Issue 53

E. M. Strungar et alii, Frattura ed Integrità Strutturale, 53 (2020) 406-416; DOI: 10.3221/IGF-ESIS.53.31 411 is performed for composite samples. Strain diagram are built at particular level of strain ( σ ) 150, 250, 350 MPa for a sample with the hole diameter d=3, 6, 9 mm (Fig. 7). Figure 7: Longitudinal strain diagrams d=3,6,9 mm on the sample surface with diameter size at various strain level; a thermogram of unloaded sample before the test d=6 mm. It has been found that in the process of inelastic deformation the maximal values of longitudinal strain at extension of the sample displace from the boundary of the hole. It is possible to assume that such peculiarity of mechanical conduct is related to the presence of defects in the vicinity of the hole. To confirm this fact, thermal scanning is performed after short-term heating. The corresponding results are provided in Fig. 7. A local heating is found in the area of the opening which indirectly confirms the supposition of a defect area. Structural and deformational properties determining the composite’s behavior at shear, belong to important characteristics of any composite. The study of these properties of materials is associated with specific methodic difficulties [25,26]. The paper considers Iosipescu method ASTM D5379. There are various international standards for these mechanical tests. The paper shows that these standards need adjustment for a number of structures. The authors suggested recommendations for obtaining and mathematical processing of experimental data using contactless optical video-system. To determine shear deformations, ASTM D5379 recommends to use resistance strain gauges with 1.5mm basis situated at the angle of ±45 о to the loading area in the working area of the sample (between V-shaped cutout), but the video-system software makes it possible to simulate the resistance strain gauges using supplementary virtual instruments. Based on the tests, deformation fields were built for each of the 10 samples in their working areas in consideration of the structural properties. Fig. 8 shows the analyzed options of averaging the deformations in the working area of spatially reinforced samples using such video-system elements as “virtual extensometer T” and “rectangular area R” [28]. In the course of deformation fields study it was found that shear deformations distribution is of non-homogeneous nature, depending on non-homogeneity areas location, the data values may vary by shear module by more than 1.6 times, by nominal shear strength – by 1.4 times, by strength limit – by 1.1 times [28]. It should be pointed out that experimental studies were conducted at 8 spatially reinforced structures, but only two structures have such peculiarity For determination of shear deformations for spatially reinforced structures according to ASTM D5379, a video-system has advantages over resistance strain gauges and is more preferable to use because it provides the full pattern of shear deformations distributions on sample surface [28]. T HE ANALYSIS OF DEFORMATION AND DAMAGE ACCUMULATION PROCESSES IN COMPOSITE OBJECTS WITH STRESS CONCENTRATORS OF PROCESS AND MAINTENANCE ORIGIN he previously provided results illustrate deformation fields in consideration of sizes of the sample concentrators and structure elements. Defects, fissures, healing areas may also be the possible concentrators. The next part of the work is devoted to it. The process of manufacture of the sample with imbedded process defects of “delamination” type is based on the use of fluoroplastic film laid between the layers. T