A fragmentation criterion for highly viscous bubbly magmas estimated from shock tube experiments
A fragmentation criterion for highly viscous bubbly magmas estimated from shock tube experiments
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DOI：
10.1016/j.jvolgeores.2008.02.008
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发表时间：
2008-11-30
影响因子：
2.9
通讯作者：
Melnik, Oleg
中科院分区：
文献类型：
--
作者：
Koyaguchi, Takehiro;Scheu, Bettina;Melnik, Oleg
当一个高粘性的泡沫状岩浆被充分减压时，逐层破裂以一定的速度（破碎速度）在岩浆中传播。根据Koyaguchi和Mitani最近提出的激波管理论[Koyaguchi，T. Mitani，N. K.，2005.激波管中粘性泡状岩浆破碎的理论模型。地球物理研究杂志110（B10），B10202。doi：10.1029/2004JB 003513.），根据天然火山岩不同孔隙度的激波管破碎速度实验数据，估算了破碎面气体超压。结果表明，破碎面气体超压随试样初始压力的增大而增大，随试样孔隙度的减小而减小。提出了一种新的破碎准则，用以解释破碎面气体超压与初始压力和孔隙度之间的关系。我们的标准是基于这样的想法，即当气泡之间的中点处的张应力超过临界值时，高粘度气泡状岩浆发生总的破碎。当我们假设临界值与气泡壁厚的平方根成反比时，我们得到了令人满意的模拟和实验之间的协议。这种破碎标准表明，长微裂纹或等效缺陷（例如，不规则形状的气泡）是决定气泡状岩浆的体积强度的主要因素。(C)2008 Elsevier B. V.保留所有权利。
When a highly viscous bubbly magma is sufficiently decompressed, layer-by-layer fracturing propagates through the magma at a certain speed (fragmentation speed). On the basis of a recent shock tube theory by Koyaguchi and Mitani [Koyaguchi, T.. Mitani, N. K., 2005. A theoretical model for fragmentation of viscous bubbly magmas in shock tubes. Journal of Geophysical Research 110 (B10), B10202. doi:10.1029/2004JB003513.), gas overpressures at the fragmentation surface are estimated from experimental data on fragmentation speed in shock tube experiments for natural volcanic rocks with various porosities. The results show that gas overpressure at the fragmentation surface increases as initial sample pressure increases and sample porosity decreases. We propose a new fragmentation criterion to explain the relationship between the gas overpressure at the fragmentation surface, the initial pressure and the porosity. Our criterion is based on the idea that total fragmentation of highly viscous bubbly magmas occurs when the tensile stress at the midpoint between bubbles exceeds a critical value. We obtain satisfactory agreement between our simulation and experiment when we assume that the critical value is inversely proportional to the square root of bubble wall thickness. This fragmentation criterion suggests that long micro-cracks or equivalent flaws (e.g., irregular-shaped bubbles) that reach the midpoints between bubbles are a dominant factor to determine the bulk strength of the bubbly magma. (C) 2008 Elsevier B.V. All rights reserved.