Deformation processes of polymer composites with stress concentrators under different reinforcement schemes

This paper is dedicated to an experimental investigation of an effect of a stress concentrator orientation on a mechanical behavior of polymer composites with various reinforcement schemes. Composite specimens have been made of layered carbon fiber reinforced polymer (CFRP) with lay-up patterns of ±45 16 and 0/90 16 . The stress concentrators have been cut in a form of a rectangle (with rounded corners) orientated at angles of 0°, 45°, and 90° to a loading axis. The novel data about the composite’s mechanical behavior has been obtained by the digital image correlation (DIC) method, the acoustic emission (AE) method and the optical microscopy. Quasistatic tests have been carried out taking into account recommendations of the ASTM D5766, ASTM D3039, ASTM D3518. The effect of the stress concentrator orientation on the composite’s strength has been evaluated. It has been found that the stress concentrator does not affect the strength of the composite with the ±45 16 lay-up pattern. This peculiarity has been explained by the absence of the layers preventing the fibers system turning in the direction of the load application. The DIC method has allowed to study the evolution of inhomogeneous strain fields on the specimens’ surfaces. Computational simulations have been carried out within the elasticity stage. The results have shown that the strain fields obtained by both the DIC method and the numerical simulation were similar for the composites with the 0/90 16 reinforcement pattern. However, significant differences have been found for the ±45 16 reinforcement pattern, which have been explained by the development of inelastic zones near the stress concentrator even if the elastic stage is realized at the macrolevel. The using of the AE method and the optical microscopy has allowed to reveal typical mechanisms of the structural damage and to study their occurrence during the tests. It has been concluded that the orientation of the stress concentrator significantly influences the deformation processes of the CFRP with various reinforcement patterns.