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Evaluation of Tow-Steering Effects—Mechanical Coupon Testing



Tow-steering of composites using Automated Fiber Placement (AFP) provides significant flexibility for the composite designer to spatially tailor fiber orientation within a given ply. However, tow-steering is not without drawbacks which may negatively impact the strength and stiffness of the material. In general, there are two sources of strength reduction of concern: inherent geometric complexities due to tow convergence zones (e.g., gaps and overlaps) and manufacturing defects related to the in-plane curvature of the tows. The purpose of the present work is to identify the mechanical properties of towsteered laminates relative to those of an unsteered laminate for the application of a 39- foot passive-aeroelastically tailored wingbox. The tow-steered laminate currently studied employs a fixed ply fraction wherein all tows are steered together and maintain fixed relative angles to each other, thus minimizing the number of unique effective layup sequences. An alternate approach wherein half the plies (the equivalent quasiisotropic component) are unsteered is also considered. The design and fabrication of tow-steered and unsteered panels for mechanical coupon testing is described. Normalized test results for modulus and strength are presented for tow-steered laminates, relative to equivalent unsteered laminates.

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