Effect of Thermal Cycling on the Progressive‐Load Scratch Behavior of 3D ‐Printed PLA Composites Reinforced With Milled Glass Fiber

Abstract

Thermo‐hygrometric aging is applied to additively manufactured polylactic acid (PLA) parts meant for outdoor or aerospace service, while the effect of reinforcement on scratch resistance of single asperities after aging is yet unknown. The study was performed on the pure PLA, PLA composite with 10 wt.% milled glass fiber (GF), and PLA composite with 15 wt.% milled GF fabricated using the fused deposition modeling technique. The samples were thermally cycled (−20°C/+40°C, 93% relative humidity) for 0, 200, and 400 thermal cycles and tested by means of progressive load scratch test (0.03–10 N) using Rockwell diamond indenter. The least deep indentation (66.0 μm) and the greatest elastic recovery (63%) were observed for the as‐printed PLA sample, while the addition of glass fibers caused increasing friction (0.46) and variability of its value. After 400 cycles, the depth of penetration was almost doubled (159 μm for 15 wt.% GF), elastic recovery became 24% and 30%, and stick–slip oscillations were increased 10 times. According to the two‐way ANOVA results, 87.0% (depth of penetration) and 90.8% (depth of residual indentation) variance depended on thermal aging ( p  < 0.0001) rather than reinforcement (5.0%–7.2%).