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"''THINK outside the box'' design practices for optimal, more competitive and durable structural COMPOSITEs"

Final Report Summary - THINKCOMPOSITE (''THINK outside the box'' design practices for optimal, more competitive and durable structural COMPOSITEs)

Scientific and engineering insights in materials research are crucial for being at the cutting edge that has not only scientific value, but also immediate applicability and added value for the society. This requires scientists and practitioners to communicate well and ideally tune their efforts from basic science to engineering ends. Making composites more competitive is no exception, and calls attention for advances and innovation in materials, and “thinking outside the box” design practices. THINKCOMPOSITE project aims to contribute bridging the basic scientific research to the more applied and engineering oriented research and focuses the skills for composites engineering and structural design end of this challenge.

Two primary objectives of the THINKCOMPOSITE have been set
(1) to investigate innovative manufacturing/material alternative, namely thin-ply bi-angle non-crimp fabric (NCF) for optimal composite designs: New generation material, thin-ply multi-axial prepregs (in the sprit of noncrimp fabric- NCF composites) can substitute unidirectional tapes provided that their drawbacks versus gains are well understood, characterized and taken into consideration in a multi-objective design settings.
(2) to address the design practices within structural optimization framework and implementing micromechanics of failure (MMF): The design rules and practices have certainly reasons, some dominantly intuitive, but often the motivation is for being protective and conservative. For example, the fact that composite structures have many complex failure modes that are not captured by standard macro scale modeling, may lead composite designers to follow rules such as the use of symmetrical laminates, and fiber orientations imitating the isotropy. In contrast, unconventional fiber orientations and stacks in optimization efforts shall lead to more competitive designs once the failure are well captured in modeling.

The project tasks have contributed to the exploration of the innovative bi-angle thin-ply NCF composites. The concept of bi-angle or three-angle tapes, in the spirit of non-crimp fabric (NCF) composites, is based on the elimination of laying off-axis plies by having those plies pre-combined with the [0º] ply to form [0/φ] NCFs, for instance. This unconventional concept of bi-angle along with a novel tow-spreading technology has created the thin-ply NCFs, C-PlyTM that has been made available by Chomarat. The main distinction from the traditional NCFs is the intrinsic anisotropy achieved within a [0/φ] building block as thin as a typical high performance UD tape. An evolving research program on the thin-ply NCF has been driven by the outgoing host Stanford Composite Design group. The group and its global team involve industrial partners and academic institutions and collaborative efforts including the THINKCOMPOSITE project have been shedding light on why bi-angle thin ply NCF is a novel competitor for the composite structures. The thin-ply NCF promises better mechanical performance, ease of lay-up process, reduced amount of scrap, and tailored building block for sublaminate based homogenized design strategies to design composite structures out-of-the box. With these multi-angle NCF tapes, the axis of tape laying can be limited to one only along the x-axis, or two equal tape axes along the x- and y-axis. Ply drop can also be done on a tape drop basis. Great time savings can be achieved through not having to drop off-axis plies. For panels where more than one axis layup is needed, multi-directional tapes may be designed to fulfill special structural and manufacturing needs. One disadvantage of multi-angle tape is that the seams between two adjacent off-axis plies may be needed.