Issue 53

E. M. Strungar et alii, Frattura ed Integrità Strutturale, 53 (2020) 406-416; DOI: 10.3221/IGF-ESIS.53.31 409 T HE ANALYSIS OF THE MECHANISMS OF INELASTIC DEFORMATION AND THE COMPOSITES DESTRUCTION IN THE CONCENTRATORS ZONES IN CONSIDERATION OF STRUCTURAL PARAMETERS n the process of creation of structures, it is often necessary to make the holes of various size in their elements due to the process considerations. The following part of the paper presents the results of experimental studies of mechanical behavior of a fiber-laminated composite material in the vicinity of stress concentrators. The authors tested the fiberglass samples for uniaxial tension with different values of through hole diameter. Fig. 3 presents the comparative analysis of the descending sections of the diagram for diameters d1-d5. With the increase of diameter, the descending sections extend, the degree of implementation of the supercritical stage rises. The angle (slope modulus) of the curves changes as well. Figure 3: Load diagram for samples with different hole diameters during uniaxial tensile tests; the comparative analysis of the descending sections of the diagram. The analysis of the composite material damage due to macro-fissure development was carried out using a stereo microscope Carl Zeiss SteREO Discoverj у .V12 in the upper layers. In large deformation areas, the fiber breakage is observed around the holes on both sides, the evidence of this fact is shown in the image of the sample surface (Fig. 4). Due to the results obtained, the geometrically similar samples are of special interest; the program of assessment of the effect of structural parameters of the composite samples with the tension concentrator included mechanical tests for uniaxial tension of three groups of strip samples with different hole diameters 3, 6 и 9 mm. Figure 4: The images of fiberglass structure after the destruction of the sample on the upper layer. When selecting the width and length of the working part of the sample, the similarity of geometric dimensions was observed: the hole diameter d (mm), the width of the working part h=6d (mm), the length of the working part l =14d (mm), the speed of movement l  0.01 (mm/min) of the movable grabber provided similar strain rate in the working areas of all samples (1.7  10 -4 s -1 ). The average stress value was determined by the formula σ = P/(5dh). Fig. 5 shows the characteristic deformation diagrams. The destruction occurred due to the formation of the fiber breakage band, besides, the formation of extensive delamination regions was recorded. In the course of study the authors found a large-scale effect, the bearing capacity decreased with the increase of the hole diameter. The detected scale effect can be attributed to the fact that, depending on the hole size, various volumes of a structurally non-homogeneous medium are involved in the work. I