Abstract: Aircraft that incorporates a rounded-hat composite stringer connected to an inner side of the skin of the aircraft to form an elongate conduit that defines a conduit axis, where the conduit axis includes at least one curving portion. The rounded-hat composite stringer can be manufactured by constructing a lower forming die and an upper forming die, each forming die having a length and defining a curve along at least a portion of the length of the die, cutting a pre-cured flat composite charge dimensioned to form the rounded-hat composite stringer, pressing the flat composite charge between the lower and upper forming dies to shape the composite charge into a pre-formed stringer having an inner side between curved fillet portions, contacting a forming member against the inner side of the pre-formed stringer, applying radius fillers to the curved fillet portions of the pre-formed stringer, curing the pre-formed stringer, and removing the forming member from the cured stringer.

Abstract: A composite structure that includes a multi-layer laminate including a plurality of layers of material, and at least one crack barrier layer extending within the plurality of layers of material. The multi-layer laminate is folded to define a first web region and a second web region in a face-to-face relationship, and a folded tip region defined between the first web region and the second web region. The at least one crack barrier layer is configured to restrict crack propagation from spreading through the plurality of layers of material in the folded tip region.

Abstract: Aircraft that incorporates a rounded-hat composite stringer connected to an inner side of the skin of the aircraft to form an elongate conduit that defines a conduit axis, where the conduit axis includes at least one curving portion. The rounded-hat composite stringer can be manufactured by constructing a lower forming die and an upper forming die, each forming die having a length and defining a curve along at least a portion of the length of the die, cutting a pre-cured flat composite charge dimensioned to form the rounded-hat composite stringer, pressing the flat composite charge between the lower and upper forming dies to shape the composite charge into a pre-formed stringer having an inner side between curved fillet portions, contacting a forming member against the inner side of the pre-formed stringer, applying radius fillers to the curved fillet portions of the pre-formed stringer, curing the pre-formed stringer, and removing the forming member from the cured stringer.

Abstract: An example method for forming a flat composite charge into a composite blade stiffener includes cutting a flat composite charge along a cut line into a first piece and a second piece having an angle, positioning the first piece and the second piece of the flat composite charge on a forming mandrel about a tooling plunger, activating the tooling plunger to drive the first piece and the second piece into a cavity of the forming mandrel resulting in the first piece and the second piece folding at the cut line, withdrawing the tooling plunger from the cavity of the forming mandrel, compressing the forming mandrel to apply a lateral pressure to the first piece and the second piece folded into the cavity, and applying a vertical pressure to a first flange and a second flange of the first piece and the second piece, respectively, to form the composite blade stiffener.

Abstract: An example method for forming a flat composite charge into a composite blade stiffener includes cutting a flat composite charge along a cut line into a first piece and a second piece having an angle, positioning the first piece and the second piece of the flat composite charge on a forming mandrel about a tooling plunger, activating the tooling plunger to drive the first piece and the second piece into a cavity of the forming mandrel resulting in the first piece and the second piece folding at the cut line, withdrawing the tooling plunger from the cavity of the forming mandrel, compressing the forming mandrel to apply a lateral pressure to the first piece and the second piece folded into the cavity, and applying a vertical pressure to a first flange and a second flange of the first piece and the second piece, respectively, to form the composite blade stiffener.