Here is a collection of research projects that I've had the opportunity to
work on during my time at UC Berkeley. Through my research, I have found an appreciation for the intersection
between 3D printing and composite materials; I believe that these two areas represent the current paradigm of
engineering. Composites are fascinating to me – by combining familiar materials in new ways, we are able to
realize spectacular new properties and unlock new mechanisms. And by taking advantage of the freedom of design
that comes with 3D-printing, we have the capability to design and engineer structures and machines that can
revolutionize the way we approach mundane tasks. For example, "4D-printing" is a novel way to manufacture
stimuli-responsive materials and metamaterials that are used
in a variety of applications. It combines existing 3D-printing processes with engineered materials and
structures to expand the design space of what's currently printable.
I am especially grateful to Professor Lin and Professor Gu in the ME Department, as well as Dr. Jacqueline
Elwood, my research supervisor in the Lin Lab, for giving me the opportunity to pursue this research. Although I
am investigating my passion at only a small scale, one drop in the bucket of the composites research that is
being done across the world, I hope that my work will one day be part of the backdrop of engineering innovation.
Multi Jet Fusion Printed Lattice Materials: Characterization and Prediction of Mechanical Performance
HP Labs, Palo Alto, CA
Now that we had characterized monolithic specimens of MJF-printed nylon, the next step was to understand how to harness the potential for large-scale structures with highly-tunable material properties. In particular, the MJF process is especially well suited for printing lattices of almost any topology, owing to the lack of support material required during printing. The goal of this project was to characterize the stiffness and strength scaling behavior of MJF-printed polyamide (PA)-12, as well as investigate particular trends in lattice material properties due to packing parameters like printing orientation or location within the build volume. To accomplish this, we print and test several distinct lattice geometries to uncover the stretching, bending, and buckling behavior of printed structures over a wide range of relative densities. For the first time, we present the scaling behavior of MJF-printed PA-12 and contextualize this behavior alongisde other, previously-studied printing systems. We also control for print orientation and build location to understand the influence of print-chamber cooling on material properties. Our findings have immediate applications for large-scale printed structures and assemblies - like printed rocket airframes - that must be lightweight, stiff, and strong.
Effect of Build Parameters on the Mechanical Behavior of Polymeric Materials Produced by Multi-Jet Fusion
HP Labs, Palo Alto, CA
Multi-jet fusion is a fascinating new form of powder-bed fusion printing. Instead of relying on a laser or other directed light source, liquid-state “printing agents” are dropped onto the powder bed using traditional inkjet nozzles much like those seen on 2D-printers. In particular, a carbon black-based fusing agent is jetted onto regions of the bed where solidification is desired, and a different detailing agent is dropped to inhibit fusing in other areas. When an overhead infrared lamp is then passed over the entire print bed, energy is absorbed by the fusing agent, building a layer of the printed part. The MJF process has incredible potential for directly fabricating large-scale polymer parts – there is no support material, and the only post-processing required involves cleaning unused powder from the surface of the finished part.
This project attempts a characterization effort that has never been seen in the present literature. It is known that varying the nesting parameters (e.g. print angle, print location) and physical parameters (e.g. part size, inter-part spacing) has an impact on the mechanical properties of the printed parts. However, these effects, which are due to complex interactions between the printing agents, applied power, and polymer material, are only “benchmarked” at a high level. To perform a thorough characterization of the print process across two materials (polyamide 11 and polyamide 12), we print a total of 1,485 specimens over nine printing buckets, varying the printing angle, nominal dimensions, and three-dimensional center location. We then test the specimens in tension, three-point bending, or impact, and use the results to characterize tensile and flexural strength and stiffness, elongation at break, and fracture energy as a function of our input parameters. To produce quantitative correlations in the data, we apply a normalization algorithm to isolate specimen data as a function of a particular variable, allowing us to uncover the trends we seek.
CFRP Composites: A Comparison of Manufacturing Methods on Mechanical Properties
Professor Grace Gu, UC Berkeley Department of Mechanical Engineering
Composite materials present an attractive solution to the problem of material selection for many applications. In particular, carbon fiber-reinforced polymer (CFRP) composites are known for their high strength-to-weight and stiffness-to-weight ratios, which make them excellent structural materials. CFRP composites are used in a wide variety of industries; you'll see them in automobiles, boats, golf clubs, skateboards, and rockets. A recent development in the composites industry is the advent of additive manufacturing (AM) methods that can automate the fiber placement process. Compared to "traditional" methods like wet layups and compression molding, which often requires the use of an autoclave. Years of development of these "traditional" manufacturing methods have yielded well-known techniques that produce excellent finished products. But AM presents an attractive alternative, greatly reducing "hands-on" time needed with parts, realizing complicated geometries, and allowing for a high degree of repeatability. The question remains, however, of how the material properties of parts using new AM technologies compares with those of parts made using more "traditional" methods like a wet layup. (To make FDM printing of continuous fibers possible, 3D printers often combine the fibers with a thermoplastic material that provides printability at the expense of strength and stiffness.)
