Application of Kolmogorov–Sinai Metric Entropy to Determine the Exploitation Parameters of Epoxy–Glass Composites with Carbonisate

This study investigates how the addition of a carbon-based filler obtained through the pyrolysis of medium-density fibreboard (MDF) waste affects the mechanical behaviour of epoxy-glass laminates. Two laminate series with different matrix-to-reinforcement ratios (60/40 and 65/35) were fabricated and modified with carbonised particles of up to 500 μm in size, introduced at 5% and 7.5%. The strength of the samples made of the materials mentioned above was assessed in a static three-point bending test by analysing the values of stresses (σfM) and strains (εfM). For an in-depth analysis of the dynamics of the destruction process, the recorded deformation data were subjected to Kolmogorov-Sinai metric entropy (EK-S). The test results showed that the addition of carbonisate in series A (60/40) increased the flexural strength by 32.56% for the sample with 5% addition and by 27.08% for the sample with 7.5% addition, compared to the reference material. In series B (65/35), characterised by a higher resin content, the opposite effect was observed-a decrease in strength of 9.89% (for 5% carbonisate) and 15.53% (for 7.5% carbonisate). The use of EK-S calculations in combination with phase portrait reconstruction to analyse the results obtained allowed for the precise determination of the limit values of stresses and strains (σfMK_S and εfMK_S) at which irreversible structural changes occur in the material, initiating the destruction process. This method proved to be an effective tool for identifying early signs of composite degradation, which is crucial for assessing its long-term strength and designing safe structures.