Research on the Interlaminar Shear Performance of 3D Needle-Punched Preforms

The interlaminar strength of 3D needle-punched composites is determined by the microstructure and mechanical properties of the preform. However, effective testing and characterization methods for evaluating the interlaminar performance of 3D needle-punched preforms are still lacking. This paper proposes a novel interlaminar offset tear test method to characterize the interlaminar tear strength of 3D needle-punched preforms and investigates the influence of needling density, layup process, and needling method on the interlaminar properties of the preforms. Micro-CT technology was employed to analyze the microstructural characteristics of preforms with different parameters, revealing the relationship between process parameters, internal microstructure, and interlaminar properties of 3D needle-punched preforms. The results indicate that increasing the needling density, raising the proportion of fiber felt layers in the layup, and adopting staggered needling patterns all contribute to enhancing the amount of z-directional needled fibers in the preform, thereby improving interlaminar performance. When the needling density was increased from 15 needles/cm² to 35 needles/cm², the interlaminar tear strength increased by 222.26%; when the proportion of fiber felt layers was raised from 1/6 to 1/2, the interlaminar tear strength improved by 159.3%; and staggered needling resulted in a 65.11% higher interlaminar tear strength compared to in-situ needling.