NinjaFlex is a flexible thermoplastic polyurethane (TPU) material manufactured for use with Fused Deposition Modelling 3D printers. It is widely available, relatively inexpensive, and is useful in various applications including gaskets, wearable electronics, and customized prosthetics because of its great flexibility and strength. The objective of this research was to expand on the limited information available regarding the mechanical characteristics of NinjaFlex and learn how infill density and printing orientation influence those characteristics.

An experiment was designed using the ASTM D638-14 standard to evaluate tensile properties of NinjaFlex specimens printed in two different orientations with their longitudinal axis parallel to the printing surface and with their longitudinal axis normal to the printing surface. Four different infill densities were used. Specimens were subjected to tensile loading along their longitudinal axes. A calibrated load cell measured applied force while a camera filmed the experiment for determining the corresponding extension using computer vision methods.

The results show that NinjaFlex has sizably greater ultimate strength, elongation, and toughness when loaded parallel to its print layers then when loaded normal to its print layers. The effects of infill density on tensile properties vary depending on loading direction relative to the print layer direction.

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