PSI - Issue 66

María Moreno-Rubio et al. / Procedia Structural Integrity 66 (2024) 362–369 Author name / Structural Integrity Procedia 00 (2025) 000 – 000

363

2

1. Main text Fretting fatigue is type of damage that occurs in a wide variety of mechanical components, such as bolted joints, sealing joints, gaskets, chains, cables, and disk-blade connections in gas turbines and compressors, as noted by several authors as Golden (2009), Ciavarella et al (2001), and Erena et al (2020). This type of damage occurs when a mechanical contact pair is subjected to variable forces and moments over time. These forces generate micro-relative displacements, which, in conjunction with friction, can lead to the formation and growth of surface cracks, possibly causing the failure of the component, as described by Waterhouse (1981). The aim of this study is to investigate the behavior of Inconel 718 under fretting fatigue. For this purpose, experimental tests were carried out for both simple fatigue and fretting fatigue at room temperature (RT) and 650ºC (HT), as well as under different levels of axial load. The goal of these tests is to quantify the reduction in fatigue life caused by increased temperature and fretting fatigue. Additionally, the experimental fretting fatigue life is compared with estimated values. The life estimation model used here combines both the crack initiation and propagation phases, without pre-defining when one phase ends and the other begins, assuming that cracks initiate and propagate perpendicularly to the surface of the contact area. Inconel 718 is a nickel-chromium-based superalloy developed by Special Metals. This material is commonly used in the aerospace industry to manufacture certain turbine components, thanks to its excellent resistance to oxidation and corrosion at high temperature, as noted by Mouritz (2012). The heat treatment applied to achieve the desired properties was as follows: solution treatment at 980ºC for 1 hour, followed by rapid cooling, and precipitation hardening at 720ºC for 8 hours, furnace cooling down to 620ºC, maintaining 620ºC for a total aging time of 18 hours, followed by air cooling. The chemical composition of the material and its mechanical properties after treatment can be found in Tables 1 and 2, respectively.

Table 1. Chemical compositions of Inconel 718 alloy (wt%)

C

Mn

Fe

S

Si

Cu

Ni

Cr

Al

Ti

0.03

0.11

18.02

0.0004

0.7

0.13

53.52

18.23

0.47

1.03

Co

Mo

Nb

Ta

B

Bi

P

Pb

Se

0.13

3.01

5.18

0.004

0.002

0.000001

0.008

0.00003 <0.000001

Table 2. Mechanical properties

Material properties

RT

HT

Young ’s modulus ( E ) Poisson coefficient ( ν ) Yield strength ( σy ) Tensile strength ( σu ) Friction coefficient ( μ ) Pari’s law coeff. ( C ) Pari’s law exp. ( m )

217 GPa*

163 GPa

0.294

0.283

1325 MPa* 1435 MPa*

1080 MPa 1172 MPa

0.43*

0.288

2.30 ‧ 10 -11

1.30 ‧ 10 -11

2.29

2.72

Fatigue strength coefficient ( σ f ´ ) Fatigue ductility coefficient ( ε f ´ ) Fatigue strength exponent ( b ) Fatigue ductility exponent ( c ) -10.01 Mode I SIF threshold ( ∆ ℎ ) 13.45 MPa√m 7 MPa√m *Data obtained from our laboratory 4332 MPa -0.000674 -0.1537 1169 MPa 49.03 -0.05282 -4.8