Method of fabricating a composite article having an integral, co-cured composite stiffening member

A method for fabricating a composite article having a composite stiffening member co-cure bonded in integral combination therewith wherein the composite article comprises outer mold line (OML) and inner mold line (IML) composite skins and a modified honeycomb core interposed therebetween. The method includes a first set of steps for modifying the honeycomb core of the composite article and includes the steps of providing a detail mold that defines a detail cavity and a core engagement surface, aligning the honeycomb core with the detail mold by abuttingly engaging a first surface of the honeycomb core with the core engagement surface wherein a base segment of the honeycomb core is aligned with the detail cavity, to injecting a RIM foam to fill the detail cavity and the honeycomb cells of the base segment, and curing the injected RIM foam to form the modified honeycomb core that includes a densified base segment and a detail mandrel integral with the densified base segment. The detail mandrel is operative to define the configuration of the composite stiffening member to be co-cure bonded in integral combination with the composite article. A second set of steps includes laying up a first set of prepreg composite plies that define the OML composite skin in combination with a fabrication mold, laying up the modified honeycomb core in combination with the layed-up first prepreg composite plies, mold, laying up additional prepreg composite plies that define the IML composite skin and the composite stiffening member in combination with the modified honeycomb core and co-curing the layed-up prepreg plies to form the composite article having the composite stiffening member co-cure bonded in integral combination therewith.