Novel filler materials for skin-stiffener structures

To manufacture out-of-plane joints in composite stiffened panels, such as the connection between skin and T, I, omega (hat) shaped stiffeners, a filler material is needed to fill the void between the skin, flanges and web. The most common filler is a unidirectional prepreg tape rolled into a “noodle”, which is not only expensive to fabricate, but also has low strength that can lead to premature failure of the loaded joint. In this paper, eight novel filler concepts are introduced and experimentally validated against the baseline filler (noodle) via T-joint tensile tests. Polyamide nonwoven interleaved joints increase the damage tolerance of the structure at the cost of reduced strength, vertical nanotubes yield no difference, but thermoplastic nonwoven nanofibres increase the failure initiation load by 6%. Additively manufactured fillers have lower strength but demonstrate the possibility of thermoplastic-thermoset hybrid structures. Fillers made of chopped unidirectional and woven prepreg match the strength of the baseline noodle and can serve as a cost-effective replacement. Another low cost, resin infused braided concept has lower strength, but its counterpart made of multiple individual braids has the same strength as the baseline filler. Moreover, the latter concept indicates that different resin systems (infusion and prepreg) can be successfully cured together without causing a knockdown in strength, and can serve as a basis for a new range of novel applications besides out-of-plane joints.