PSI - Issue 50

14 R.S. Akhmetkhanov et al. / Procedia Structural Integrity 50 (2023) 11–16 R.S.Akhmetkhanov / Structural Integrity Procedia 00 (2019) 000 – 000 processes occur simultaneously, the refinement of filler grains and the aggregation of small grains into larger grains in size (mean radius). As a rule, three basic parameters define phase structure of composites with disperse fillers: filler content in PCM; size and form of filler particles; interphase interaction. The distance between the particles depends on their number per unit volume. The latter is greater the greater the volume fraction of the filler in the polymer and the smaller the size of the particles. With a decrease in the size of the particles, their total specific surface increases sharply, the number of particles at the same volumetric content sharply increases, and consequently, the distance between the particles of the filler in PCM decreases and their ability to form agglomerates increases.

Fig. 3. Multifractal spectra of filler grain distribution at the processing time of the composite material mixture: a - t=1 minute; b - t=90 minutes; c - t=120 minutes

To assess the homogeneity, we apply the characteristic - the location of the center of the static moment of inertia of the section. In this case, we consider that the material image (material structure) reflects the entire volume of the material. After blending of a matrix with the filler t=90 minutes, distribution of grains of the filler is defined by deviation of the cents of the moment of inertia (Favorin M.V., 1977) of section from the material image on the following parameters - on Δ x =0.885 mm, on Δ y =0.46 mm; and at t=120 minutes of blending: on Δ x =0.865 mm, on Δ y =0.84 mm. The variant at mixing time t=120 minutes is somewhat worse in distribution of the filler's center of masses - the center has moved by 0,38 mm and there appeared non-uniformity of filler's grains distribution on material image - fractal dimension decreased from D =1.8229 to D =1.7678 (fig.3b, fig.3c, table 2). The fractal dimensional of the image can vary within 1< D <2. The higher the value of fractal dimensional and closer to the value of 2, the more uniform the distribution of the filler over the matrix of the composite material. In other words, the closer is the fractal dimensional of the image for the given mixture (PCM) to the value of 2, the more reasons to consider this material as homogeneous. Figure 4 shows the images of the grain boundaries of the filler in the composite material.