Experimental study on the biaxial compressive behaviour of anisotropic Octet lattices caused by fused deposition modelling

The fabrication flexibility of increasingly mature additive manufacturing techniques makes it possible to formulate and characterise novel lattice designs for improved energy absorption capabilities. However, the mechanical properties and energy absorption characteristics of most lattices are examined by uniaxial compression tests along their vertical build directions, which cannot approximate the complex loading conditions experienced in practical applications. Therefore, experimental examination on biaxial properties of lattices is essential to facilitate designing novel lattices with preferred performance for real protective applications. Moreover, the angle-dependent strut material properties induced by additive manufacturing result in anisotropic compressive responses for cubic-symmetric strut-based lattices. Thus, loading directions also need to be considered when examining the multiaxial properties of lattices. In this study, a homemade biaxial testing machine equipped with custom fixtures was employed to prescribe uniaxial compression, constrained uniaxial compression with lateral expansion prevented, and biaxial compression to the Octet lattice. Considering the anisotropy of the Octet fabricated via the fused deposition modelling with polylactic acid filaments, seven test scenarios were investigated in this work. Different stress–strain responses and crushing patterns are observed for various loading scenarios, implying the changed responses under complex loading conditions compared to those obtained by traditional uniaxial tests. The experimental works provide insights into designing and optimising lattices applicable to absorbing energy in engineering.