PhD Thesis Colloquium: Mr. Swanand Telpande (26/09/23)
Thesis title:
Effect of Electric Current Pulses on Prec-cracked Metallic Foils: From Crack Propagation to Healing of Cracks
Faculty advisor(s):
Prof. Praveen Kumar
When?
26th September, 2023 (Tuesday), 03:00 PM (India Standard Time)
Where
K I Vasu Auditorium, Department of Materials Engineering
Abstract:
Both scientifically and technologically, it is important to study the effects of electric current pulses on the structural integrity of metallic components. As an electric current reverses its direction across a crack, massive current crowding occurs at the crack tip, generating a non-uniform temperature field sourcing away from the crack tip. Additionally, considerable electromagnetic forces are generated on the crack faces that open it in Mode I. Recent studies have shown that due to the synergistic effects of the above two stimuli, a pre-existing flaw may either grow or heal upon applying an electric pulse of high density. While one is a bane for structural integrity, the other is a boon to in-service components. Building upon the prior research on flaw/ crack propagation due to self-induced electromagnetic forces, the synergistic effects of external fields (i.e., external magnetic field and mechanical loading) on the fracture of current-carrying pre-notched Al foils are investigated using an experimental-numerical coupled approach. The coupling of the external fields with the electromagnetic loading is analyzed using the finite element method. Linear elastic fracture mechanics is applied to ascertain that the crack initiated and propagated from a notch existing in the Al foil at a stress intensity factor marginally greater than the plane stress fracture toughness of Al foils. Interestingly, a transition of in-plane fracture to a mixed mode fracture (essentially occurring due to local buckling) of a current-carrying Al foil in the presence of a high external magnetic field is observed and discussed with the help of finite element analysis. Finally, a fully automated tool is developed for the toolless machining of thin metallic conductors using a combination of electromagnetic and mechanical loading. Further, the study explores the attributes responsible for transitioning from flaw propagation to flaw healing upon passing an electric current pulse. A comprehensive understanding of the electro-pulsing parameters on the crack healing process is obtained using finite element analysis. The conjugate experiments performed on SS 316 reveal a complete solid-state bonding of a through-thickness fatigue crack due to high-density electro-pulsing. One of the key strengths of this study lies in the in-depth understanding of the bonding mechanisms. In addition to elucidating the role of electromagnetic and thermal effects of electric current on the healing process, the study also thoroughly discusses the influence of athermal effects, such as electroplasticity and electromigration, on the crack healing process. Overall, the developed understanding in this work opens up new avenues for exploring material healing techniques.