Strain-rate softening has been associated with a wide variety of material instabilities, from the Portevin–Le Chatelier effect in metal alloys to stick-slip motion in crust faults. Dynamic instability patterns have been recently discovered in brittle porous media: diffused, oscillatory, and erratic compaction. Using model simulations inspired by experiments with puffed rice, we question the link between these dynamic patterns and strain-rate sensitivity in such media. An important feature of our model is that it can recover strain-rate softening as an emergent phenomenon, without imposing it a priori at its microstructural scale. More importantly, the model also demonstrates that the full range of dynamic patterns can develop without presenting macroscopic strain-rate softening. Based on this counterexample model, we therefore argue that strain-rate softening should not be taken as a necessary condition for the emergence of instability patterns. Our findings in brittle porous media have implications on models that require strain-rate softening to explain earthquake and metal alloy instabilities.

中文翻译：

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材料不稳定模式不需要应变速率软化的证据

应变速率软化与多种材料不稳定性相关，从金属合金中的Portevin–Le Chatelier效应到地壳断层中的粘滑运动。最近在脆性多孔介质中发现了动态不稳定性模式：扩散，振荡和不稳定压实。使用以膨化大米为实验对象的模型模拟，我们质疑了这些动态模式与此类介质中应变率敏感性之间的联系。我们模型的一个重要特征是它可以将应变率软化恢复为一种新兴现象，而无需先验地将其强加于人在其微观结构规模上。更重要的是，该模型还表明，可以在不呈现宏观应变率软化的情况下开发出完整的动态模式。因此，基于该反例模型，我们认为不应将应变率软化作为不稳定模式出现的必要条件。我们在脆性多孔介质中的发现对需要应变率软化以解释地震和金属合金不稳定性的模型有影响。