Static mechanical properties of hybrid RTM-made composite I- and Π-beams under three-point flexure

This paper deals with three-point flexure tests on hybrid I- and Π-beams, made out of multi-layer carbon fiber/epoxy resin (including twill woven fabric CF3031/5284 and unidirectional cord fabric U3160/5284) reinforced composites, processed using the RTM (resin transfer molding) technique. Static bending properties were determined and failure initiation mechanism was deduced from experimental observations. Failure mode of the tested hybrid RTM-made I-beams can be reckoned to be characteristic of the delamination from the cutout edge within the web and the debonding propagation along the interface between the inverted triangular resin-rich zone and the adjacent curved web until local buckling within the curved webs around the conjunction fillet region. In contrast, as distinct from hybrid RTM I-beams subjected to three-point bending loading, hybrid RTM-made Π-beams in three-point flexure tests experienced the resin debonding in the inverted triangular resin-rich zones and the debonding propagation along the interface between the inverted triangular resin-rich zone and the adjacent curved web until complete separation of the curved web from the flange. Progressive damage models (PDMs) were presented to predict failure loads and process of hybrid RTM-made I- and Π-beams under three-point flexure. Good correlation was achieved between experimental and numerical results.