Shear mechanical characterization of balsa wood as core material of composite sandwich panels

An experimental study was performed using Iosipescu specimens to evaluate the effects of parameters such as shear plane, density and adhesive joints on the shear stiffness and strength of balsa wood panels as well as the variation of ductility with respect to the shear planes. The shear planes exerted a significant effect on shear stiffness and strength. Highest values were obtained for the shear plane parallel to the end grain, intermediate values for the plane parallel to the flat grain and lowest values for the plane transverse to the flat grain. Shear stiffness and strength increased with increasing density of the balsa. The thin adhesive joints in the balsa panels between the lumber blocks increased the shear stiffness and strength with one exception. The strength of specimens with the shear plane transverse to the flat grain was reduced because of a change in the failure mode. Due to plastic deformations in the tracheids, specimens with shear planes parallel to the end grain and transverse to the flat grain exhibited significant ductility. The ductility of specimens with the shear plane parallel to the flat grain was less pronounced as it was affected by the relatively brittle lignin material of the middle lamella.