Compressive properties of bidirectionally graded lattice structures

Functionally graded lattice structures are gaining increasing attention due to their potential to enable the customization of the structural response and development of multi-functional applications. However, some grading methods may lead to weak layers or discontinuous unit cells. These problems can be overcome by varying the morphology, but the mechanical performance is only slightly improved, limiting the application of lattice structures. This work proposes a bidirectionally graded lattice structure, wherein the gradient design is simultaneously implemented in parallel and perpendicularly to the load direction. Experimental samples fabricated through laser powder bed fusion (L-PBF) and using PA2200 as the matrix material, were subjected to quasi-static compression tests. The results showed that the bidirectionally graded lattice structure attains a significantly higher compressive modulus, yield stress, and plateau stress (59.8%, 43.0%, and 33.9% higher, respectively) compared with a unidirectionally graded lattice structure. Moreover, a proposed stiffness prediction method was appropriate for effectively estimating the modulus of graded body-centered cubic lattice structures, which combined with the understanding of the influence of gradient parameters, allows the realization of a tailored structural performance. In conclusion, the proposed bidirectionally graded strategy and experimental findings provide an effective reference for the design of multi-functional lightweight additive manufactured parts.