The incorporation of fiber reinforcements into polymer matrices has emerged as an effective strategy to enhance the mechanical properties of composites. This study investigated the tensile and fracture behavior of 3D-printed polylactic acid (PLA) composites reinforced with chopped carbon fibers (CCFs) through experimental characterization and finite element analysis (FEA). Composite samples with varying CCF orientations (0°, 0°/90°, +45°/−45°, and 0°/+45°/−45°/90°) were fabricated via fused filament fabrication (FFF) and subjected to tensile and single-edge notched bend (SENB) tests. The experimental results revealed a significant improvement in tensile strength, elastic modulus, and fracture toughness compared to unreinforced PLA. The 0°/+45°/90° orientation exhibited a 3.6% increase in tensile strength, while the +45°/−45° orientation displayed a 29.9% enhancement in elastic modulus and a 29.9% improvement in fracture toughness (259.12 MPa) relative to neat PLA (199.34 MPa√m). An inverse correlation between tensile strength and fracture toughness was observed, attributed to mechanisms such as crack deflection, fiber bridging, and fiber pull-out facilitated by multi-directional fiber orientations. FEA simulations incorporating a transversely isotropic material model and the J-integral approach were conducted using Abaqus, accurately predicting fracture toughness trends with a maximum discrepancy of 8% compared to experimental data. Fractographic analysis elucidated the strengthening mechanisms, highlighting the potential of tailoring CCF orientation to optimize mechanical performance for structural applications.

Natural materials (be it fibers or particles) are porous materials due to their nature, which make them valuable in sound absorbing. Natural materials (NM) in general are environmentally friendly. Composite sandwich plates made from different types of natural materials in contribution with glass fibers and polyester had been used in this study, precisely, Dried Cooked Tea Leaves DCTL, Husks of Fresh Beans FBH, Egg Peels EP, Garden’s Sand GS, Wood Fiber WF, Chicken Feathers CF and Palm Fronds PF with different thicknesses (6, 8, and 10) mm. These composites were tested as sound insulating materials. A test rig is prepared. Different frequencies from a function generator were used and sound waves were measured utilizing sound pressure level (SPL) practically to estimate the sound transmission losses (TL) and the coefficient of sound transmission losses (TC). The preferable results in transmission losses recorded for the samples fabricated from (Palm Fronds, Wood Fiber, Garden’s Sand and FBH) and the 10 mm thickness samples were the best. The TL for these samples were greater than the neat random fiberglass samples (195%, 155%, 133%, 116% and 92%) respectively at high frequencies. The other two natural materials also have permissible results but with less percentages than the others, the results were (50% and 45%) greater than the neat random fiberglass samples for the (DCTL and CF) respectively.