Effect of Build Orientation on Uniaxial Time-Dependent Ratcheting of Polyamide 12 Fabricated by Selective Laser Sintering

ABSTRACT

This study examined the impact of build orientation on the time-dependent ratcheting of polyamide 12 fabricated by selective laser sintering, focusing on the effects of voids and sintering interfaces. Results demonstrate that the ratcheting of the materials is notably time-dependent, with ratcheting strain increasing by 107% when the peak stress duration is extended from 0 to 10 s and by 95% when the loading rate is reduced from 15 to 1 MPa·s⁻¹; additionally, an interaction between creep and ratcheting is identified, suggesting that the loading history also influences the ratcheting of the materials; at high-stress levels (16 ± 22 MPa), the ratcheting of the materials shows a strong dependence on the build orientation, with the ratcheting strain increasing in the order of X0, X90, and X45 orientations (i.e., an increase of approximately 30% from the X0 to X45 orientation), which is attributed to the higher porosity of the materials with the X45 orientation and the larger projection area of voids perpendicular to the loading direction; in contrast, at low-stress levels (12 ± 18 MPa), the ratcheting strains of the materials built in the different orientations are almost the same. These findings provide experimental data support for the structural design of selective laser sintering polyamide 12 and highlight the significant impact of voids and sintering interfaces on the ratcheting of printed parts.

Highlights

• The effect of build orientation on uniaxial time-dependent ratcheting was investigated.
• The significant impact of voids and sintering interfaces on ratcheting was revealed.
• At high-stress levels, the X0 build orientation shows the smallest ratcheting strain.
• As void defects preferentially orient in the X45 build orientation, the ratcheting is more pronounced.