Factors like material porosity and weak blending can cause poor bonding between layers, which weakens the structure of 3D printed components. This has prevented additive manufacturing from being used for many critical parts, but researchers at the Air Force Research Lab (AFRL) and elsewhere have been working to remedy these issues. Reinforcement fillers are sometimes added to the 3D printing material, and researchers have also tried adding nanofillers to the material to add as flow and set (rheology) modifiers and to aid in structural bonding. As a result, the printing material acts like toothpaste – it flows easily, yet stays in place once it’s set.
The amount of nanofiller, when added to a reinforcement filler such as carbon fiber, can largely improve the mechanical properties of a 3D printed part. More research needs to be done regarding how different combinations of nanofillers and printing materials interact and behave; once we have a better understanding of these combinations, it will be a big step towards making additive manufacturing a more commonly used technology for critical parts.
AFRL researchers recently made some progress in the research of these materials. Materials Scientist Dr. Hilmer Koerner of the Polymer Matrix Composite Materials and Processing team got the opportunity to work with beamline scientists at the National Synchrotron Light Source II at Brookhaven National Laboratory, allowing them to gather data and conduct real-time experiments.The facility allows researchers to use the bright X-rays for analytical research purposes. Researchers are required to submit a proposal detailing their work; that proposal is then peer-reviewed and a decision is made regarding equipment use.
The team passed the ultra-bright X-rays through the layers of 3D printed material, gathering real-time information on the alignment and dynamics of the nanofiller. According to Dr. Koerner, when the composite 3D printing material is extruded from the nozzle, it turns from a shear-thinned, flowable liquid into a gel within seconds. As the nanofiller particles randomize their orientation, they form a network that gives the material self-supporting properties. Through the experiment with the beamline, the researchers were able to gain a more detailed understanding of this process. With the information gained from the experiment, the researchers will be able to optimize both the printing material and printing process.
“We were awarded beam time at the XPCS [X-ray Photon Correlation Spectroscopy] beamline, which allows us to simultaneously look at the dynamics and structure of materials during processing with millisecond time resolution,” said Dr. Koerner.
“We were excited to find out that we had been granted beam time at this unique beamline,” said Dr. Koerner. “We conducted our experiments and gathered data that will allow us to better characterize these materials and shed some light into the 3-D printing process of Air Force-relevant thermosetting resins and their post processing.”
According to Dr. Koerner, the data gathered from the experiment can be correlated with other, simpler characterization methods for a number of purposes, including new closed-loop feedback controls for 3D printers and a new way to characterize AFRL-developed materials that experience much higher temperatures during printing.
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