Experimental and theoretical study of a foldable composite beam

This paper presents a new concept of a foldable composite beam made up of wooden blocks bonded to carbon fiber sheets. The wooden blocks are assembled by mortise and tenon. The composite beam can be folded into a spiral shape. In the unfolded configuration, the dry carbon fiber sheets are in tension and the blocks are in contact. The main practical advantage is the ease of handling and transport. In the first part of this study, we have tested seven foldable beam specimens in three-point bending. The beam length and the number of layers of carbon fiber sheets varied according to the specimen. All foldable beams have a non-linear elastic behavior which was approximated by a bi-linear behavior. Failure is brittle and it is by cutting of carbon fiber sheets or by shear of the most loaded block. After analyzing the experimental results, an analytical model based on the equilibrium of blocks was proposed to predict the behavior of beams. The model provides the load–deflection relationship and failure modes of the foldable beams and this response is compared to the experimental data. The prediction provided by the theoretical model shows an agreement with the experimental results. Finally, the validated model is used for a parametric theoretical study to further examine the effects of the number of the blocks, the number of nails used to reinforce wooden blocks and the dry carbon fiber sheets thickness on the mechanical behavior of the foldable beam. The results indicate that the structural behavior is sensitive to the varied parameters.

► We present a new concept of a foldable beam made up of wooden blocks bonded to carbon fiber sheets. ► The conceived foldable beam presents a good faculty to be folded and unfolded. ► The foldable beams have a nonlinear elastic behavior. ► A simplified model based on the equilibrium of every block is proposed. ► The theoretical and the experimental structural behavior present a good agreement.