Evaluation and Quantification of
Fretting Fatigue Induced Damage - V. Chandrasekaran and D.W.
Hoeppner
Fretting fatigue
experiments were conducted on 7075-T6 and 2024-T3 Aluminum
alloy specimens. The primary objective of this study was to
quantitatively characterize fretting damages that resulted
on the fatigue specimens. Fretting fatigue experiments were
performed in laboratory air at various maximum fatigue
stress levels at a constant normal pressure. From the
confocal microscopy analysis of fretting damages, it was
observed that fretting-generated multiple cracks on
the faying surface could be responsible for the fracture of
7075-T6 aluminum alloy specimens (see Fig. 2) where as the
fracture of 2024-T3 aluminum alloy specimen could be
attributed to fretting-generated multiple pits on the
faying surface (see Fig. 3). From the results, it is
proposed that fretting nucleates damages of different nature
depending on the material microstructure as well as its
composition and the methods to alleviate fretting should
consider issues pertaining to a specific material.
Stage I, Stage II, and Stage III
respectively
Figure 2 -- Digitized confocal images
showing the stages in the nucleation and the development of
fretting damages on the faying surface of 7075-T6 Aluminum
alloy specimen, Stage I Formation
of debris - after 44100 cycles;
Stage II Removal of
material - after 96200 cycles;
Stage III Nucleation of cracks - after
128400 cycles; s max =
172 MPa (25 ksi), s n
= 13.8 MPa (2 ksi), R = 0.1, f=10 Hz, Lab air.
Figure 3 --Digitized image showing
fretting nucleated multiple pits on the faying surface of
2024-T3 aluminum alloy specimen (analyzed after fracture,
81,100 cycles).
In addition, fretting
damages were quantified in terms of material removal by
characterizing the depth as well as the geometry of
fretting-generated pits on the faying surface of the
specimen. Pit size in terms of pit depth (Pd),
pit area (PA), and pit dimension perpendicular (PDy)
as well as parallel (PDx) to the applied load
also were quantified. The quantified fretting-nucleated pits
revealed a fair correlation between the pit depth and the
area of the pits (see Fig. 4).
Figure 4. -- Correlation between pit
depth and pit area, Material: 2024-T3 aluminum alloy, Normal
stress = 13.8 MPa (2 ksi), Max. fatigue stress = 207 MPa (30
ksi), Environment: Lab air.
