Measurement, characterization, and modeling of thin prepreg consolidation during Automated Tape Placement process
Date
2021
Authors
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Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Automated Tape Placement (ATP) is an attractive candidate composite manufacturing process to replace the hand-layup method as it reduces labor cost, increases production rate, and improves repeatability. In this method, the part is built by consolidating one unidirectional prepreg tape layer at a time with a placement head using a compaction roller. ATP is a complex process, and the structural performance of the part is highly dependent on material quality and process parameters such as temperature, placement speed, consolidation force, and alignment. Defects such as gaps between neighboring tapes are inevitable. This challenge becomes more critical in the ATP of the thin ply prepreg tapes as the ratio of the gap width to the tape thickness increases. Thin–ply composites, with thickness down to 1/6th of conventional plies (i.e., < 125 μm), are an attractive option to overcome the lack of damage tolerance of composite materials. ☐ The prepreg is heated during the ATP process to increase tape tackiness. This also reduces the viscosity of the resin by several orders of magnitude and various flow processes can occur during the placement. These may include the squeeze flow of prepreg due to the pressure applied by the compaction roller. The transverse deformation due to the squeeze flow can increase the tape width in a non-uniform manner. In this work, a non-isothermal model is formulated with temperature-dependent viscosity, which is coupled with a constitutive description of material properties. The tape laying process was then applied under carefully controlled process conditions of change in pressure to measure tape deformation as well as to characterize the changes in its internal structure. The tape deformation dependent on processing conditions, including the width variation, were measured and compared with model predictions. This work enhances the current fundamental understanding of thin-ply tapes used in the ATP process and allows us to predict the effects of material and processing parameters on its outcome. ☐ Gap defects between adjacent tapes during the ply layup process in ATP are investigated by addressing the filling process of gap defects during the cure cycle which causes resin-rich areas and fiber waviness. In this study, we also present a model to numerically simulate the gap-filling process by coupling the squeeze flow behavior of the resin within the tapes adjacent to the gap and the deformation of the top layers into the empty space within the gap. First, the experimental results clarify the microstructural physics of the gap-filling process. This is followed by proposing a model to predict the gap thickness and the filling of the gap. The predictions of the model are compared with experimental results and validated with the micrographs of fabricated samples. This work should prove useful in addressing the gap defects and fiber waviness encountered in the ATP process.
Description
Keywords
Automated tape placement, Gap defect, Ply waviness, Squeeze flow, Thin-ply material, Toughened thermoset prepreg