A rotating stack of stiff and compliant layers
The effects of rotating stiff PLA and compliant TPU layers on load-bearing capacity and deformation were investigated through mechanical testing and finite element analysis. The study examines how this architecture influences strength, energy absorption, and damage development under tensile and bending loads.
Why a Bouligand architecture
Inspired by the rotating layers of biological protective structures, the Bouligand architecture introduces small changes in direction between successive layers. This gradual rotation distributes load-bearing paths and helps spread local damage through the stack. The smallest pitch tested gave the highest bending strain energy density and tensile toughness among the Bouligand configurations, alongside sustained deformation.
The focus of this work is the combination of helicoidal orientation with alternating, discrete PLA and TPU layers. Stiff PLA provides mechanical resistance, while compliant TPU accommodates deformation between neighboring layers. Evaluating this combination under both tension and bending shows how material contrast and layer orientation work together to balance strength and toughness.
Computational Investigation
An Abaqus finite element model was developed with 19 separate layers representing alternating stiff PLA and compliant TPU. Material assignments and PLA orientation-dependent behavior captured the contrast between neighboring layers. The model closely reproduced bending stiffness and peak strength; following calibration, tensile predictions also agreed with the measured stiffness and peak strength. The analysis describes the mechanical response up to peak loading, while the fracture images illustrate the experimentally observed damage.
Fracture Behavior under Bending and Tension
Under bending, progressive cracking and layer separation developed around the damaged regions, while TPU connections helped maintain deformation after localized PLA fracture. Under tension, PLA fractures occurred at different positions through the laminate, with compliant TPU layers bridging the resulting openings. These observations illustrate how alternating stiff and compliant layers accommodate damage under different loading conditions.