Strength improvement of adhesively bonded single lap joints with date palm fibers: Effect of type, size, treatment method and density of fibers

Abstract In this paper, natural fibers and particles provided from different parts of date palm trees are considered to improve the static strength of adhesively bonded joints. Some influencing factors such as type, size, alkaline treatment and the weight ratio of the natural fibers/particles are the parameters that have been experimentally studied. The date palm fibers are provided from four parts of the tree including Mesh, Rachis, Petiole and Bunch. In order to investigate the effect of treatment of the fiber surface, the raw fibers and treated fibers with two different concentrations of aqueous NaOH solution were considered. To study the effect of fiber size, fibers with different sizes including short fibers (0.5–2 mm) and long fibers (30 mm) were separately added to the adhesive. To find the best weight ratio of the fibers corresponding to maximum joint strength, single lap joints with three different weight ratios of date palm fibers (2, 5 and 10%) were experimentally tested. The results show that date palm fibers significantly improve the strength of adhesively bonded joints. For example, the strength of adhesive single-lap joints reinforced by 2 wt% of Rachis fiber treated with 6 wt% NaOH solution, increased by 140%. To investigate the micromechanisms of failure, the fractured surfaces were analyzed. The results show that the date palm fibers can improve the strength of adhesive joints by slowing down the crack propagation, absorbing energy and load endurance.