Abstract
In this study, acoustic emission (AE) measurements on polycrystalline tin as a function of temperature at different driving rates under compression were carried out. It is shown that there is a definite difference between the acoustic emission characteristics belonging to twinning (low temperatures) as well as to dislocation slip (high temperatures). The stress averaged values of the exponents of the energy probability density functions decreased from = 1.45 ± 0.05 (−60 °C) to = 1.20 ± 0.15 (50 °C) at a driving rate of , and the total acoustic energy decreased by three orders of magnitude with increasing temperature. In addition, the exponent γ in the scaling relation SAE~DAEγ (SAE is the area and DAE is the duration) also shows similar temperature dependence (changing from γ = 1.78 ± 0.08 to γ = 1.35 ± 0.05), illustrating that the avalanche statistics belong to two different microscopic deformation mechanisms. The power law scaling relations were also analyzed, taking into account that the detected signal is always the convolution of the source signal and the transfer function of the system. It was obtained that approximate values of the power exponents can be obtained from the parts of the above functions, belonging to large values of parameters. At short duration times, the attenuation effect of the AE detection system dominates the time dependence, from which the characteristic attenuation time, τa, was determined as τa ≅ 70 μs.
Highlights
It is well known that processes taking place during plastic deformations have intermittent character and avalanches of acoustic emission (AE) signals are often emitted during these processes [1,2,3,4,5,6,7,8,9,10]
For the detection of the acoustic signals, the threshold value was 0.04 V and the hit definition time (HDT) was chosen to be 80 μs well as the AE amplitude was defined as the peak voltage
The scatter between the exponents belonging to the repeated runs was about 15% for ε. It can be seen from the data that there is no systematic dependence of γ on the driving rate
Summary
It is well known that processes taking place during plastic deformations have intermittent character and avalanches of acoustic emission (AE) signals are often emitted during these processes [1,2,3,4,5,6,7,8,9,10]. It was already known earlier that AE reflects the intermittent character of plastic deformations, real statistical analysis of AE signals, collected during plastic deformation, started only at the beginning of this century [3] It was shown by numerical simulations and experiments on creeping ice [3] that dislocations organize into scale free patterns of avalanches, characterized by damped power law distributions [16,17]: x. RD size (S = o |U (t)|dt (where D is the duration time of the avalanche and |U (t)| is the absolute value of the voltage signals detected, this being proportional to the velocity of the elemental plastic shift and related to the motion of dislocations or deformation twinning, V(t)) versus D (S~Dγ ))), γ, should be different for different universality classes (i.e., for example for different deformation mechanisms). It will be demonstrated that, in accordance with [10,29,30,31], reliable approximate estimates of the exponents of the above scaling relations can be obtained only at large values of the parameters while, for example, at short duration times the attenuation effects of the AE detecting device dominate
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