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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d Fig. 5. Typical loading diagrams of CFRP specimens when testing for interlayer shear at a loading rate of 0.1 mm/min (solid line), 1 mm/min (dashed line) and 10 mm/min (dotted line) at temperatures of 22 ° С (a); 120 ° С (b); 160 ° С ( с ) and 200 ° С (d). After analysis of the test results were noted that at temperatures of 22 º С , 120 º С and 160 º С the drop-down section of the diagrams begins with a dynamic load reduction by 40 % with second local peak is observed with a dynamic decrease of load by 10-15 % (when the temperature rises to 160 º С the second peak becomes not pronounced). With further deformation, a gradual reduction in load occurs. When testing at 200 °C (fig. 5, d), the dependence of the mechanical behavior of the material on the loading rate becomes most pronounced. At a speed of 0.1 mm/min, there are no dynamic failures and, upon reaching the stress limit values, an equilibrium postcritical deformation zone is realized. At speeds of 1 mm / min and 10 mm / min in the diagrams to achieve the ultimate strength in interlayer shear, the postcritical deformation stage is realized, consisting of two equilibrium drop-off sections with different inclination, which characterize the intensity of load reduction with increasing deflection. In the course of the work, methodological issues of the experimental study of the postcritical behavior patterns of layered composite materials in tests for three-point bending using the short beam method are considered. Tests were carried out at different stiffness of the loading system, loading rates (deflection) and temperatures. Deformation diagrams were constructed and characteristic dependences of the influence of the considered test parameters on the manifestation and realization of the postcritical deformation stage were established. It is noted that an increase in the strain rate leads to large unstable load failures at the postcritical stage. An increase in the test temperature leads to a more pronounced realization of the stage of deformation softening of the considered composites, which manifests itself as a gradual decrease in load with an increase in the deflection and an increase in the limiting deformation reached by the time of complete destruction. Reducing the rigidity of the loading system, as was shown earlier in the works of the authors for metallic materials, leads to a decrease in the stability of the processes of postcritical 4. Conclusion