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J.-H.
Shih, A. K. Mal, M. Vemuri, 1998, “Plate Wave
Characterization of Stiffness Degradation in Composites
During Fatigue,” Research in Nondestructive
Evaluation, 10, 147-162
Plate
Wave Characterization of Stiffness Degradation
in Composites During Fatigue
ABSTRACT
Crossply
composite specimens of metal matrix (SCS-6/Ti-6-4
[90/0]s) and polymer matrix (graphite/epoxy
AS4/3502 [0/90]s) were subjected to tensile
fatigue tests to induce stiffness degradaton. Extensional
plate wave velocities in the 0, 45, and 90° directions,
together with the quasi-shear wave velocity in the
90° direction, were used to characterize the degradation
of the stiffness constants of each specimen during
fatigue. The laminate stiffness constants in the x-
and y-directions (Ex, Ey)
and the shear modulus (Gxy) were
determined. The laminate stiffness, Ex,
was also monitored through direct measurement by using
an extensometer during fatigue loading. The trend
in the stiffness degradation of the titanium matrix
composite was identical in both measurement techniques,
but the stiffness values calculated from the extensional
velocity measurements were higher than those obtained
from the extensometer. This discrepancy was shown
to be due to microcrack closure during wave velocity
measurements when the tensile stress was removed from
the specimen. The graphite/epoxy specimens appeared
to suffer only a small reduction in their stiffness.
(Article
in PDF, SpringerLink)
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