Prepreg platelet molding compound (PPMC) can be used to create structural grade material with a heterogeneous mesoscale morphology. The present work considered various platelet lengths of the prepreg system IM7/8552 to study the effect of platelet length on the flexural behavior of PPMC composite. A progressive failure finite‐element analysis was used to understand competing failure modes in PPMC with the different platelet length. The interlaminar and in‐plane damage mechanisms were employed to describe complex failure modes within the mesostructure of PPMCs. Experimental results of the flexural tests of the PPMC with different platelet length sizes were used to validate the modeling prediction. The experimental and modeling results revealed complex behavior of the flexural mechanical properties (modulus and strength) on the platelet length. The experimental results indicate that PPMC composites processed with a plate length of 12.7 mm have a higher flexural modulus and strength than 25.4 and 6.35 mm. The platelet length effect on the flexural mechanical behavior was attributed to interactions between various damage mechanisms and the stochastic fiber orientation distribution variability in the material.

Graphene has generated substantial interest as a filler due to its exceptional strength, flexibility, and conductivity but faces obstacles in supply and implementation. A renewable, plant‐based graphene nanoparticle (pGNP) presents a more accessible filler with the same properties as mineral graphenes. In this study, we examine the effects of pGNP, which was sprayed on a carbon fiber/epoxy prepreg at loadings from 1.1 to 4.2 g/m². The study considered the mechanical, thermal, and electrical properties of pGNP‐composite. An even particle dispersion was achieved using a spray application of pGNP in a water/alcohol suspension with the addition of surfactants and dispersion aides. Results show that pGNP addition increases flexural modulus 15%, flexural strength 17%, interlaminar shear strength 17%, and mode I fracture toughness by 146%, as well as increases electrical conductivity 294% and thermal conductivity 24%, with these improvements observed at 1.1–2.3 g/m² spray loadings.

Composite sandwich structures are widely used in weight-critical applications such as aerospace and automotive engineering due to their high strength-to-weight ratio. This study investigates the flexural performance of sandwich structures fabricated with 3D-printed glass fiber-reinforced nylon (GF-PA6) cores, comparing fully printed composite sandwich structures (PCSS) to hybrid composite sandwich structures (HCSS) reinforced with woven carbon fiber/epoxy face sheets. Two core geometries, triangular and tri-hexagonal, were fabricated at infill densities of 20% and 40% using fused filament fabrication (FFF). HCSS configurations were produced by bonding carbon fiber/epoxy face sheets to the printed cores via vacuum-assisted wet layup. All specimens were tested under three-point bending per ASTM C393, with stress characterization performed using sandwich beam theory applied consistently to both PCSS and HCSS configurations. HCSS specimens achieved facing stress values of 184.40–349.70 MPa, compared to 86.96–103.35 MPa for PCSS, with the failure mode transitioning from brittle fracture in PCSS to progressive classical sandwich failure in HCSS, involving local face-sheet indentation, core shear failure, face-core debonding, and fiber pull-out. Increasing infill density from 20% to 40% produced significantly larger improvements in facing stress in HCSS (+57.1% and +89.6% for triangular and tri-hexagonal geometries, respectively) than in PCSS (+8.3% and +18.8%), confirming that a denser core more effectively transfers load to the carbon fiber face sheets. A density-dependent trade-off between strength and energy absorption was observed, with 20% infill HCSS exhibiting greater displacement capacity and energy absorption despite lower facing stress. These findings highlight the effectiveness of combining 3D-printed fiber-reinforced thermoplastic cores with high-stiffness composite face sheets, and provide insight into how core density and architecture govern flexural performance and failure behavior in additively manufactured sandwich composites.