An investigation into the bolt layout and washer type in nanocomposite joints

The increasing use of polymer-based composites and fiber metal laminates in structural applications necessitates improved joint design strategies. This study investigates the effects of bolt layout and washer type on the failure behavior of double-lap bolted joints in polypropylene-based nanocomposite plates. Experimental tests were conducted using a GOTECH AM-20 machine, and numerical simulations were performed with ABAQUS/CAE 2016. The Sb522 configuration with a flat washer showed the most severe rupture, while Sb311, Sb312, Sb511, and Sb512 exhibited strength improvements of up to 9.94% when flat washers were used instead of spring washers. Load-displacement curves and failure patterns showed strong agreement between experimental and finite element results, confirming the reliability of the simulation approach. The maximum Von Mises stress in the bolts (excluding plates) reached 2364 Pa, indicating that the bolts carried over 50% of the load. An artificial neural network model was also developed to predict joint performance parameters, demonstrating high accuracy and complementing experimental and numerical results. This hybrid approach enables efficient evaluation and optimization of nanocomposite joint configurations.