Effect of stitch parameters on tensile and low velocity impact performance of empty fruit bunch oil palm fiber epoxy composite

Abstract

Empty fruit bunch (EFB) from oil palm has become one of the widely used natural fiber reinforced composites since it possesses specific properties that offer exceptional performance for structural load bearing applications. However, overall mechanical performances of EFB oil palm composites have been limited due to its hydrophilic characteristic. It is essential to enhance the in-plane and out-of-plane mechanical performances of EFB oil palm fiber composites by using advanced reinforcement method of through thickness stitching. Stitching parameters consisting of thread thickness, stitching density and stitching orientation are investigated to evaluate the tensile performance of its composite structure. Pitch length of 10 mm and 15 mm were used for stitch density variation, thread thickness of Nylon 210D and Polyester 380D for thread thickness variation, stitching pattern of 00,450, and 900 were used for stitching orientation variation. Result of mechanical characterization tests of unstitched palm fiber composites and mechanical properties of a single strand of stitch material are analyzed and updated in the simulation model. The finite element analysis study evaluates low velocity impact test of z-directional stitching for EFB oil palm fiber composite by employing LS-DYNA software as its analysis tool. Several sets of investigations were carried out to study the influence of stitch density and thread thickness on their impact response when subjected to low velocity impact. Pitch length of 6 mm and 10 mm were used for stitch density variation, whereas, thread thickness of 1 mm (Nylon 210D) and 1.5 mm (Polyester 380D) for thread thickness variation. Experimental test case of low velocity impact test of unreinforced polyester and random oriented non-woven hemp fiber polyester reinforced composite plates were used to validate the finite element model. Outputs of maximum load, energy absorption, and failure behavior for impacted specimens of experimental and simulation results were compared. Tensile strength and modulus elasticity decrease by 61% and 38% respectively when oil palm fiber composite is compared to unreinforced epoxy. Tensile strength and modulus of elasticity of stitched EFB oil palm fiber composite have improved by 66% and 46% respectively when compared to unstitched composite due to the additional load bearing capability and compaction effect from the increase in fiber volumetric fraction of stitch threads. High dense stitch density, thinner thread thickness, longitudinal orientation stitched EFB composite have corresponded to a higher tensile performance when compared to its predecessor. Impacted stitched EFB fiber reinforced composite exhibit superior load bearing capability when compared to unstitched EFB composite. The energy absorption for unstitched, 6 mm x 6 mm stitch density, and 10 mm x 10 mm stitch density stitched EFB composite were recorded at 0.143, 0.368, and 0.158 J respectively. High dense stitch density and thinner thread thickness stitched EFB composite have corresponded to a higher maximum load, higher force and displacement level for the occurrence of structural degradation, and higher amount of energy absorption. Impacted specimen exhibits fragmented fracture due to its nature of brittle failure behavior. Matrix cracking, fiber breakage, and penetration of impacted surface were the composite damage mechanism of stitched EFB composite.