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General framework for acoustic emission during plastic deformation

机译：塑性变形过程中声发射的一般框架

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Despite the long history, so far there is no general theoretical framework for calculating the acoustic emission spectrum accompanying any plastic deformation. We set up a discrete wave equation with plastic strain rate as a source term and include the Rayleigh-dissipation function to represent dissipation accompanying acoustic emission. We devise a method of bridging the widely separated time scales of plastic deformation and elastic degrees of freedom. While this equation is applicable to any type of plastic deformation, it should be supplemented by evolution equations for the dislocation microstructure for calculating the plastic strain rate. The efficacy of the framework is illustrated by considering three distinct cases of plastic deformation. The first one is the acoustic emission during a typical continuous yield exhibiting a smooth stress-strain curve. We first construct an appropriate set of evolution equations for two types of dislocation densities and then show that the shape of the model stress-strain curve and accompanying acoustic emission spectrum match very well with experimental results. The second and the third are the more complex cases of the Portevin-Le Chatelier bands and the Liiders band. These two cases are dealt with in the context of the Ananthakrishna model since the model predicts the three types of the Portevin-Le Chatelier bands and also Liiders-like bands. Our results show that for the type-C bands where the serration amplitude is large, the acoustic emission spectrum consists of well-separated bursts of acoustic emission. At higher strain rates of hopping type-B bands, the burst-type acoustic emission spectrum tends to overlap, forming a nearly continuous background with some sharp acoustic emission bursts. The latter can be identified with the nucleation of new bands. The acoustic emission spectrum associated with the continuously propagating type-A band is continuous. These predictions are consistent with experimental results. More importantly, our study shows that the low-amplitude continuous acoustic emission spectrum seen in both the type-B and type-A band regimes is directly correlated to small-amplitude serrations induced by propagating bands. The acoustic emission spectrum of the Liiders-like band matches with recent experiments as well. In all of these cases, acoustic emission signals are burstlike, reflecting the intermittent character of dislocation-mediated plastic flow.
机译：尽管历史悠久，但到目前为止，还没有用于计算伴随任何塑性变形的声发射谱的通用理论框架。我们建立了一个以塑性应变率作为源项的离散波动方程，并包括瑞利耗散函数来表示伴随声发射的耗散。我们设计了一种方法，将塑性变形和弹性自由度的时间尺度分开。虽然此方程适用于任何类型的塑性变形，但应使用位错微观结构的演化方程进行补充，以计算塑性应变率。通过考虑三种不同的塑性变形情况来说明框架的有效性。第一个是典型的连续屈服过程中的声发射，表现出平滑的应力-应变曲线。我们首先针对两种类型的位错密度构建了一套合适的演化方程，然后表明模型应力-应变曲线的形状以及伴随的声发射谱与实验结果非常吻合。第二个和第三个是Portevin-Le Chatelier乐队和Liiders乐队较为复杂的案例。这两种情况都在Ananthakrishna模型的上下文中处理，因为该模型预测了Portevin-Le Chatelier乐队和类似Liiders乐队的三种类型。我们的结果表明，对于锯齿状振幅较大的C型波段，声发射频谱由声发射的突发分开组成。在较高的B型跳变应变率下，猝发型声发射谱趋于重叠，形成几乎连续的背景，并带有一些尖锐的声发射猝发。后者可以通过新带的成核来识别。与连续传播的A型频带相关的声发射谱是连续的。这些预测与实验结果一致。更重要的是，我们的研究表明，在B型和A型频段中都可以看到的低振幅连续声发射频谱与传播频段引起的小振幅锯齿直接相关。类Liiders波段的声发射谱也与最近的实验相匹配。在所有这些情况下，声发射信号都是突发性的，反映了位错介导的塑性流动的间歇性特征。

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