The Air Force Research Laboratory (AFRL) Materials and Manufacturing Directorate researchers recently took advantage of a unique and rare research opportunity to better understand the behavior of materials used in the additive manufacturing process.
As AFRL explained in an Oct. 20 article, while additive manufacturing has grown tremendously over the past few years, the technology available isn’t “mature” enough to be used for an Air Force warfighter. AFRL notes that the way printed layers keep their shape when bonding to each other is the problem. Material porosity and other factors such as weak blending can result in poor bonding between layers, weakening the overall structure of additively manufactured composite components.
To address this problem, researchers add nanofillers to aid in overall structural bonding. The precise amount of nanofiller, when added to a reinforcement filler such as carbon fiber, will greatly improve the mechanical properties of a printed part. Therefore, understanding the material properties and dynamics of different mixtures of composites and nanofillers is an important step in making additive manufacturing technology more practical for common use.
To advance the body of knowledge in this topic, AFRL researchers identified and made use of a unique research opportunity to gain an unprecedented view into the behavior of these materials. Materials scientist Dr. Hilmar Koerner of the Polymer Matrix Composite Materials and Processing team was granted the opportunity to work in collaboration with beamline scientists at the National Synchrotron Light Source II at Brookhaven National Laboratory, allowing the team to conduct real-time experiments and gather unique data. The National Synchrotron Light Source II is a unique facility that allows researchers from academia and industry to take advantage of extremely bright X-rays for analytical research purposes.
“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 Koerner. He said that the team used their beam time to pass the ultra-bright X-rays through the layers of deposited material, allowing real-time information to be gathered on the alignment and dynamics of the nanofiller.
Koerner explained that when the composite ink exits the 3-D printing nozzle, it turns from a shear-thinned, easily flowable liquid into a gel within just a few seconds. As the nanofiller particles randomize their orientation, they form a network that gives the composite ink self-supporting properties (similar to toothpaste). The XPCS experiment allowed the researchers to understand this fast process in great detail, providing information that can help optimize both the composite inks and the printing process as a whole for better performance.
The team will use newly-gathered data from the experiment to optimize composite ink formulations and printer parameters. Koerner says that correlating this data with other, simpler characterization methods can provide a number of benefits to the team’s in-house research efforts, including new closed-loop feedback controls for 3-D printers and a new ability to characterize AFRL-developed materials that experience much higher temperatures during printing.