Elastic Slow Dynamics in Polycrystalline Metal Alloys

Jan Kober,Marco Scalerandi,Alena Kruisova

doi:10.3390/app11188631

Abstract

Elastic slow dynamics, consisting in a reversible softening of materials when an external strain is applied, was experimentally observed in polycrystalline metals and presents analogies with the same phenomenon more widely observed in consolidated granular media. Since the effect is extremely small in metals, precise experimental techniques are needed. Reliable measurement of relative velocity variations of the order of 10−7 is crucial to perform the analysis. In addition, the grain structure and the nature of grain boundaries in metals is very different from that in rocks or concrete. Therefore, linking relaxation elastic effects to the microstructure is needed to understand the physical origin of slow dynamics in metals. Here, interpreting the relaxation phenomenon as a multirelaxation process, we show that it is sensitive to the spatial scale at the microstructural level, up to the point of allowing the identification of the existence of features at different spatial scales, particularly distinguishing damage from microstructural inhomogeneities.

Highlights

Slow dynamics is perhaps the most characteristic feature of elastic hysteresis manifested in media with a grain structure [1,2,3,4]
We have shown that slow dynamics in metal alloys could be monitored with a high degree of accuracy and repeatability by introducing a proper experimental protocol based on the MoDaNE approach
The interpretation given to the data allowed us to link experimental observations of slow dynamics with the spatial scale at the micro-structure level

Summary

Introduction

Slow dynamics is perhaps the most characteristic feature of elastic hysteresis manifested in media with a grain structure [1,2,3,4] These materials exhibit memory effects and hysteresis in their response even when subjected to a low amplitude dynamic excitation (strain of the order of 10−6). Given a fully relaxed sample (with unperturbed values of modulus and damping), an external perturbation is applied producing a strain This phase is called conditioning and the conditioning strain could be generated with a propagating elastic wave [19], by heating/cooling a sample [20,21] or with an impact [22]. The process can be monitored by tracking the evolution of wave velocity in time using a very low amplitude excitation

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