PSI - Issue 66

Andrea Zanichelli et al. / Procedia Structural Integrity 66 (2024) 471–477 Author name / Structural Integrity Procedia 00 (2025) 000–000

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Lindley, (1985); Vázquez et al., (2017)). Such a stress gradient is especially typical of partial slip conditions, that is, when the contact surface consists of an inner stick region, with no relative displacements, and an outer micro-slip region, where relative micro-displacements of the order of few microns arise. Subsequently, the cracks can propagate in the presence of cyclic loading (that is, under fretting fatigue conditions), thus leading to premature fatigue failure of the component itself (Vantadori et al., 2022c). Note that most failures due to fretting fatigue occur in high-cycle fatigue regime conditions, and are characterised by high stress gradients and multiaxial stress state (Nowell and Hills, 1987; Vantadori et al., 2020). In order to analyse fretting fatigue problems, the stress state within the structural component needs to be determined firstly and, to this aim, either analytical formulations or numerical models can be employed (Almeida et al. (2020); Erena et al. (2020); Zanichelli et al. (2021)). Then, the fatigue assessment follows. Considering the fact that, in the case of fretting fatigue elastic partial slip loading conditions, the crack nucleation phase generally involves around 90% of total fatigue life, crack-nucleation models can be applied in order to assess the fatigue behaviour of fretting-affected components (Vantadori et al. (2022a)). Finally, due to the high stress gradient in the vicinity of the contact zone, it seems more appropriate to analyse suitable quantities summarizing the stress field related to a process zone instead of examining the fatigue load history related to a single point. Moreover, the fatigue assessment should be performed at a certain distance from the contact surface, that is, a non-local approach should be employed in conjunction with the above fatigue criteria (Vantadori et al. (2023)). In the present paper, a comprehensive experimental campaign available in the literature (Araújo et al. (2004)) is examined. The experimental tests, carried out on an aluminium alloy in partial slip regime by using two cylindrical fretting pads pushed against a dog bone specimen, are here simulated by means of an analytical methodology (Vantadori and Zanichelli (2021); Zanichelli et al. (2022)) recently proposed by the present authors. Such a methodology allows us to estimate both crack orientation and fatigue life of metallic structural components under constant amplitude fretting fatigue loading. In more detail, it is based on the joint application of (i) the multiaxial fatigue criterion by Carpinteri et al. (2015); and (ii) the critical direction method by Araújo et al. (2017). The paper is structured as follows. Section 2 deals with the analytical methodology employed for the fretting fatigue assessment, whereas Section 3 is devoted to the description of the experimental tests examined. Then, the results obtained are presented and discussed in Section 4. Finally, the main conclusions are summarized in Section 5.

Nomenclature d

average grain size of the material

elastic modulus

E H m

hot-spot on the contact surface

S-N curve slope under fully reversed normal stress S-N curve slope under fully reversed shear stress equivalent normal stress amplitude calculated number of loading cycles to failure experimental number of loading cycles to failure critical point for the fretting fatigue assessment amplitude of the alternating cyclic tangential load constant normal load

m*

N eq,a N f,cal N f,exp

P

P crit

Q a

radius of the pad

R

crit 

orientation of the critical plane

friction coefficient



Poisson coefficient , 1 af   fully reversed normal stress fatigue limit , B a  ultimate tensile strength , 1 af   fully reversed shear stress fatigue limit u 

v

amplitude of the alternating cyclic axial stress