Effect of automated fibre placement (AFP) process induced defects: dynamic compression properties at intermediate strain rates

Abstract

Automated fibre placement (AFP) has emerged as a prominent manufacturing technique in the aerospace industry for producing high-performance composite structures. However, defects such as gaps and overlaps inevitably occur during the AFP process, and can significantly influence the end-product quality of composite structures. Compression strength can play an important role in composite structures, especially in the residual load-bearing capability in presence of damages, and its characterisation is necessary for the correct sizing of structures. To evaluate their impact on mechanical properties, dynamic compression testing of carbon fibre-reinforced low-melt polyaryletherketone (CF/LM-PAEK) is conducted using a high-speed test machine. An end-loading compression fixture with honeycomb is used to perform dynamic compression tests at strain rates up to 200 s-1. Ultrasonic C-scan images of as manufactured defects in test specimens are examined to correlate the contents of gap defects and compressive strength. The results show a clear strain-rate effect on compressive strength within the range of tested strain rates. Also, a transition of failure modes from kink band to wedge splitting is observed at high strain rates. No clear correlation between the gap contents and compressive strength is identified. Those results indicate that the staggered gaps in tested specimens have a minimal impact on compression properties. The findings from this experimental study highlight the effect of defects induced by AFP manufacturing processes on compressive properties at intermediate strain rates. This research contributes to a deeper understanding of the complex relationship between AFP-induced defects and strain-rate effects, providing valuable insights into designing AFP components.