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A study of compression loading of composite laminates

The compressive behavior of continuous fiber composites is not as well
understood as their tensile behavior because research and industrial applications have until
recently focused on the latter. Furthermore, most theoretical and experimental studies on
the compression of composites have examined the case of unidirectional specimens with
fibers along the loading direction (0�� fibers). While this is a logical approach since it
isolates the failure mode specific to this geometry (kinking), the study of multidirectional
laminates is essential because these are used in all practical applications. Few theories
model the compressive behavior of multidirectional laminates. None of the theories
account for the stress field or the sequence and interaction of the various observed failure
modes (kinking, delamination, matrix failure) specific to the multidirectional configuration.
The principal objective of this investigation is to construct a realistic theory to
model the compressive behavior of multidirectional composites. Compression
experiments have repeatedly shown that the initial failure mode was in-plane kinking of 0��
fibers initiated at the edges of the specimens. We decided to base our compressive failure
theory upon interlaminar stresses because in multidirectional laminates these are known to
exist in a boundary layer along the edges. This required development of an analytical
theory giving the amplitude of these stresses at the free edges. We then incorporated these stresses into a new general microbuckling equation for 0�� fibers. The global laminate failure strain was determined through several fiber and matrix failure criteria. Theoretical predictions were compared with experimental results obtained from compression testing of graphite/thermoplastic laminates with the same ply sequence but different off-axis ply angles. The theory correlated well with experiments and confirmed that in-plane kinking was the critical failure mode at low and medium angles, while revealing that out-of-plane buckling was responsible for failure at high angles. Furthermore, the theory correctly predicted the sequence of various fiber and matrix failure modes. / Graduation date: 1997
Date03 April 1997
CreatorsBerbinau, Pierre J.
ContributorsWolff, Ernest G.
Source SetsOregon State University
Detected LanguageEnglish

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