Failure analysis and strength prediction for needled composites prepared by different needling processes with out-of-plane tensile load

The out-of-plane tensile properties of needled carbon fiber reinforced composites are greatly associated with the complex needle-punching processes. The microstructures of carbon fiber needled preforms and their composites are examined utilizing microscopic observation technologies. The out-of-plane tensile experiments of needled composites with different needling processes are developed. The effects of needling processes on the out-of-plane tensile properties are analyzed. The increase of needling depth will lead to the increase of the tensile properties, but the increase of needling density has the opposite rule. Furthermore, the failure mechanism is identified combined with fracture morphology analysis. According to the microstructure, the propagation of internal cracks and the fracture of the needled fiber bundle are the main causes of material failure, which affects the out-of-plane tensile strength of needled composites. The theoretical model and numerical model are established respectively for analyzing out-of-plane tensile strengths. Two models can be used to predict the out-of-plane tensile strength of needled composites with different needling processes, and the maximum error of the prediction result is only 11.98%. This work provides a theoretical and experimental basis for the study of the out-of-plane properties of needled composites and the design of needling processes based on material properties.