All engineering materials have the potential to contain inhomogeneities that can act as initiators for fatigue cracks during cyclic loading. One class of inhomogeneity that can occur as a result of the processes used to create metallic materials is a ceramic inclusion, typically resulting from the raw material contamination during the melting process. This article examines the predicted behavior of hard ceramic inclusions in a nickel-base superalloy metallic matrix. Compressive residual stresses are created in the inclusion during cool down from a stress-free state at high temperature. The influence of the proximity of the inclusion to the surface of the matrix material is examined, together with the impact of subsequent uniaxial loading on the stress field in the inclusion and in the surrounding material. The stress field in the ceramic inclusion is observed to transition from compressive to tensile as a function of the proximity of the inclusion to the surface of the material and the applied uniaxial stress field. For deep subsurface inclusions, the uniaxial stress field required to achieve a tensile stress in the inclusion is close to the yield stress of the material. The sensitivity of this critical stress to material cyclic hardening behavior and to the temperature difference between the stress-free state and the operating state is also explored. The significance of these modeling results is discussed in terms of the sensitivity of nickel-base superalloys to crack formation and growth from ceramic inclusions and hence the impact on probabilistic fatigue life assessments of the presence, location and size of the ceramic inclusions.

中文翻译：

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金属基体中亚表面陶瓷夹杂物的建模

所有工程材料都有可能包含不均匀性，这些不均匀性可能会在循环加载过程中引发疲劳裂纹。由于用于制造金属材料的过程而可能出现的一类不均匀性是陶瓷夹杂物，通常是由熔化过程中的原材料污染引起的。本文研究了镍基高温合金金属基体中硬质陶瓷夹杂物的预测行为。在高温下从无应力状态冷却的过程中，夹杂物会产生压缩残余应力。检查夹杂物与基体材料表面的接近度的影响，以及随后的单轴载荷对夹杂物和周围材料中应力场的影响。观察到陶瓷夹杂物中的应力场从压缩转变为拉伸，作为夹杂物与材料表面的接近度和施加的单轴应力场的函数。对于深层地下夹杂物，在夹杂物中实现拉伸应力所需的单轴应力场接近材料的屈服应力。还探讨了这种临界应力对材料循环硬化行为以及无应力状态和运行状态之间的温差的敏感性。根据镍基高温合金对陶瓷夹杂物裂纹形成和生长的敏感性以及陶瓷夹杂物的存在、位置和尺寸对概率疲劳寿命评估的影响，讨论了这些建模结果的重要性。