This study comparatively investigates the in-plane compressive properties of 3D braided honeycomb composite core (3D-BHC) and 3D braided honeycomb-foam sandwich composite (3D-BHFSC). The effects of joint wall length on mechanical properties, energy absorption, and failure mechanisms were analyzed using quasi-static compression tests and 3D digital image correlation (3D-DIC). The results show that the maximum load and energy absorption of 3D-BHFSC increase with the number of free wall columns, while the failure displacement is primarily governed by free wall rows number. The addition of foam filling and face sheets to form sandwich structure (3D-BHFSC) significantly enhances structural performance: the maximum load approximately doubles compared with that of 3D-BHC, energy absorption improves by 1.7–1.8 times, and the in-plane compressive modulus rises by about 500 MPa. However, 3D-BHFSC exhibit reduced failure strains and displacements due to progressive damage accumulation. Strain-field analysis reveals shear-dominated failure modes in 3D-BHC, evolving into V-shaped or cross-shaped fractures in 3D-BHFSC. These findings unravel the interplay between honeycomb topology and sandwich performance and provide quantitative guidance for designing lightweight sandwich structures in aerospace, automotive, and defense applications.

This paper presents the design and development of three-dimensional braided honeycomb structures. The basic principles and braiding process are described. The relationship between braiding parameters and honeycomb geometric parameters is established and several three-dimensional (3D) braided honeycomb fabrics are introduced. Based on the principle of the 3D braiding ‘four-step’ method, the interlaced state of yarns can be changed by controlling the movement of yarn carriers, so the separation and combination of the braid can be controlled, then 3D braided honeycomb fabric can be formed. As the number of braiding cycles of wall length increases, the relative density will gradually decrease, but the number of braiding cycles of free wall length has a greater effect on the relative density. When the number of columns of yarns participating in wall thickness increases, the relative density will gradually increase. The relative density also showed a positive correlation with the braiding angle. With the increase of the opening angle, the relative density gradually decreases, although there is a minimum point after which a little increase is observed. This paper provides significant guidance for designing various 3D braided honeycomb structures and evaluating their relative density, and can be a reference for the design and development of new honeycombs structures.