Deformation and failure mechanisms in austenitic steel under coupled compressive and torsional loading

压缩和扭转耦合载荷下奥氏体钢的变形和失效机制

• 批准号: 441180620
• 负责人: Dr.-Ing. Stefanie Hanke
• 金额: --
• 依托单位: Lehrstuhl für Werkstofftechnik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/441180620?language=en
• 关键词: Deformation; failure; mechanisms; austenitic; steel

The understanding of material behavior under multiaxial mechanical loads is of great importance for the application of structural materials, because components are usually exposed to multiaxial stresses in practice. In addition, the load is typically time-dependent and reversing. Experimental investigations under such complex loading conditions are very laborious, such that our understanding of the mechanisms leading to plastic deformation and failure of materials under multi-axial reversing loads is quite insufficient. This leads, moreover, to an uncertainty whether the common solid mechanics failure hypotheses are valid under such conditions. The proposed research project seeks to close this gap in the current state of research by experimentally investigating the deformation and damage mechanisms in a nitrogen-alloyed austenitic steel with superimposed compressive and cyclic torsional loading. Effects of the special loading condition on microstructural mechanisms of strain and damage accumulation and their changes will be analyzed by high resolution microscopy. Based on the experimental results, a constitutive model is formulated within the framework of crystal plasticity that reliably describes cyclic plasticity and damage under multiaxial loads on the microstructural level. In addition to pure dislocation plasticity, mechanical twinning and grain boundary sliding are also considered within the model. Concerning the damage mechanisms, in particular the processes taking place at the material surface are characterized and modeled.Under combined compression and cyclic torsional loading, the phenomenon is observed that samples undergo plastic axial strain, although the compressive load by itself is well below the yield strength of the material. This compressive strain occurs as soon as a critical angle for the cyclic torsion is exceeded. The proposed research project investigates whether this phenomenon can be described with the common failure hypotheses or whether they need to be generalized accordingly. Moreover, the comparison of experimental findings and numerical modeling can lead to a fundamental understanding of the deformation and damage mechanisms under complex mechanical loads. These mechanisms can further be correlated with softening and hardening behavior of the material. In order to ensure the widest possible scope of the micromechanical model of fatigue under multiaxial loads, the influence of prior cold working on the material behavior under superimposed compressive-torsional loads is experimentally investigated and used for model validation.

了解多轴机械载荷下的材料行为对于结构材料的应用非常重要，因为部件在实践中通常会受到多轴应力。此外，负载通常与时间相关并且是可逆的。在如此复杂的载荷条件下进行实验研究非常费力，使得我们对多轴反向载荷下材料塑性变形和破坏的机制的理解还很不足。此外，这导致了常见固体力学失效假设在这种条件下是否有效的不确定性。拟议的研究项目旨在通过实验研究叠加压缩和循环扭转载荷的氮合金奥氏体钢的变形和损伤机制来缩小当前研究状态的这一差距。通过高分辨率显微镜分析特殊加载条件对应变和损伤累积微观结构机制的影响及其变化。基于实验结果，在晶体塑性框架内制定了本构模型，该模型可靠地描述了微观结构水平上多轴载荷下的循环塑性和损伤。除了纯位错塑性之外，模型中还考虑了机械孪生和晶界滑动。关于损坏机制，特别是对材料表面发生的过程进行了表征和建模。在压缩和循环扭转载荷的组合下，观察到样品经历塑性轴向应变的现象，尽管压缩载荷本身远低于屈服强度材料的强度。一旦超过循环扭转的临界角，就会出现这种压缩应变。拟议的研究项目调查这种现象是否可以用常见的失效假设来描述，或者是否需要相应地进行推广。此外，实验结果和数值模型的比较可以使人们对复杂机械载荷下的变形和损伤机制有一个基本的了解。这些机制可以进一步与材料的软化和硬化行为相关。为了确保多轴载荷下疲劳微机械模型的范围尽可能广泛，通过实验研究了预先冷加工对叠加压缩扭转载荷下材料行为的影响，并用于模型验证。