Browsing by Author "Thevamaran, Ramathasan"

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    Extreme Energy Dissipation via Material Evolution in Carbon Nanotube Mats
    (Wiley, 2021) Hyon, Jinho; Lawal, Olawale; Thevamaran, Ramathasan; Song, Ye Eun; Thomas, Edwin L.
    Thin layered mats comprised of an interconnected meandering network of multiwall carbon nanotubes (MWCNT) are subjected to a hypersonic micro-projectile impact test. The mat morphology is highly compliant and while this leads to rather modest quasi-static mechanical properties, at the extreme strain rates and large strains resulting from ballistic impact, the MWCNT structure has the ability to reconfigure resulting in extraordinary kinetic energy (KE) absorption. The KE of the projectile is dissipated via frictional interactions, adiabatic heating, tube stretching, and ultimately fracture of taut tubes and the newly formed fibrils. The energy absorbed per unit mass of the film can range from 7–12 MJ kg−1, much greater than any other material.
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    High-velocity projectile impact induced 9R phase in ultrafine-grained aluminium
    (Springer Nature, 2017) Xue, Sichuang; Fan, Zhe; Lawal, Olawale B.; Thevamaran, Ramathasan; Li, Qiang; Liu, Yue; Yu, K.Y.; Wang, Jian; Thomas, Edwin L.; Wang, Haiyan; Zhang, Xinghang
    Aluminium typically deforms via full dislocations due to its high stacking fault energy. Twinning in aluminium, although difficult, may occur at low temperature and high strain rate. However, the 9R phase rarely occurs in aluminium simply because of its giant stacking fault energy. Here, by using a laser-induced projectile impact testing technique, we discover a deformation-induced 9R phase with tens of nm in width in ultrafine-grained aluminium with an average grain size of 140 nm, as confirmed by extensive post-impact microscopy analyses. The stability of the 9R phase is related to the existence of sessile Frank loops. Molecular dynamics simulations reveal the formation mechanisms of the 9R phase in aluminium. This study sheds lights on a deformation mechanism in metals with high stacking fault energies.