Due to the unique properties of polymer composites, these materials are used in many industries, including shipbuilding (hulls of boats, yachts, motorboats, cutters, ship and cooling doors, pontoons and floats, torpedo tubes and missiles, protective shields, antenna masts, radar shields, and antennas, etc.). Modern measurement methods and tools allow to determine the properties of the composite material, already during its design. The article presents the use of the method of acoustic emission and Kolmogorov-Sinai (K-S) metric entropy to determine the mechanical properties of composites. The tested materials were polyester-glass laminate without additives and with a 10% content of polyester-glass waste. The changes taking place in the composite material during loading were visualized using a piezoelectric sensor used in the acoustic emission method. Thanks to the analysis of the RMS parameter (root mean square of the acoustic emission signal), it is possible to determine the range of stresses at which significant changes occur in the material in terms of its use as a construction material. In the K-S entropy method, an important measuring tool is the extensometer, namely the displacement sensor built into it. The results obtained during the static tensile test with the use of an extensometer allow them to be used to calculate the K-S metric entropy. Many materials, including composite materials, do not have a yield point. In principle, there are no methods for determining the transition of a material from elastic to plastic phase. The authors showed that, with the use of a modern testing machine and very high-quality instrumentation to record measurement data using the Kolmogorov-Sinai (K-S) metric entropy method and the acoustic emission (AE) method, it is possible to determine the material transition from elastic to plastic phase. Determining the yield strength of composite materials is extremely important information when designing a structure.

The article presents a method of determining the yield point, applying calculations based on the Kolmogorov-Sinai (K-S) metric entropy model. Data used in metric entropy calculations was obtained during a static tensile test of the AW-7020 aluminium alloy. The methodology of K-S entropy calculations was presented and illustrated by a selected example from a data collection. Analyzing the results obtained, the values of an arbitrary yield point were compared for R02 selected samples with the values ReK−S.

The article describes the technologies of recycling polyester–glass waste and the influence of manufacturing technology on the properties of layered composites with polyester–glass recyclate additive. Milled polyester–glass waste was used as the recyclate. Polyester–glass composites with a specific content of recyclate were manufactured by means of manual laminating and vacuum bagging. The influence of the recyclate content and manufacturing method on the mechanical properties of composites was determined with the aid of specimens exposed to static tensile testing. Test results indicated that the composite without recyclate additive manufactured by means of vacuum bagging exhibits higher strength properties than the same composite manufactured by means of manual laminating. Additionally, its plasticity is much higher than that of the composite manufactured by means of manual laminating. The tests indicated that the tensile properties of the composite are, essentially, influenced by the content of recyclate (apart from the manufacturing method). Adding recyclate to the manufactured composite in the amount of 10% and 20% causes a significant decrease in its tensile properties in relation to the composite without the recyclate.

This study analyzes the possibility of applying the acoustic emission method (AE) and the Kolmogorov-Sinai (K-S) metric entropy phenomenon in determining the structural changes that take place within the EN AW 7020 aluminum alloy. The experimental part comprised of a static tensile test carried out on aluminum alloy samples, and the simultaneous recording of the acoustic signal generated inside the material. This signal was further processed and diagrams of the effective electrical signal value (RMS) as a function of time were drawn up. The diagrams obtained were applied on tensile curves. A record of measurements carried out was used to analyze the properties of the material, applying a method based on Kolmogorov-Sinai (K-S) metric entropy. For this purpose, a diagram of metric entropy as a function of time was developed for each sample and applied on the corresponding course of stretching. The results of studies applying the AE and the K-S metric entropy method show that K-S metric entropy can be used as a method to determine the yield point of the material where there are no pronounced yield points.

The aim of the research was to determine the effect of polyester-glass recyclate on the deflection of composite samples subjected to three-point bending. The polyester-glass recyclate was obtained from the part of the ship’s hull made of polyester-glass composite, constituting scrap metal. The pieces of scrap were pre-fragmented and then processed into a prepared stand for this purpose. Such a fragmented recycling will be used to make composites with different scrap / recycled content. For this purpose, research materials were made using the vacuum bag method with the percentage of 0%, 10% and 20% recyclate) as well as various granulation (i.e. 1.2 mm and 3.0 mm). The research material consisted of rectangular plates with a thickness corresponding to the thickness of the samples. The samples for testing were made by water cutting. The tests were carried out on a suitably prepared stand, which was made of a universal Zwick Roell testing machine and three-point bending handles and a dial indicator. The spacing of the supports has been determined in accordance with the binding standard for three-point bending. Obtained results from tests, i.e. strain, stress, deflection, deformation allowed analysing the impact of recyclate on bending strength and defining the deflection arrow. Based on the results obtained from three-point bending, it can be concluded that the polyester-glass recycling has an influence on the decrease of strength, stress and deflections of the tested composites.