Characterization Of Cyclic Hygrothermal Swelling And Shrinkage Behavior Of Balsa Wood And Gfrp-Balsa Sandwich Structures

TL;DR

This study investigates the cyclic hygrothermal swelling and shrinkage behavior of balsa wood and GFRP-balsa sandwich structures, focusing on moisture-induced strains, internal stresses, and thermal shrinkage during aging cycles to inform sustainable composite design.

Contribution

It provides a detailed characterization of moisture diffusion, hygroscopic strains, and thermal shrinkage in balsa-based sandwich structures under cyclic aging conditions, which is novel in understanding long-term durability.

Findings

Moisture content and strains vary with cyclic aging.

Hygroscopic swelling occurs in all specimens.

Thermal shrinkage is observed during desorption phases.

Abstract

The objective of developing bio-based composite sandwich structures with greener core materials is to facilitate the decarbonization of industries such as aviation and maritime. This field of research has received increasing attention over the past decades. For example, balsa wood has emerged as a highly promising alternative to foam or honeycomb cores, offering a lightweight, rapidly renewable and cost-effective solution. However, plant fibers such as balsa wood and flax often display high hydrophilic behavior, which could affect their mechanical performance and long-term durability. It is therefore imperative to promote further research into the characterization of the cyclic hygrothermal aging behavior of balsa wood core sandwich structures, in particular the identification of moistureinduced strains and internal stresses in the skins and cores, as well as the investigation of moisture desorption processes and the associated thermal shrinkage phenomena in wood fibers, resins and glass fibers. Accordingly, this work employs two complete moisture absorption-desorption cycles to characterize the moisture diffusion behavior of specimens comprising three different materials, including the pure balsa wood, resin-infused balsa and balsa core sandwich structures with two Glass-Fiber-Reinforced-Polymer (GFRP) skins. The changes in moisture content and hygroscopic strains in the thickness, length and width directions of all specimens were investigated with a view to identifying the hygroscopic swelling and thermal shrinkage behaviors exhibited during long-term aging cycles.