Brittleness of fracture in flowing magma
Brittleness of fracture in flowing magma
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DOI：
10.1029/2010jb007820
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发表时间：
2010-12-10
影响因子：
3.9
通讯作者：
Rubin, M. B.
中科院分区：
文献类型：
--
作者：
Ichihara, M.;Rubin, M. B.
了解流动岩浆向脆性断裂的转变对于估计火山喷发的爆炸性至关重要。为了量化流动岩浆的脆性，引入了一个新的参数β，它是弹性畸变变形引起的应变能变化率与总畸变变形率引起的机械功率之比的函数。从β角度出发，综述了岩浆脆性断裂对应力、减压速率、应变速率和剪切稀化效应的依赖性。 Kameda等人的实验数据。 (2008)对气泡岩浆模拟物的快速减压也进行了重新审查。结果表明，β 表现出强烈的转变，与观察到的延性膨胀到脆性破碎之间的转变密切相关。此外，β 可用于考虑剪切稀化和稳态蠕变条件对脆性断裂的影响。文献中表明材料在足够高的应变率下表现出脆性的说法是正确的。然而，这些陈述并没有精确量化高应变率的概念，因此在考虑剪切稀化的影响时很容易被误解。尽管剪切稀化往往会增加总应变率的绝对值，但它并不一定会增加脆性。另外，原则上，稳定蠕变时不太可能发生脆性断裂。在岩浆稳态蠕变实验中观察到的裂纹可能是由于频率足够高以满足脆性断裂条件的小波动所致。
Understanding the transition to brittle fracture of flowing magma is essential for estimating the explosiveness of a volcanic eruption. In order to quantify brittleness of flowing magma, a new parameter beta is introduced, which is a function of the ratio of the rate of change of the strain energy due to elastic distortional deformation to the mechanical power due to total distortional deformation rate. From the perspective of beta, dependence of brittle fracture of magma on stress, decompression rate, strain rate, and shear-thinning effects are reviewed. The experimental data of Kameda et al. (2008) for rapid decompression of simulants of bubbly magma have also been reexamined. The results show that beta exhibits a strong transition that correlates well with the observed transition between ductile expansion to brittle fragmentation. Moreover, beta is useful in considering the effects of shear-thinning and steady-creep conditions on brittle fracture. Statements in the literature that suggest that materials behave in a brittle manner at sufficiently high strain rate are correct. However, these statements do not precisely quantify the notion of high strain rate so they are easy to misinterpret when considering the effect of shear thinning. Although shear thinning tends to increase the absolute magnitude of the total strain rate, it does not necessarily increase brittleness. Also, in principle, it is unlikely for brittle fracture to occur at steady creep. Cracking observed in steady-creep experiments of magma may be attributed to small fluctuations with sufficiently high frequencies to satisfy the conditions for brittle fracture.