The aim of our research was to investigate the effect of a small nanocellulose (NC) addition on an improvement of the mechanical properties of epoxy composites. A procedure of chemical extraction from pressed lignin was used to obtain nanocellulose fibers. The presence of nanoparticles in the cellulose pulp was confirmed by FTIR/ATR spectra as well as measurement of nanocellulose particle size using a Zetasizer analyzer. Epoxy composites with NC contents from 0.5% to 1.5% w/w were prepared. The obtained composites were subjected to strength tests, such as impact strength (IS) and resistance to three-point bending with a determination of critical stress intensity factor (Kc). The impact strength of nanocellulose composites doubled in comparison to the unmodified epoxy resin (EP 0). Moreover, Kc was increased by approximately 50% and 70% for the 1.5 and 0.5% w/w NC, respectively. The maximum value of stress at break was achieved at 1% NC concentration in EP and it was 15% higher than that for unmodified epoxy resin. The highest value of destruction energy was characterized by the composition with 0.5% NC and corresponds to the increase of 102% in comparison with EP 0. Based on the analysis of the results it was noted that satisfactory improvement of the mechanical properties of the composite was achieved with a very small addition of nanofiller while other research indicates the need to add much more nanocellulose. It is also expected that this kind of use of raw materials will allow increasing the economic efficiency of the nanocomposite preparation process. Moreover, nanocomposites obtained in this way can be applied as elements of machines or as a modified epoxy matrix for sandwich composites, enabling production of the structure material with reduced weight but improved mechanical properties.

Composite materials are widely used in the construction of means of transport. Due to their low density and high stiffness, sandwich composites generate significant interest. The authors conducted static and dynamic tests in order to determine the effect of density and core thickness on the mechanical properties of a sandwich composite. Particular attention was paid to the impact properties of such composites. Herex and Airex polymer foams of different densities were used as cores, whereas the faces were made up of two layers of fabrics: glass and carbon. The matrix base of the tested materials was made of epoxy resin cured with a dedicated hardener. As a result of the study, a significant influence of the core on the strength parameters of the tested spacer materials was found. The examined polymer foams were found to have different adhesive properties, which affected their residual strength after an impact and the nature of destruction of the studied composites. It was observed that sandwich composites with a thicker core of higher density have higher impact strength and resistance to puncture. In the sandwich composites, low-energy impact loads result in damage only to the layer to which the load has been applied and has a core, so repairing such an element is much easier than in classic layered composites without a core. What is very important is that, in contrast to classic laminates, the bottom cover of the composite is not destroyed at low-impact energy values.

Fibre-metal laminates combine both the properties of metal and composite materials, reinforced with fibres; first such laminates already appeared at the end of the 70s. Alongside with the emergence of spacecraft, in which the external plating heats up to temperatures even exceeding 3000 °C,...

For this work, fibre-reinforced composites were prepared using 14 layers of aramid fabric and 6 layers of carbon fabric. The matrix was composed of epoxy resin Epidian 52, cured with TFF hardener. The composite cross-linked at ambient temperature. Additionally, a phase change material (PCM) in...

The experimental tests presented in this work concern the impact resistance test and residual strength properties after an impact performed by a drop tower INSTRON CEAST 9340. The authors prepared samples of a composite material with a polymeric matrix L285 and H285 hardener, reinforced with eight ply fabric of carbon fibre. Two shapes of the impactor (spherical and V-shape) were used to perform the testing. The samples were impacted by three values of energy (10, 15, 20 [J]). Three-point bending tests were performed to the residual strength of the samples subjected to impact tests and compared to samples which had not been damaged earlier. The study showed differences in the influence of the shapes of the impactor on the nature of the composite damage. After the test, conclusions were drawn about the influence of the shape of the impactor on the area of composite damage and its character. Also, its influence on residual strength was described. Despite the clear differences in the area of damage to composites impacted by different impactors, this does not have a significant influence on the residual strength.