This work investigates the mechanical properties of 3D printed polymers namely Polylactic Acid (PLA) and Polypropylene (PP), which underwent the process of tensile and bending testing. The PP material is utilized in the production of scoliosis braces as shown in Figure 1. 3D printing has evolved in recent years and it has become widely used in several engineering applications for its numerous advantages summarized in this document. The purpose of this work is to determine the most suitable material for 3D printing scoliosis braces, which one can use as a reference to gain insights as it applies to other parts involving 3D printed PLA and PP materials in general.
When tensile testing, the PLA and PP samples are printed in two orientations – on their side and upright. The nozzles used to print the PLA samples are 0.4 mm and 0.6 mm. The samples are tested and the results are compared and evaluated. The other 3D printing parameter examined in this work is infill density, specifically 50% and 100%. This parameter is used to identify which setting significantly affects the weight of mechanical parts, cost, and production speed. PP samples show great flexibility, as some of the samples are stretched without breaking. The upright 3D printed orientation PP samples have higher Ultimate Tensile Strength and Young’s Modulus than side 3D printed orientation samples.
This experiment shows that for the side printed 3D samples, the PLA dominates in terms of tensile strength compared to the upright print orientation. The samples printed with the bigger nozzle have a higher tensile strength. The 100% infill density has more than double the strength compared to 50% infill density. This document shows the breaking loads during the bending test of PLA samples and the bending loads of PP samples.
When bending testing PLA samples, side printed samples clamped on the wide side show the highest strength, while side printed samples clamped on the short side illustrate predictable breaking load. Upright printed samples show unpredictable strength evident by some samples being able to hold big loads before breaking whereas some break at small loads. For PP bending testing, 3D printed samples made of Ultimaker and Formfutura filaments are compared which resulted in a slight difference of deflections in different loads. There are three design criteria for scoliosis brace material such as strength, flexibility and impact resistivity. This project focuses only on testing the strength and flexibility of material by tensile and bending testing.