These are the ASTM D638-14 Type IV (4) designs used in a study to compare Type I with Type IV using a ton of RepRap 3-D printers and users. You can read the full study: John J. Laureto and Joshua M. Pearce. Anisotropic mechanical property variance between ASTM D638-14 type I and type IV fused filament fabricated specimens. Polymer Testing 68: 294-301 (2018). DOI: 10.1016/j.polymertesting.2018.04.029 open access preprint
Abstract of study
The open source introduction of fused filament fabrication (FFF) enables distributed manufacturing of consumer products. However, with a wide range of low-cost FFF 3-D printers and settings possible, there is a lack of information on the variability in printed mechanical properties. This paper utilizes a large pool of 47 user-assembled 3-D printers to quantify the mechanical property variations of ultimate tensile strength (UTS) and yield strength of FFF printed components using ASTM D638-14 horizontally-oriented Type I and IV geometries for poly lactic acid (PLA). The results indicate that utilizing Type IV tensile test piece geometry may overestimate the UTS relative to the Type I. Furthermore, anisotropic mechanical property variances were quantified for Type IV specimens (vertical and horizontal orientations). Vertical tensile specimens had an ultimate tensile strength 47.9% less than horizontal. Finally, the abundant supply of PLA 3-D prints suggest open-source printers assembled by individual operators can produce quality plastic components although the mechanical performance of the given part can vary dramatically based on the operator selection of printing parameters that provide a visually acceptable part.