Dynamic and static mechanical performance of 3D printed porous Bouligand structured polymer.

Natural Bouligand structures are desirable templates for lightweight damage-tolerant materials; however, experimental data on the porous polymeric implementation of these Bouligand structures remains limited. This thesis investigates stereolithographically printed porous Bouligand structured polymers (PBSPs) inspired from the dactyl plunger of snapping shrimp, over a wide range of pitch angles (10°-90°) and fibre spacing (0.5-1.25 mm) to independently tune helicoidal angle and porosity. These 3D printed specimens were mechanically characterised under tensile, three-point bend, short beam shear, low-velocity impact (15 J) and stab (8 J) loading supported by finite element analysis with strong experimental numerical agreement (Pearson r = 0.91-0.97). Mechanical response showed non-monotonic behaviour across all loading conditions in relation to pitch angle. Helicoids with 30° and 90° cross-plies demonstrate superior performance compared to the other tested angles, while quasi-isotropic 45° lay-ups underperformed due to less favourable stress distributions. The current study shows that the optimal 30°/0.5 mm architecture provides ∼30-40% higher tensile strength and ∼15-20% higher flexural strength and modulus than the 1.25 mm variants, yields ∼10% higher peak impact force at a fixed pitch, and improves stab resistance by ∼25-35%, all while weighing only ∼52-73% of the solid resin equivalent. Fibre spacing had the strongest influence on overall strength and stiffness, producing a 35-40% strength increase when reduced from 1.25 mm to 0.5 mm, at the expense of higher density. Although PBSP’s exhibit some of the highest specific property values reported for porous polymeric architecture in this density range, they still fall short of matching the performance of natural Boulignad systems and fibre-reinforced composites. Overall, this work establishes porous Bouligand structured polymers as a tunable class of bioinspired cellular solids whose mechanical response can be systematically optimised through coupled control of pitch angle and fibre spacing (porosity), providing a rational guideline for the design of lightweight, impact and stab resistant structures in aerospace, automotive, and protective engineering applications.