Mäkinen Tero, Koivisto Juha, Pääkkönen Elina, Ketoja Jukka A, Alava Mikko J
Department of Applied Physics, Aalto University, P.O. Box 11100, 00076 Aalto, Espoo, Finland.
Soft Matter. 2020 Aug 7;16(29):6819-6825. doi: 10.1039/d0sm00286k. Epub 2020 Jul 7.
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.
我们研究了由木纤维制成的低重量泡沫成型材料的压缩性能。最初，应力-应变行为遵循类似平均场的响应，这与由随机三维几何结构决定的纤维段屈曲有关。随着应变增加，我们的声发射（AE）测量结果与预测的段屈曲数量相关。然而，实验表明，当应变充分增加时，会过渡到集体现象。这也体现在理论逐渐无法解释应力-应变曲线。集体雪崩在AE能量分布和AE等待时间分布方面都呈现出无标度特征，两个指数的值都接近2。在循环压缩试验中，只有当压缩超过前一循环的位移时，累积声能才会显著增加，这进一步证实了除纤维弯曲之外的其他声事件来源。
