Matthew R Begley, University of California, Santa Barbara

Dynamic Response of Coatings on Substrates Subjected to Impulse Loading
When Aug 27, 2014
from 02:00 PM to 03:00 PM
Where LR8, IEB Building, Engineering Science
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Femtosecond laser pulses with low energy can be used to precisely debond the interface between oxide films and substrates, which creates novel opportunities to characterize the properties of the film and the interface between the film and substrate.  This talk will describe theory and experiments that establish a framework that relates laser pulse parameters to film deformation, which can be used to infer coating/interface properties from experiments, or design experimental protocols that produce well defined interface flaws for subsequent testing.  First, an analytical model will be used to highlight two (apparently) underappreciated aspects of the problem: (i) the time-scale of the laser pulse is much shorter than that of the inertial time-scale of the film, such that the details of the pressure generated by the pulse are largely immaterial (greatly simplifying the problem) and (ii) the inertial contribution to the energy release rate can be substantial, with important implications for reliability in this and other dynamic scenarios (e.g. foreign object damage). The model will be used to generate regime maps that indicate failure modes as a function of pulse characteristics and film properties, which will be shown to be in good agreement with experiments. Second, the talk will present a brief discussion of several facets of dynamic debonding that can only be captured numerically, notably those relating to crack arrest after dynamic initiation. Illustrative simulations will be presented of such phenomena, which were generated using an explicit discrete element method with widely embedded cohesive zones.  The simulations demonstrate that it is possible to trigger dynamic kinking out of the interface (thus leading to a spalled section of film), even when quasi-static calculations suggest otherwise.