Analysis of the Effect of Raster and Loading Orientations on the Mechanical Properties and Fracture Behavior of Polylactic Acid Polymer Produced by Additive Manufacturing

Document Type : Research Article

Authors

1 Department of Mechanical Engineering, Technical and Vocational University (TVU), Tehran, Iran

2 Department of Mechanics and Aerospace Engineering, Southern University of Science and Technology, Shenzhen, 518055, China

3 Moganshan Institute ZJUT, Kangqian District, Deqing 313200, China

4 High-speed Rotating Machinery Laboratory, Zhejiang University, Hangzhou 310027, China

Abstract

The mechanical properties and crack growth resistance of polylactic acid samples produced via additive manufacturing (3D printing) were investigated. Standard dumbbell-shaped specimens were prepared in accordance with ASTM standards in three print orientations: 0°, 90°, and 0°/90°. These orientations corresponded to layer deposition in the longitudinal, transverse, and alternating (cross-ply) directions, respectively. The stress-strain curves revealed that changing the print orientation from 0° to 90° or 0°/90° resulted in a significant increase in maximum tensile stress by approximately 39% and an average increase in strain at failure of about 30%. This was attributed to differences in layer arrangement and stress distribution within the internal structure of the samples. To assess crack growth resistance, fracture tests were performed in tensile and shear loading conditions. Butterfly-shaped specimens, designed per standards, were tested using a modified Arcan fixture. Also, the geometric factors corresponding to each loading angle were extracted using finite element simulation. The critical values of fracture energy in shear mode were reduced by about 58% compared to tensile mode. The samples printed in the 90° direction showed less resistance to crack growth than the 0° and 0/90° directions due to the weakness in interlayer bonding. Among the cases studied, the 0/90° printing direction was suggested as the optimal orientation due to the favorable balance between high tensile strength and adequate resistance to crack growth.

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Amirkabir Journal of Mechanical Engineering
Volume 57, Issue 3
June 2025
Pages 379-398

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