Paper number 537

DYNAMICS OF VOID FORMATION UPON CURING OF EPOXY RESIN

Yongsung Eom, Louis Boogh, Véronique Michaud, Paul Sunderland and Jan-Anders Månson

Laboratoire de Technologie des Composites et Polymères (LTC)
Ecole Polytechnique Fédérale de Lausanne (EPFL)
CH-1015 Lausanne, SWITZERLAND

Summary

The role of internal stresses in the formation of voids during cure of neat epoxy resin and fibre reinforced epoxy has been identified. The combined evolution of the modulus and of the volume shrinkage often leads to voiding when the resin is constrained during cure. To analyse this phenomenon, the shrinkage of an epoxy resin was studied in a constrained volume. Void initiation was observed at two different stages during isothermal cure, before gelation and around or after gelation. A corresponding critical internal stress at void initiation was calculated by viscoelastic analysis. This stress criterion is used to construct a process window for production of void-free composites.

Keywords

void formation, internal stresses, process window.