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Preprint / Version 6

Size Matters: Impact Energy Absorption Across Five Decades of Length Scale

##article.authors##

  • Jacob A. Rogers J. Mike Walker ’66 Department of Mechanical Engineering, Texas A&M University, College Station, Texas, 77843. https://orcid.org/0000-0003-2152-3129
  • Kailu Xaio Department of Material Science and Engineering, Texas A&M University, College Station, Texas, 77843.
  • Paul Mead J. Mike Walker ’66 Department of Mechanical Engineering, Texas A&M University, College Station, Texas, 77843.
  • Charles U. Pittman, Jr. Department of Chemistry, Mississippi State University, Starkville, Mississippi, 39762.
  • Edwin L. Thomas Department of Material Science and Engineering, Texas A&M University, College Station, Texas, 77843.
  • Justin W. Wilkerson J. Mike Walker ’66 Department of Mechanical Engineering, Texas A&M University, College Station, Texas, 77843.
  • Thomas E. Lacy, Jr. J. Mike Walker ’66 Department of Mechanical Engineering, Texas A&M University, College Station, Texas, 77843.

DOI:

https://doi.org/10.31224/3516

Keywords:

Laser induced particle impact test (LIPIT), Single-stage gas gun, Scanning electron microscopy (SEM), Optical microscopy, Specific energy absorption, Length scale, Strain rate, Polycarbonate, Alumina, Thin films, Profilometry, Laser confocal microscopy, Microspheres, Impact scaling, Geometric scaling, Elastic Plastic Impact Computation (EPIC) code

Abstract

The Laser-Induced Particle Impact Test (LIPIT) can be used to probe projectile, target, and synergistic projectile-target responses to high strain rate deformation at the microscale. LIPIT’s advantages over other microscale launching techniques include the ability to controllably launch a single microparticle and precisely characterize the projectile momentum and kinetic energy before and after target impact. In addition, a LIPIT apparatus possesses a small laboratory footprint and is suitable for extension to high-throughput testing. Hence, LIPIT experiments have been used to study the dynamic response of many polymers, gels, and metals in different structural forms with various ht/dp ratios. These microscopic high-rate deformation behavior and impact energy absorption studies were used to suggest promising materials for macroscopic applications. Geometric scale, however, can significantly influence dynamic material behavior through scale-induced changes in event time, strain rate, projectile/target material homogeneity, and more. In this study, such geometric-scale effects are intentionally investigated. Noncrystalline alumina spheres ranging five orders of magnitude in diameter (dp = 3 μm–10 mm) were launched into scaled ht/dp amorphous polycarbonate targets of thickness ht at normal incidence using either LIPIT or a gas gun, depending on the scale. Projectile impact velocity and the projectile diameter to target thickness ratio were held constant in all experiments (vi = 550 m/s and ht/dp = 0.25, respectively). Impact energies spanned from hundreds of joules down to nanojoules (eleven decades). The specific impact energy absorption (Ep*), local plastic deformation, and deformation microstructure were compared across all scales. Length scale reduction sets in motion a remarkable 230% amplification in specific energy absorption and a 240% increase in relative impact deformation area. Corresponding numerical impact simulation results emphasize key limitations of current continuum-based material models and indicate potential areas of improvement. These findings demonstrate that material property discoveries made using emerging high-throughput methods (LIPIT, nanoindentation, laser-driven flyers, etc.) may not be directly indicative of macroscopic behavior and performance.

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Posted

2024-02-05 — Updated on 2024-09-19

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