The use of additive manufacturing to rapidly test and evaluate solutions to engineering problems has been demonstrated. Selective laser sintering (SLS) is a subset of additive manufacturing that is particularly well suited to producing structural thin wall models and end use parts which can improve the ability to prototype and manufacture certain designs at a substantially lower cost and time compared to current methods. However, a more comprehensive understanding of the material properties of these parts is warranted. The presented research investigates the influence of print orientation and sample thickness on the material properties of printed SLS parts. This novel work involves holding a hatch pattern constant across SLS prints using polyamide 12 material to isolate the anisotropic effects of orientation and thickness. An evaluation of ultimate tensile strength, modulus of elasticity, strain at failure, yield strength, and Poisson’s ratio, and scanning electron microscope fractography are conducted. Transverse strain and Poisson’s ratio are a key aspect that provide insight into the feasibility of building numerical orthotropic models. These data are used to calculate the degree of anisotropy due to both thickness and orientation. The results support the future use of SLS printing and modeling of thin-walled structures, such as scaled structural ship modeling. The presented data provide guidance on the impact of print orientation and thickness that will aid in manufacturing structural parts with intentionally tuned material properties.

Discontinuous fibers are commonly added to matrix materials in additive manufacturing to enhance properties, but such benefits may be constrained by print and fiber orientation. The additive processes of forming rasters and layers in powder bed fusion inherently cause anisotropy in printed parts. Many print parameters, such as laser, temperature, and hatch pattern, influence the anisotropy of tensile properties. This study characterizes fiber orientation attributed to recoating non-encapsulated fibers and the resulting anisotropic tensile properties. Tensile and fracture properties of polyamide 12 reinforced with 0%, 2.5%, 5%, and 10% discontinuous carbon fibers by volume were characterized in two primary print/tensile loading orientations: tensile loading parallel to the recoater (“horizontal specimens”) and tensile load along the build axis (“vertical specimens”). Density and fractographic analysis indicate a homogeneous mixture with low porosity and primary fiber orientation along the recoating direction for both print orientations. Neat specimens (zero fiber) loaded in either direction have similar tensile properties. However, fiber-reinforced vertical specimens have significantly reduced consistency and tensile strength as fiber content increased, while the opposite is true for horizontal specimens. These datasets and results provide a mechanism to tune material properties and improve the functionality of selectively laser-sintered fiber-reinforced parts through print orientation selection. These datasets could be used to customize functionally graded parts with multi-material selective laser-sintering manufacturing.

Additive manufacturing has enhanced medical trainers and their functionality, but synthetic tissues that are both anatomically accurate and capable of replicating musculoskeletal load responses remain largely unexplored. The purpose of this study is to demonstrate fabrication of synthetic tissue using active filament-mixing fabrication to enable local composition control with thermoplastic compositions tuned to match the modulus of elasticity of the respective tissues and functionally graded transitions between ligament and bone. Synthetic femoral anterior cruciate ligament (ACL) tibial complexes were fabricated and tested at 30° flexion along the tibial and anatomical load orientations matching the test procedure performed on cadaveric femoral ACL tibial complexes by Woo et al. in 1991. Load parameters were facilitated by section grips integrated into the design of test specimens without requiring a multi-axis jig. Anatomical accuracy was achieved by modeling tissues from magnetic resonance imaging data. Specimens loaded in the tibial orientation have an ultimate load of 287 ± 37 N and stiffness of 62.8 ± 11 N/mm. Specimens loaded in the anatomical orientation have an ultimate load of 312 ± 6.5 N and a stiffness of 43.5 ± 3.4 N/mm. Although load response in the synthetic tissue was less than its cadaveric counterpart due to bending load from flexion, the methods of this study are versatile, repeatable, and compatible with a wide variety of printable thermoplastics and composites which can be applied to other tissues, joints, and load conditions.

Additive manufacturing is rapidly evolving and finding a place in nearly every industry. Recent advances make selective laser sintering especially well positioned to rapidly create complex parts with material properties capable of withstanding rigorous end use applications. However, these properties still pale in comparison to their metal powder bed fusion counterparts and can be plagued by anisotropy due to print orientation. This can be especially true for large parts with relatively thin structural walls. Combining selective laser sintering with metal electroplating has shown promise to increase both strength and isotropy. While traditional metal–polymer hybrid composites have struggled to maintain consistent properties across varying geometries, this work demonstrates control over material properties at scales previously not possible, enabling a new class of lightweight structures with improved survivability. This novel research has experimentally found the tensile properties and isotropy of different electroplating coatings and investigates techniques that can be used to increase coating adhesion and uniformity over the rough non-conductive printed part surface. It is shown that though both the printed and electroplated material are individually anisotropic, the combination of printing and subsequent electroplating can improve overall build direction isotropy. This research represents a shift in additive manufacturing by transforming what was once considered a limitation of SLS printing—thin-wall anisotropy—into an opportunity for creating customized material properties through strategic metal deposition but also opens up new design spaces where minimum weight and minimum volume design trajectories are needed.