Tensile behavior of individual fibers and films made via material extrusion additive manufacturing

Abstract

The mechanical behavior of thermoplastic materials processed via material extrusion additive manufacturing (MEAM) is a topic of great interest in several disciplines. Most of the material behavior characterization that has been done on the materials produced by material extrusion has been on macro-scale (“bulk”) parts. In order to better model and understand the process effects and take advantage of these during design, it is necessary to study the meso-scale material elements extruded by the process used to build the part geometry. While modeled effectively in previous works, full mechanical characterization at the meso-scale is yet to be accomplished. At this level, the essential material elements are known as “beads” or “roads”, the sum of which comprise each layer of the part. These elements are approximately uniform in cross-section and are defined by their dimensions, length, and placement angle. Therefore, they are effectively fibers and a set of them together constitute a layer, which can be built as a film (usually but not always flat). To further progress on this topic, this article explored the manufacturing and testing of these elements (fibers) and layers (films) at the meso-scale. The dimensional consistency was measured for each case in order to determine the process repeatability, followed by tensile tests on the fibers and films made from three common thermoplastic materials: Acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and polycarbonate (PC). For the fibers, both extruded (round, as produced) and deposited (rectangular, after printing on a surface) fibers were tested. Films were tested in single- and double-layer configurations with several different element layout patterns. The results and potential process sensitivities were discussed in detail, providing recommendations for use and future development of design rules when using these materials. These results will be useful in driving design decisions (for both macro-scale products and structured materials) and providing characterization data for further modeling and simulation of the MEAM process. These results will also help ensure the manufacturability of designed parts and materials built of these deposited thermoplastic fibers and films. This article also introduced and described mechanical testing methods that are useful for thermoplastic MEAM parts and have not yet been utilized elsewhere.