Impact of Build Direction, Infill Pattern and Raster Angle on Mechanical Properties and Damage Tolerance of 3D Printed PLA

Structures made by additive manufacturing processes are highly anisotropic and carry defects. Complete elimination of these defects is not possible, and these defects degrade the mechanical properties (such as elastic modulus, tensile strength, and fracture strain). In the present study, mechanical properties are quantified as a function of building parameters, in particular, filling patterns, raster angle and orientation of build direction with respect to that of loading, in polylactic acid (PLA). The tensile strength of 3D printed PLA is the same for hexagonal and linear pattern filling when build direction is along thickness and width, while better toughness is offered by hexagonal pattern filling. Build direction along specimen gauge length gives very low tensile strength and toughness. Damage tolerance was quantified in terms of work of fracture and hexagonal filling provided better damage tolerance than line filling patterns for conditions of 0° and 45° with respect to crack whereas line filling tolerated damage better than hexagonal filling for the 90° orientation.