Meccanica (2008) 43: 251–262 DOI 10.1007/s11012-008-9120-z Structural optimization and experimental analysis of composite material panels for naval use G. Marannano · G. Virzì Mariotti Accepted: 3 December 2007 / Published online: 28 February 2008 © Springer Science+Business Media B.V. 2008 Abstract The purpose of the work is the realization of a composite material with long glass fibers having better characteristic than a fiber random composite, to permit the reduction of weight and costs to shipyards for pleasure craft. Structural optimization is performed by ANSYS for the choice of the layers disposition to obtain the maximum stiffness with minimum material employment, saving weight. The study is centered on the research of the better configurations of plies pack- ing in relation of pure shear stress for four different plies. Unidirectional plies, both symmetric orthotropic and symmetric non-orthotropic ones, are realized suc- cessively by the vacuum bag technique. Experimental tests of traction, bending, inter laminar shear and pure shear are executed to characterize the three different type of material. Experimental results are compared to ones obtained numerically to validate the procedures; the comparison with the analytical results permitted to attribute an adequate value to shape factor of the fibers. In all the cases the optimization permitted the construction of much more resistant plies than random ones, with a lower thickness. Keywords Random composite · Composite material test · Structural optimization G. Marannano · G.V. Mariotti ( ) Dipartimento di Meccanica, Università di Palermo, Viale delle Scienze, 90128, Palermo, Italy e-mail: virzi@dima.unipa.it 1 Introduction This work takes rise on a previous work [1] for the characterization of a random composite in use in the naval industry. The shipyard for pleasure craft achieves the parts in composite material in order to ob- tain the best compromise of strength, stiffness, weight and cost of the structures with the purpose to achieve performances that cannot be obtained by traditional materials. In general the shipyards do not put great at- tention in the building of fiber glass laminated, that is they do not consider the possibility of obtaining more strength laminates to several solicitations characteris- tics, simply disposing the strength fibers in an ade- quate direction. The study of the typology of the plies and their correct arrangement is finalized to the ob- taining of the maximum strength with the minimum employment of material, assuring a greater mobility and a lower energy request for the boat motion [8, 9]. The purpose of the paper is the realization of a com- posite material with long fibers having better general characteristics than a random composite material hav- ing normal use in the naval industry. The developed work is summarized in the following points: • Initial material: composite with random glass fibers supplied by a boat manufacturer [1]. In this pa- per the existing rules for materials with unidirec- tional fibers are applied in all cases to specimens dimension and to the procedure of test execution [2–5]. The experimental tests are conduced on a