enabled a generation of different ratios of monotonic and cyclic plastic zones, which in turn helped to reproduce
the crack closure values observed experimentally. Discussion and explanations were provided regarding the
material microstructure. The proposed approach considers unequal tensile and compressive yield stresses caused
by the different irreversibility of plastic deformation, which explains the dissimilarities in the load ratio effect
observed in the investigated materials. It can also improve the accuracy of residual fatigue life estimations.
Permanent Link: https://hdl.handle.net/11104/0352669