Abstract:

Objective Glass fiber/phenolic resin composites are widely valued for their cost-effectiveness, mechanical strength, and excellent flame retardancy. However, conventional laminates suffer from delamination and poor durability. In order to overcome these limitations, a novel high-performance composite is designed by integrating phenolic resin with 3-D woven spacer glass fiber fabrics. The obtained 3-D woven spacer composites (3DWSCs) achieve a combination of light weight, high strength, and superior thermal insulation, offering enhanced safety and reliability for fire-resistant applications.

Method Glass fiber 3-D woven spacer fabrics were prepared by a self-made 3-D loom. The fabric was impregnated with phenolic resin by hand lay-up molding method. By compressing the pile yarns to varying degrees, pile yarns can reach to different heights. The compression ratio between the three-dimensional spacer fabrics was set to 1∶0.8∶0.6, ensuring that the thickness of 3DWSCs is 15 mm (3DWSC-15), 12 mm (3DWSC-12), and 9 mm (3DWSC-9). 3DWSCs with different bending shapes of pile yarns are obtained. The influence of the intersection angle of the pile yarn and the angle between the pile yarn and the surface layer on the flat compression performance of the composites were investigated (the cross angles of the pile yarns are 30°, 60°, and 90°). The flat compression performance, flat compression failure mode, heat insulation performance and flame retardant performance of 3DWSC-15 were systematically analyzed.

Results Flat compression performance was significantly influenced by bending shapes of pile yarns. All stress-strain curves showed elastic, failure, and densification stages. As the cross-angle increased and the surface-layer angle decreased, the compression modulus first increased and then decreased, while densification became more prominent. Flat compressive strength was highest for 3DWSC-15 (0.28 MPa), compared to 0.18 MPa for 3DWSC-12 and 0.21 MPa for 3DWSC-9 due to lateral constraints among pile yarns. Specific flat compressive strength of the three samples exhibited similar trends, with 1.49, 0.59, 0.95 MPa/(g·cm^-3) for 3DWSC-15, 3DWSC-12 and 3DWSC-9, respectively. Compressive modulus changed from 6.28 MPa (3DWSC-15) to 1.41 MPa (3DWSC-12) and 2.68 MPa (3DWSC-9). Energy absorption at 30% strain was 0.81, 0.44, and 0.66 J. Failure modes of the three sample were found to be buckling (3DWSC-15), brittle fracture (3DWSC-12), bending with cracking/fiber pull-out (3DWSC-9). Thermal insulation tests showed 3DWSC-15 was the best with balance temperature 45.8℃ and efficiency 54.2%, because the height reduction shortens the heat conduction path, reduces thermal resistance, and accelerates heat transfer. Its heating rate was slowest (9.4×10^-2℃/s). Flame retardancy tests of 3DWSC-15 revealed self-extinguishing, minimal smoke, 3.47% mass loss, and post-fire compressive strength retention of 89.29%.

Conclusion The mechanical and thermal properties of glass/phenolic 3DWSCs can be effectively tailored by controlling the bending shapes of the pile yarns. The results indicate that while moderate bending of pile yarn (3DWSC-12) leads to a reduction in flat compressive strength and modulus due to decreased buckling resistance, further bending (3DWSC-9) can generate effective lateral constraints and synergistic load-bearing effects between the pile yarns, thereby enhancing the overall stability and crush resistance of the structure. As the cross-angle of the pile yarn increases and the angle between the pile yarn and the surface layer decreases, the failure mode shifts from buckling dominant to crushing dominant. The composites exhibited outstanding thermal insulation and flame retardancy, attributable to the abundant air cavities within the 3-D spacer structure and the inherent char-forming ability of phenolic resin. The self-extinguishing behavior, low mass loss, and high residual compressive strength after fire exposure highlight the material's potential for applications requiring both structural integrity and fire safety. These findings suggest that 3DWSCs are promising for use in aerospace, transportation, and building interiors where light-weight, high strength, thermal insulation, and fire resistance are critical. Future work should focus on optimizing the pile yarn architecture and resin distribution to further enhance mechanical performance without compromising thermal properties. Additionally, long-term stability under cyclic thermal and mechanical loads warrants further investigation to support real-world applications.

Key words: composites, 3-D woven spacer fabric, glass fiber, flat compression performance, heat insulation performance, fire resistance