Mechanical engineering doctoral student Ara Kim won the Best Data Presentation award at the American Society of Mechanical Engineers (ASME) 2019 International Mechanical Engineering Congress and Exposition (IMECE), ASME’s largest research and development conference focused primarily on mechanical engineering. Kim’s presentation described her work with her faculty advisor, Assistant Professor Jae-Hwang Lee of the Mechanical and Industrial Engineering Department, researching “High-strain-rate Dynamics of Copolymer Microparticles for Advanced Additive Manufacturing.”
As Kim and Lee explained in their abstract, “Exploring inherent mechanical behaviors of materials, especially under high-strain rates, is essential to develop and accomplish advanced and efficient additive manufacturing processes such as the cold spray method.”
The researchers went on to say that, as the application of the cold spray method has expanded to non-metallic materials and composites, “we envisioned that the control of nanoscale structures of cold-spray-able powder materials can achieve advanced performances of the end-product by tailoring inherent material properties.”
In order to investigate high-strain-rate behaviors of multi-phase polymers, Kim and Lee conducted precisely controlled, single-particle, impact experiments with polystyrene-block-polydimethylsiloxane co-polymer microparticles, which have distinctive “glassy” and “rubbery” phases. The researchers did so by using the Laser Induced Projectile Impact Test system, known as LIPIT.
“In this project,” explained Kim and Lee, “microphase-separated particles were investigated, and different volume fractions of [the glassy phase] and [the rubbery phase] and diverse annealing conditions were applied to obtain different phases, such as cylinders and lamellae, and degrees of ordered nanostructures.”
Kim and Lee noted that they explored particle morphologies before impact, and they also studied plastic deformation of microparticles after impact, by using scanning electron microscopy. Furthermore, they used focused ion beam milling to demonstrate degrees of ordered phases depending on annealing conditions and impact-induced morphological changes of nanostructures.
According to Kim and Lee, this project demonstrated that high-strain-rate behaviors in block co-polymers, including critical velocities, coefficients of restitutions, and plastic deformation after impact, are related to the nanostructures of microparticles which were related to the volume fraction of the glassy and rubbery phases.
What’s more, said Kim and Lee, “Pre-impact inelastic deformation and post-impact plastic deformations indicated the correlation between kinetic energy generated by acceleration force and material characteristics.”
This research (September 2018 – August 2021) is supported by the National Science Foundation (NSF) under Grant No. CMMI-1760924 (Dr. Siddiq M. Qidwai). The authors said they would also like to thank the NSF for supplemental travel funds to this competition from grant CMMI-1935462. (January 2020)