PSI - Issue 17

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

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fiber plastic (CFRP) based on AKSA F49 12K carbon fiber sateen 5/1 and epoxy binder T26 manufactured by direct extrusion. Samples geometry was selected taking into account the recommendations of ASTM D 2344. The distance between the supports for fiberglass was 30 mm, for carbon plastics 20 mm. Experimental studies on the interlayer shear in a wide range of temperatures and load rates were carried out on an Instron 5882 electromechanical system (100 kN) which includes a non-contact video extensometer and a temperature chamber with an operating temperature range from -100 º С to +350 º С (fig.1, a). Based on the analysis of the methodological features of the standard tests of polymer composite materials, methods have been developed for conducting studies of the laws of postcritical deformation and fracture. The developed techniques for studying the postcritical stage of deformation provide for the fulfillment of the conditions for the stability of the processes of deformation and structural destruction of polymer composites by ensuring sufficient rigidity of the loading system, including using specialized equipment for various types of tests. The change in stiffness when testing for interlayer shear (short beam method) is implemented by adding a set of disc springs to the loading circuit. The tests were carried out without cup springs, with a combination of 4 disc springs and with a combination of 8 disc springs connected in series to the loading chain (between the bottom plate and equipment for bending tests) (fig.1, b).

a b Fig. 1. Test for interlayer shear in the temperature chamber (a) with adjustable stiffness of the loading chain (b): 1 - fiberglass sample; 2 - equipment for bending tests; 3 – set of disc spring. Tests of fiberglass specimens for interlayer shear were carried out at loading rates (deflection) of 0.2 mm / min, 2 mm / min, 20 mm / min and temperatures of 22 º С , 100 º С , 135 º С , 150 º С . CFRP samples were tested at temperatures of 22 º С , 120 º С , 160 º С , 200 º С and loading speeds of 0.1 mm / min, 1 mm / min, 10 mm / min. According to the test results, diagrams were construc ted and analyzed in the coordinates “load (P) - deflection (  )”, characterized by developed areas of postcritical behavior.

3. Result and discussion

3.1 Test results on interlayer shear with various stiffness The test results are presented in the form of load diagrams in the coordinates “load (P) - deflection (  )” in Figure 2 (a). Figure 2 (b) shows the curves characterizing the rigidity of the loading chain with various combinations of disc springs.