Effect of Natural Fibers on the Strength and Damage in Adhesively Bonded Joints

Adhesively bonded joints provide uniform stress distribution resulting in low stress concentrations and high strength-to-weight ratio, though concerns arise due to the limited strength of adhesives. The study focuses on enhancing the static strength of these joints by using natural fibers in the adhesive region. The effect of natural fibers on the adherent failure caused by cracks is also examined. The date palm fibers, Rachis and Petiole, are used in the adhesives to improve their strength. UHU plus endfest 300, FM 73, and Araldite 2015 adhesives are used for the analysis. A parametric study to obtain an optimum number of fibers in the adhesive region is performed. Three-dimensional numerical analysis is performed where the adhesives are modeled using cohesive-zone modeling (CZM). The fibers are modeled as one-dimensional members in the loading direction. The average von Mises stress criterion over the characteristic distance in the overlap region is used in determining the failure of the joint. The crack is introduced at different locations in the adherent plate to assess its severity on adherent failure, wherein the fracture parameters are computed using modified virtual crack closure integral (MVCCI) technique. Reinforcing the joint with Rachis and Petiole fibers improved the strength by 2 and 1.3 times, respectively. Rachis reinforced UHU plus endfest 300 reduced crack intensity by 7% at overlap ends and 22% within the overlap region. The approach and the results help develop robust damage tolerance designs of these joints that may assist in better structural health monitoring.