Thermo-mechanical fatigue of polymer matrix composites. Ph.D. Thesis
This research was undertaken to evaluate the effects of mechanical constraint on the response of polymer composites during thermal cycling. Analytical and experimental techniques were used to characterize the response of carbon fiber reinforced cyanate ester (IM6/BT3008) and bismaleimide (IM7/5250-4) composites. Cross-ply laminates were subjected to thermal cycles from 24 to 177 C in the unconstrained, fully-constrained and over-constrained conditions. Laminate response, damage mechanisms and residual compressive properties were characterized. Predicted ply stress distributions are significantly different for the various degrees of constraint and are highly sensitive to temperature-dependent lamina properties and laminate stress free temperature. Predictions of laminate response correlate well with experimental results. Deviations are apparent at elevated temperature which are attributed to the effects of time-dependent deformation. Changes in laminate response are observed during thermal cycling of IM6/BT3008 in the unconstrained and fully-constrained conditions. The changes are attributed to time-dependent deformation in the 90 deg plies which leads to changes in the ply stress distribution and ultimately to transverse microcracking. Microcracking initiates more rapidly for fully-constrained laminates due to higher 90 ply stresses which result in more time-dependent deformation per cycle. With continued cycling, microcrack densities converge and become equivalent after 1000 cycles. The ply stress distribution in over-constrained laminates is substantially different from those in unconstrained and fully-constrained laminates. Time-dependent deformation in the 90 deg plies results in changes in the ply stress distribution but does not significantly alter the laminate response. The microcrack density in over constrained laminates is equivalent to that in unconstrained and fully constrained laminates after 1000 cycles.
- Research Organization:
- Pennsylvania State Univ., University Park, PA (United States). Davey Lab.
- OSTI ID:
- 264010
- Report Number(s):
- N-96-23591; NIPS-96-08281; TRN: 9623591
- Resource Relation:
- Other Information: TH: Ph.D. Thesis; PBD: Jan 1994
- Country of Publication:
- United States
- Language:
- English
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