Effects of Size Reduction on the Failure Mechanism of 3D Printed PLA+ Parts

Fused Deposition Modeling (FDM) with Poly(lactic Acid) plus (PLA+) is frequently used in rapid prototyping and 3D printing of complex shapes. Owing to their light weight, manufacturability and cost effectiveness, thermoplastic parts made by FDM are increasingly used in several applications ranging from tissue engineering to consumer goods industry. Understanding the size effects on the strength of these parts is essential to extend their use in the microsystem applications. This paper studies the effect of scale on the mechanical properties and failure mechanisms of a 3D printed parts made by FDM. Process parameter such as extrusion temperature, infill density, infill pattern, print speed, layer thickness and nozzle diameter were kept consistent for this experiment. Five samples each with a square cross-sectional area of side lengths of 2mm, 4mm, 6mm, and 10mm were subjected to a tensile test. It was observed that parts with a smaller cross-sectional area experienced ductile failure as opposed to brittle fracture in larger cross-sectional area. Failure is shown to occur at sections where the geometry changes for brittle fractures while it occurs at the center of the parts displaying ductile failure. Results of the tensile test show a non-uniform ultimate yield strength across the four sizes. Crystallization of the material due to nozzle temperature at extrusion could be a contributing factor to failure discrepancies. Increase in the cycle time is theorized to improve the layer to layer adhesion of the part thereby affecting its mode of failure.