Buckling of variable angle tow plates: From concept to experiment

Preliminary experimental results are compared with finite element analysis for composite laminated plates where the fiber orientation in each layer is a function of position. The novelty of the current work lies in the added design freedoms bestowed by embroidery compared with known tow placement systems. Specifically, we have designed plates in which the inter-tow distance may vary, with the associated benefit of greater variation of fiber angles within the planform. An associated feature is the gradual (and slight) variation in plate thickness that arises. The aim of the current work was to design, manufacture and test such variable angle tow plates paying particular attention to plate quality. Ultrasound tests for voidage coupled with flatness of the plate were used as quality measures. Fiber volume fractions greater than 65% were obtained and perceived quality was found to be excellent. Test results for the variable stiffness panels show similar (if not superior) buckling performance to a quasi-isotropic baseline whilst demonstrating significantly improved postbuckling performance. The ratio of post-buckled to pre-buckled stiffness of one such panel design was found to be 0.92 compared to the value of 0.72 found for an equal weight quasiisotropic plate demonstrating the potential for substantial improvements in structural efficiency.