Abstract

This article presents the results of monotonic tensile and fatigue tests conducted on commercial polylactide or polylactic acid (PLA). The results of fatigue tests for this material present in the literature are limited, especially for additive manufactured elements. The specimens were manufactured using the injection molding and the fused filament fabrication (FFF) method. The FFF specimens were divided into five subgroups, depending on the direction of filament deposition and infill density. The achieved results are aimed to verify the selected experimental method of fatigue testing of materials used in the additive manufacturing technology. It was considered an important issue, since there is no standard practice for fatigue testing of FFF- manufactured polymers, and research reported in the literature is usually obtained for a small number of specimens. In this work, over 20 specimens per S-N curve were used, which enables to classify them as reliability data type according to ASTM E 739 standard. It has been shown that the resultant fatigue lives can be related with applied nominal stress amplitudes using the classical S-N curve, described with Basquin-type power law function. This is evidenced, among the others, by the very similar scatter of results for both manufacturing technologies and the similar slopes of S-N curves. Some similar conclusions are hard to find in other works. The achieved results can also provide knowledge regarding the differences of monotonic and fatigue behavior of PLA, which is a commonly used biodegradable polymer, with respect to the technology of specimen’s manufacturing method. They can be useful in the development of biodegradable implants and other devices used in tissue or biomedical engineering. It has been shown that, to some extent, the fatigue testing of FFF-manufactured parts can be performed in the similar way as parts manufactured by injection molding.

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