| Summary: | 博士 === 國立成功大學 === 航空太空工程學系 === 82 === Based on a stiffness degradation model under constant amplitude
cyclic loading, the fatigue damage behaviors of composite
laminates subjected to service loading spectra are investigated
both theoretically and experimentally. Two theoretical
approaches useful for different stages of the fatigue design
are presented and verified experimentally in this dissertation.
In the first approach, a residual stiffness degradation model
for composite laminates subjected to spectrum loadings is
proposed. Baseline stiffness reduction data under spectrum
loadings are incorporated in this model to predict the
statistical distributions of the residual stiffness and fatigue
life for composite laminates subjected to different levels (or
severities) of spectrum loadings. This approach is very useful
at the later stage of the fatigue design when the service load
spectrum is well-defined and the scheduled inspection and
maintenance of structural components should be established. In
the second approach, the residual stiffness degradation for
composite laminates subjected to service loads is derived from
the stiffness degradation model under constant amplitude cyclic
loadings. With the constant amplitude baseline data, the
statistical distributions of the residual stiffness and fatigue
life under service loads can be predicted. This approach is
very useful at the preliminary design stage in which service
load spectra are not well-defined. An experimental test program
is conducted on $[0^o/90^o/\pm 45^o]_{2s}$ graphite/epoxy
laminates to generate statistically meaningful data for the
verifications of the theoretical approaches presented.
Experimental test results demonstrate that the predictive
capabilities of the proposed theoretical methods are quite
satisfactory.
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