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Dr. Albert Patterson.
Dr. Albert Patterson dives into a study on the mechanical behavior of thermoplastic materials processed through material extrusion additive manufacturing. | Image: College of Engineering.
Researchers from Texas A&M University and the University of Illinois Urbana-Champaign recently completed a project studying the mechanical behavior of thermoplastic materials processed through material extrusion additive manufacturing (MEAM) at the element scale, a process similar to 3D printing but far more complex.
Dr. Albert Patterson, from the Department of Engineering Technology and Industrial Distribution at Texas A&M, collaborated with Dr. Iwona M. Jasiuk, Dr. James T. Allison and doctoral candidate Charul Chadha on the experiments.
Results of the study were published in March 2023, in the journal Next Materials
MEAM, often known as fused filament fabrication, is a manufacturing process that involves extruding melted thermoplastic materials and polymer matrix composites through a nozzle in a series of elements — sometimes referred to as “roads,” “beads” or “fibers” — to build layered parts based on a digital model or design.
The selectively deposited elements create a fairly uniform cross section defined by its dimensions, length and placement angle. The cross sections are the fibers or “beams” of a layer, and the sum of all the layers produces a useful and customizable final part. 
“When designing tailored materials, especially when there are manufacturability concerns, it is essential that we consider the fundamental elements or building blocks of the printed parts,” said Patterson. “We can think of these elements as something akin to bricks in a wall or boards in a roof truss on a house — each one is small and cannot be considered a part on its own, but all of them together make a good house.”
To better understand how design-scale elements can affect and improve the additively manufactured thermoplastic process, researchers studied the basic part geometries of the extruded mesoscale material elements.
First, the team measured the dimensional consistency of each experimental trial to determine the process’s repeatability. This was followed by tensile tests on the fibers and films made from three common thermoplastic materials: acrylonitrile butadiene styrene, polylactic acid and polycarbonate. Results showed that the individual beads or material elements are structurally stable and repeatable.
“The 3D-printed parts combine a series of independent elements, each with their own physics and mechanical properties," Patterson said. "This expands our understanding of 3D-printed materials from a design perspective and opens the doors for new approaches in designing architected materials that are guaranteed to be manufacturable.”
Patterson also said the researchers gained insight into the mechanics of built materials by better understanding them as a combination of independent elements. This insight adds support for a new modeling perspective for some additively manufactured materials called the "beam/truss model," where each element is modeled as a beam, each layer as a truss consisting of several beams, and each part as a structure composed of many separate trusses. The findings will help drive design decisions and modeling of the process for macro-scale products and structured materials.
Because this study focused on thermoplastics, Patterson said the next steps are to apply the lessons from this study to develop better process models and design methods for additively manufactured materials, such as deposited solid metal, metal powder, ceramic powders and thermosetting polymers.
Overall, the research provides essential insights into the tensile behavior of individual fibers and films made with material extrusion additive manufacturing, offering valuable information for researchers and engineers working with it in the field.