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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Rheology of welding: inversion of field constraints
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Rheology of welding: inversion of field constraints

机译：焊接流变学：场约束的反演

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At present the mechanisms and rheological behaviour of pyroclastic deposits during welding and compaction are poorly understood. Here, we explore the extent to which the rheological properties of pyroclastic deposits are constrained by physical property distributions in welded ignimbrite. Physical properties of samples from a 20-m section of the Bandelier Tuff, New Mexico are used as proxies for strain. The observed strain (ε_T) is ascribed to a combination of a time-dependent viscous compaction (ε_v) and a time-independent mechanical compaction (ε_m) described by: ε_T=(1-φ_o)/α ln{1+(ασΔt)/(η_o(1-φ_o))exp~(αφ_o)/(1-φ_o)}+σ/(E(1-φ_o)) where φ_o is the original porosity, a is load, and η_o and E are the viscosity and Young's modulus of the deposit at zero porosity, respectively. The quantity a is an experimentally determined parameter used to relate the viscosity and porosity of porous aggregates. Simple conductive heat transfer models are used to generate cooling curves for individual samples; these curves dictate times of residence (Δ_t) at temperatures above the glass transition temperature. We adopt an inverse model approach whereby the observations on the natural material and model cooling curves are used to constrain the values of η_o (10~(14.5) Pa s) and E (3-7 MPa). Our optimization also predicts the relative components of viscous and mechanical compaction throughout the welded ignimbrite. Viscous compaction dominates the lower two thirds of the section (ε_v: ε_m > 1.0); the maximum in ε_v is coincident with the observed peak in welding intensity. Lastly, we present two dimensionless numbers (Q_A and Q_B) which are used to create a map of welding potential for pyroclastic deposits. The map has four quadrants which coincide with (ⅰ) no welding, (ⅱ) welding and compaction driven by temperature (ε_v > ε_m) or (ⅲ) by gravitational loading (ε_m > ε_v), and (ⅳ) welding aided by temperature and load (ε_v ≈ ε_m).
机译：目前，人们对焊接和压实过程中火山碎屑沉积物的机理和流变行为知之甚少。在这里，我们探讨了火山碎屑沉积物的流变特性受焊接火成岩的物理特性分布限制的程度。来自新墨西哥州班德利尔凝灰岩20米段的样品的物理性质用作应变的代理。观察到的应变（ε_T）归因于时间相关的粘性压实（ε_v）和时间无关的机械压实（ε_m）的组合，其描述为：ε_T=（1-φ_o）/αln {1+（ασΔt） /（η_o（1-φ_o））exp〜（αφ_o）/（1-φ_o）} +σ/（E（1-φ_o））其中φ_o为原始孔隙度，a为载荷，η_o和E为粘度孔隙率为零时的沉积物的杨氏模量。数量a是实验确定的参数，用于关联多孔聚集体的粘度和孔隙率。简单的传导传热模型用于生成单个样品的冷却曲线；这些曲线决定了在高于玻璃化转变温度的温度下的停留时间（Δ_t）。我们采用逆模型方法，利用对天然材料的观察和模型冷却曲线来约束η_o（10〜（14.5）Pa s）和E（3-7 MPa）的值。我们的优化还可以预测整个焊接点的粘性和机械压实的相对成分。粘性压实作用占该段下部三分之二（ε_v：ε_m> 1.0）； ε_v的最大值与观察到的焊接强度峰值一致。最后，我们给出两个无因次数（Q_A和Q_B），它们用于创建火成屑沉积物的焊接潜力图。该图有四个象限，它们与（ⅰ）不焊接，（ⅱ）焊接和压实由温度（ε_v>ε_m）或（ⅲ）由重力载荷（ε_m>ε_v）驱动，以及（welding）由温度和温度辅助焊接相一致。负载（ε_v≈ε_m）。

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