My research seeks to answer this question by directly comparing the material properties of a 3D-printed composite sample with a hand laid-up composite specimen (normalized to an equal fiber volume fraction). In addition to preliminary computations using equations developed in the literature, we use a twofold approach to sample comparison. Both the printed and handmade samples are simulated in tension, compression, and flexure using ANSYS, and the physical specimens undergo mechanical testing following ASTM standards. The results of this study will hopefully provide a fair point of comparision between the two methods as well as perspective on the viability of new AM technology for industrial applications.
Development of an Electrically Conductive Nanomaterial for SLA 3D Printing
Professor Liwei Lin, UC Berkeley Department of Mechanical Engineering
Additive manufacturing using stereolithography (SLA) is a promising way of obtaining rapid prototypes with excellent (sub-millimeter) detail. Current research points to the use of SLA (and additive manufacturing in general) as a fabrication alternative to traditional soft lithography for microfluidics. The layer-by-layer nature of modern 3D printing processes suggests a viable alternative to soft lithography, which is by comparison quite time-consuming and labor-intensive. But the process of using a liquid resin necessarily limits the materials compatible with SLA. Notably, there are very few printable electrically-conductive materials.
This project aims to develop a conductive, 3D-printable multi-material resin that is compatible with commercial printers. The direct printing of so-called "multi-functional" devices using a composite material or a system of materials has been well explored using fused deposition modeling (FDM), but not in the context of SLA. The stereolithography process features dramatically improved resolution and surface finish quality, making it attractive for the field of microfluidics. In this work, the challenge lies in developing a composite that has enough nanoparticle loading to be measurably conductive; however, the amount of the solid phase that can be dispersed in a printable resin is limited by a threshold concentration, above which the resin becomes overly viscous and unprintable. Mixing, dispersing, and printing strategies are developed to realize this composite as a printable material. As a simple demonstration of our printable conductive resin, we print a microfluidic capacitive pH sensor.
Publications
Journal Articles
Chen, A. Y., Chen, A., Fitzhugh, A., Hartman, A., Kaiser, P., Nwaogwugwu, I., Zeng, J., & Gu, G. X. (2023). Multi Jet Fusion printed lattice materials: Characterization and prediction of mechanical performance. Materials Advances, 4, 1030-1040. https://doi.org/10.1039/d2ma00972b
Chen, A. Y., Chen, A., Wright, J., Fitzhugh, A., Hartman, A., Zeng, J., & Gu, G. X. (2022). Effect of Build Parameters on the Mechanical Behavior of Polymeric Materials Produced by Multijet Fusion. Advanced Engineering Materials, 24(9), 2100974. https://doi.org/10.1002/adem.202100974
Chen, A. Y., Pegg, E., Chen, A., Jin, Z., & Gu, G. X. (2021). 4D-printing of electro-active materials. Advanced Intelligent Systems, 3(12), 2100019. https://doi.org/10.1002/aisy.202100019
Chen, A. Y., Baehr, S., Turner, A., Zhang, Z., & Gu, G. X. (2021). Carbon-fiber reinforced polymer composites: A comparison of manufacturing methods on mechanical properties. International Journal of Lightweight Materials and Manufacture, 4(4), 468–479. https://doi.org/10.1016/j.ijlmm.2021.04.001
Guardincerri, E., Bacon, J. D., Barros, N., Blasi, C., Bonechi, L., Chen, A. Y., D’Alessandro, R., Durham, J. M., Fine, M., Mauger, C., Mayers, G., Morris, C., Newcomer, F. M., Okasinski, J., Pizzico, T., Plaud-Ramos, K., Poulson, D. C., Reilly, M. B., Roberts, A., Saeid, T., Vaccaro, V. & Van Berg, R. (2018). Imaging the dome of Santa Maria del Fiore using cosmic rays. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 377(2137), 20180136. https://doi.org/10.1098/rsta.2018.0136
Conference Presentations
Chen, A. Y., Chen, A., Wright, J., Fitzhugh, A., Hartman, A., Zeng, J., & Gu, G. X. (2022). Multi-jet fusion printed lattice materials: characterization and prediction of mechanical performance. 2022 MRS Spring Meeting and Exhibit, Honolulu, HI.
Chen, A. Y., Chen, A., Wright, J., Fitzhugh, A., Hartman, A., Zeng, J., & Gu, G. X. (2021). Effect of build parameters on the material properties of printed parts produced by multi-jet fusion. 2021 Solid Freeform Fabrication Symposium, Austin, TX.
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