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The Evolution of Persistent Slip Bands in Metals: Coarse-Grained Simulations and In Situ Experiments

Seminar Group: 


Professor Jaafar El-Awady


Dept. of Mechanical Engineering
Johns Hopkins University


Friday, October 20, 2017 - 11:00am


ESB 1001


Prof. Tresa Pollock

A fundamental understanding of deformation mechanisms during cyclic loading is essential to predict the usable life of engineering components in aerospace applications. While conventional bulk scale fatigue tests provide a way to quantify the fatigue life of materials, specific microstructural features that result in failure are difficult to ascertain. One of the common dislocation microstructures forming during cyclic loading of face centered cubic metals are persistent slip bands (PSBs). Over the years, many experimental, theoretical, and computational studies have led to significant understanding of plasticity in PSBs, however, many open questions remain in the prediction of the formation and evolution of these complex dislocation structure. In this work, we will present one of a kind large scale three-dimensional (3D) discrete dislocation dynamics (DDD) simulations coupled with a novel in situ, high frequency fatigue testing methodology to investigate PSB formation and evolution in single crystal Ni microcrystal.

 In these simulations partially developed PSB structures are simulated under fully reversible loading conditions. The maximum stress of the hysteresis loops and the local dislocation density in the channels/walls are shown to increase with increasing loading cycle. The dislocation interactions in the channels and the 3D contours of the local shear stress within the channels as a function of distance from the PSB walls are characterized to reevaluate the composite model proposed by H. Mughrabi and the bowing and passing model by L.M. Brown. In addition, the spatio-temporal point defect (vacancies and interstitials) generation and evolution is quantified as a function of the dislocation density in the PSB channels and walls. The results are discussed in view of a point defect diffusion model to study their migration rates to the surface. Finally, preliminary results from the in situ experiments will also be discussed.