The strength and elastic property of PLA + graphite composites: experimental and theoretical analyses

Background. The combination of additive technologies with reinforced materials opens up new vistas for creating lightweight and durable products having unique characteristics. Implementing these technologies into the production requires effective evaluation methods of the ultimate limit state of such products. Objective. The article deals with the mechanical properties of samples, manufactured by the method of surfacing FDM with two polylactide-based thermoplastic threads: PLA-Cg+ with 5% layered graphite filling and PLA-CCF with 10% carbon fiber filling. Methods. The impact of 3D printing process parameters, such as print orientation and layer thickness, on specimens' mechanical characteristics under conditions of tension and compression, has been experimentally researched. Results. It is shown that both print orientation and layer thickness substantially influence specimens' mechanical properties of both materials. A comparative analysis of experimental data with calculations by failure criteria has been carried out: Tsai-Hill, Tsai-Wu, Hoffman, Mises, and maximum stresses. Conclusions. The results of the tests proved that there is a significant influence of the studied parameters of the printing process on the mechanical characteristics of PLA + graphite specimens under both tension and compression. For the most part, samples with a smaller thickness have both a higher ultimate strength (limit of proportionality) and a greater relative elongation. It is defined that the best concurrence between experimental and calculated data for both materials can be achieved through using the generalized von Mises criterion.