Mechanical Properties of Lightweight Sandwich Panels with Corrugated Plywood Core

Abstract

Lightweight and sustainable panels are desired for many applications, including wall linings, ceilings and decorative xtures. The focus of this thesis were sandwich panel structures sourced from Radiata pine wood, a renewable and biodegradable raw material. Major objectives were to characterise, and develop models to predict, key mechanical properties of the novel corrugated plywood sandwich core and overall sandwich structures. Tensile, bending and shear tests were carried out on the base plywood material to establish orthotropic properties for subsequent modelling, with signi cant in-plane values determined to be EL=10.2 GPa, ET =0.15 GPa and GLT =0.85 GPa. Numerical models were developed to predict out-of-plane properties of the corrugated core, and were compared with compression and block shear experiments, and existing analytical solutions. In single corrugation tests, 1-ply and 2-ply laminate models were found to match experiments well, while the sti ness and strength of 3-ply specimens were over-predicted. Numerical nite element (FE) predictions of sti ness and strength for shear along and across the corrugations, through-thickness compression, and corrugation bending also exceeded experimental results. It was concluded that the plywood laminate was damaged during forming, reducing elastic mate- rial properties and, more signi cantly, the strength of interlaminar adhesion. Unit-cell models were used to investigate several di erent core con gurations and pro le geometries, including bi-directional corrugations and circular-straight pro les. FE models predicted the behaviour of four point bend tests reasonably accurately, presum- ably due to face-sheets being una ected by forming. Sandwich beams often showed signi cant through-thickness compression under the loading points, and failure modes observed included face-sheet buckling and excessive shear deformation. Vibration testing revealed that beams generally behaved as homogeneous below 1.5 kHz, but after this signi cant core breakup was observed. FE models predicted the free-free modes of vibration of beams well to higher frequencies, and revealed unique modes caused by the corrugated core. In conclusion, the mechanical behaviour of corrugated plywood sandwich structures has observed in several critical load cases. With this understanding, such sandwich panels show great potential for application. Avenues of future work are nally suggested, including pro le forming, investigating certain mechanical tests, and potential modi cations for FE models.