Mechanical characterization of bend-twist coupling behavior in composite marine hydro-kinetic turbine blades

Bend-twist coupling is a phenomenon in some structures whereby bending moments produce not only transverse deflection, but also twist. Recent decades have seen a growing trend toward exploiting this mechanism to advance the performance of structures. This coupling effect can be caused by geometric factors such as eccentric loading, or it can be induced by leveraging the anisotropic nature of fiber-matrix composites. This study focuses on the purposeful use of unbalanced layups in laminated fiber-reinforced polymer spars to tailor bend-twist coupling behavior.

An especially promising application of bend-twist coupled composite structures is their potential use in marine energy turbines. Recent efforts have shown that bend-twist coupling can be used to reduce loading on turbine blades in overload conditions, thereby improving their robustness, without significantly reducing power generation under normal operating conditions. This work robustly characterizes, using both experimental and numerical methods, the relationship between the effective fiber angle (a design parameter) and the: (i) degree of bend-twist coupling, (ii) bending stiffness, and (iii) natural frequencies (system properties) of laminated composite blades. The outcomes of this work will help designers choose the optimal fiber angles for specific applications and will serve as a strong benchmark for the validation of computational models.