Ph.D. (Engg) : Compression & LVI of closed-cell metallic foam

Innovative high-performance structural designs play a critical role in mitigating insecure events such as low-velocity and ballistic impacts. These events involve significant kinetic energies, requiring structures that are lightweight, safe, and capable of absorbing energy effectively. Closed cell metallic foams have been widely adopted in aerospace, marine, civil, mechanical, and automotive industries due to their superior resistance to such impacts. Despite extensive research over the years, further advancements are still required in the design of lightweight protective structures. In impact applications, the impactor need not always strike perpendicular to the structure. Characterization of dissipation energies , impact load histories, and load–displacement curves under varying impact angles revealed, Contact force intensity and penetration time decrease as the impact angle increases. Energy absorption increases while penetration time decreases with increasing impact angle. Contact force decreases and contact time increases as the angle decreases. Displacement under oblique impact increases with increasing angle. The study was extended to finite element simulations of low-velocity impact behaviour in silicon–aluminium composite foams using ABAQUS/Explicit®. Numerical estimations of both full and partial damage were carried out for different impactor shapes and velocities. Key parameters such as dissipation energies, impact load histories, and load–displacement behaviour under penetration were systematically reported. The numerical scheme was validated against available experimental results, confirming the accuracy and reliability of the model. The following observations were made: Impact velocity effects: Contact force intensity and penetration time decrease with increasing impact velocity. Energy absorption increases while penetration time reduces as velocity increases. Impactor nose radius effects: Contact force reduces with smaller nose radii. Contact time is enhanced as the nose radius decreases. Impactor shape effects: The computed energy absorption effectiveness factor revealed that performance depends not only on material properties but is also strongly influenced by the geometry of the impactor. The study was further extended to numerical simulations of aluminium foam subjected to low velocity impacts. Both full and partial damage estimations were performed on foam samples across varying impact energies and thicknesses. Dissipated energy, impact load histories, and load–displacement responses were systematically reported under different penetration conditions. Foam samples with a thickness of 10 mm exhibited bending and global failure, characteristic of thin plate behaviour. In contrast, samples thicker than 10 mm underwent local failure, displaying behaviour typical of thick plates. For partial penetration cases, contact force, dissipated energy, deformation, and penetration time all increased with rising impact energy. For fully penetrated samples, contact force, dissipated energy, and deformation increased monotonically with impact energy, while penetration time decreased significantly. Across all aluminium foam samples, greater thickness led to monotonic increases in contact force, dissipated energy, deformation, and contact time. These findings underscore the critical influence of plate thickness in governing the impact resistance of aluminium foam structures. Furthermore, closed cell foam was modelled at the mesoscale to replicate the intrinsic geometry of real foam structures. LVT based 3-D models were employed to generate complex morphologies, including irregular pore sizes, uneven cell wall thicknesses & geometric variability. Morphological parameters such as equivalent diameter & sphericity factor were used to quantify pore size & irregularities. The influence of pore number & porosity on cell wall thickness was examined & the quasi-static compressive behaviour was assessed through load-displacement & stress-strain responses, alongside energy absorption & plastic dissipated energies. Results revealed that plateau strength exhibited only a marginal increase with pore number, while energy absorption showed a slight counterintuitive decline. Plastic dissipation energy increased monotonically with increasing pore number. Conversely, increasing porosity led to a monotonic decrease in yield point, energy absorption capacity & plastic dissipation energy. The study underscores that energy absorption capacity is strongly governed by porosity, cell wall thickness & pore size. These parameters must be incorporated into the design of closed-cell foams to ensure safe & reliable performance in protective structural applications.

Speaker: THIMMESH T

Research Supervisor: Dineshkumar Harursampath