Experimental study of ultimate deformation and fracture of FRP with stress concentrators

This work experimentally studies the influence of the scale effect on the processes of initiation and development of defects in the region of stress concentrators in a structurally inhomogeneous material under quasi-static loading. Composite specimens were made of glass-textolite STEF. A through hole of different diameters located in the geometric center of the specimen was considered as a concentrator. New data on the mechanical behavior of the composite were obtained using digital image correlation (DIC), acoustic emission (AE) method and optical microscopy. In this work, experimental investigations of the mechanical behavior of composites in the hub zones have been carried out considering the structural parameters. As the hole diameter increases, the load carrying capacity decreases. The DIC method allowed us to study the evolution of inhomogeneous strain fields on the surface of the samples. A characteristic growth of cumulative energy was observed in all types of specimens regardless of the size and presence of stress concentrators, namely a smooth insignificant growth of values with a sharp spike of high energy at the end of the test. The values of spectral maximum frequencies were analyzed, additional frequency intervals were marked, and the contribution of each to the total number of signals was shown, the regularities between the frequency intervals and the presence of the concentrator on the samples were established. On the basis of the microstructural studies, the main types of defects have been identified, the data obtained confirm the results recorded by the acoustic emission. Thus, the experimental data demonstrating the presence of a scale effect of the strength of glass-reinforced plastics with concentrators depending on the structural parameters have been obtained in this work.