Transverse microcracking in Celion 6000 graphite/PMR-15 polymide composite
Abstract
The effects of room temperature tensile loading and five thermal
loadings upon the development of transverse microcracks (TVM) in Celion
6000/PMR-15 graphite-epoxy laminates were investigated. Microcracks
were observed using a replicating technique, microscopy and x-ray. The
mechanical or thermal load at which microcracking initiates and the ply
residual stresses were predicted using laminate analysis with stress and
temperature-dependent materials. The TVM density as a function of
tensile load was predicted using the multiple cracking theory proposed
by Garrett, Parvizi and Bailey. Reasonably good correlation between
theory and experiment was obtained for both the load at initial failure
and the TVM density as a function of tensile load.
It has been shown that TVM density and the load to initiate microcracking are functions of the type of loading and the laminate configuration. Generally, cross-ply laminates exhibit higher TVM density after thermal loading than do quasi-isotropic laminates, but the converse is true for tensile loading. Cross-ply laminates attain saturation TVM density prior to failure, but the TVM density of quasi-isotropic laminates continues to increase until failure. Edge effects have a significant influence on the development of TVM, and TVM present at the free edge of a laminate extend throughout the entire width of the laminate.
[Vita removed Feb. 15, 2011. GMc]
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