On the slip burst amplitude cutoff in dislocation-rich microcrystals

The plastic deformation of small-scale face-centered cubic metals exhibits intermittent slip burst events that appear on stress-strain curves as sudden strain jumps and/or load drops. These events are generally attributed to the avalanche-like cooperative motion of several dislocations, or to the repeated activation of single-arm dislocation sources. We explore the influence of the load train compliance on the amplitude of such slip bursts by testing in tension microcast monocrystalline silver specimens 3.4 mu m in diameter under two different load-train compliance conditions. Resulting data show that the statistics of slip burst amplitudes in the higheramplitude, cutoff, regime depend on the compliance of the total testing load train, whereas the stress drop distributions do not. We propose a mechanism and derive an expression for the slip burst cutoff by assuming that higher-intensity slip bursts are driven by the stochastic activation of dislocation sources induced by forest dislocation motion. The resulting expression accounts for the influence of the load train compliance on the statistics of larger-amplitude slip bursts, resembles the expression for the slip amplitude cutoff that was proposed by Zaiser and Nikitas, and agrees with observed cutoff amplitude data from this and earlier studies on microcast FCC single crystals tested in tension.