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Birte Riechers1 Konrad Samwer2

1, Arizona State University, Tempe, Arizona, United States
2, Georg-August-Universitaet Goettingen, Goettingen, , Germany

Experimental results are presented which analyze the global nonlinear response of a metallic glass in terms of avalanche statistics.
Samples of Pd40Ni40P20 are measured using a dynamic mechanical analyzer in single cantilever mode at temperatures slightly below the glass transition temperature. The metallic glass is excited by a sinusoidal stress at 1 Hz frequency and fixed field amplitude. Initially, the field amplitude is in the linear regime of the stress strain relation, and is switched to a higher amplitude value sufficiently long to allow for time-resolved analysis.
By a period-by-period Fourier-analysis, the evolution of nonlinear contributions to the first harmonic and the emergence of additional odd harmonics with time are revealed, similar as in preceding dielectric experiments on amorphous media by Richert [1]. The timescale of the evolution of nonlinearity is connected to the structural relaxation time of the material, suggesting long-range interactions between relaxation modes.
A new incremental analysis approach on the highly resolved strain data yields a very different sight on elastic and plastic response regimes [2]. Independent of low or high field amplitude, power-law behavior in strain response distributions identifies the full investigated range of temperatures and stresses to be connected to a superposition of elastic and plastic response.
These findings question the differentiation between linear and nonlinear response regimes. The analysis of the data in terms of intermittency results in the observation of power-law behavior, which is typical for systems with underlying avalanche dynamics as observed for metallic glasses [3, 4]. The data thus suggest a microscopic view on elastic and plastic sample response to mechanical fields, which is based on the existence of interacting shear transformation zones with a coupling via their mechanical Eshelby stress fields.

References
1. Richert, R., Weinstein, S., Nonlinear Dielectric Response and Thermodynamic Heterogeneity in Liquids, Physical Review Letters. 97, 095703 (2006).
2. Riechers, B. and Samwer, K. Nonlinear Response and Avalanche Behavior in Metallic Glasses, The European Physical Journal Special Topics, 226, 14 (2017) 2997.
3. Krisponeit, J.-O., Pitikaris, S., Avila, K. E., Küchemann, S., Krüger, A., Samwer, K., Crossover from random three-dimensional avalanches to correlated nano shear bands in metallic glasses, Nature Communications 5, 2013.
4. Herrero-Gómez, C., Samwer, K., Stress and temperature dependence of the avalanche dynamics during creep deformation of metallic glasses, Scientific Reports 6 (2016).

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