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On the Plastic Strain Accumulation in Notched Bars During High-Temperature Creep Dwell
Journal of Mechanics ( IF 1.7 ) Pub Date : 2020-02-21 , DOI: 10.1017/jmech.2019.56
Daniele Barbera , Haofeng Chen

Structural integrity plays an important role in any industrial activity, due to its capability of assessing complex systems against sudden and unpredicted failures. The work here presented investigates an unexpected new mechanism occurring in structures subjected to monotonic and cyclic loading at high temperature creep condition. An unexpected accumulation of plastic strain is observed to occur, within the high-temperature creep dwell. This phenomenon has been observed during several full inelastic finite element analyses. In order to understand which parameters make possible such behaviour, an extensive numerical study has been undertaken on two different notched bars. The notched bar has been selected due to its capability of representing a multiaxial stress state, which is a practical situation in real components. Two numerical examples consisting of an axisymmetric v-notch bar and a semi-circular notched bar are considered, in order to investigate different notches severity. Two material models have been considered for the plastic response, which is modelled by both Elastic-Perfectly Plastic and Armstrong-Frederick kinematic hardening material models. The high-temperature creep behaviour is introduced using the time hardening law. To study the problem several results are presented, as the effect of the material model on the plastic strain accumulation, the effect of the notch severity and the mesh element type and sensitivity. All the findings further confirm that the phenomenon observed is not an artefact but a real mechanism, which needs to be considered when assessing off-design condition. Moreover, it might be extremely dangerous if the cyclic loading condition occurs at such a high loading level.

中文翻译:

高温蠕变停留期间缺口钢筋塑性应变积累的研究

结构完整性在任何工业活动中都发挥着重要作用,因为它能够针对突然和不可预测的故障评估复杂系统。这里介绍的工作研究了在高温蠕变条件下承受单调和循环载荷的结构中出现的一种意想不到的新机制。在高温蠕变停留期间,观察到发生意外的塑性应变累积。这种现象已在几个完全非弹性有限元分析中观察到。为了了解哪些参数使这种行为成为可能,我们对两个不同的缺口钢筋进行了广泛的数值研究。选择缺口杆是因为它能够表示多轴应力状态,这是实际组件中的实际情况。考虑了由轴对称 V 形缺口杆和半圆形缺口杆组成的两个数值示例,以研究不同的缺口严重程度。塑性响应考虑了两种材料模型,由弹性-完美塑性和 Armstrong-Frederick 运动硬化材料模型建模。使用时间硬化定律引入高温蠕变行为。为了研究这个问题,提出了几个结果,如材料模型对塑性应变累积的影响、缺口严重程度的影响以及网格元素类型和敏感性。所有研究结果进一步证实,观察到的现象不是人工制品,而是真实的机制,在评估非设计条件时需要考虑这一点。而且,
更新日期:2020-02-21
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