The compaction of uncured toughened prepreg laminates in relation to automated forming

Composite manufacturing uses pressure and temperature in lay-up to produce parts with high volume fractions, limited features, and low porosity. Modern prepregs are very complex, incorporating significant levels of thermoplastic toughener that makes them behave dually: as unconsolidated thermoplastics at low temperatures, and conventional thermoset prepregs at elevated temperatures. This paper presents an experimental programme to study the compressibility of a modern prepreg at various temperatures and constraint conditions using a Dynamic Mechanical Analyser. Testing revealed a number of physical phenomena, including gradual transition from shear squeezing flow to bleeding percolation flow, strong constraining effects of adjacent non-cured plies, and non-monotonic compressibility over the temperature range of 20-90°C.