Validation of Pneumatic Actuation for Fast Fatigue Testing of Additive-Manufactured Polymers

In the modern industrial context, many manufacturers design universal testing machines (UTMs) equipped with servo-hydraulic or electromechanical linear actuators, which offer excellent control capabilities and high-quality force signal measurement, at the expense of high costs due to the need for hydraulic power units or dedicated electrical networks. The complexity of these systems discourages manufacturers of mechanical components, especially the ones produced through additive manufacturing (AM), from investing in machines for the determination of mechanical properties according to international standards, settling instead for information derived from technical datasheets of the base material (filament or powders), which rarely include information about fatigue life. Within this context, the Fast Fatigue Machine (FFM), designed by KnoWow srl and ItalSigma srl, makes mechanical characterization of materials a process accessible to any organization that may require it. This was made possible by designing a pneumatic benchtop testing machine with a built-in setup for Thermographic Methods (TMs) usage. The aim of this work is to validate pneumatic actuators as a viable alternative to servo-hydraulic systems, demonstrating their effectiveness and reliability. Frequency analysis on both sinusoidal waveforms, root mean square error (RMSE) evaluation, and percentage total harmonic distortion (THD%) calculations showed that, while the servo-hydraulic system closely follows the load signal with a THD of around 5%, regardless of the applied load intensity, the pneumatic system exhibits higher distortion (THD of approximately 9%, strongly dependent on the load levels) and a high-frequency harmonic component, which, however, does not affect the overall results. Life cycle assessment (LCA) analysis confirmed the convenience of the pneumatic system and TMs in material testing and fatigue characterization.