Effect of Stacking Sequence and Alkali Surface Treatment Optimization on Tensile Properties of Interlayered Cross-Ply Carbon/Ramie/Epoxy Hybrid Composites: An Experimental and ANN Study

The increasing needs of high-performance, lightweight and eco-friendly materials have led to the evolution of hybrid fiber-reinforced polymer composites (synthetic and natural fibers) to provide high mechanical performance and reduce the environmental impact for aerospace, automotive and structural applications. This paper examines the tensile behavior of cross-ply interlayer hybrid carbon/ramie-fiber-reinforced epoxy composites via experimental tests and artificial neural network (ANN) modeling based on the influence of the stacking sequence and alkali treatment with a strong alkali, sodium hydroxide (NaOH). Fourier transform infrared spectroscopy analysis of the ramie fibers proves the removal of non-cellulosic elements of the fiber such as wax, hemicellulose and lignin. Field emission scanning electron microscopy images reveal better fiber matrix interfacial bonding of surface-treated ramie fiber and fractured tensile test hybrid specimens. In the case of the untreated laminates, specimen-S3 containing a carbon/ramie/ramie/carbon sequence of [0°/90°]s orientation offers the best tensile performance, achieving tensile stress of 378 MPa and a modulus of 10,441 MPa. The hybrid composite (S3-3) with 3 wt% of NaOH considerably improves its tensile strength and modulus values (466 MPa and 24,145 MPa), which is owed to enhanced fiber-matrix interfacial bonding. On the other side, an increase in NaOH levels leads to weakening the ramie fibers and reduces performance. ANN predicts tensile properties with extremely high accuracy with regression coefficient of R = 0.99996 and regression error of less than 10%. The statistical analysis indicates that alkali treatment and stacking sequence have a significant effect on tensile properties (p ≤ 0.0001).