Strut-based lattice metamaterials exhibiting near-zero Poisson’s ratio (NZPR) behaviour have been identified as potential candidates for orthopaedic implants because of their limited lateral expansion and dimensional stability. This study presents a systematic, comparative evaluation of three previously reported honeycomb-based NZPR lattices, namely RSRE, P-ZPR, and SRE-1, and two novel honeycomb-based NZPR lattices, namely SRE-2 and SRE-3, relative to conventional body-centred cubic and face-centred cubic reference lattices, which exhibit positive Poisson’s ratios (PPR). The evaluation is performed within the context of bone tissue engineering, using load-bearing lumbar interbody fusion (LIF) as an exemplary application. Compressive behaviour, deformation mechanisms, Poisson’s ratio evolution, von Mises stress distribution, energy absorption, and morphological parameters were characterised through experimental investigations and finite element simulations. All NZPR lattices exhibited bending-dominated deformation with near-zero lateral strain, whereas SRE-type lattices displayed comparatively more homogeneous stress distributions than the other NZPR and PPR configurations. The P-ZPR lattice demonstrated superior compressive strength and energy absorption capacity, while RSRE and SRE-3 exhibited highly compliant mechanical responses with stable progressive collapse, though insufficient load-bearing capacity for use in primary structural components. Among the designs investigated, SRE-2 was the most promising for load-bearing LIF implants, offering an effective compromise between material consumption and mechanical performance, combined with controlled collapse behaviour and favourable morphological characteristics. The findings highlight the substantial potential of NZPR lattices to advance the development of biomaterials for bone tissue engineering applications. Further, a qualitative basis for the initial rational selection of NZPR lattice configuration for bone tissue engineering applications was established.
This study investigates the flexural durability of FFF-printed gyroid-core sandwich structures made from neat PLA and PLA-flax under accelerated humid/dry aging. Both materials were printed using the same sandwich configuration, with a gyroid core of 10 mm cell size and 20% infill density. Specimens were exposed to 0, 200, 400, 600, 800, and 1000 cycles, alternating between dry conditions at 40 +/- 2 degrees C and 10 +/- 5% RH and humid conditions at 23 +/- 2 degrees C and 85 +/- 5% RH. Three-point bending tests showed that both materials degraded with aging, but PLA-flax was more affected. After 1000 cycles, neat PLA showed reductions of 11.6% in apparent flexural modulus and 10.6% in apparent flexural strength, while PLA-flax showed greater losses of 24.1 and 25.0%, respectively. The degradation of PLA-flax remained limited during the initial aging stages, then became more pronounced after 600 cycles. Optical observations showed that neat PLA retained similar damage features after aging, mainly facesheet cracking, interlayer debonding, and local layer deformation. In contrast, PLA-flax showed a change in failure morphology after prolonged exposure, with more evident interlayer debonding, matrix cracking, and facesheet-core delamination. A first-order analytical model based on classical sandwich beam theory was used to predict the midspan displacement in the linear bending range. By introducing a stiffness retention factor and an effective correction factor for non-ideal skin-core interaction, the model reproduced the global deformation trend, with average absolute deviations of 1.55% for neat PLA and 2.62% for PLA-flax.
Triply Periodic Minimal Surface (TPMS) structures, e.g., Diamond (D), Gyroid (G), and I-WP, possess excellent specific strength and geometric designability, thereby achieving high load-bearing capacity and lightweight design. However, when serving as the core in sandwich structures, the uniform relative density (uni-den) design and conventionally functionally graded (con-fun-gra) design do not fully utilize the mechanical properties of materials. To overcome this limitation, a variable-density topology optimization (var-top-opt) design is adopted in the D, G, and I-WP cores to enhance the bending performance of sandwich structures, and the enhancement effects are explored. The fitting functions between the isosurface threshold and relative density are constructed for the D, G, and I-WP cells. The var-top-opt design, taking the relative density of the topology element as the design variable and the structural compliance minimization as the design objective, is performed to obtain the optimal relative density field (ORDF). The ORDF is divided into multiple segments, and the relative densities in every segment are fitted to construct the relative density function matrix of topology elements. The isosurface threshold function matrices of the optimized D, G, and I-WP cores are constructed through the relative density mapping relationship between the topology elements and TPMS cells. The D, G, and I-WP sandwich structures from the uni-den, con-fun-gra, and var-top-opt designs are fabricated using the SLA technology, followed by the three-point bending test and numerical simulation. The results show that the var-top-opt design significantly enhances the bending stiffness and energy absorption of the TPMS sandwich structures at different core volume fractions, and the improvement is larger than that of the con-fun-gra design.
This study investigates the transient dynamic response of an additively manufactured polylactic acid (PLA) honeycomb sandwich panel with glass-fiber-reinforced plastic (GFRP) face sheets through experimental characterization and finite element analysis. The PLA honeycomb core was fabricated using fused deposition modelling, while the GFRP face sheets were prepared using the hand lay-up technique. Tensile, flexural, and density tests were conducted to experimentally characterize the material properties used in the numerical model. A finite element model was developed in ANSYS using the experimentally obtained effective properties and was initially assessed against benchmark results reported in the literature. The experimental and numerical displacement–time histories under cantilever harmonic excitation at 500 Hz and 0.2 N showed similar trends for the investigated laboratory condition. A separate numerical calculation was performed to examine the early-time global displacement response under a hypothetical prescribed modified Friedlander pressure pulse using a linear-elastic material representation. The blast analysis showed maximum deformation in the central region of the panel and relatively lower displacement near the supported boundaries. Within the 30 ms simulation window, the panel exhibited a bounded transient displacement response. The blast calculations represent early-time global displacement predictions under the assumption of a linear-elastic material. Failure initiation, progressive stiffness degradation, core crushing, and interfacial separation were not modelled, and energy absorption was not quantified. Accordingly, the calculated histories do not establish retained structural integrity or validated blast-protection performance. The study provides experimental characterization and a laboratory assessment of the global dynamic response of the investigated configuration, along with preliminary elastic calculations under the prescribed pressure pulse.
To address the anti-blast demands of military equipment such as armoured vehicles and naval vessels, lightweight sandwich structures with silica aerogel core and polycarbonate (PC) panels are experimentally investigated via shock tube tests under four blast pressures (P1 = 105 kPa, P2 = 180 kPa, P3 = 227 kPa, P4 = 275 kPa). Codes “1” and “0” stand for aerogel sandwich and pure PC sheet; “10” denotes aerogel-fronted double-layer arrangement and “01” the PC-first counterpart. Single-layer, double-layer (10) and triple-layer (110) structures achieve peak overpressure attenuation of 45.68%, 54.32% and 64.20% under low-medium loads. Structural protection degrades with rising load beyond the critical threshold P3, and aerogel-fronted layouts outperform PC-first schemes throughout tests. This study supplies experimental basis for optimizing lightweight anti-shock structures.
