Examination of Pre-gelation Behavior in AS4/8552 Prepreg Composites

Abstract

Recent work on the topic of manufacturing defects in composite parts has focussed on understanding the changes between initial uncured state and final cured state of the material. Increasingly it is clear that understanding the early state, or pre-gelation behaviour, of a material becomes essential in controlling popular manufacturing techniques such as automated fibre placement (AFP) and forming. It is therefore timely to re-examine the behaviour of materials during the pre-gelation regime. This paper presents a method for characterizing the pre-gelation regime of unidirectional Hexcel AS4/8552 prepreg material system using the Digital Image Correlation (DIC) technique and microscopy. Through experimental observations in this study, we show that the pre-gelation regime can be broken into two phases. In the first phase, the material behaviour is dominated by surface tension of the liquid resin. In the second phase, behaviour is dominated by tool response via tool-part interaction. The findings in this study contribute to our understanding of how processing is influenced by the initial material state and will inform the simulation of processes such as AFP and forming.