We experimentally study the unjamming dynamics of strongly compressed particle rafts confined between two fixed walls and two movable barriers. The back barrier is made of an elastic band, whose deflection indicates the local stress. The front barrier is pierced by a gate, whose opening triggers local unjamming. Prior to gate opening, the rafts are quasistatically compressed by moving only one of the two barriers, in the vicinity of which folds form. Using high-speed imaging, we follow the raft relaxation with folded, jammed, and unjammed areas and measure the velocity fields inside and outside the confined domain. Two very different behaviors develop. For rafts compressed by the back barrier, only partial unjamming occurs. At the end of the process, many folds remain and the back stress does not relax. The flow develops mostly along the compression axis and the particles passing the gate form a dense raft whose width is the gate width. For rafts compressed at the front, quasitotal unjamming is observed. Almost no folds persist and only minimal stress remains, if any. The particles flow along the compression axis but also normally to it and form a rather circular and not dense assembly. Both the force chain network orientation and the initial fold location could cause the unjamming difference. Other effects, such as a different pressure field or simple steric hindrance, cannot be excluded.

中文翻译：

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解开强压缩筏：压缩方向的影响

我们通过实验研究了限制在两个固定壁和两个可移动屏障之间的强压缩粒子筏的无干扰动力学。后挡板由弹性带制成，其挠度表示局部应力。前面的屏障被一扇门刺穿，它的打开触发了局部疏通。在门打开之前，通过仅移动两个屏障中的一个来准静态压缩筏，在其附近形成褶皱。使用高速成像，我们跟踪具有折叠、阻塞和未阻塞区域的筏松弛，并测量受限域内外的速度场。发展出两种截然不同的行为。对于被后挡板压缩的筏板，只有部分疏通发生。在该过程结束时，许多褶皱仍然存在，并且背应力不会松弛。流动主要沿压缩轴发展，通过闸门的颗粒形成密集的筏板，其宽度为闸门宽度。对于在前部压缩的筏，观察到准完全畅通。几乎没有褶皱持续存在，如果有的话，只剩下最小的压力。颗粒沿压缩轴流动，但也垂直于压缩轴流动，形成一个相当圆形且不致密的集合体。力链网络方向和初始折叠位置都可能导致畅通差异。不能排除其他影响，例如不同的压力场或简单的空间位阻。颗粒沿压缩轴流动，但也垂直于压缩轴流动，形成一个相当圆形且不致密的集合体。力链网络方向和初始折叠位置都可能导致畅通差异。不能排除其他影响，例如不同的压力场或简单的空间位阻。颗粒沿压缩轴流动，但也垂直于压缩轴流动，形成一个相当圆形且不致密的集合体。力链网络方向和初始折叠位置都可能导致畅通差异。不能排除其他影响，例如不同的压力场或简单的空间位阻。