Polymer fiber composites are increasingly being used in many industries, including the defense industry. However, for protective applications, in addition to high specific strength and stiffness, polymer composites are also required to have a high energy absorption capacity. To improve the performance of fiber-reinforced composites, many researchers have modified them using multiple methods, such as the introduction of nanofillers into the polymer matrix, the modification of fibers with nanofillers, the impregnation of fabrics using a shear thickening fluid (STF) or a shear thickening gel (STG), or a combination of these techniques. In addition, the physical structures of composites have been modified through reinforcement hybridization; the appropriate design of roving, weave, and cross-orientation of fabric layers; and the development of 3D structures. This review focuses on the effects of modifying composites on their impact energy absorption capacity and other mechanical properties. It highlights the technologies used and their effectiveness for the three main fiber types: glass, carbon, and aramid. In addition, basic design considerations related to fabric selection and orientation are indicated. Evaluation of the literature data showed that the highest energy absorption capacities are obtained by using an STF or STG and an appropriate fiber reinforcement structure, while modifications using nanomaterials allow other strength parameters to be improved, such as flexural strength, tensile strength, or shear strength.

This paper presents ways to modify epoxy resin matrix composites to increase their electrical conductivity. Good electrical properties are particularly important for materials used in the construction of vehicles (cars, trains, airplanes) and other objects exposed to lightning (e.g., wind turbines). When the hull plating is made of an electrical conductor (e.g., metal alloys) it acts as a Faraday cage and upon lightning discharge the electrical charge does not cause damage to the structure. Epoxy-resin-based composites have recently been frequently used to reduce the weight of structures, but due to the insulating properties of the resin, various modifications must be applied to improve the conductivity of the composite. The methods to improve the conductivity have been categorized into three groups: modification of the matrix with conductive fillers, modification of the composite reinforcement, and addition of layers with increased electrical conductivity to the composite.

The effect of conductive carbon black (0.5 wt%) on the properties of carbon fiber-reinforced epoxy resin (Rockwell hardness, Charpy impact strength, tensile and flexural properties, electrical conductivity, and resistance to lightning discharges) was investigated. The composites were obtained by the infusion method. A slight decrease in flexural modulus was observed, while the hardness and Young's modulus increased. The resistivity decreased four times. Simulated multiple lightning discharges confirmed the better electrical conductivity of the composite with the addition of conductive carbon black, which resulted in five times decrease in the laminate damage area.

Effect of hybrid carbon fillers system (multi-walled carbon nanotubes and graphene sheets) on mechanical and electrical properties of epoxy resin was investigated. The best mechanical properties and electrical conductivity were achieved using both fillers simultaneously, demonstrating their synergistic effect. The composite with only carbon nanotubes exhibited better electrical conductivity and higher Charpy impact strength than the composite with only graphene sheets. Furthermore, the use of graphene nanosheets resulted in higher Rockwell hardness.

This paper investigates the effect of material type, shape and cell size of cores on impact energy absorption properties. For this purpose, thermoplastic cores were prepared by 3D printing and compared with commercially available composites containing aluminum and aramid cores. The impact energy absorption properties were evaluated using “falling arrowhead” impact puncture tests. Obtained results showed that composites containing thermoplastic cores had significantly higher impact energy absorption compared to reference composites. Structures with a small cell area, especially those with a rectangular shape and parallel cell arrangement, performed the best. In contrast, composites with aramid and aluminum cores, despite their lower weight, had worse impact properties. It was also shown that increased energy absorption by thermoplastic structures was associated with higher composite weight, which may be an important factor in applications requiring optimization of mass and impact-ballistic resistance.

This study investigated the effect of conductive carbon fillers on the electrical and mechanical properties of glass fiber-reinforced composites based on powdered epoxy resin. Carbon black and graphene were used as conductive fillers to modify the polymer matrix. The composites were manufactured using the Resin Powder Molding (RPM) technique with a hydraulic press. The effect of filler type and content on electrical resistivity, tensile strength, flexural strength, Rockwell hardness, and Charpy impact strength was assessed. The results showed that the incorporation of conductive carbon fillers significantly reduced the electrical resistivity of the composites while maintaining satisfactory mechanical properties. The effectiveness of the modification depended on both the type and loading of the conductive filler. These findings demonstrate that the functional performance of epoxy composites can be tailored through the appropriate selection of conductive carbon fillers, enabling the development of materials that combine enhanced electrical conductivity with good mechanical performance. Expanded graphite contained in the commercial epoxy resin formulation was maintained at a constant concentration in all composites and was not considered an experimental variable.