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The paper analyzes the issues relating to the applicability of innovative material systems for flexible composite armors. The authors made several samplings of aramid fibers (Kevlar 49) by replacing the epoxy resin base, which is often described in the literature, with the thermoplastic matrix - polyethylene (HDPE) and polypropylene (PP). The samples were fired with .38 Special Full Metal Jacketed (FMJ) ammunition produced by the S&B Company, and then the process of firing was modeled in the ABAQUS program. The advantages and disadvantages of the new material system including the possibility of its use in the construction of hybrid composite armors have been presented on the basis of the results of numerical analyses and ballistic tests.

Wykorzystanie w³ókien naturalnych jako nape³niaczy kompozytów polimerowych Streszczenie-Na podstawie literatury scharakteryzowano w³ókna naturalne (lniane, konopne, drzewne) stosowane jako nape³niacze kompozytów polimerowych. Omówiono te¿ kryteria doboru termoplastycznych matryc polimerowych do takich kompozytów, modyfikacjê (hydrofobizacjê) w³ókien maj¹c¹ na celu polepszenie ich adhezji do matrycy polimerowej, a tak¿e dziedziny mo¿liwych zastosowañ omawianych kompozytów. S³owa kluczowe: kompozyty polimerowe, nape³niacze, w³ókna naturalne, hydrofobizacja w³ókien. APPLICATION OF NATURAL FIBERS AS THE FILLERS FOR POLYMER COMPOSITES Summary-The natural fibers (flaxen, hemp, wood ones), applied as the fillers of polymer composites were characterized on the basis of literature. The criteria of choice of thermoplastic polymeric matrices for such composites were discussed as well as the fibers' modification (making them hydrophobic) with the aim to improve their adhesion to the polymer matrix. The fields of possible applications of the composites discussed were also described.

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The chemically treated hemp fibres to reinforce polymers Summary-The effect of different chemical treatments of hemp fibres, carried out by alkali treatment, acetylation and modification with maleic anhydride, on their physical, thermal and chemical properties as well as their surface characteristic was discussed in this paper. The morphology of the fibres was investigated by SEM. Thermal properties were investigated by TGA and DTA methods and the chemical composition of fibres by FT-IR spectroscopy. Chemical modifications resulted in the lowered content of lignin, pectin and hemicellulose, what is especially observable with mercerised fibres. Another effect of the chemical treatment applied is related to the removal of waxy substances from the surface, which was indirectly ascertained by SEM observation, which revealed a relatively smooth hemp fibres surface. TGA results showed that the applied chemical fibre treatment resulted in the lowered thermal degradation of the treated fibres, after the removal of non-cellulose components, especially lignin.

The quasi-static penetration properties of hybrid laminates were experimentally investigated. Aramid fabrics, carbon fabrics, and short hemp fibres were applied as the reinforcements of hybrid and non-hybrid composite laminates with polyurethane–polyurea (PUR/PUA) matrix. The laminates were made by hand, in a mould. They were cured at room temperature for 24 h. Hybrid laminates consisted of aramid and carbon layers in two different configurations, i.e., aramid at the innermost layers and outermost layers. Aramid/PUR/PUA and carbon/PUR/PUA composites were fabricated for comparison purposes. Laminates were also prepared via an analogue sequence of laying the reinforcement layers with the addition of 5% by weight of hemp fibres in the PUR/PUA matrix. Quasi-static penetration tests (QSPT) were conducted using a tensile testing machine with a surface-hardened, hemispherical, steel punch (9 mm diameter tip), reflecting the geometry of the Parabellum projectile. A quasi-static puncture test was carried out until the laminate was perforated. The ratio between the support span (Ds) and the punch diameter (Dp) was SPR = Ds/Dp = 5.0. The results showed the influences of laminate hybridisation on the values of absorbed energy, punch shear strength, and damage mechanism in the QSPT test. The addition of hemp fibres to aramid laminates resulted in a positive hybridisation effect. The order of layers of aramid and carbon fabrics in hybrid laminates influenced the results obtained in the QSPT test.

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This paper contains experimental results of mechanical testing of the AISI 304 steel with composite coatings. The main goal was to investigate the impact of the applied polyurea composite coating on selected mechanical properties: Adhesion, impact resistance, static behavior, and, finally, fatigue lifetime of notched specimens. In the paper the following configurations of coatings were tested: EP (epoxy resin), EP_GF (epoxy resin + glass fabric), EP_GF_HF (epoxy resin + glass fabric hemp fiber), EP_PUA (epoxy resin + polyurea) resin, EP_GF_PUA (epoxy resin + glass fabric + polyurea) resin, and EP_GF_HF_PUA (epoxy resin + glass fabric + hemp fiber + polyurea) resin. The highest value of force required to break adhesive bonds was observed for the EP_PUA coating, the smallest for the single EP coating. A tendency of polyurea to increase the adhesion of the coating to the base was noticed. The largest area of delamination during the impact test was observed for the EP_GF_HF coating and the smallest for the EP-coated sample. In all tested samples, observed delamination damage during the pull-off test was located between the coating and the metallic base of the sample.