L. Pruitt et S. Suresh, CYCLIC STRESS-FIELDS FOR FATIGUE CRACKS IN AMORPHOUS SOLIDS EXPERIMENTAL MEASUREMENTS AND THEIR IMPLICATIONS, Philosophical magazine. A. Physics of condensed matter. Defects and mechanical properties, 67(5), 1993, pp. 1219-1245
The evolution cyclic residual stress fields within the damage zone ahe
ad of fatigue cracks is known to have a significant influence in the f
atigue fracture response of materials during constant-amplitude and va
riable-amplitude cyclic loading. In this paper, we present direct and
in situ measurements of cyclic stress fields ahead of fatigue flaws in
a model amorphous solid subjected to far-field cyclic compression loa
ding. Photoelasticity and laser interferometry experiments conducted o
n single-edged-notched plates of a photoelastic resin are used to dete
rmine the residual stresses within the near-tip damage zone during the
inception and subcritical growth of the fatigue flaw from the stress
concentration. Quantitative analyses of the relevant stress components
are used to establish a link between the evolution of cyclic near-tip
fields and the conditions for the onset and advance of fatigue flaws.
Transmission electron microscopy observations are presented for a rub
ber-toughened polystyrene to illustrate how the residual tensile stres
ses developing within the cyclic damage zone cause crazes to form alon
g the plane of the fatigue crack, in a direction normal to the far-fie
ld compression axis. A series of systematic experiments on the effects
of mean stress on fatigue fracture is reported, and the results of th
e experiments are rationalized with the aid of the near tip cyclic str
ess measurements. The applicability of the results of this study to a
broad range of materials, including crystalline metals and ceramics, s
emicrystalline and amorphous polymers, and composites, is demonstrated
. Implications of this work for a variety of fatigue phenomena involvi
ng constant- and variable-amplitude fatigue are also addressed.