Development and performance evaluation of low-density cork/phenolic composites for high-temperature aerospace use

Cork-reinforced resole-type phenolic composites have emerged as promising materials for high-temperature aerospace applications due to their unique combination of low density, high mechanical strength, and superior thermal insulation. In this study, composites with densities ranging from 300 to 700 kg/m³ were fabricated and subjected to comprehensive mechanical, thermal, and ablation performance evaluations. Mechanical testing revealed that increasing density enhanced flexural, impact, and compressive strengths, with values ranging from 1–9 MPa, 0.1–2.1 kJ/m2, and 0.5–7.5 MPa, respectively. The thermal conductivity of the material remained constant at approximately 0.1 W/mK, demonstrating excellent insulation capability. The results of oxyacetylene flame tests, conducted with exposure durations from 5 to 25 s, showed good thermal stability with reasonable degradation up to 20 s. However, with further increase in exposure duration, the material losses increased significantly, and reached upto 60% at 25 s, due to ablation. The formation of a protective char layer was observed, which helped in mitigating heat penetration and preserving the structural integrity. These results establish cork-phenolic composites as viable candidates for aerospace thermal protection systems, offering an optimal balance between mechanical robustness, insulation efficiency, and ablation resistance.