Investigation and modelling of plastic deformation aided by in situ monitoring techniques

Abstract

A synergy from three modern in situ techniques - infrared thermography, digital image correlation, and acoustic emission - used concurrently has been obtained to gain deeper insight into deformation kinetics and energy partitioning in monotonic tensile tests performed on various representative structural materials. Multiple experimental challenges have been addressed, and the specific methodological procedures developed to mitigate them are described in great detail. The original experimental setup designed in the present work is used to unite a wealth of data acquired to meet the above stated objective. Integrated in the experimental design, a thermodynamic modelling methodology is presented, based on the first law of thermodynamics and informed by the dislocation evolution theory inspired by the classic Kocks and Mecking formalism. The advantage of the model is that only physically motivated variables are used, and the outcome, a successful prediction of energy partitioning in materials with dislocation mediated plasticity in monotonic deformation. On the basis of the unifying thermodynamic principles and the first-order dislocation kinetics, interlinked models are proposed for the energy storage as well as dissipation in the form of heat and acoustic emission. The model strategy is verified using austenitic 316L stainless steel and a set of CuZn alloys with varying Zn content and stacking fault energies, controlling dislocation mobility. The combination of infrared thermography and acoustic emission is used to characterise the evolution of dislocation ensembles through the developed model link providing direct access to the fundamental properties of dislocation kinetics. The factors controlling the dislocation production and dynamic recovery rates in the strain hardening process, are recovered for the first time from the modelbased acoustic emission, and infrared thermography analyses respectively. Consequently, the developed toolset can be used as a powerful means for prediction of the strain hardening behaviour and quantitative evaluation of the dislocation kinetics in situ.