Effect of Fabric Areal Weight on the Mechanical Properties of Composite Laminates in Carbon-Fiber-Reinforced Polymers

The present work aims at studying the effect of the reinforcing fabric areal weight on the mechanical properties of composite laminates in carbon-fiber-reinforced polymers. Three different pre-impregnated 2 × 2 twill weaves, characterized by the different areal weight values of 380, 630, and 800 g/m2 were used to produce laminates. These areal weights were selected to represent typical values used in structural application. A hand lay-up technique followed by an autoclave cycle curing was employed to produce the laminates. The desired final thickness of the laminates was obtained by laying-up a different ply number, as a function of the areal weight and thickness of each fabric. Uniaxial tensile and in-plane shear response tests were performed on samples obtained from laminates after curing. Furthermore, the presence of voids in composite materials were detected by performing resin digestion tests. Finally, light optical microscopy and stereomicroscopy analyses allowed observing the different arrangement of the plies in the cross-sections of laminates after curing and evaluating the degree of compaction as a function of the reinforcing fabric used. It was demonstrated that the fabric areal weight significantly affects the mechanical performances of the composite laminates; specifically, the decrease in the areal weight of the twill weave leads to an increase in tensile strength, elastic modulus, and in-plane shear stress, i.e., of about 56.9%, 26.6%, and 55.4%, respectively, if 380 g/m2 and 800 g/m2 fabrics are compared. These results are crucial for an optimal material selection during the design process for industrial applications and help to better understand composite material behavior.