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Exfoliated graphite nanoplatelets (xGnP)-filled impact-modified polypropylene (IMPP) composites were prepared at 2, 4, 6, and 8 wt % xGnP with and without the addition of a coupling agent and manufactured using melt mixing followed by injection molding. The coupling agent used in this study was polypropylene-graft-maleic anhydride (PP-g-MA). The nanoparticles used were xGnP with three different sizes: xGnP 5 has an average thickness of 10 nm, and an average platelet diameter of 5 lm, whereas xGnP 15 and xGnP 25 have the same thickness but average diameters are 15 and 25 lm, respectively. Test results show that nanocomposites with smaller xGnP diameter exhibited better flexural and tensile properties for both neat and compatibilized composites. For composites containing a coupling agent, tensile and flexural modulus and strength increased with the addition of xGnP. In the case of neat composites, both tensile and flexural modulus and strength decreased at higher filler loading levels. Increasing xGnP loading resulted in reduction of elongation at break for both neat and composites containing coupling agent. Explanation of this brittle behavior in a nanoplatelet-filled IMPP is presented using scanning electron microscopy and transmission electron microscopy.

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The variability of tensile mechanical properties of a polymer matrix composite material with woven fabric reinforcement is studied using both experimental work and numerical simulations. Four E-glass/vinyl ester composite plates were fabricated using the vacuum-assisted resin transfer molding (VARTM) by a US Navy contractor. The materials and process selected are representative of Marine grade composites typically used by the US Navy. Standard and modified D3039 tensile coupons were obtained from the plates and the laboratory results were compared with those of a 3D probabilistic finite element analysis (FEA). In the probabilistic FEA model, elastic properties, strength parameters, and geometric properties of the woven fabric E-glass/vinyl ester coupons were considered as random fields, and generated using Monte Carlo simulations. The study evaluates the effects of spatial correlation, finite element size, probability distribution functions (PDF) types, and failure criteria on statistical strength properties of the [(0 w /90 f )/(0 f /90 w )] 2s tension coupons. Comparisons of experimental and probabilistic FEA results provide useful information on how to assign mean, COV, and PDF of material properties to individual finite elements within a mesh. The results are relevant in developing design properties for these composites.