Modelling the coupling between hydrogen diffusion and the mechanical behaviour of metals
Modelling the coupling between hydrogen diffusion and the mechanical behaviour of metals
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DOI：
10.1016/j.commatsci.2016.05.030
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发表时间：
2016-09-01
影响因子：
3.3
通讯作者：
Cocks, A. C. F.
中科院分区：
文献类型：
--
作者：
Barrera, O.;Tarleton, E.;Cocks, A. C. F.
众所周知，氢会对金属的机械性能产生有害影响。这里的目的是提供一个完全耦合的模型的HELP（氢增强局部塑性）机制与氢输送。利用热扩散方程和质量扩散方程之间的相似性，采用了耦合的温度-位移过程，以模拟氢扩散和材料力学行为之间的耦合。扩散方程考虑了氢原子存在于间隙位置和陷阱位置（如位错）的事实。在这里提出的模拟中，假设位错处的氢浓度与基质间隙位点中的浓度平衡。该材料的机械行为是由各向同性硬化法表示的，其中流动应力随着基体中氢含量的增加而减小，该基体通过求解完全耦合的机械扩散方程来评估。我们使用该模型分析了一个平面应变元件，其中包含深和尖锐的双刃缺口的响应。对于这种高度受约束的构件，应力的流体静力分量与材料的局部屈服强度成比例。高的局部流体静压应力将导致高的氢浓度，但是高的氢浓度导致软化，即低的屈服强度，并且因此导致低的流体静压应力。这些相互矛盾的关系导致在流体静力学应力、氢浓度和屈服强度之间实现平衡，即响应不会变得不稳定。此外，在部件变形的方式中存在高度的运动学确定性，即，存在氢的应变模式与不存在氢时的应变模式非常相似。这两种效应的结果是，由于氢的存在，软化的本构响应，不导致应变的局部化和宏观脆性响应。软化必须与其他降解过程相结合，使材料脆化。(C)2016作者（S）由Elsevier B. V.发布，这是CC BY许可下的开放获取文章。
It is well known that hydrogen can have a detrimental effect on the mechanical properties of metals. The aim here is to provide a fully coupled model of the HELP (Hydrogen Enhanced Local Plasticity) mechanism with hydrogen transport. Using the similarities between the heat and mass diffusion equations, a coupled temperature-displacement procedure has been adopted to allow the coupling between hydrogen diffusion and the mechanical behaviour of the material to be simulated. The diffusion equation takes into account the fact that hydrogen atoms reside in interstitial sites and in trapping sites such as dislocations. In the simulations presented here it is assumed that concentration of hydrogen at the dislocations is in equilibrium with the concentration in the matrix interstitial sites. The mechanical behaviour of the material is represented by an isotropic hardening law in which the flow stress decreases with increasing hydrogen content in the matrix which is evaluated by solving the fully coupled mechanical diffusion equations. We use the model to analyse the response of a plane strain component which contains deep and sharp doubled-edged notches. For highly constrained components of this type the hydrostatic component of stress scales with the local yield strength of the material. A high local hydrostatic stress would result in a high hydrogen concentration, but a high hydrogen concentration results in softening, i.e. a low yield strength, and therefore a low hydrostatic stress. These conflicting relationships result in a balance being achieved between hydrostatic stress, hydrogen concentration and yield strength, i.e. the response does not become unstable. Also there is a high degree of kinematic determinacy in the way which the component deforms, i.e. the strain pattern in the presence of hydrogen is very similar to that when there is no hydrogen. A consequence of these two effects is that softening of the constitutive response due to the presence of hydrogen, does not lead to localization of strain and a macroscopic brittle response. Softening must be combined with other degradation process for the material to embrittle. (C) 2016 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license.