PSI - Issue 17

M.P. Tretyakov et al. / Procedia Structural Integrity 17 (2019) 865–871 Author name / Structural Integrity Procedia 00 (2019) 000 – 0 0

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a b Fig. 2. (a) Diagrams of loading samples on the interlayer shear with different stiffness: without cup springs (solid lines); with four springs (dashed lines); with eight springs (dash-dotted lines); (b) Stiffness characteristics of the loading chain: without cup springs (solid line); with four springs (dashed lines); with eight springs (dash-dotted lines). According to the test results, it can be noted that with a decrease in the rigidity of the loading system with respect to the deformable sample, the slope of the P vs w loading curve changes significantly. At the same time, from the point of view of the influence of the rigidity of the loading system on the implementation of the postcritical deformation stage, it can be noted that with a decrease in stiffness, the length of the equilibrium regions in the diagrams decreases, and the destruction occurs more intensively. Regardless of the stiffness, the specimens collapsed due to bending, i.e. during the primary stretching of the lower layers with subsequent loss of stability and destruction. When studying the effect of the rigidity of the loading system on the postcritical deformation and destruction of composite materials, the conditions affecting the degree of realization and staging of the formation and flow of the falling sections of the deformation of composite materials were determined. The test results for fiberglass specimens at loading rates of 0.2 mm / min, 2 mm / min, and 20 mm / min are presented in Figure 3 (a). As a result of processing and analyzing the obtained data, it is noted that with an increase in the loading rate by two orders of magnitude, there is a slight increase in the rigidity of the samples (no more than 7%) and a significant increase in the strength characteristics (up to 40%). A falling branch begins with a dynamic breakdown, accompanied by a sharp decrease in the load by 15% to 30% followed by a stepwise decrease in the load on the softening section, which is characterized by the presence of equilibrium deformation sections. At the same time, from the point of view of the effect of speed on the postcritical stage of deformation, it can be noted that with an increase in speed, the length of the equilibrium areas at the softening stage decreases, the destruction occurs more intensively, and the value of the initial dynamic breakdown also increases. The results of testing samples of fiberglass at different temperatures are presented in Figure 3 (b). When analyzing the experimental diagrams, it is noted that with increasing temperature, the strength characteristics decrease from 20% to 80%. In this case, the drop-down section of the diagrams begins with a dynamic breakdown of 30% to 50%, followed by stepped sections of load reduction and the presence of equilibrium deformation areas. The destruction of the samples occurred from bending, with the primary stretching of the lower layers, followed by loss of stability and destruction. At a temperature of 150 º С , it is possible to obtain complete equilibrium drop-off areas of the diagrams, and the samples are destroyed by the interlayer shear. Analysis of fracture patterns showed that as the temperature rises to 150 º С , as in the previous test, a partial destruction of the matrix occurs, accompanied by the appearance of interlayer cracks, which leads to a change in the mechanisms of destruction, and, consequently, to the realization of equilibrium descending areas at the postcritical stage deformation. 3.2 The test results of GFRP on the interlayer shear in a wide range of loading rates and temperatures