The Effect of Three Dimensional Printed Infill Pattern on Structural Strength

The aim of this study is to analyze and obtain the impact of the infill pattern on structural strength for 3D printed objects using (Polylactic Acid) PLA material via Fused Deposition Modeling Technique (FDM). Linear, hexagonal and diamond types of infill patterns were selected to investigate as they are the most common for FDM. The tensile test specimens were created and prepared for simulation through Computer Aided Design (CAD) and analyzed with Computer Aided Engineering (CAE) methods. For the tensile test simulation; all of the specimens were prepared with 50% infill density. Shell of the specimens were created with the thickness of 0.8 mm, the structure was designed and supported with linear, diamond and hexagonal types of infill patterns. Layer heights were selected as 0.4 mm to decrease the analysis and printing time. A new type of infill pattern named as pyramid was also proposed and developed to obtain better results from the 3D printed objects. Nodal displacement was applied as 0.04 mm to specimens as 8 steps to create realistic tensile test simulation. For comparison; the key parameters for structural strength and pattern influence were obtained from the simulation results. Obtained results showed that the equivalent maximum stress is in the range between 7.6 to 68.6 MPa for the raw PLA, it is up to 112.3 MPa for diamond. The other significant observation is the stress value for the specimen with diamond infill reached 70.7 MPa that is close to Ultimate Tensile Strength (UTS) of PLA in the fifth step. It can be assumed from the results that specimens with linear, hexagonal and diamond are broken at the third or fourth steps of the tensile simulation as they were created with 50% infill density and their UTS is about 35 MPa. Range from 2 to 12 MPa occurred stress differences can be observed for each pattern between first and fifth steps. The diamond pattern shows the highest values. This can be due to a low density and infill structural shape effect. For the structural strength the patterns can be listed from high to low as Hexagonal > Linear > Diamond.