Length scale effects on the shear localization process in metallic glasses: A theoretical and computational study
Length scale effects on the shear localization process in metallic glasses: A theoretical and computational study
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DOI：
10.3970/icces.2011.020.079
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发表时间：
2011-04
期刊：
影响因子：
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通讯作者：
T. P. G. Thamburaja
中科院分区：
文献类型：
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作者：
T. P. G. Thamburaja
最近对亚微米和纳米尺寸的金属玻璃(非晶态合金)样品的一些实验表明，与大样品尺寸的响应相比，剪切局部化过程变得更加稳定和不那么灾难性。这导致发现，减少样品体积可以延缓剪切局部化过程和断裂。在这项工作中，我们建立了一个基于非局部有限变形的本构模型，利用热力学原理和微力平衡理论来研究上述现象的原因。通过编写用户材料子程序，实现了本构模型在商用有限元程序中的应用。在有限元模拟的帮助下，我们的本构模型预测金属玻璃样品具有固有的能力：(A)随着样品尺寸的减小，(灾难性)剪切局部化的延迟，以及(B)样品体积小于剪切带核时的均匀变形行为。出现上述现象的原因是随着样本量的减少，非局部相互作用应力的影响越来越大。这种相互作用应力具有能量来源，并由于塑性剪切和自由体积产生之间的强烈耦合而影响塑性变形。类似于应变梯度塑性理论，相互作用应力的作用是在缺陷密度/自由体积比金属玻璃样品的其余部分更高的位置强化材料。
Some recent experiments on sub-micron and nano-sized metallic glass (amorphous alloy) specimens have shown that the shear localization process becomes more stable and less catastrophic when compared to the response exhibited by large sample sizes. This leads to the discovery that the shear localization process and fracture can be delayed by decreasing sample volume. In this work we develop a non-local and finite-deformation-based constitutive model using thermodynamic principles and the theory of micro-force balance to study the causes for the aforementioned observations. The constitutive model has also been implemented into a commercially available finite-element program by writing a user-material subroutine. With the aid of finite-element simulations, our constitutive model predicts that metallic glass samples have the intrinsic ability to exhibit: (a) the delaying of (catastrophic) shear localization with decreasing sample size, and (b) homogeneous deformation behavior for sample volumes smaller than the shear band nucleus. The cause for the observations listed above is the increasing influence of a non-local interaction stress with decreasing sample volume. This interaction stress has energetic origins and it affects plastic deformation due to the strong coupling between plastic shearing and free-volume generation. Akin to strain-gradient plasticity theory, the role of the interaction stress is to strengthen the material at locations where the defect density/free volume is higher compared to the rest of metallic glass sample.