Mechanical, Thermal Insulation, and Ablation Behaviors of Needle-Punched Fabric Reinforced Nanoporous Phenolic Composites: the Role of Anisotropic Microstructure

Needle-punched fabric reinforced nanoporous phenolic composite (NPC) is a kind of promising ablative thermal protection material for spaceflight. However, in practical applications, typically anisotropic microstructure of NPC may lead to different performances and damage mechanisms under various directional mechanical or thermal loads. Herein, NPC is prepared and cut into specimens along three typical plane directions including XY- plane (0 degrees), Z-plane (90 degrees), and transitional-plane (45 degrees), and their mechanical, thermal insulation, and ablation behaviors are systematically investigated. Benefiting from the woven fabric in XY-plane, NPC in 0 degrees -plane di-rection exhibits highest tensile strength (169.2 +/- 12.6 MPa), and CT image-based simulation further verifies that woven fabrics are primary load-bearing structure. Meanwhile, NPC in 45 degrees -plane direction shows highest compressive strength (443.1 +/- 18.2 MPa) but low compressive stress at low strain, demonstrating a weak bonding between two layers of woven fabrics. Moreover, the heat transfer simulation indicates that horizontally stacked woven fabrics effectively protect the internal material from thermal erosion, thus NPC in 0 degrees -plane di-rection exhibits optimal thermal insulation. The ablation testing and micro-CT observations further demonstrate that the angle between woven fabric and thermal load significantly influences the ablation mechanism. The present work will further promote the structural reliability and optimization of needle-punched composites.