Material defects as the basis of fatigue design
Material defects as the basis of fatigue design
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DOI：
10.1016/j.ijfatigue.2011.12.001
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发表时间：
2012-08-01
影响因子：
6
通讯作者：
Murakami, Yukitaka
中科院分区：
文献类型：
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作者：
Murakami, Yukitaka
金属中可能存在显微组织不均匀性，如沉淀物和夹杂物。这些可以有目的地引入以强化金属基质（例如：α相铝中的CuAl 2）或制造缺陷（例如：大夹杂物）。金属疲劳历史的主要部分是消除或至少减少有害的沉淀物、夹杂物和制造缺陷，例如铸铁中的划痕、表面粗糙度和收缩，因为这些会引发疲劳裂纹。异物或其他形式的不均匀性的有害性质，例如：微观结构中的孔隙或脱粘区与它们的尺寸、位置、形状、取向和物理性能有关。小尺寸的沉淀物和夹杂物比大尺寸的沉淀物和夹杂物更受欢迎;这些缺陷在晶粒内部比在晶界处危害更小，在晶界处，它们可以同时影响两个或三个相邻的晶粒。如果缺陷倾向于第一阶段和/或第二阶段裂纹扩展平面的未来方向，则缺陷的取向是危险的。分析师的一个重要职责是减少制造过程中产生的这些不同形式的微观缺陷的有效性，而机械工程师则需要导出一种合适的断裂力学形式，以便在定量疲劳断裂分析中解释它们的行为。本文将从它们的尺寸、位置、形状、取向和性能，以及它们对材料抗疲劳性的影响。这将与断裂力学（FM）方法相结合，该方法根据其与疲劳裂纹扩展的关系量化其行为。在这种方法中，使用FM作为小裂纹的阈值条件，结合代表该条件的材料的维氏硬度HV，探索失效与非失效之间的边界条件（Δ K-th表示裂纹从缺陷开始生长所需的微塑性（屈服）的开始和裂纹的非扩展行为。微观结构的统计散射，缺陷和夹杂物是疲劳强度和疲劳寿命统计离散的主要因素。从基于缺陷和夹杂物极值统计的均匀性控制角度阐述了优化组织以提高疲劳强度的方向，提出了一种基于氢脆现象极值统计的高强度钢夹杂物评级方法。(C)2011爱思唯尔有限公司保留所有权利。
Microstructural inhomogeneities can exist in metals, such as precipitates and inclusions. These can be introduced purposely to strengthen the metal matrix (e.g.: CuAl2 in alpha-phase aluminium) or by faulty manufacture (e.g.: large inclusions). A major part of the history of metal fatigue has been to eliminate, or at least reduce, detrimental precipitates, inclusions and manufacture defects such as scratches, surface roughness and shrinkages in cast irons since these can initiate fatigue cracks. The deleterious nature of foreign bodies or other forms of inhomogeneities, e.g.: pores or de-bonded zones within a microstructure are related to their size, position, shape, orientation and physical properties.Small sizes of precipitates and inclusions are to be preferred to large ones; such defects being less detrimental inside a grain rather than at grain boundaries where they can simultaneously affect two or three near-neighbour grains. The orientation of a defect is dangerous should it be inclined to the future direction of Stage I and/or Stage II crack growth planes. An important duty of a metallurgist is to reduce the effectiveness of these different forms of micro-defects produced during manufacture whilst a mechanical engineer is required to derive a suitable form of fracture mechanics in order to account for their behaviour in a quantitative fatigue fracture analysis.In this paper, some important types of microstructural defects will be illustrated and discussed in terms of their size, position, shape, orientation and properties, together with their effect on the fatigue resistance of a material. This will be coupled with a fracture mechanics (FMs) approach that quantifies their behaviour in terms of their relationship to fatigue crack propagation. In this approach, the boundary condition between failure and non-failure is explored using FM as a threshold condition for a small crack coupled with the Vickers hardness HV of the material that represents the condition (Delta K-th for the onset of micro-plasticity (yielding) required for the growth of a crack from the defect and the non-propagation behaviour of the crack.Statistical scatters of microstructures, defects and inclusions are the major factors of statistical scatters of fatigue strength and fatigue life. Directions for optimizing microstructure to improve fatigue strength are explained from the viewpoint of equality control based on the statistics of extremes of defects and inclusions.A new efficient and reliable inclusion rating method for high strength steels based on the statistics of extremes using the phenomenon of hydrogen embrittlement is proposed. (C) 2011 Elsevier Ltd. All rights reserved.