Co-authors​ :

 Ceren YILDIRIM (TURKEY), Isa ISA EMAMI TABRIZI (UNITED KINGDOM), Abdulrahman AL-NADHARI (TURKEY), Serra TOPAL (TURKEY), Bertan BEYLERGIL (TURKEY), Mehmet YILDIZ  

This comprehensive study focuses on the progressive failure of high-performance carbon fiber/poly(ether ketone ketone) (CF/PEKK) composites manufactured using automated fiber placement (AFP) technique and consolidated in autoclave in compliance with the requirement of aerospace requirements. This investigation suggests a systematic and complimentary utilization of multi-instrumental structural health monitoring (SHM) approaches that enable studying the behaviour of the damage development and damage classification in high performance thermoplastic composite laminates. Void analysis based on density measurement, thermal analysis, and optical microscopy observations are performed to better understand the secondary consolidation effect on the microstructure of the composite. It is observed that the degree of crystallinity increases from 13.47% to 24.49% following the autoclave consolidation. The microscopy images of the cross-section of in-situ consolidated laminates show that the larger portion of voids are interlaminar voids which are present throughout the initial intimate contact regions; however, autoclave process enables the removal these voids, resulting in reduction in the void content from 5.65 % to 0.46%. Additionally, acoustic emission (AE), digital image correlation (DIC), and infrared thermography (IRT) techniques are performed simultaneously during the tensile test to further identify damage progression. It is proven that the AE, DIC, and IRT techniques provide unmatched advantages in continuous data acquisition and understanding the physics behind the critical damage types occurring in the material, such as edge splits leading to failure. Upon assessing damage accumulation in detail, one can clearly note the change in cumulative AE counts slope, categorizing laminate failure into two distinct stages, each representing a dominant failure mode. Another important finding is that the increase in AE energy correlates with observable macro-level damage in the laminate. These macro-level damages are captured by the thermal camera in the form of various edge splitting large-scale damages. The initiation of these damage events can be predicted through concurrent monitoring of DIC strain maps. The examination of the fractured surfaces through SEM analysis allows for the identification of various types of failures, thereby correlating them with the distinct stages of the tensile response.