Processing Induced Warpage of Filament Wound Composite Cylindrical Shells

Abstract

In this paper a systematic procedure is developed to eliminate the processing induced warpage in filament wound and fiber placed composite parts. This is accomplished by first developing a through-thickness strain model based on fiber/resin cure consolidation (also referred to as a compaction) and tooling thermal expansion. The lay-up or stacking sequence can be arbitrary (i.e., symmetric or asymmetric). The strain profile model is then integrated into classical laminate theory and solutions for predicting and eliminating warpage are obtained. The accuracy of both solutions is evaluated by comparison with experimental data. To facilitate this, cylindrical test specimens were manufactured and the cure consolidation and warpage measured. It was found that the predictions were accurate and the warpage could be reduced and eliminated in most cases. The majority of cure consolidation in composites results from resin bleed-out and evacuation of entrapped air (voids). The magnitude is dependent on manufacturing parameters including cure pressure, winding tension, and material characteristics (i.e., pre-preg fiber volume fraction, resin viscosity, etc.). The strain profile that develops is set once the resin cures and is therefore not a hygrothermal phenomenon and is independent of cure temperature, or finished part operational environment.