V-Shaped Truss Architectures for Strengthening Double-Layer Woven Lattice Sandwich Composites

Fiber-reinforced polymer (FRP) composites are vital in modern lightweight structural engineering because of their favorable high specific strength, high specific stiffness, and broad design flexibility. They are used in transportation, aerospace, and various civilian sectors, where reductions in structural weight directly translate into improved energy efficiency and performance. Sandwich composites are especially interesting in engineering because the separation of stiff face sheets by a lightweight core yields substantial increases in bending rigidity without significant mass penalties and among the numerous core configurations explored, woven lattice sandwich (WLS) composites based on three-dimensional woven spacer fabrics have received great interest because their integrated architecture, in which the skins and truss-like core members are woven as a single textile preform, imparts advantageous resistance to delamination, improved impact tolerance, and the possibility of tailoring cell geometry to meet multifunctional design requirements. Despite these advantages, existing WLS composites exhibit mechanical limitations linked directly to the geometry and stability of their truss-like cores. Most prior studies have focused on 1-shaped cores, in which the piles are isolated and inclined, forming a relatively slender load-bearing structure. Although this design offers ease of manufacturing, it suffers from insufficient shear stability, especially when the core height increases. Previous efforts to address this issue have relied on multi-layered configurations or core-filling strategies, but these approaches introduce their own challenges. Multi-layer weaving increases fabrication complexity and may compromise the structural shape of lower layers during curing, while foam-filling or similar techniques alter material composition and add processing steps. Consequently, a need remains for core designs that can enhance shear resistance while preserving manufacturability and the intrinsic advantages of woven architectures.

To this account, new research paper published in Polymer Composites and led by Dr. Ben Wang from the Yangzhou University alongside Dr. Qu Yan, and Dr. Hualin Fan from the Nanjing University of Aeronautics and Astronautics, researchers developed two matched double-layer woven lattice sandwich systems: one containing traditional isolated 1-shaped core piles and another featuring a new V-shaped, node-connected truss arrangement. The V-shaped geometry provides a more stable shear-resistant architecture that shifts failure away from vulnerable mid-sections. This structural change improves compressive strength, bending stability, and energy absorption without altering materials or processing. Their analytical model further quantifies how the V-shape increases effective core shear stiffness.

The authors fabricated all panels using E-glass 3D woven spacer fabrics followed by a two-step consolidation route—vacuum infusion to create individual WLS layers and vacuum-bag molding to co-cure them into double-layer assemblies. Each DWLS panel contained either isolated 1-shaped core piles or node-connected V-shaped piles, and the overall thicknesses, face-sheet dimensions, and densities were kept comparable to ensure that any differences in performance arose from core geometry alone. Microscopy verified that 1-shaped piles were thinner at mid-height, whereas V-shaped ones formed a more uniform and mutually supporting network. The authors performed flatwise compression tests on 60 × 60 mm specimens, revealing an immediately noticeable distinction in how the two architectures carried load. Although both exhibited the characteristic two-peak response associated with double-layer cores, the V-shaped panels showed consistently higher peaks and steeper initial slopes. Their average compressive strength reached 2.07 MPa compared to 1.71 MPa for the 1-shaped version, and the modulus increased from roughly 93 MPa to over 130 MPa. Microscopy after failure provided the physical explanation: the 1-shaped piles fractured at their mid-sections, where bending stiffness is lowest, while the V-shaped piles fractured near the ends, where the surrounding fabric and neighboring piles offer additional bracing. This shift in fracture location correlates directly with enhanced stability and delayed structural collapse. Afterward, the team performed three-point bending experiments which offered an even clearer comparison. Tests were conducted at spans of 90, 120, and 150 mm to manipulate the contribution of shear deformation. They found across all core orientations, V-shaped specimens displayed more stable load–displacement curves: instead of the two distinct failure peaks that characterized the 1-shaped ATT and APT panels, the VTT and VPT curves rose steadily to a single, dominant peak, signaling synchronized failure of the upper and lower layers. For short spans—where shear dominates—the advantages of V-shaping were strongest. Their initial failure loads exceeded the 1-shaped counterparts by significant margins, and energy absorption was consistently higher. The effect was most pronounced for the weft–weft direction, which naturally offers greater structural efficiency in these woven systems. Additionally, the authors studied damage observations to evaluate the geometric effect and found large inflection-point deformations formed near the supports for both systems, but only the 1-shaped cores showed early debonding and asymmetric pile collapse. The V-shaped configurations, owing to mutual support at the nodes, resisted local buckling more effectively and maintained panel integrity over a longer deformation window. Finally, they performed reverse analysis of the elastic slopes across span combinations, to compute core shear moduli and noticed that V-shaped cores consistently showed higher values—43.23 MPa versus 26.23 MPa in the weft–weft case which confirmed that geometry, not material, governs the improvement.

In conclusion, the new study by Dr. Ben Wang and colleagues demonstrates that small geometric changes in the architecture of woven truss cores can produce disproportionately large mechanical gains. The authors have effectively altered the way shear and compression propagate through the lattice by replacing isolated 1-shaped piles with node-connected V-shaped ones and instead of allowing local bending to initiate at the weakest mid-height region, the V-shaped configuration anchors the deformation at structurally supported ends, delaying crack formation and promoting more uniform load transfer. The change in failure mode observed with the V-shaped cores turns out to be more than a geometric curiosity; it fundamentally shifts how the entire lattice behaves under load. Instead of allowing individual piles to give way in isolation, the interconnected truss network encourages the kind of collective response that efficient structural systems rely on—loads are shared, local instabilities are suppressed, and the members tend to deform in a more synchronized fashion. This stands in clear contrast to what happens in the 1-shaped cores. There, the double peaks seen in the bending curves almost act as signatures of a structural system falling out of step: the upper core layer reaches its limit first, the lower layer continues to resist, and the panel stumbles through two separate failure moments rather than one coherent event.

By comparison, the V-shaped configuration holds the system together long enough for a single, more substantial peak to form, followed by a plateau that carries load surprisingly well. In situations where impact energy needs to be absorbed rather than immediately transmitted—crash panels, radomes, and other protective structures—this steadier high-load region could be a practical advantage. It buys time, and in structural engineering, time under load often translates into safety. One lesson that becomes difficult to ignore is how profoundly geometry shapes performance. Because the researchers kept the materials constant—same yarns, same resin, same processing—the improved response cannot be attributed to anything but the configuration of the core. This is a reminder that, in composite design, architectural refinement can outpace material substitution in terms of efficiency. It also helps that the fabrication route remains entirely conventional. Standard vacuum infusion and vacuum-bag molding were sufficient to produce both core types with no signs of delamination, which means the V-shaped concept is not constrained by manufacturing limitations. We think the implications can reach even further and if a simple V-shape can bring this level of improvement, there is little doubt that other node-connected patterns (Y-configurations, branched trusses, or hybrid geometries) may push performance even further. Lastly, the analytical strategy used in the study especially the reverse extraction of shear stiffness from elastic slopes can provide a practical way to evaluate these future designs without relying on isolated core testing.