Descriptive and inferential study of hardness, fatigue life, and crack propagation on PLA 3D-printed parts

This research work deals with the development of a methodology for the preliminary assessment of hardness, fatigue, and crack propagation performance of plastic parts manufactured employing polylactic acid (PLA), deposited layer by layer using Fused Filament Fabrication (FFF) technology. A commercial polylactic acid fila-ment was used to print different sample geometries to assess shore D hardness and its correlation with raster direction angles of 0 & DEG;, 0 & DEG;/90 & DEG;, and 0 & DEG;/45 & DEG;/-45 & DEG;, relative to a reference point, and with three different heat treatment temperatures namely 60 ?, 100 ?, and 140 ?. Additionally, fatigue life and crack propagation were assessed as a function of raster direction angle. Finally, a statistical modeling methodology was employed to obtain both linear equations and response surface plots to correlate performance with layer orientation and heat treatments. The results showed that samples produced at 0 /90 and 0 /45 /-45 raster direction angles and heat-treated at 100 & DEG;C showed the highest hardness performance. Also, the samples produced at 0 /45 /-45 raster direction angle showed the lowest crack propagation rate until a 200 mu m length was achieved, after that the crack rate increased abruptly, reaching 1500 mu m at around 4500 fatigue cycles; the 0 ;/90 raster direction angle reached a crack length of approximately 800 mu m at the same number of cycles. The fatigue results showed that samples printed at 0 & DEG;/45 & DEG;/-45 ; raster direction angles showed a fatigue life of 18,505 cycles, which is above the fatigue life found in samples produced employing the 0 & DEG; and 0 & DEG;/90 & DEG; raster direction angles. The statistical analysis derived from the obtained results shows that the raster direction angle is key to defining the bulk properties of the 3D-printed PLA parts. It was also demonstrated that the use of statistical modeling is a design alternative in contrast to the theory of laminates for composites, which is worth studying and developing for the manufacturing of mechanical parts by 3D printing.