We study the compression of low-weight foam-formed materials made out of wood fibers. Initially the stress–strain behavior follows mean-field like response, related to the buckling of fiber segments as dictated by the random three-dimensional geometry. Our Acoustic Emission (AE) measurements correlate with the predicted number of segment bucklings for increasing strain. However, the experiments reveal a transition to collective phenomena as the strain increases sufficiently. This is also seen in the gradual failure of the theory to account for the stress–strain curves. The collective avalanches exhibit scale-free features both as regards the AE energy distribution and the AE waiting time distributions with both exponents having values close to 2. In cyclic compression tests, significant increases in the accumulated acoustic energy are found only when the compression exceeds the displacement of the previous cycle, which further confirms other sources of acoustic events than fiber bending.

中文翻译：

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在低密度泡沫形成的纤维材料中，从平均场压缩到集体现象的转换。

我们研究了由木纤维制成的低重量泡沫成型材料的压缩。最初，应力-应变行为遵循类似均值场的响应，这与随机三维几何形状所指示的纤维段的屈曲有关。我们的声发射（AE）测量值与应变增加的节段屈曲的预计数量相关。但是，实验表明，随着应变的充分增加，向集体现象的过渡。从理论上逐渐无法解释应力-应变曲线也可以看出这一点。集体雪崩在AE能量分布和AE等待时间分布方面都表现出无尺度的特征，两个指数的值都接近2。在循环压缩测试中，