A NOVEL STAMP FORMING TECHNIQUE FOR CRUSH RESISTANT STRINGERS MADE OF THERMOPLASTIC COMPOSITES

摘要

This paper describes the development of thermoformed composite stringers with an 80 percent improvement in crushing strength relative to basic thermoformed composite stringers. The strength improvement is achieved through controlled migration of material within the stringer to produce variable-thickness corners. This novel, patent-pending technique enables weight and or cost savings for stringers sized by crushing loads. C-section stringers are formed from tailored blanks~(~R) of TenCate AS4/PEEK unidirectional continuous-fiber tape laid up by the Fiberforge RELAY~(~R) machine. The stringers are unconventionally tooled to produce internal and external corner radii of 1.5 mm (0.06 in). In the Fiberforge thermoforming process, 0 deg fibers are migrated from the stringer webs and flanges into the corners in order to enable a tighter external radius than possible with conventional methods while still maintaining a reasonable internal radius. The stringers are tested for radius-crushing strength under multiple configurations of vertical loads. The results are compared with stringers of constant-thickness corners. Test results show a crushing yield strength improvement of up to 80 percent for the variable-thickness stringers relative to constant-thickness stringers.